Carburation Fine Tuning
Discussion
My 84 turbo now has the S4 engine running pretty well. There are a couple of minor issues to overcome. The carbs, dhla 40s were rebuilt but theres always a stumble off idle. I have balanced them and reset the floats during the overhaul; is the problem likely to be the accelerator pumpsor something else.
There is also a minor hessitation higher up the rev range possibly as it goes onto turbo and I am presuming this is to do with the fuel pressure regulator, this hasnt been replaced.
The last issue with the engine is that I have reduced the shim diameter in the wastegate to get a little more boost now that it can handle it but it doesnt seem to be working yet. Does the blow off valve on the plenum work at the same pressure if so how is this modified.
Any thoughts appreciated.
Steve
There is also a minor hessitation higher up the rev range possibly as it goes onto turbo and I am presuming this is to do with the fuel pressure regulator, this hasnt been replaced.
The last issue with the engine is that I have reduced the shim diameter in the wastegate to get a little more boost now that it can handle it but it doesnt seem to be working yet. Does the blow off valve on the plenum work at the same pressure if so how is this modified.
Any thoughts appreciated.
Steve
hotrod1000 said:
(Snip)... The carbs, dhla 40s were rebuilt but theres always a stumble off idle. I have balanced them and reset the floats during the overhaul; is the problem likely to be the accelerator pumpsor something else.
There is also a minor hessitation higher up the rev range possibly as it goes onto turbo and I am presuming this is to do with the fuel pressure regulator, this hasnt been replaced.
Steve,
How are the carbs jetted, and to what level did you set the floats?
The stumble off idle could be the accelerator pumps, pump jets, idle jets or idle air correctors (aka, idle jet holders).
Move the throttle slowly such that the accelerator pump isn't an issue. If the engine hesitates off-idle, then the idle air correctors are too lean.
If the higher speed stumble occurs around 3200 rpm (+/-), then the idle jet is too small and the circuit is running out of capacity before the main circuit takes over. Increasing the idle jet size to cure the 3200 stumble will enrichen the overall idle circuit and may also resolve the off-idle hesitation... but not always. And simply increasing idle jet sizes isn't always the best solution overall.
The idle air correctors should be as lean as possible without causing an off-idle hesitation. The idle jets should be as lean as possible without causing a 3200 rpm stumble... a little richer for improved driveability and power.
When jetting the idle circuit from scratch, set the idle air correctors first. Then set the idle jets. Large changes to the idle jet size may significantly affect the off-idle hesitation (normally the idle air corrector's domain). Follow any large jet changes by re-visiting the idle air correctors and then the jets one more time. Always idle air correctors first followed by idle jets. A fussy tuner will go back and forth several times.
If slow throttle movements are not an issue (jetting is correct), but quick movements cause an off-idle hesitation, then the cause may be the pump jets are too small, the accelerator pump is not adjusted properly, or the pump is defective... or combinations of all three.
hotrod1000 said:
The last issue with the engine is that I have reduced the shim diameter in the wastegate to get a little more boost now that it can handle it but it doesnt seem to be working yet. Does the blow off valve on the plenum work at the same pressure if so how is this modified.
Take the car (or just the wastegate) to a Diesel truck service center. Many of them are authorized Garrett service centers and can service both the turbo and the wastegate. Just ask them to set the wastegate to provide a boost limit of 9.5 – 10 psi (under ten). You would have to shim the boost level by trial and error, but they have the equipment to set the desired value correctly the first time. Let them do it.
Bottom-center on your wastegate, is there a hex-head bolt or an open hole? The hex head is another adjustment in addition to the spring shim. If your wastegate has both, then the shim sets the pressure at which the wastegate just begins to open, and hex head sets the upper limit boost level.
"Handling more boost" isn't necessarily a matter of the engine's structural strength, and installing a later engine block/head assembly doesn't mean you can crank the boost up to S4s levels.
True, you're old engine had cast pistons that were a weak point, and the new one has stronger forged pistons. Based upon pistons alone, the boost can be cranked up a bit. But high boost is primarily limited by the induction/ engine management systems' ability to control fuel mixture and ignition timing to safe limits appropriate for higher boost. The old carbs and distributor ignition aren't up to that task.
The dump valve is set for approximately 10 psi, and I suggest you keep boost to just below that level. Boost for standard engines (cast pistons) was limited to 0.55 bar (8.0 psi), while HC engines were limited to 0.65 bar (9.5 psi). Setting the wastegate to deliver 9.5 - 10 psi (or just under the dump valve's setting) will take your car up to HC levels and would be a good target. For anything more than that, you should take the car to a professional tuner who specializes in turbo set-up. A 1.5 psi increase doesn't sound like much, but it's definitely noticeable.
The best way to alter the boost would be by installing a boost controller.
The OEM Lotus system has a boost pressure tube direct to the wastegate, and boost pressure is continuously fed to the wastegate as it builds. Since the wastegate valve is working against a spring rate, it starts to open way before peak boost so that it reaches the upper-limit opening in time to limit peak boost. The down side is that boost the turbo is struggling to build is bled off by the early opening wastegate as it works against the spring.
A boost controller splices a solenoid valve into the boost pressure tube to the wastegate. The valve is off at any boost pressure below the set limit. That means the wastegate sees no boost signal and remains fully closed at anything less than full limit boost. An electronic controller senses boost pressure and energizes the solenoid valve when limit boost is reached, sending a pressure signal to the wastegate, opening it fully.
Since no building boost is bled off prior to reaching the limit, boost builds more quickly and the engine runs with more boost in the sub-limit range. The engine feels more responsive and stronger without using a higher boost limit. Combine a boost controller with a BOV (no, the dump valve is not a BOV) and the engine will be much more responsive (minimal turbo lag).
With a boost controller, there is no need to shim the wastegate since the controller determines when it opens and the upper boost limit. Simply dial in a boost limit that's just under the dump valve's opening pressure.
Regards,
Tim Engel
Lotus Owners Oftha North
Tim
Thanks for the comprehensive explanation. To answer a few of the questions you raised, the jets are all standard from the original engine 84 LC turbo, dhla 40s. The float levels are set to those in the manual for the original engine as well, 15mm I think. Accelerating slowly off idle is fine but a quick throttle opening leaves it stumbling for a second. The accelerator pumps were overhauled as part of the carb overhaul with new diaphrams but reset to the original positions. After driving it again tonight it has minor hessitations at lots of different points through the revs but seems to be ok once the throttles have been open for a second ie opening the throttlw at 2000 or 3000 gives minor hessitation before smoothing out. I am still running in at the moment so 3500 is about the limit.
On the turbo side only a minor increase was ever planned to stay within the limits of the citroen gearbox. I have reduced the 20mm shim to 10mm so far and also have a 6mm which I will try. Theres no hex nut on the wastegate and it operates directly from the exhaust manifold, its the original 84 system so unfortunately no possibilty of a boost controller.
Thanks for the comprehensive explanation. To answer a few of the questions you raised, the jets are all standard from the original engine 84 LC turbo, dhla 40s. The float levels are set to those in the manual for the original engine as well, 15mm I think. Accelerating slowly off idle is fine but a quick throttle opening leaves it stumbling for a second. The accelerator pumps were overhauled as part of the carb overhaul with new diaphrams but reset to the original positions. After driving it again tonight it has minor hessitations at lots of different points through the revs but seems to be ok once the throttles have been open for a second ie opening the throttlw at 2000 or 3000 gives minor hessitation before smoothing out. I am still running in at the moment so 3500 is about the limit.
On the turbo side only a minor increase was ever planned to stay within the limits of the citroen gearbox. I have reduced the 20mm shim to 10mm so far and also have a 6mm which I will try. Theres no hex nut on the wastegate and it operates directly from the exhaust manifold, its the original 84 system so unfortunately no possibilty of a boost controller.
Hi,
The standard issue carburettors for an '84 USA model are the Dellorto DHLA 45M (The 'M' designation is for the pressurized DHLA used in turbo applications). The correct float setting is 14.5 - 15.0mm.
So far as adjusting the wastegate, the issue is not the dump valve, this is set for 12PSI, not 10 as previously mentioned. I have had the wastegate on my '85 Turbo rebuilt and calibrated to 10PSI and the dump valve does not open prematurely. The real issue is detonation. The increased boost causes the fuel to heat to it's combustion point before the spark ignites it and before the compression stroke is complete. This is very harmful to the engine components. Rule of thumb is that anything over 10PSI must be run through an intercooler. This is especially true as your 'new' engine has a higher CR (8.0:1 vs 7.5:1). Be sure you are using fresh quality fuel with a 93 octane rating. I am also running a cooler plug as an additional safeguard to detonation. And my CR was increased to 8.5:1. Even on the hottest days, there is no detonation. NGK rates their plug temps by the 1st number in the designation, but inversely, the higher the number, the cooler the plug. The stock plug - NGK BPR6ES runs hotter than the BPR7ES and cooler than the BPR5ES plugs. I am running the BPR7ES with excellent results, they do not foul at this cooler temp. They may not be necessary, but I use them and do not detonate.
Happy Motoring! ...Jim'85TE
The standard issue carburettors for an '84 USA model are the Dellorto DHLA 45M (The 'M' designation is for the pressurized DHLA used in turbo applications). The correct float setting is 14.5 - 15.0mm.
So far as adjusting the wastegate, the issue is not the dump valve, this is set for 12PSI, not 10 as previously mentioned. I have had the wastegate on my '85 Turbo rebuilt and calibrated to 10PSI and the dump valve does not open prematurely. The real issue is detonation. The increased boost causes the fuel to heat to it's combustion point before the spark ignites it and before the compression stroke is complete. This is very harmful to the engine components. Rule of thumb is that anything over 10PSI must be run through an intercooler. This is especially true as your 'new' engine has a higher CR (8.0:1 vs 7.5:1). Be sure you are using fresh quality fuel with a 93 octane rating. I am also running a cooler plug as an additional safeguard to detonation. And my CR was increased to 8.5:1. Even on the hottest days, there is no detonation. NGK rates their plug temps by the 1st number in the designation, but inversely, the higher the number, the cooler the plug. The stock plug - NGK BPR6ES runs hotter than the BPR7ES and cooler than the BPR5ES plugs. I am running the BPR7ES with excellent results, they do not foul at this cooler temp. They may not be necessary, but I use them and do not detonate.
Happy Motoring! ...Jim'85TE
hotrod1000 said:
(Snip)... its the original 84 system so unfortunately no possibilty of a boost controller.
Steve,
The wastegate is held closed by spring pressure and operates (opens) on intake boost pressure. Without it, the wastegate will not open.
A tube from the output side of the turbo's compressor delivers the required boost pressure to the diaphragm to open the wastegate. Block that tube with a closed solenoid valve and the wastegate will not open no matter how high the boost climbs.
Add an electronic black box that monitors plenum pressure and electrically energizes the solenoid valve at a pre-set boost pressure and the wastegate will quickly open. Not slowly as boost gradually builds, but almost immediately when the solenoid is energized by the black box. That's a boost controller and everything neccessary to add one is there. At least on a Federal Turbo Esprit... are DOM/ROW cars different?
Regards,
Tim
lotusguy said:
The standard issue carburettors for an '84 USA model are the Dellorto DHLA 45M (The 'M' designation is for the pressurized DHLA used in turbo applications).
True for the USA model and the DOM/ROW HC-carb model. However, Steve is in the UK and his DOM low-compression carb-Turbo uses DHLA 40H carbs... also pressurized. Same but different.
Tim Engel
hotrod1000 said:
Accelerating slowly off idle is fine but a quick throttle opening leaves it stumbling for a second. The accelerator pumps were overhauled as part of the carb overhaul with new diaphrams but reset to the original positions. After driving it again tonight it has minor hesitations at lots of different points through the revs but seems to be ok once the throttles have been open for a second ie opening the throttlw at 2000 or 3000 gives minor hesitation before smoothing out.
Steve,
That sounds like the accelerator pump more than anything else. The pump should deliver 7cc of fuel in 20 strokes. It would be interesting to know what it's actually delivering.
On Dellortos it's possible for the actuator arm not to be in direct contact with the diaphragm's metal base. There should be zero clearance and the accelerator pump should deliver fuel immediately with the smallest throttle movement. With the engine off, look in the throat while moving the throttle linkage a small amount, and watch for immediate fuel delivery. If there's "any" delay, adjust the two nuts (nut and jamb nut) on the actuator rod to take out any free play that may exist. Don't over adjust or the stroke length may be limited, resulting in less than the specified total fuel delivery (7cc in 20 strokes).
hotrod1000 said:
I am still running in at the moment so 3500 is about the limit.
Man, isn't that a frustrating time period. Agony. However, 3500 rpm seems awfully low. Is that what's recommended in the owner's manual, or are you being conservative?
Best regards,
Tim Engel
Lotus Owners Oftha North
Thanks Tim/Jim
I will check the accelerator pump settings in place first, make sure theres no slack. As for the turbo yes there is the pressure pipe and a boost controller could be an option. When the basics are sorted I will probably put it in the hands of a tuner to sort jets. Will let you know how it goes.
Steve
I will check the accelerator pump settings in place first, make sure theres no slack. As for the turbo yes there is the pressure pipe and a boost controller could be an option. When the basics are sorted I will probably put it in the hands of a tuner to sort jets. Will let you know how it goes.
Steve
Esprit2 said:
lotusguy said:
Rule of thumb is that anything over 10PSI must be run through an intercooler.
Hmmm... Interesting since the manual indicates the non-chargecooled GM injected Esprit gets 12 psi of boost at 8.0:1 compression.
Tim Engel
It also has a knock sensor and ECU to dynamically retard the timing to avoid this... As I said, Rule of Thumb.
Rule of Thumb:
An easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination. Not an absolute.
Happy Motoring! ...Jim'85TE
>> Edited by lotusguy on Tuesday 12th April 22:32
After finding out some typical dyno prices I think its worth a go DIY first.
Where and what is used to check fuel pressure, the regulator has been rebuilt and will probably get replaced but Im concerned about the right pressure.
What jet size changes would be a good start as I dont want to end up with a bag full of expensive jets at the end of the exercise.
Where and what is used to check fuel pressure, the regulator has been rebuilt and will probably get replaced but Im concerned about the right pressure.
What jet size changes would be a good start as I dont want to end up with a bag full of expensive jets at the end of the exercise.
Steve,
Sorry about not responding, but I haven't had much time for hanging out on PH. I just haven't re-visited this thread until now. Have you made any progress in the meantime?
There really isn't one magic set of jets that works. Normal engine and carb differences make it necessary to treat each one as an individual when it comes to the fine tuning. That, plus the fact that we really don't have a hard diagnosis of what's going on with your engine makes it impossible to say exactly what will cure the hesitation.
You've described what you think is happening and there's been some, "... sounds like" opinions, but no solid diagnosis. From that vague starting point, it's going to be a bit of a blind search for improvement. Dyno time by an expert might seem expensive, but it could prove to be a bargain in the long run. I would strongly suggest that you reconsider that route.
Since these same carbs used to run smoothly on the old engine, and since no settings have been intentionally changed, I'd start by checking the installation.
Triple check the accelerator pump stroke and clearance settings. There should be zero delay between throttle movement and the start of a squirt from the accelerator pump. Stock delivery is 7cc/ 20 strokes… if anything, change it to the later setting of 8cc/ 20 strokes. Then balance the carbs with a 4-tube manometer (other methods pale by comparison).
The symptoms you describe could very well result from errors in those two areas. Especially focus on the accelerator pump since you mention hesitation occurs throughout the low speed range (under 3500-4000 rpm).
Set the idle speed to 1000 rpm (I like to use 1000-1100 rpm). The faster idle speed makes closed-to-open throttle transitions less of an issue.
If you do elect to play with the jetting, start by considering the various factory set-ups. For the sake of comparison, here's the factory jetting for the DOM carb 910's. Charts don't come through on PH very well… the columns tend to get staggered a bit. But here goes. Contact me if it's not readable and I'll forward it to you as an attachment.
Factory Carb Jetting, DOM (Domestic) Market
Compression ........... Low, 7.5:1 ... High, 8.0:1 ... High, 1988 on
Carb Type ............... DHLA 40H .... DHLA 45M .... DHLA 45M
Choke ..................... 36 mm ........ 35 mm ........ 35 mm
Main Jet .................. 185 ............. 160 ............. 160
Main Air Corrector Jet. 200 ............ 180 ............. 180
Main Emulsion Tube .. 7772-12 ...... 7772-14 ....... 7772-14
*~*~*~*~*
Idle Jet ................... 40 ............... 58 ............... 58
Idle Jet Holder ......... 7850-7 (rich). 7850-9 (lean) .. 7850-10 (LEAN)
*~*~*~*~*
Float Weight ............ 8.5 gr .......... 8.5 gr ........... 8.5 gr
Float Setting Height .. 14.5/ 15.0 mm 14.5/ 15.0 mm 14.5/ 15.0 mm
Float Needle Valve .... 200 ............ 200 .............. 200
Pump Jet ................. 48H (Spcl) ... 35(Spcl) ...... 35(Special)
Starter Jet ............... 80 .............. 80 ............... 80
Starter Emulsion Tube 7482-3 ....... 7482-3 ......... 7482-3
Slow Running RPM .... 850 ............ 850-950 ....... 900-1000
Idle CO Level (hot) ... 1.0% +/- 0.5% 1.0% +/- 0.5% 0.5 - 1.5%
*~*~*~*~*
Pump Delivery .......... 7cc/ 20 strokes 8cc/ 20 strokes 8cc/ 20 strokes
Pump Lever Clearance ................. 0.1 +/- 0.05 mm
*~*~*~*~*
Fuel Delivery Pressure 4.0 +/- 0.5 psi… 4.0 +/- 0.5 psi… 4.0 +/- 0.25 psi
Idle Jet Holders (aka, Idle Air Corrector Jets) are not numbered sequentially, but totally randomly. Don't get caught making any assumptions about which one is the next size richer or leaner. Go by the following chart:
Weaker ......................... Normal ......................... Richer
7850.5 __ .10 __ .9 __ .4 __ .1 __ .3 __ .6 __ .7 __ .2 __ .8
All that is basically just for reference. Compared to the factory idle jetting for the later hi-compression engines, your carbs already have richer Idle Jet Holders (Idle Air Bleeds).
However, it's important to note that it's not a simple apples-to-apples comparison. The smaller 40H carb is running 36mm chokes. Since the chokes determine the effective minimum throat size, your 40H's with 36mm chokes are actually larger than the later 45M's with 35mm chokes. Not to mention that the later engines were saddled with tighter emissions requirements and the factory "may" have been shooting for a leaner mixture.
The 40H's larger chokes mean lower gas velocities, hence less vacuum and poorer fuel pull-over. So the 40H's basic idle circuit setting would have to be richer just to be even with the 45M's smaller choke/ higher velocity set-up with leaner Idle Jet Holders. Your current .7 Idle Jet Holders are the third richest available and probably about right. I've used .2's before, but they aren't always necessary.
The OEM 40 Idle Jets do look strangely small. I'd be inclined to bump them up just to see what happens. I'd probably start with 52's and go from there. On a USA Fed car (I'm more familiar with them), larger Idle Jets like those on the UK Hi-Compression engines are often required for hesitation-free running… 58-62. But those engines also have the very lean Holders and even larger 37mm chokes. Again, direct comparison is hazardous. I doubt that you'll have to go that far.
With your rich holders (.7) the large Idle Jets may very well be overkill. Try 52 first. If that fails to solve the problem, jump to 58. In the end, you want to use the smallest Idle Jet possible consistent with no hesitation below 3500-4000 rpm. Above that speed range, the main circuit takes over.
Regards,
Tim Engel
Lotus Owners Oftha North
>> Edited by Esprit2 on Wednesday 27th April 21:25
>> Edited by Esprit2 on Wednesday 27th April 21:51
>> Edited by Esprit2 on Wednesday 27th April 22:05
>> Edited by Esprit2 on Wednesday 27th April 22:17
Sorry about not responding, but I haven't had much time for hanging out on PH. I just haven't re-visited this thread until now. Have you made any progress in the meantime?
There really isn't one magic set of jets that works. Normal engine and carb differences make it necessary to treat each one as an individual when it comes to the fine tuning. That, plus the fact that we really don't have a hard diagnosis of what's going on with your engine makes it impossible to say exactly what will cure the hesitation.
You've described what you think is happening and there's been some, "... sounds like" opinions, but no solid diagnosis. From that vague starting point, it's going to be a bit of a blind search for improvement. Dyno time by an expert might seem expensive, but it could prove to be a bargain in the long run. I would strongly suggest that you reconsider that route.
Since these same carbs used to run smoothly on the old engine, and since no settings have been intentionally changed, I'd start by checking the installation.
Triple check the accelerator pump stroke and clearance settings. There should be zero delay between throttle movement and the start of a squirt from the accelerator pump. Stock delivery is 7cc/ 20 strokes… if anything, change it to the later setting of 8cc/ 20 strokes. Then balance the carbs with a 4-tube manometer (other methods pale by comparison).
The symptoms you describe could very well result from errors in those two areas. Especially focus on the accelerator pump since you mention hesitation occurs throughout the low speed range (under 3500-4000 rpm).
Set the idle speed to 1000 rpm (I like to use 1000-1100 rpm). The faster idle speed makes closed-to-open throttle transitions less of an issue.
If you do elect to play with the jetting, start by considering the various factory set-ups. For the sake of comparison, here's the factory jetting for the DOM carb 910's. Charts don't come through on PH very well… the columns tend to get staggered a bit. But here goes. Contact me if it's not readable and I'll forward it to you as an attachment.
Factory Carb Jetting, DOM (Domestic) Market
Compression ........... Low, 7.5:1 ... High, 8.0:1 ... High, 1988 on
Carb Type ............... DHLA 40H .... DHLA 45M .... DHLA 45M
Choke ..................... 36 mm ........ 35 mm ........ 35 mm
Main Jet .................. 185 ............. 160 ............. 160
Main Air Corrector Jet. 200 ............ 180 ............. 180
Main Emulsion Tube .. 7772-12 ...... 7772-14 ....... 7772-14
*~*~*~*~*
Idle Jet ................... 40 ............... 58 ............... 58
Idle Jet Holder ......... 7850-7 (rich). 7850-9 (lean) .. 7850-10 (LEAN)
*~*~*~*~*
Float Weight ............ 8.5 gr .......... 8.5 gr ........... 8.5 gr
Float Setting Height .. 14.5/ 15.0 mm 14.5/ 15.0 mm 14.5/ 15.0 mm
Float Needle Valve .... 200 ............ 200 .............. 200
Pump Jet ................. 48H (Spcl) ... 35(Spcl) ...... 35(Special)
Starter Jet ............... 80 .............. 80 ............... 80
Starter Emulsion Tube 7482-3 ....... 7482-3 ......... 7482-3
Slow Running RPM .... 850 ............ 850-950 ....... 900-1000
Idle CO Level (hot) ... 1.0% +/- 0.5% 1.0% +/- 0.5% 0.5 - 1.5%
*~*~*~*~*
Pump Delivery .......... 7cc/ 20 strokes 8cc/ 20 strokes 8cc/ 20 strokes
Pump Lever Clearance ................. 0.1 +/- 0.05 mm
*~*~*~*~*
Fuel Delivery Pressure 4.0 +/- 0.5 psi… 4.0 +/- 0.5 psi… 4.0 +/- 0.25 psi
Idle Jet Holders (aka, Idle Air Corrector Jets) are not numbered sequentially, but totally randomly. Don't get caught making any assumptions about which one is the next size richer or leaner. Go by the following chart:
Weaker ......................... Normal ......................... Richer
7850.5 __ .10 __ .9 __ .4 __ .1 __ .3 __ .6 __ .7 __ .2 __ .8
All that is basically just for reference. Compared to the factory idle jetting for the later hi-compression engines, your carbs already have richer Idle Jet Holders (Idle Air Bleeds).
However, it's important to note that it's not a simple apples-to-apples comparison. The smaller 40H carb is running 36mm chokes. Since the chokes determine the effective minimum throat size, your 40H's with 36mm chokes are actually larger than the later 45M's with 35mm chokes. Not to mention that the later engines were saddled with tighter emissions requirements and the factory "may" have been shooting for a leaner mixture.
The 40H's larger chokes mean lower gas velocities, hence less vacuum and poorer fuel pull-over. So the 40H's basic idle circuit setting would have to be richer just to be even with the 45M's smaller choke/ higher velocity set-up with leaner Idle Jet Holders. Your current .7 Idle Jet Holders are the third richest available and probably about right. I've used .2's before, but they aren't always necessary.
The OEM 40 Idle Jets do look strangely small. I'd be inclined to bump them up just to see what happens. I'd probably start with 52's and go from there. On a USA Fed car (I'm more familiar with them), larger Idle Jets like those on the UK Hi-Compression engines are often required for hesitation-free running… 58-62. But those engines also have the very lean Holders and even larger 37mm chokes. Again, direct comparison is hazardous. I doubt that you'll have to go that far.
With your rich holders (.7) the large Idle Jets may very well be overkill. Try 52 first. If that fails to solve the problem, jump to 58. In the end, you want to use the smallest Idle Jet possible consistent with no hesitation below 3500-4000 rpm. Above that speed range, the main circuit takes over.
Regards,
Tim Engel
Lotus Owners Oftha North
>> Edited by Esprit2 on Wednesday 27th April 21:25
>> Edited by Esprit2 on Wednesday 27th April 21:51
>> Edited by Esprit2 on Wednesday 27th April 22:05
>> Edited by Esprit2 on Wednesday 27th April 22:17
Hi,
Seems to be a bit of theorizing going on in this thread, which may not be all bad. But how about something more fundamental...What do your plugs look like?
Each one in turn will provide some insight into what it's dedicated carb barrel is doing. This may narrow the issue(s) some.
Happy Motoring! ...Jim '00 Boxster
Seems to be a bit of theorizing going on in this thread, which may not be all bad. But how about something more fundamental...What do your plugs look like?
Each one in turn will provide some insight into what it's dedicated carb barrel is doing. This may narrow the issue(s) some.
Happy Motoring! ...Jim '00 Boxster
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