spark plugs for 74 2500M
Discussion
My 2500M's spark plugs are inclined to build up carbon and foul. I've leaned out the mixture about as much as I feel I can, without causing pinking. The problem persists. (I have converted from Stromberg carbs to new dual Mikunis)
I'm now wondering about spark plugs. Seems to be some confusing recommendations out there about heat range. Conventional wisdom seems to be Champion N9Y or NGK BPR 6ES.
However, some expert advice seems to suggest a hotter plug -- like Champion N12Y or NGK BPR 5ES is fine to try. In fact, they're recommended for some versions of the 2.5 six.
Anyone have any thoughts or advice on this? Much appreciated!
I'm now wondering about spark plugs. Seems to be some confusing recommendations out there about heat range. Conventional wisdom seems to be Champion N9Y or NGK BPR 6ES.
However, some expert advice seems to suggest a hotter plug -- like Champion N12Y or NGK BPR 5ES is fine to try. In fact, they're recommended for some versions of the 2.5 six.
Anyone have any thoughts or advice on this? Much appreciated!
I actually used N7Y in my tuned 2500 with 1.75 SU (in a kit car), and never had a soot problem - is it running too rich at a particular point ? (been there....tried several needles before getting it right)
Yep hotter plugs may cause pinking....which is why I went colder
Yep hotter plugs may cause pinking....which is why I went colder
Edited by RCK974X on Sunday 4th December 20:19
Guys, thanks for your interest and comments. Good suggestion about the air/fuel gauge.
I'm pretty satsified with the way she's running, except at tickover. Rather rough tickover and resists my best attempts to smoothen it out. I put a vacuum gauge on it briefly and got a steady reading of about 12. Pretty low!
Anyway, the engine burns no oil to speak of and the plugs are carbon fouled, no oil fouling.
I replaced the dual Strombergs, with dual Mikunis to enhance performance and I'm pretty happy with my choice. The car performs well at speed.
But not so much at tickover. And the carboning up is frustrating!
I'm pretty satsified with the way she's running, except at tickover. Rather rough tickover and resists my best attempts to smoothen it out. I put a vacuum gauge on it briefly and got a steady reading of about 12. Pretty low!
Anyway, the engine burns no oil to speak of and the plugs are carbon fouled, no oil fouling.
I replaced the dual Strombergs, with dual Mikunis to enhance performance and I'm pretty happy with my choice. The car performs well at speed.
But not so much at tickover. And the carboning up is frustrating!
hi ronaldo
what is the ignition timing at tickover ,and are the engine breathers fed into the inlet ? if you have a fair bit of duration on the cam inlet lobe ,that would cause a low vacuum ,say over 285 degrees ,but if its a stock cam , id say something is a little bit off .
regards
robert
what is the ignition timing at tickover ,and are the engine breathers fed into the inlet ? if you have a fair bit of duration on the cam inlet lobe ,that would cause a low vacuum ,say over 285 degrees ,but if its a stock cam , id say something is a little bit off .
regards
robert
Robert, thanks for replying. I guess it's pretty obvious that I'm no mechanical expert.
I bought the car about 2.5 years ago. One of its selling points was it had performance cam installed. Sadly, I don't have the specs on the cam. (I guess the cam could be causing my lumpy tickover?)
As far as timing goes, I've been flying by the seat of my pants. To smooth out the tickover, I tried turning the distributor clockwise a bit to advance the timing (recommended by the supplier of my new Mikuni carbs).
I think it smoothed things out slightly, but not nearly enough for my liking. Now, I think I've likely advanced it too much, because the starter is hanging up a little.
But back to the spark plugs briefly: I imagine if I've got a sooting problem, I'd be just be putting a band-aid on it by using a hotter spark plug. Now I'm wondering if I'm facing a vacuum leak?
Any further thoughts?
I bought the car about 2.5 years ago. One of its selling points was it had performance cam installed. Sadly, I don't have the specs on the cam. (I guess the cam could be causing my lumpy tickover?)
As far as timing goes, I've been flying by the seat of my pants. To smooth out the tickover, I tried turning the distributor clockwise a bit to advance the timing (recommended by the supplier of my new Mikuni carbs).
I think it smoothed things out slightly, but not nearly enough for my liking. Now, I think I've likely advanced it too much, because the starter is hanging up a little.
But back to the spark plugs briefly: I imagine if I've got a sooting problem, I'd be just be putting a band-aid on it by using a hotter spark plug. Now I'm wondering if I'm facing a vacuum leak?
Any further thoughts?
Yeah, I was wondering about a vac leak...Some random ideas, just in case ...
An inlet/vacuum leak somewhere - this will affect idle much more than cruise - 12 (inches?) vac seems pretty low. OK...
My mate had a fault around one of the three upper manifold bolts...bogged it with red hermetite as a temp fix, then got new gasket later.
Does it idle roughly - 2500 has something of a reputation for burning inlet valves, which would behave like a vacuum leak. Er, that might have been the PI setup, but anyway. I've had that problem. Head off unfortunately. Typically one plug would be worse then the others, which is a clue.
I had a mild road cam and it didn't affect idle vacuum THAT much - it was about 18 I think.
Have you got that horrid banjo thing for the breather ? (centre of inlet mfold, or is that the mk1 setup ?) they can fail and cause an effective vac leak too.
Starter hanging probably does mean static timing a bit too advanced.
Silly stuff - (you never know) If mikunis are like strombergs/SU ...
1. are they properly balanced (for flow)
2. do they have the same needles/jets (I've seen that on a pair of SUs !! )
Um...can't think of anything else right now.
An inlet/vacuum leak somewhere - this will affect idle much more than cruise - 12 (inches?) vac seems pretty low. OK...
My mate had a fault around one of the three upper manifold bolts...bogged it with red hermetite as a temp fix, then got new gasket later.
Does it idle roughly - 2500 has something of a reputation for burning inlet valves, which would behave like a vacuum leak. Er, that might have been the PI setup, but anyway. I've had that problem. Head off unfortunately. Typically one plug would be worse then the others, which is a clue.
I had a mild road cam and it didn't affect idle vacuum THAT much - it was about 18 I think.
Have you got that horrid banjo thing for the breather ? (centre of inlet mfold, or is that the mk1 setup ?) they can fail and cause an effective vac leak too.
Starter hanging probably does mean static timing a bit too advanced.
Silly stuff - (you never know) If mikunis are like strombergs/SU ...
1. are they properly balanced (for flow)
2. do they have the same needles/jets (I've seen that on a pair of SUs !! )
Um...can't think of anything else right now.
Edited by RCK974X on Monday 5th December 07:39
Renaldo said:
Robert, thanks for replying. I guess it's pretty obvious that I'm no mechanical expert.
I bought the car about 2.5 years ago. One of its selling points was it had performance cam installed. Sadly, I don't have the specs on the cam. (I guess the cam could be causing my lumpy tickover?)
As far as timing goes, I've been flying by the seat of my pants. To smooth out the tickover, I tried turning the distributor clockwise a bit to advance the timing (recommended by the supplier of my new Mikuni carbs).
I think it smoothed things out slightly, but not nearly enough for my liking. Now, I think I've likely advanced it too much, because the starter is hanging up a little.
But back to the spark plugs briefly: I imagine if I've got a sooting problem, I'd be just be putting a band-aid on it by using a hotter spark plug. Now I'm wondering if I'm facing a vacuum leak?
Any further thoughts?
first is , what rpm are you aiming for for tickover ? if there IS a 285 sort of cam in it , i wouldnt really try to make it tick over much below 950 to 1000 rpm .I bought the car about 2.5 years ago. One of its selling points was it had performance cam installed. Sadly, I don't have the specs on the cam. (I guess the cam could be causing my lumpy tickover?)
As far as timing goes, I've been flying by the seat of my pants. To smooth out the tickover, I tried turning the distributor clockwise a bit to advance the timing (recommended by the supplier of my new Mikuni carbs).
I think it smoothed things out slightly, but not nearly enough for my liking. Now, I think I've likely advanced it too much, because the starter is hanging up a little.
But back to the spark plugs briefly: I imagine if I've got a sooting problem, I'd be just be putting a band-aid on it by using a hotter spark plug. Now I'm wondering if I'm facing a vacuum leak?
Any further thoughts?
the problem with turning the distributor ,is that ,whilst you may make the timing more appropriate for lower rpm , you still have the same amount of advance in the distributor ,so your max advance at high speed becomes to much .
eg ,timing change in the dist is 20 degrees max ,(so as your rpm goes up the timing advances 20 degrees) , now , set the timing at ,say, 20 degrees at tickover ,and at 4k rpm you now have 40 degrees ,which MAY be too much ,and create heat and maybe detonation .
its safer to run stock timing really , unless you modify the dizzy to limit advance movement .... if you can limit it to ,say, 10 degrees max ,then you can run 20 at tickover ,and it will go to 30degrees at higher rpm ,which is more like it if it has a cam and maybe a higher comp head .oops digressing a bit there lol.
i would stick with the 6's plugs wize ,make sure the breathers are not pouring oil smoke inot the carbs , make sure the engine is running a good mixture ,and that it is getting up to temperature properly .oh ,also check to make sure your fuel pressure is not too high .
regards
robert
Robert, I've been aiming for ~ 850 rpm at tickover. About right for a standard engine maybe, but not so appropriate for mine with the performance cam (whatever that cam may be).
I can get a better idle if I aim for ~ 1000. Not perfectly smooth, but better.
And I think you're right about the timing. I think I'll just set it properly and leave it alone.
Interesting point about fuel pressure too. I know I've got a Facet electric fuel pump, and I've assumed it was pretty foolproof.
I can get a better idle if I aim for ~ 1000. Not perfectly smooth, but better.
And I think you're right about the timing. I think I'll just set it properly and leave it alone.
Interesting point about fuel pressure too. I know I've got a Facet electric fuel pump, and I've assumed it was pretty foolproof.
More ideas -
(I had several 2500PI and carb powered vehicles)
Yeah fuel pressure is a good idea, can cause flooding - I didn't think of that.
Basic checks - assuming similar setup to twin Strombergs etc....
Are the front 3 plugs same as rear 3 ? If not suspect carb balance or one of the carbs
Is one plug worse/different than the others ?
It's possible the cam timing is off too, but this is harder to check. It is possible to get the
timing cover off to inspect, but it's a bit messy.
Are you sure the valve clearances are right and none are binding ? (it can happen)
Have you tried disconnect vac advance - it's unlikley, but possible that it is leaking.
My Marlin kit had a 2500 with mild road cam, gas flowed head with raised CR, 1.75 HIF6 SU on manifold which was opened up to match (ever wondered why the carb mount castings are square ?) extractor exhaust, went very well, but a bugger to get it right.
Does it pink anywhere in the rev/load range ? (I had loads of trouble with this, but it didn't foul the plugs all that much. ) You might need different advance springs to get it just right
Hope this helps !!
(I had several 2500PI and carb powered vehicles)
Yeah fuel pressure is a good idea, can cause flooding - I didn't think of that.
Basic checks - assuming similar setup to twin Strombergs etc....
Are the front 3 plugs same as rear 3 ? If not suspect carb balance or one of the carbs
Is one plug worse/different than the others ?
It's possible the cam timing is off too, but this is harder to check. It is possible to get the
timing cover off to inspect, but it's a bit messy.
Are you sure the valve clearances are right and none are binding ? (it can happen)
Have you tried disconnect vac advance - it's unlikley, but possible that it is leaking.
My Marlin kit had a 2500 with mild road cam, gas flowed head with raised CR, 1.75 HIF6 SU on manifold which was opened up to match (ever wondered why the carb mount castings are square ?) extractor exhaust, went very well, but a bugger to get it right.
Does it pink anywhere in the rev/load range ? (I had loads of trouble with this, but it didn't foul the plugs all that much. ) You might need different advance springs to get it just right
Hope this helps !!
Robert, thanks for the great suggestions! From what you're telling me, it may take a bit of time and analysis to get this right.
The front 3 plugs seemed to be more sooted up than the rear, so I guess my problem is (at least in part)improperly balanced carbs.
No vacuum advance on my dizzie, only retard. By the way, I installed a Pertronix electronic ignition some time ago too.
I don't think there's any pinking to speak of. Engine really does seem to run well at speed. It's that damn idle!
And I reset the valve clearances. Wow, were they out of whack! But again, it didn't seem to make much difference to the idle.
If you think of anything else, please let me know. A great help to hear from someone who knows his stuff!
The front 3 plugs seemed to be more sooted up than the rear, so I guess my problem is (at least in part)improperly balanced carbs.
No vacuum advance on my dizzie, only retard. By the way, I installed a Pertronix electronic ignition some time ago too.
I don't think there's any pinking to speak of. Engine really does seem to run well at speed. It's that damn idle!
And I reset the valve clearances. Wow, were they out of whack! But again, it didn't seem to make much difference to the idle.
If you think of anything else, please let me know. A great help to hear from someone who knows his stuff!
Happy to help ...
NB> if it's a hot cam, valve clearances may be a bit bigger than standard. I can't remember mine for sure, I think the inlet was the same and the exhaust was +2 thou ? or possibly +1 and +2.
For carbs It's worth using a flow balancer.
Not sure if the old Gunsons Carbalancer is still around, that was cheap'n'cheerful.
Anyway if you can find/borrow a flowmeter of some kind, start there, after valve clearances set.
In the old days the guys used a length of tube and listened to the hiss. I could never tell the
difference !
THEN try adjusting mix for best idle. Weaken whichever carb feeds the blacker plugs first, and then do small adjustments on each. After having done it a few times, you'll get the feel for it.
Even with electronic ignition - is the dizzy OK ? The shafts used to wear and go sloppy, and the advance springs get slack too in orig Lucas ones. This can cause erratic idle - should be able to see that with timing light though.
(it's Andy by the way, but I'll forgive you !)
NB> if it's a hot cam, valve clearances may be a bit bigger than standard. I can't remember mine for sure, I think the inlet was the same and the exhaust was +2 thou ? or possibly +1 and +2.
For carbs It's worth using a flow balancer.
Not sure if the old Gunsons Carbalancer is still around, that was cheap'n'cheerful.
Anyway if you can find/borrow a flowmeter of some kind, start there, after valve clearances set.
In the old days the guys used a length of tube and listened to the hiss. I could never tell the
difference !
THEN try adjusting mix for best idle. Weaken whichever carb feeds the blacker plugs first, and then do small adjustments on each. After having done it a few times, you'll get the feel for it.
Even with electronic ignition - is the dizzy OK ? The shafts used to wear and go sloppy, and the advance springs get slack too in orig Lucas ones. This can cause erratic idle - should be able to see that with timing light though.
(it's Andy by the way, but I'll forgive you !)
Edited by RCK974X on Tuesday 6th December 04:13
Andy, I'm sorry about the name mix-up. Do you mind if I keep calling you Robert? Or maybe I'll switch to Al. (with apologies to Paul Simon) (joking)
A wealth of good suggestions. I especially like your tip about the dizzie. With all my focus on the carb/fuel issues, maybe this whole thing is ignition related. Pretty hard to get a good idle I imagine, if your distributor is sloppy.
I was under the impression that the Pertronix would take care of any and all dizzie issues. Wrong impression, I guess.
TVR = fun + frustration
A wealth of good suggestions. I especially like your tip about the dizzie. With all my focus on the carb/fuel issues, maybe this whole thing is ignition related. Pretty hard to get a good idle I imagine, if your distributor is sloppy.
I was under the impression that the Pertronix would take care of any and all dizzie issues. Wrong impression, I guess.
TVR = fun + frustration
Hey, no worries at all. Happy to help !
I've been around this block too many times, and experience teaches you that it's often something that was bl**dy obvious, but you get sidetracked onto a 'favourite' problem. A mate says "what about..." and suddenly you realise.
This is why I suggested all the basic stuff first....
It seems to me you do need to balance and adjust carbs first, and then see if dizzy is also a bit worn.
It may still be an odd vac leak somewhere....An ages old test for inlet mfold gasket is to dribble a few drops of oil on the gasket and see if it gets sucked in. Check you haven't got any broken 'fingers' or loose bolts between inlet and exhaust mfolds.
Hopefully you can gradually improve the idle as you go....
When I said mine was a bugger to get right, if I did it over again I wouldn't go for the high CR head, as messing with multiple sets of advance springs was a pain. Mixture wasn't too bad, but again it took 3 sets of needles before I got good running throughout the range.
Andy.
I've been around this block too many times, and experience teaches you that it's often something that was bl**dy obvious, but you get sidetracked onto a 'favourite' problem. A mate says "what about..." and suddenly you realise.
This is why I suggested all the basic stuff first....
It seems to me you do need to balance and adjust carbs first, and then see if dizzy is also a bit worn.
It may still be an odd vac leak somewhere....An ages old test for inlet mfold gasket is to dribble a few drops of oil on the gasket and see if it gets sucked in. Check you haven't got any broken 'fingers' or loose bolts between inlet and exhaust mfolds.
Hopefully you can gradually improve the idle as you go....
When I said mine was a bugger to get right, if I did it over again I wouldn't go for the high CR head, as messing with multiple sets of advance springs was a pain. Mixture wasn't too bad, but again it took 3 sets of needles before I got good running throughout the range.
Andy.
Edited by RCK974X on Wednesday 7th December 02:55
Renaldo,
Beg, steal, or borrow a Gunson's Colortune. The Mikunis were surely designed for a different application. I am certain that air/fuel metering & progression can be tuned to your car. Are they motorcycle type round/or flat slide carbs? You may simply have to switch to a different needle shape to alleviate your problem. From the previous posts, I'd put a Dollar on it running rich in the lower range, and/or at idle. Is there a separate idle circuit in those? Maybe you can jet the idle A/F mix to leaner. If not, you may want to see if you can lower the needles in the slide body. Some, like Dell'Ortos use a needle with circlip position adjustment. In either case, I would get a manual for those carbs, before going too much further.
The old timey mechanic's test is to run the car at a constant RPM for a while, then shut the ignition down, coast to a stop, and check the plugs. Do so in 1000 increments, and you'll see where, in the range the problem lies.
Best,
B.
Beg, steal, or borrow a Gunson's Colortune. The Mikunis were surely designed for a different application. I am certain that air/fuel metering & progression can be tuned to your car. Are they motorcycle type round/or flat slide carbs? You may simply have to switch to a different needle shape to alleviate your problem. From the previous posts, I'd put a Dollar on it running rich in the lower range, and/or at idle. Is there a separate idle circuit in those? Maybe you can jet the idle A/F mix to leaner. If not, you may want to see if you can lower the needles in the slide body. Some, like Dell'Ortos use a needle with circlip position adjustment. In either case, I would get a manual for those carbs, before going too much further.
The old timey mechanic's test is to run the car at a constant RPM for a while, then shut the ignition down, coast to a stop, and check the plugs. Do so in 1000 increments, and you'll see where, in the range the problem lies.
Best,
B.
Bernard, thanks a million for weighing in. I think you're on to something too.
They're motorcycle carbs designed for Harleys. Honestly, I haven't gone through the whole tuning thing with them yet, and I likely need to -- desperately! (been a bit scared to make the problem worse).
I did follow Mikuni's recommendation for setting up the idle circuit, but I haven't done all you've suggested regarding any other tuning. The supplier of the carbs (John Parker of Vintage Performance Developments out of Syracuse New York) suggested I might want to try smaller pilot jet needles. Do you think this is worthwhile doing?
And I have a Gunson's Colortune languishing somewhere in may basement! I'll dig it out and try it.
They're motorcycle carbs designed for Harleys. Honestly, I haven't gone through the whole tuning thing with them yet, and I likely need to -- desperately! (been a bit scared to make the problem worse).
I did follow Mikuni's recommendation for setting up the idle circuit, but I haven't done all you've suggested regarding any other tuning. The supplier of the carbs (John Parker of Vintage Performance Developments out of Syracuse New York) suggested I might want to try smaller pilot jet needles. Do you think this is worthwhile doing?
And I have a Gunson's Colortune languishing somewhere in may basement! I'll dig it out and try it.
Renaldo said:
...I did follow Mikuni's recommendation for setting up the idle circuit, but I haven't done all you've suggested regarding any other tuning. The supplier of the carbs (John Parker of Vintage Performance Developments out of Syracuse New York) suggested I might want to try smaller pilot jet needles. Do you think this is worthwhile doing?
And I have a Gunson's Colortune languishing somewhere in may basement! I'll dig it out and try it.
Renaldo, And I have a Gunson's Colortune languishing somewhere in may basement! I'll dig it out and try it.
My pleasure.
Dig the Colortune out before anything else. You need to know where you are at various RPM, and that's the best tool for the job. Only then should you make changes.
What model Mikunis are they? I'll look up a circuit/or/parts diagram on line.
If the carbs have a nice idle/progression circuit, with ratio jets AND metering jets, AND the excess enrichment is occurring on idle & transition, DON'T TOUCH THE NEEDLES FOR NOW.
Best,
B.
Bernard, the carbs are HSR 45mm Mikunis. If I'm hearing you right, I probably shouldn't be jumping to changing needles yet, until I've tried out the Colortune to figure out at what stages I'm running rich.
These carbs are modern Japanese engineering by all accounts, so I'm thinking with the right tuning, the car should be idling much, much better than it is. Better than with the Strombergs. But frankly, right now, probably worse.
I await any other expert thoughts or advice you may have for me. And thanks again!
Ron
These carbs are modern Japanese engineering by all accounts, so I'm thinking with the right tuning, the car should be idling much, much better than it is. Better than with the Strombergs. But frankly, right now, probably worse.
I await any other expert thoughts or advice you may have for me. And thanks again!
Ron
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