Jaguar 3.8 Down On Power
Discussion
1950s 3.8 triple carb Jag
Changed the plugs as the previous owner had a mix of 5s - 8s fitted
They all look about right fuelling wise and it has good compression at 150 -160 psi on all 6
It is burning a bit of oil on hard acceleration
IMO it's around 100bhp down on power, a quick google tells me this is a Mallory dual points distributor, is it a worthwhile modification, my mechanic wants to put it back to standard as he says it's needlessly complicated
Are the 'sponges' correct ?
Changed the plugs as the previous owner had a mix of 5s - 8s fitted
They all look about right fuelling wise and it has good compression at 150 -160 psi on all 6
It is burning a bit of oil on hard acceleration
IMO it's around 100bhp down on power, a quick google tells me this is a Mallory dual points distributor, is it a worthwhile modification, my mechanic wants to put it back to standard as he says it's needlessly complicated
Are the 'sponges' correct ?
For a start it looks like you've got no vacuum advance, so that's going to mess up your idle and cruise. Secondly who knows what mechanical advance curve is fitted -it's highly unlikely Mallory made a distributor curved to a 3.8 Jaguar, this is probably for a Chevy stovebolt six or similar. Your mechanic is correct -put it back to standard!
I suspect this topic will bring out two thoughts
Thought 1: if the original set up was good in the 60's then why would it not work just fine now.
Thought 2: fit a 123+ dizzy
I have two Jags running the 123+ they are really good and very much fir and forget the one on the Mk2 has not been touched in 8 years, which is good seeing as how on the mk2 it's hardly in a handy location.
These have the big advantage of being a new bit of kit so there is not 50-60 years worth of ware on the drive gears and shaft. and the + version has the advantage of being able to map the ignition via your phone.
https://www.123ignitionshop.com/gb/132-tune-jaguar...
Thought 1: if the original set up was good in the 60's then why would it not work just fine now.
Thought 2: fit a 123+ dizzy
I have two Jags running the 123+ they are really good and very much fir and forget the one on the Mk2 has not been touched in 8 years, which is good seeing as how on the mk2 it's hardly in a handy location.
These have the big advantage of being a new bit of kit so there is not 50-60 years worth of ware on the drive gears and shaft. and the + version has the advantage of being able to map the ignition via your phone.
https://www.123ignitionshop.com/gb/132-tune-jaguar...
I cannot possibly see how those sponges are correct.
If that isn't the problem, my money would be on the centrifugal advance not working - have you a timing light you could plug in?
But - just to echo other posters - I would be very tempted just to go back to standard set-up, or electronic conversion for all the reasons already given.
If that isn't the problem, my money would be on the centrifugal advance not working - have you a timing light you could plug in?
But - just to echo other posters - I would be very tempted just to go back to standard set-up, or electronic conversion for all the reasons already given.
Thanks, I've been having a Google
Hot and cold starting, idle and cruise are all fine. It's just missing a lot of power - which of course may not be down to the distributor
AI suggested fitting the Pertronix kit, I thought I may as well change the cap too and it seems they're no longer available, copies cost £100 at which point it doesn't seem worthwhile
I have just started looking into the 123 kit
Hot and cold starting, idle and cruise are all fine. It's just missing a lot of power - which of course may not be down to the distributor
AI suggested fitting the Pertronix kit, I thought I may as well change the cap too and it seems they're no longer available, copies cost £100 at which point it doesn't seem worthwhile
I have just started looking into the 123 kit
MDT said:
I suspect this topic will bring out two thoughts
Thought 1: if the original set up was good in the 60's then why would it not work just fine now.
Thought 2: fit a 123+ dizzy
I have two Jags running the 123+ they are really good and very much fir and forget the one on the Mk2 has not been touched in 8 years, which is good seeing as how on the mk2 it's hardly in a handy location.
These have the big advantage of being a new bit of kit so there is not 50-60 years worth of ware on the drive gears and shaft. and the + version has the advantage of being able to map the ignition via your phone.
https://www.123ignitionshop.com/gb/132-tune-jaguar...
This seems a reasonable starting point.Thought 1: if the original set up was good in the 60's then why would it not work just fine now.
Thought 2: fit a 123+ dizzy
I have two Jags running the 123+ they are really good and very much fir and forget the one on the Mk2 has not been touched in 8 years, which is good seeing as how on the mk2 it's hardly in a handy location.
These have the big advantage of being a new bit of kit so there is not 50-60 years worth of ware on the drive gears and shaft. and the + version has the advantage of being able to map the ignition via your phone.
https://www.123ignitionshop.com/gb/132-tune-jaguar...
It might help if you could update a little more, ie. how the lack of power has been determined, how long have you had the car, ie. is it a sudden /gradual loss, or a recent purchase with unknown history. Is it an original 3.8 triple, or a retro-fit of some description, SUs or Webers? Do you know which cyl. head is fitted.
100 bhp down is a lot, ie. what 'figure' were you expecting to start with, and is the reduction based on a dyno read-out or a seat of the pants feel, in which case is it a reduction in perceived performance, or simply 'not what I expected from (for example) 300 bhp'.
A lot of questions but that's one heck of a power drop.
How long have you had the car? What do you know about the maintenance history of the (triple) SU HD8 set up? Same as I have, but differently jetted
Plenty of places to wear and degrade individual performance, let alone with 3 linked in a row. Float settings, throttle spindle and bearing wear, wrongly jetted (because non-standard distributor?) and or badly set, duff fuel, perforated diaphragms, dashpot wear/wrong oil, dirty internals. Back to basics I'd think, having changed the distributor (with/without contactless ignition). Also check HT leads and coil for breakdown, and LT circuit for the right components. Also fuel pump for proper flow rate
What does it sound like? Is it struggling to breath etc
Plenty of places to wear and degrade individual performance, let alone with 3 linked in a row. Float settings, throttle spindle and bearing wear, wrongly jetted (because non-standard distributor?) and or badly set, duff fuel, perforated diaphragms, dashpot wear/wrong oil, dirty internals. Back to basics I'd think, having changed the distributor (with/without contactless ignition). Also check HT leads and coil for breakdown, and LT circuit for the right components. Also fuel pump for proper flow rate
What does it sound like? Is it struggling to breath etc
I have recently bought it from the guy who built it,
he is in his 90s and hasn't used it much for many years, unfortunately his memory is fading, he couldn't remember what the various switches do, let alone the engine spec
The fuel is good, there's no pinking, the plugs are tan coloured, the exhaust is sooty
It's a bored out 3.4 to 3.8 with a skimmed head to raise compression and triple carbs. I'd guess it should be approx 240bhp and seat of the pants says it's less than 150
The guy built it in the 70s from a 50s donor, he was a good, amateur racer so it would have been well built at the time
When I test drove it, it wouldn't rev above 4500, changing the plugs has improved it but it's not pulling above 4500 really
There's plenty of torque and it drives well at lower revs, it might not have been driven hard for 30 years
he is in his 90s and hasn't used it much for many years, unfortunately his memory is fading, he couldn't remember what the various switches do, let alone the engine spec
The fuel is good, there's no pinking, the plugs are tan coloured, the exhaust is sooty
It's a bored out 3.4 to 3.8 with a skimmed head to raise compression and triple carbs. I'd guess it should be approx 240bhp and seat of the pants says it's less than 150
The guy built it in the 70s from a 50s donor, he was a good, amateur racer so it would have been well built at the time
When I test drove it, it wouldn't rev above 4500, changing the plugs has improved it but it's not pulling above 4500 really
There's plenty of torque and it drives well at lower revs, it might not have been driven hard for 30 years
I converted a modern 3.0 6 cylinder injection engine to triple side drafts and for while ran with the original ECU providing the sparks but it wasn't very good.
H&H ignition solutions converted the original hall effect distributor converted to swing adjustment with bob weight advance.
Despite saying in the advance that he'd taken a guess on the weights/springs/advance (based on a 2 litre version) and he would be happy to adjust if required it turned out to be spot on.
H&H ignition solutions converted the original hall effect distributor converted to swing adjustment with bob weight advance.
Despite saying in the advance that he'd taken a guess on the weights/springs/advance (based on a 2 litre version) and he would be happy to adjust if required it turned out to be spot on.
Jap90s said:
When I test drove it, it wouldn't rev above 4500, changing the plugs has improved it but it's not pulling above 4500 really
There's plenty of torque and it drives well at lower revs, it might not have been driven hard for 30 years
I'll reiterate my original diagnosis - check the centrifugal advance is working.There's plenty of torque and it drives well at lower revs, it might not have been driven hard for 30 years
Jap90s said:
When I test drove it, it wouldn't rev above 4500, changing the plugs has improved it but it's not pulling above 4500 really
There's plenty of torque and it drives well at lower revs, it might not have been driven hard for 30 years
Remember these units are not built or really designed for high revs, there is little benefit to be got North of 4500, but yes they should red line about 5500. In the absence of a rolling road. I would suggest you get a 123+ and set this up, this will give you a known good base line and you will know the ignition side of things is good. There's plenty of torque and it drives well at lower revs, it might not have been driven hard for 30 years
Then you can start looking at the fuel side of things. it could be some thing like a blocked or restrictive fuel filter, will be fine 90% of the time but these XK units drink like a German on a Friday night, once you get higher up the revs... will be hard to spot as the plugs will not show much from a problem during a short window and after you have driven 8 miles back to the house and popped them out.
You need to work on these issues in stages and concentrate on one thing at a time.
The sponges are not correct! They should be on brackets to “wipe” the cam, not be between the cam and the heel of the points. Regardless, all your symptoms are explained by non functional mechanical advance which should easily be solved by some lubrication and “working” the mechanism. Vacuum advance would be nice (you’ve Iost it with the Mallory) but is only really beneficial to increase the fuel efficiency on part throttle cruise; it wouldn’t impact quality of running otherwise.
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