Engine idles at 1400 RPMs I am working to get it lower. Idle too low the ign light comes on. I have the synchronizer stems with indicator in the SU carburetors both rise and lower at the same rate. When turning the throttle to rev up the engine I get backfire on intake side. The timing is not perfect due to the distributor has not been rebuilt but is close.
What is my next action? Adjust the mixture because it is too lean? Advance or retard the timing? Any other thoughts?
Maddy
Is the engine warmed up? Is the starting carb engaged? You may have a vacuum leak causing the high idle speed.
Maybe your butterfly spindles are worn allowing air in?
Any of those are possibilities. I for got to mention that when putting the trans mission in reverse or first the engine quits unless I give it a ridiculously high rpm then I can get the intake backfire with those high rpm’s. Is the engine warmed up? At first no but after 5 minutes it is and I make minor adjustments mostly to lower the rpm’s. More need to be done but I do not want to undo any progress made by messing with things I do not fully understand.
This is my first Jaguar and I have no ear for how the engine is running compared to another that runs well.
Marianne
I suggest you go about this methodically.
warm it up, and make sure the starting carb is off.
(1) Get the timing close to right. Due to your high idle, set an advance of perhaps at 12degrees. That’s enough that the timing will not be an issue. At this point you can try backing off the idle screws to see if the rpm come done to a more reasonable 600-700.
Then balance the carb air flow with the idle screws and you pointy wire things. For this operation I loosen the linkage connection between the throttle rod and the rear carb and also between the two carbs. This allows the two carb throttle plates to be set independently using the idle speed screws. Balance them and set the idle rpm in the 600-700 range with the idle speed screws. If you can’t get the idle speed down at this stage, something is mechanically wrong with the carbs (maybe the throttle plates are crooked and letting too much air in).
If at this point idle is 600-700rpm, the timing is right and carbs are balanced, you can check the mixture. Check the mixture using the lifting pins per the manual. The manual process will leave you with a somewhat rich idle, which is ok.
Finally tighten the throttle linkage connections.
Doing it like this works well for me.
Now, after all this if you still get backfiring/popping , high idle and poor running the. You likely need to take the carbs apart for an minor rebuild (DIY stuff).
John
Ignition light has nothing to do with this, I presume you still have the old generator.
Could be that the regulator needs some adjustment.
Do you have the right oil in the dash pots?
good post by John
Do you have the Service Manual, you should own it and use it
I too would ignore the light just for the minute
You need to know when the ASC is on or off, for which a manual switch is best
Once the vehicle has been allowed to idle long enough to warm up, then the ASC should be disengaged, and the carburettors tuned
First the timing should be checked with a strobe light, and static timing with a test light
The vehicle should not stall when gearbox is engaged
Probably something simple, may be a few simple faults
Its critical to be systematic for fault diagnosis, hence the service manual
The engine will certainly cough/backfire if given too much throttle when the dashpot oil is too low or absent.
Maddy, regarding the 1400 RPM idle speed, I found this photo of your engine from last year.
It appears your starting carb solenoid is wired to the Otter switch in the original way. It’s possible the Otter switch isn’t shutting off the solenoid after the engine warms up, which would continue the fast idle. After you start the engine, try disconnecting the wire at the Otter switch to see if the idle speed drops.
For now, disregard the ignition light coming on at low idle speed. The generator doesn’t begin to charge until the engine is running above idle speed.
Yes the gen light shoulfcome on at lower idle speeds. If everything else checks out I’d suspect the throttle plates not centered correctly. With the carbs off hold them up to the light with the throttles fully closed, there shouldn’t be any visible light around the edges of the throttle plates.
All the suggestions and diagnoses are good…knowing what you know…BUT…Since I have been involved in some of the start up work, with a few morning visits, I can say: …the start carb is NOT operating when I last saw it. The reason was not investigated. The timing is “close” but not precise. It was set static : we found and verified TDC #6 compression…then made a mark on flywheel tooth…set for approx 2 teeth before. BUT…had to turn distributor by hand back and forth a little to get the initial start up and smoother running, and did not check the final position. The points…while new, have a bent point holder…and do not make flat contact. We set at 016 but is is not ideal to the not flat mating surface of the points. ALL of this will affect idle and running. We also know that the carbs setting was not even close at first. The jet screws were all the way loose…(downn) We made adjustments to the bottom center adjustment, …to get the initial start up…and did not re-set or further adjust. We got the start up and ok running …further carb adjust being futile with the other issues mentioned above. Plugs are new, with new wiring, new dizzy cap. Maddy rebuilt the carbs…but checking the running adjustments, even float levels etc would need to be done AFTER addressing the several other issues…all of which combined…with the carbs…make it kind of lucky that we got the start up at all…but we did, and …it continues to start well…and while at that faster idle actually runs quite smoothly…no popping, no black smoke. I was able to back it…and make a short run in the driveway. My advice to Maddy…as you plan to sell…it starts, it runs, it needs quite a bit of fiddling with timing-points-carbs…including the start carb. Good enough…the next owner knows it has no engine noises of concern (a re-check of cam-follower clearances will be part of the check…you got it close enough…just a little tappet noise to check…but some is normal). I’d leave all that…alone. Too many things to chase…in the time you have. Engine sounds fine…65psi oil cold, and 40-45 at warmer idle. Only observed major oil leak was at cam covers which we did not do a final install with good gasket…we used the cheap thin one for now, with no sealer at all.
Nick
Lots of suggestions, thanks all. John pretty much nailed it for procedure. Thank you John. Nick was instrumental in getting the Jag running and as stated is aware of the issues. His friend who assisted instructed me to make an adjustment to the return spring and so I did as he suggested. Now it does not run as smoothly as it did when Nick finished with his work. I do not see the harm in trying a few things to bring that idle down.
Maddy
If it is intended to be sold, I would pay someone to fix it, as the cost of would be re-couped for a well running car versus one that does not run well
imo, its essential the ASC be made operational
maybe it depends on if its to be sold via auction or private sale, but still…
Tony,
I do see your point. However, the car would have to be towed to a repair shop. It is a considerable distance and would cost $500 each way. Surely I would recoup the expense. If I were to purchase the car with the intent to restore it I would do again what has been done already to have the confidence that it was done properly and by a knowledgeable professional. Therefore with that said I will just see what I can do on my own.
Maddy
fine idea
1st thing is you must test if the ASC works or not
I dont know how much electrical knowledge you have
The ASC is supplied 12V and is earthed via the Otter switch
the best thing to try is short the otter switch connection to ground and see if the ASC clicks in & out when you do so, ensure it has 12V going to it with the ignition switch on.
Nick said it didnt work ?
takes 5 minutes to remove it and test on bench, make sure the spring, plunger & valve dont fall out, the plunger can also get stuck in the solenoid body preventing it working
lots in the archives on this
there may even be a Youtube
they are wretched little things, but must work. If it is failed, a used one can be bought
imo, an XK motor can not be tuned and operate well without an ASC
on my first Jag, I did not know the ASC had been fitted with a manual switch (many people do this, so look for a hidden switch under the dash), it was very hard to start without the ASC
If you would please explain the acronym ASC.
Maddy
Auxiliary Starting Carburettor: it’s the black cylinder between the S.U. carburettors, earthed by the otter switch in the coolant elbow below 35°C, it opens and lets extra air and fuel while the engine is cold.
Best,
Ll.
Starting carb
The white wire is connected to the - neg side of the coil.
The black wire is what switches it on and off.
With the key on, touch a grounded test wire to the black wire and you should hear the click of the carb solenoid.
Or you can touch between the otter switch center terminal and ground with a wire or tool such as a screwdriver.
Otter switch
Adding my dos centavos. A cold engine requires a fuel rich mixture to start and run until it warms up. There are two ways to do this. First is to restrict the airflow with what is commonly called a choke. The second is to install a separate device (aka ASC) to directly inject a very fuel rich mixture unto the intake manifold. Jaguar chose to use a solenoid controlled ASC that would cut-out once the engine warmed. The Otter Switch does that by interrupting the earth connection to the solenoid. As has been stated, if you ground the terminal on the Otter Switch (with the ignition on) you should hear the ASC solenoid click. If it doesn’t you either have a bad connection or solenoid problem.
Pat H
SU chokes add air and lower the jet to raise and richen the mixture; other carbs add fuel with a separate device, the ASC adds an extra rich mixture automatically, adjusted for engine load and it doesn’t care about the temperature which makes it a compromise as it has to work between deep winter and mild summer.
But it’s simple and does the job and as important as it is, it is easy to get running!
