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Dieseling

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Webb Sledge

Webb Sledge

Jedi Warrior
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My car dieseled (kept running) on me for a few seconds after I cut it off today. Hasn't done it much, but is it caused by ignition timing being off? I know for sure that the it's off a few degrees, as it hesitates under sudden throttle.
 
Webb, you might check your idle speed and lower it if you can to below 1000rpm. Too, a hot-running engine will contribute to the dieseling effect. I run my TR6 without vacumn advance, hence the timing is set at 8 degrees BFTD at idle.

Bill
 
Dieseling is caused by a hot piece of carbon in the combustion chamber igniting a fuel-air mixture. Too high of an idle or having the throttle butterflies cracked open too much will make one run on. Setting back your timing or removing the vaccum advance might cure your run on, but will not fix your problem. Readjusting your idle speed will help. You MAY have to go so far as to remove your cylinder head and clean out the built up carbon. I have heard putting a couple of tablespoons of Marvel Mystery Oil in the spark plug hole and letting it set for several days will work, but I have never tried this so you would be own your own. GOOD LUCK!!! /ubbthreads/images/graemlins/grin.gif
 
Webb.....
Mine's a 73 TR6 and it has an anti run on device located below the charcoal cannister. Not sure if they had those on the 72 but probably.
Check the hoses and electrical operation of this. The device is basicaly a solenoid operated air valve driven off the ignition switch through the oil pressure switch. Mine was not working but I fixed it, hose was broken off and the electrical contacts were corroded, also make sure the 3 spade terminals on the oil switch are connected to the correct terminals.
You can tell it's working when you here a farly loud click a second or two after shutting off the engine, thats the valve closing. Of course if it's dieseling on you can't hear anything anyway.
I used to have an Olds Cutlass that you could go do your shopping and it was still belching away when you came back out. Of course it saved wear on the battery and starter!
 
Well... my car idles at 800 rpm, the carbs are set where they need to be, and the engine has less than 1000 miles on it's rebuilt engine, so there is no carbon buildup on the pistons. Today was actually the first time it's done it, and only for like 2 seconds. I'll try the oil though and check that valve.
 
You might want to try a higher grade of gasoline or one from a different supplier. Low octane, or dirty fuel can cause this problem.
 
I believe running-on in older cars is just a function of lower octane unleaded fuels and higher compression. One of the benifits of the lead additive was to increase the octane somewhat. Pre-unleaded cars had higher compression to take advantage of this. When you run an older high-compression engine (which after head-shaving and other mods may have higher-compression than even originally) then you may get running-on irrespective of anything else. You can fit the vaccume by-pass valves or just do as i do - turn off the ignition with the car in first and pop the clutch if it starts to run-on.

Rob.
 
You said that you only have 1000 miles on your rebuild and this is the first time it's done this. With an engine that "new" it shouldn't have any carbon to worry about. In addition to the other things that have been listed, it could also be your mixture is too lean. If you richen it up a bit the problem may go away.

However, you said that the carbs are "where they need to be". If you don't want to mess with them it sounds to me like you need to fall back to the tried-and-true method of addressing (not fixing) this problem. When you stop the engine, put the car in 4th gear and as you turn off the key ease your foot off the clutch.
 
How about advancing the timing a little bit and see what happens?

In my short time dealing with my TR6 I've already learned that timing is crucial. I would'nt mess with anything else until I got the timing sorted out. Or else you may be fooling with stuff un-necessarily.
 
Stinky, that's what I think it is. I just wanted some feedback beforehand. If it starts dieseling with more regularity and timing doesn't fix it, I'll try premium (DANG those gas prices!!).
 
By all means use Premium. If your running 87 octane that's probably a/the probem. Personally I always run Lucas Octane Booster in my TR6. Course I only drive it on weekends for the most part so adding the Booster is no big deal. The car definetly likes the booster,...it runs noticably better, and sounds better.
The Triumph owners manual I have for the car recomends the using the highest octane fuel available (in 1971) says it should be over 100.
When I read that I thought I'd better get some Booster.
 
I agree with Altaknight. If you have a carbon canister with an anti run on valve this could be the problem--it was on my '76. The canister gets pretty saturated with gas and if the anti run on valve stays open after you turn off the car the carbs draw gas vapor back from the canister. When I got rid of my old canister and anti run on valve, the problem went away.
 
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