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TR4/4A TR4a with CD175's Dieseling

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J

JDstr4a

Jedi Hopeful
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Finally found the 312 L87YC plugs and installed with new points caps and wires. Seems to run much smoother, but is dieseling severely on shut-off.Double checked mixture and wondering where to go next? Haven't touched advance or checked timing yet. Would that be next or should I go through the carbs?
Thanks
JD
 
Don't know about the TR4 engine, but I had a similar problem with my TR6. Once I went to the highest octane gas, all the dieseling went away.
 
Thanks, guess I'll have to drive the last half of the tank out!
 
Certainly timing will affect this. I wouldn't jump to any conclusions until you have the timing adjusted to a good place. My TR4 has a slightly bored engine with a bit higher compression and I got rid of some run-on with timing adjustment and changing to brand-name (Shell) gas but staying with regular.
 
Thanks, I drove it to the nursery and back (5mi) she performed reasonably well, strong pull, a little hot and maybe a little lumpy on idle when below 750rpm. All and all a successful jaunt!
:banana:
I'll put the thermostat and timing checks on my list! But first :thirsty:
Thanks
JD
 
I don't worry about dieseling. I make it a habit to put the car in 4th gear and release the clutch slowly as I turn the ignition off. It stalls the engine and prevents dieseling. No... it doesn't address the root cause but it does prevent the symptoms.
 
JD,

If I have dieseling in my TR3, I lower the idle a bit. That almost always works. Another thing that works is to make the mixture a little richer.

At least for my car, running lean with an idle that's high can lead to dieseling.

Just an idea...
 
Thanks Ed, I'm at the default for mixture (3 turns) so I'll try to rich it up a little and see what happens.Getting into the timing thing is, with my limited abilities, something I'm saving for now.
JD
 
I would try lowering your idle a bit first. It doesn't have to be by much. Run the car around the block once or twice, and then stop and turn it off and see if the dieseling stops.

Try adjusting the mixture later. (But you need to watch this. Dieseling is sometimes caused by running "too rich." What I am saying is that you don't want to run "too lean,' especially with a high idle.)

These are easy first steps. If they don't work, then you can move on to the timing and other suggestions.

If you want to read up on this problem, go to "The MGA with an attitude" on the web at https://mgaguru.com/mgtech/engine/ro101.htm I think you'll find it very helpful, even if it is for MGs. I recommend reading this before you adjust the timing or do any other work on the carburetors.

By the way... do you use the highest octane available? This is a must for the TR3.
 
Thanks for the link, very informative. I'll try the idle first.
JD
 
JDstr4a said:
...I'm at the default for mixture (3 turns) so I'll try to rich it up a little and see what happens...
Click to expand...

When you said you had "Double checked mixture" I assumed you had it dialed in using one of the several popular methods (piston lift/colortune/plug cut). That 3-turns should be viewed as a starting point to just get it running. In any case, you might find going richer makes the run-on worse.

I like to do the adjustments in a particular sequence as some are dependent on others:

With the engine cold: plugs/valves/points gap/timing/carb sync & idle

Now the that engine is warmed up: mixture

Final adjustment of timing and mixture then occur along the road as I check for pinging and pull the plugs to see their color.
 
As I said earlier, and as George has said, going rich can make the run-on worse. Like the story of the three bears: not too rich, not too lean, just right (sorry... couldn't resist that silly reference).

Hopefully, the simple initial steps I've suggested will solve your problem. (In this case, ignore my warning about "simple solutions" below.) If not, then George is absolutely right: plugs/valves/points gap/timing/carb sync and idle... and then air/fuel mixture. ... And, of course, proper grade of fuel.
 
thanks gentlemen, I'll keep plugging away! It's a fun journey and I appreciate your guidance!
JD
 
JD--

Did you ever solve the dieseling problem you were having? If so, how did you do it?
 
I cured the run-on or dieseling on mine by converting the engine to electronic fuel injection and electronic ignition, controlled by Megasquirt.

Dan B
 
I agree with Doug, I tune my car to run well if the plugs read good, no pinking and it idles and accelerates smoothly and passed all the tests and still diesels I kill it with the clutch. Have had MGs Triumphs and Healeys all do it mostly on hot days.

If your idle speed is low and your running premium and all else is in spec you can spend a lot of time with little to show for it.
 
And if you've been running rich for a long time, you likely have carbon buildup as I did in my TR4 - easy to get a hot spot with it all in there.
 
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