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TR2/3/3A low idle after a fast run - TR3

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NutmegCT

NutmegCT

Great Pumpkin
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With my TR3 engine warm, I've adjusted mixture and idle; idle is set for 800 rpm. Engine idles nice and smooth, accelerates and decelerates without problem. No modifications.

But after some highway driving, if I come to a stop sign, engine idle drops way down to about 500 rpm; really lumpy, like it's about to stall. And of course ignition light comes on.

Opening throttle causes engine to cough a couple times, then slowly speed up.

Also noticed that if I pull the choke knob all the way out, engine will speed up to fast idle. Immediately push choke knob all the way back in, idle is back to 800 rpm.

Seems that if I pulled choke knob fully out on a hot engine, it should stall, not speed up.

Is this a sign of fuel starvation? or ...?

Thanks for any thoughts.
Tom
 
There are two opposing effects, not sure which one you are seeing. One is that the mixture goes lean during deceleration, because the fuel in the float bowls slops away from the carb throat. The other is that underhood temperatures tend to soar under those conditions (plus heat radiated from the manifold to the carbs), which makes the mixture go rich.

One way to test is to turn the mixture nuts by about 1/2 turn and re-test. If leaner makes it run better, then it's going rich.

Sounds like your choke knob is mostly moving the fast idle cam. On my engine, pulling the knob all the way out won't usually stall the engine, but it will run very rough because the mixture is way too rich.
 
Thanks Randall. I'll try the suggestions and make a test drive when it stops raining. First rain we've had here in nearly a month. Welcome indeed.

I usually pull the choke knob completely out only to start the engine if it's cold. I push the choke knob back to halfway within a few seconds; if not, my engine does get very rough very fast. I was thinking fuel starvation might be the cause of the suddenly low idle speed, as all it takes to correct the problem is to give it full choke for two seconds, then push choke knob back in.

Edit: of course, if I discover that it's "going rich" only under the condition of sudden deceleration when hot, then how do I correct it?

Tom
 
I might be that the bushings and linkages from the foot pedal all the way to the carbs get to be "right" when the engine compartment, etc. gets up to operating temperature. BTW, I have a low idle at stop signs, red lights and in stop-and-go traffic - even when the coolant stays just below 185 deg. F. It idles at 400 RPM and like you, my ignition light flickers but the engine is smooth, does not falter and then pulls away as it should. BTW Tom - How is your health these days? Mine is superb.
 
Don - thanks for asking. My health is definitely better than two years ago, that's for sure. Yesterday a friend said "hey - good to see you again". I smiled and said "Better to be seen than to be viewed".

I only get the low idle problem after a fast highway run. If I'm just driving along at 40 mph (top gear), and come to a stop sign or red lights, or I'm in stop and go traffic, no problem. If I just open the throttle normally, it's slow to respond. If I pull the choke knob fully out for a second (then push back in), engine comes back to normal idle speed.

Note that the engine never falters or dies - just gets lumpy and slow.

Glad to hear you're doing well!
Tom
 
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