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poor idle 1800

posted by someone claiming to be secretsenor on Thu Dec 1 10:42 CST 2005 [RELATED]

OK.. I will outline the problem the best that I can.
Its a automatic b20 with carbs that runs very nicely about 1500-2000 rpm. No power and a little lumpy below 1500rpm (I assume this is pretty normal).

The car starts with a full choke after 2 or three attempts.. once at 1000 rpm it will run smoothly and over a period of about 1 minute I ease the choke back and it idles at around 900 rpm very smoothly (with cool engine).

After 15 minutes of driving the car warms up and the idle (in traffic) starts to get more and more rough, dropping rpm - until it again needs a little choke to keep it ticking over.

Does this sound like over heating - normal points distributor wear - carb mixture - or something else?

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poor idle 1800

posted by someone claiming to be Rhys on Thu Dec 1 19:29 CST 2005 [RELATED]

From your description the engine idles better partly warm with the choke off, and gets worse as it attains normal running temperature. That normally means the mixture is a bit rich. Try adjusting the jet nuts up about two flats and see what that does to the idle quality. That's assuming you have SU carbs. If Strombergs, well, adjusting them is another matter.....

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poor idle 1800

posted by Sil on Fri Dec 2 14:54 CST 2005
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last visit: Fri Oct 24 07:24 CST 2014

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Rhys,
Far be it from me to argue with you about carbs, so that's not my intention here. But it seems counter-intuitive to me that; if he has to make 2 or 3 attempts at full choke to get the thing started and that it runs smoothly when the manifolds have warmed up, but the thermostat is still closed, and he then has to feed choke to keep it running smoothly when the whole engine is fully warmed up; he's running rich. I would have said that he is running lean. I'd appreciate your setting me straight on this, so I'll know which way to go if this were to happen to me.
Bob S.

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poor idle 1800

posted by someone claiming to be Rhys on Sun Dec 4 19:14 CST 2005 [RELATED]

Hi Bob;
I have to admit I can see the problem as you have solved it too. I guess what lead me to my solution is that he mentions that it idles smoothly during the warm-up and gets rougher as it makes full operating temp. (if I understand him properly) I think he is using the fast idle to smooth it out, without dropping the jets to enrichen the setting. That's why I advised leaning it a bit.
For sure if I was tuning it myself, I would end up going lean and rich just to get a feel for it.
Either of us could be right. I just hope he writes back to state what kind of carbs he has. Describing how to do a piston lift to determine mixture is a bit tough over the 'net, but that might be next, and hopefully we get some feedback from him.
Rhys

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poor idle 1800

posted by Sil on Mon Dec 5 03:58 CST 2005
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last visit: Fri Oct 24 07:24 CST 2014

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Rhys,
"I think he is using the fast idle to smooth it out, without dropping the jets to enrich the setting"
Yes, I see where you are coming from. Thanks for the explanation.
Bob S.

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poor idle 1800

posted by someone claiming to be secretsenor on Mon Dec 5 15:14 CST 2005 [RELATED]

I believe they are original - stromberg?...(with black filter box on top)
They aren't SU or webber.

As an aside I have also been smelling pertol fumes in the cabin - has been pretty strong lately and doesn't seem to increase with the idle prob - sometimes the fumes are strong then not a problem for weeks.

When I pull over and start trying to smell around for the petrol under the bonnet - I cant smell anything?

This afternoon when I get home from work I will try it with the motor running - and have a better look around.

(sorry for slow reply - busy life at present)

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