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1979 Spitfire rough idle after warm up

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65or66 Jim B
Lake village, IN, USA   USA
1965 Triumph Spitfire MkII
1973 Triumph Spitfire 1500 "Jusanudda Munny Pit"
If the water choke R&R doesn't help much, try searching for vacuum leaks with either an unlit propane torch, or a can of aerosol carb cleaner. There are lots of vacuum lines on the later cars, especially around the carbon canisters (2). If one of those has a crack at the end, it can open up more as the engine gets warmer, creating a larger vacuum leak. When the engine is cold(er), the water choke may be able to mask the problem

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J.P.Rap Avatar
J.P.Rap J.P. Rap
Mount Hope, ON, Canada   CAN
1976 Triumph 1500 "Donna"
2007 Ford Ranger
In reply to # 1533179 by Doug in Vegas
In reply to # 1533158 by J.P.Rap It seems to me, if your plugs are gray with white, you're running rich. Not likely a stuck open choke.

White deposits are generally caused by a lean condition.

Of course you're correct and I actually intended to say lean. A rich mixture could certainly be a stuck choke.



"In this world, you must be oh so smart, or oh so pleasant. Well, for years I was smart. I recommend pleasant." Elwood P. Dowd

Jkaseys Avatar
Jkaseys John Saunders
Atlanta, USA   USA
When the idle drops back after it warms up, does that mean the automatic choke is releasing? Because, it does that and then that is when the idle becomes rough. At 1500 rpm, the idle is fine. Thanks for all the input. If gray plugs means it's running rich, then that adjustment might be in order. I would think that if there was a vacuum leak, it would run rough all the time, not just at warm idle.

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J.P.Rap Avatar
J.P.Rap J.P. Rap
Mount Hope, ON, Canada   CAN
1976 Triumph 1500 "Donna"
2007 Ford Ranger
In reply to # 1533401 by Jkaseys When the idle drops back after it warms up, does that mean the automatic choke is releasing? Because, it does that and then that is when the idle becomes rough. At 1500 rpm, the idle is fine. Thanks for all the input. If gray plugs means it's running rich, then that adjustment might be in order. I would think that if there was a vacuum leak, it would run rough all the time, not just at warm idle.

That was a misprint on my part. White or grey plugs means running lean. Tan or brown is good, black is rich.



"In this world, you must be oh so smart, or oh so pleasant. Well, for years I was smart. I recommend pleasant." Elwood P. Dowd

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
In reply to # 1533394 by J.P.Rap
In reply to # 1533179 by Doug in Vegas
In reply to # 1533158 by J.P.Rap It seems to me, if your plugs are gray with white, you're running rich. Not likely a stuck open choke.

White deposits are generally caused by a lean condition.

Of course you're correct and I actually intended to say lean. A rich mixture could certainly be a stuck choke.

Let's hope it's not a gasket failure.

J.P.Rap Avatar
J.P.Rap J.P. Rap
Mount Hope, ON, Canada   CAN
1976 Triumph 1500 "Donna"
2007 Ford Ranger
I skimmed through this thread again. You say your plugs are grey with white spots. You also say it runs fine when you first start it but starts to sputter when the choke closes.
Grey and white plugs indicate a lean mixture. When the (cold) choke is open, it enriches the mixture and the engine runs fine at 1500 RPM. As the engine warms and the choke closes, the mixture leans out, the throttle plate closes (part of the choke operation), and the RPMs drop. The engine is now running lean. Too lean, I would suspect, to idle properly.
You also said, once the idle is above 1000, it runs fine. Im not sure what you mean by that. Are you adjusting the idle screw to bring it up to 1000? Or do you simply mean once the revs are up? In either case, adjusting the screw or applying some throttle, opens the throttle plate enough that it draws in more fuel, enough to run smoother.
I think the problem is simply, your running too lean. There are two possibilities for that. The first to check has already been mentioned. Check carefully for vacuum leaks. If you have a leak, air is drawn into the mixing chamber (or the manifold) and leans out the mixture. The carb can not compensate for the extra air because it's coming in after the jet. If that's not it, adjust your mixture. Enrichen it a bit, (adjust the needle clockwise). Maybe 1/4 turn to start. Go for a test drive, if it's running better, check the plug colour. They should be brown or tan.Make further adjustments as needed.Test drive and check plugs (at least one) after each adjustment.


One other thing I forgot to mention before. Early this season I discovered my ARV was not functioning properly and the valve was stuck partially open. I disconnected it and plugged the vacuum line and it ran much better.

HTH



"In this world, you must be oh so smart, or oh so pleasant. Well, for years I was smart. I recommend pleasant." Elwood P. Dowd

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