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1979 Spitfire rough idle after warm up

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Jkaseys Avatar
Jkaseys John Saunders
Atlanta, USA   USA
I have a completely stock 1979 Spitfire with 35,000 miles. Replaced the plugs, distributor cap and rotor recently. Starts up great (initial idle about 1500 rpm) and runs great through all the gears without hesitation or missing. However, after it is warmed up (running about 15-20 minutes), idle goes to about 1000 rpm, the idle becomes rough and if you don't rev it, it will sputter and eventually die out. Anybody had this experience and have any recommendations? I have not replaced or checked the condition of the points surfaces or the gap. I have not checked the timing either. Thanks!

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Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
You probably don't have points unless the PO changed things.

First thing to check is the air and fuel filters.

Jkaseys Avatar
Jkaseys John Saunders
Atlanta, USA   USA
Thanks. The air filter is new. I looked in the distributor looking for points, but did not see them, so thought that was strange, so you answered that question. There are no visible modern inline fuel filters in the engine compartment...is there a factory filter somewhere? I did not check the trunk behind the cardboard panel to see if there is one there.

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TheZster Avatar
TheZster Steven Z
SAINT LOUIS, MO, USA   USA
1978 Triumph 1500 "BLK-BRY"
Is this a vehicle that has been running regularly this spring ?? Or first time out, so to speak...... ??

If she's been sitting a while..... all bets are off..... if she's been running well lately - and you changed something..... well, I don't believe in "coincidence".....

Z

Jkaseys Avatar
Jkaseys John Saunders
Atlanta, USA   USA
I got it in August last year and before doing anything to it, after driving for 30 minutes or so, the idle would drop back and you would have to rev it slightly at stop lights but it would not stall out. It would also be hard to get restarted until it cooled down again. I think the tune up items I did helped with that. I just had the oil changed, but that would not affect anything. I have been driving it this spring on weekends, so not the first time out. I probably sat unused this winter for 4-5 weeks without use. The actual almost sputtering out is a recent thing, but based on the history, may be gradual thing of getting worse. Once the rpm is over 1000, the rough idle is gone.

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
In reply to # 1532837 by Jkaseys Thanks. The air filter is new. I looked in the distributor looking for points, but did not see them, so thought that was strange, so you answered that question. There are no visible modern inline fuel filters in the engine compartment...is there a factory filter somewhere? I did not check the trunk behind the cardboard panel to see if there is one there.

They hid it in the trunk behind the back panel.

Jkaseys Avatar
Jkaseys John Saunders
Atlanta, USA   USA
I'll check it. Thanks for the input.

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Growe58 Avatar
Growe58 Greg Rowe
Hatfield, PA, USA   USA
Hi John. Good info so far - two more questions.
- do you still have the automatic choke or do you have a manual conversion?
- how did the old plugs look when you changed them? Black, white or a healthy tannish brown? Dry, sooty, wet?

Yellowhawk Valley Avatar
walla walla, WA, USA   USA
1969 Triumph Spitfire "Walla Walla"
1969 Triumph Spitfire "Portland"
1972 Triumph Spitfire MkIV "Spokane"
1975 Triumph Spitfire 1500 "Dayton"    & more
Being a 79 driver, I will suggest that perhaps your choke is not fully releasing. I had the same issues a few years back and a new adjustment and clean of the choke water housing area solved the issue. All that mechanism needs to be clean and smooth operating. It should idle down to 900 or so easily.
Dan

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Jkaseys Avatar
Jkaseys John Saunders
Atlanta, USA   USA
Original automatic choke is still on the car. When I changed the plugs, they all looked normal to me...dry and light gray for the most part...maybe a hint of brown and maybe a few white spots on the tips. The choke not releasing fully sounds most likely the culprit. I just need to locate that housing and take a look at it. Thanks! John

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
You should service the auto-choke with every tuneup.

I keep this in a 3 ring binder in the garage:

https://www.sbmsclub.com/wp-content/uploads/2018/03/choke.pdf

Jkaseys Avatar
Jkaseys John Saunders
Atlanta, USA   USA
Thanks for this. Pictures and comprehensive explanation about the water choke.

lef2wander Avatar
lef2wander Gold Member James Thomas
Hatfield, MA, USA   USA
Smiple question. Is there oil in the dash pot. What kind also. Worth a look. What plugs are you using. What gap.

I'll go with an auto choke problem. However the above won't hurt you. I had a smilair problem, my auto choke has been removed for years. Came down to old, wrong plugs, over gapped.



Edited 3 time(s). Last edit at 2018-05-14 03:25 PM by lef2wander.

J.P.Rap Avatar
J.P.Rap J.P. Rap
Mount Hope, ON, Canada   CAN
1976 Triumph 1500 "Donna"
2007 Ford Ranger
It seems to me, if your plugs are gray with white, you're running lean. Not likely a stuck open 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



Edited 1 time(s). Last edit at 2018-05-15 08:38 PM by J.P.Rap.

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
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.

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