79 351m low idel when warm
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Joined: Feb 2002
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From: Cleveland, WI USA
79 351m low idel when warm
Hi all,
I have a 79 f150 w/351m 2bbl and manual tranny that I only use for plowing my driveway. All the smog stuff has been removed and all the electrical/vac. choke stuff is gone (converted to manual choke). Timing is set at 12 deg BTDC w/ vac. advance disconnected and fuel filter is brand new.
When it's really cold, the thing starts right up and idles at around 800 rpm. As it gets warm, the idle slows way down to the point of stalling. I can't even keep it running without holding the gas down. If I let it cool down, it runs great until it gets hot again.
Any suggestions as to what could cause this? Also, any tips on tuning this 2bbl carb would be great.
TIA.
Kevin K.
I have a 79 f150 w/351m 2bbl and manual tranny that I only use for plowing my driveway. All the smog stuff has been removed and all the electrical/vac. choke stuff is gone (converted to manual choke). Timing is set at 12 deg BTDC w/ vac. advance disconnected and fuel filter is brand new.
When it's really cold, the thing starts right up and idles at around 800 rpm. As it gets warm, the idle slows way down to the point of stalling. I can't even keep it running without holding the gas down. If I let it cool down, it runs great until it gets hot again.
Any suggestions as to what could cause this? Also, any tips on tuning this 2bbl carb would be great.
TIA.
Kevin K.
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Posting Guru
Joined: Feb 2002
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From: Cleveland, WI USA
Actually, I don't have to use the choke at all to start it and I took the fast idle cam off when I took the rest of the choke stuff off. I turned the idle up a little and it stays running now, but not very good.
Yesterday I took it on the road for a while and it was acting funny. When I'd shift up a gear it would sputter backfire like crazy. I pulled the choke out for a few seconds and it smoothed out and ran fine. It seems like at low rpms under power is when it has it's problems.
I'm guessing that's a fuel delivery problem since choking it fixes it. I don't know what the initial carb settings should be and I have no clue where it's at now. Could all this just be carb adjustments?
Thanks for the responses.
Kevin K.
Yesterday I took it on the road for a while and it was acting funny. When I'd shift up a gear it would sputter backfire like crazy. I pulled the choke out for a few seconds and it smoothed out and ran fine. It seems like at low rpms under power is when it has it's problems.
I'm guessing that's a fuel delivery problem since choking it fixes it. I don't know what the initial carb settings should be and I have no clue where it's at now. Could all this just be carb adjustments?
Thanks for the responses.
Kevin K.
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Joined: Jan 2005
Posts: 24
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From: Crete, NE
Do all 8 cylinders hit strong? you may have burnt a valve or lost power to one cylinder, not real noticeable when reved up a bit but definatly noticable at an idle. my 78 did the same thing ran like a raped ape when ultra cold out then suffered in the summer heat. I had a burnt exhaust valve.
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Thread Starter
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Posting Guru
Joined: Feb 2002
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From: Cleveland, WI USA
That's a possibility, too. It does sputter and run a little rough. I'll do a compression test and check that.
Thanks!
Kevin K.
Thanks!
Kevin K.
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From: Crete, NE
Matter of fact just got mine running today, had to rebuild the heads because one exhaust valve was smoked and all the guides were real loose. My machinist said those 2bbl factory carbs were known for running lean which takes the guides out. A quicker way to check for dead cylinder is to pull a plug wire off one at a time while running and listen for the engine to slow down. I would be careful as I pulled 2 wires apart checking mine.