bad power valve?
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Freshman User
Joined: May 2010
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From: st.peters, mo.
bad power valve?
hello i have a 87 f250,460, auto. (i know this the wrong area but there seems to be more carb people here.) stock carb.
my truck has had a backfiring problem since Ive had it and the exhaust pops lot when i let the truck coast.
but just in the last few days the exhaust has gotten really rich and my plugs are now black . also the idle is a little rough but not to bad .
but besides that the truck runs pretty good. does this sound like a bad power valve?
my truck has had a backfiring problem since Ive had it and the exhaust pops lot when i let the truck coast.
but just in the last few days the exhaust has gotten really rich and my plugs are now black . also the idle is a little rough but not to bad .
but besides that the truck runs pretty good. does this sound like a bad power valve?
Moderator
Joined: Jan 2001
Posts: 56,980
Likes: 2,735
From: Virginia
Yes, those are the symptoms of a bad power valve. A carb rebuild would take care of that plus freshen up the rest of the carb. The alcohol content in the fuel now is hard on the rubber parts of a carb.
Moderator
Joined: Jan 2001
Posts: 56,980
Likes: 2,735
From: Virginia
Just tell then what year truck and engine you have, and they will give you the correct kit. You have a Motorcraft made by Holley carb, and the kit will be for several of those year carbs. You will have parts left over when you are done since they cover several years. I have also heard some of these carbs had a dual stage power valve that is a little bit expensive, and some of the kits don't include that one in the kit.
Laughing Gas
Joined: Feb 2010
Posts: 781
Likes: 8
From: Sanford, NC
It does sound like a power valve leak from what you describe. A good rebuild should
solve your problem. I would use either a Motorcraft or Holley kit to rebuild it. I have
found they are the best quality kits. The kits are pricey but the best quality.
solve your problem. I would use either a Motorcraft or Holley kit to rebuild it. I have
found they are the best quality kits. The kits are pricey but the best quality.
Thread Starter
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Freshman User
Joined: May 2010
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From: st.peters, mo.
well i got a rebuild kit but the power valve is different. the smaller one is the original. the bigger one is from the kit.
the other parts seem fine so did they redesign them? or is the carb from a different year?
the other parts seem fine so did they redesign them? or is the carb from a different year?
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pedant
Joined: Jan 2008
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From: EXTREME southwest CT
Edit: after going out to the garage and pulling an old 4180 off the shelf the one on the left of the first photo looks correct.
This is a 2 stage power valve, no?
Are the numbers the same?
What kit did you get? Genuine Holley or aftermarket knock off?
This is a 2 stage power valve, no?
Are the numbers the same?
What kit did you get? Genuine Holley or aftermarket knock off?
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Post Fiend
Joined: Jan 2000
Posts: 5,330
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From: Dryden, ON, Canada
By the numbers, that is the proper carb for your truck.
I don't know holley carbs at all other than the one I had on my 460 liked dumping fuel on the intake and catching fire... So, your question about the power valve I can't answer unfortunatley. If that carb kit is the proper one for your truck, that power valve should interchange however.
I don't know holley carbs at all other than the one I had on my 460 liked dumping fuel on the intake and catching fire... So, your question about the power valve I can't answer unfortunatley. If that carb kit is the proper one for your truck, that power valve should interchange however.
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Freshman User
Joined: May 2010
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From: st.peters, mo.
ok, thanks guys. im just finishing up and i will see if it runs any better. i did find that my floats were adjusted wrong, i was missing a check ball in the secondary diaphragm and my secondary throttle plates were seized up .
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Freshman User
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From: st.peters, mo.
it runs great now, it idles smoother and finally no more backfiring.
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