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Old 01-15-2017, 09:39 PM   #1
santino2010
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Default Flathead v8 rough idle

Hello all I'm having an issue with my flathead,
It started off one day I tried to start it and as I would give it gas it felt like it wanted to die out, so I looked inside the carburetor as I restarted it and gave it some gas and I could see that one of the venturi wasn't spraying enough gas I'dk if that was a bad thing or not but I rebuilt the carburetor and it's still doing the same thing. It has a new fuel filter and new fuel pump...
I drove it around the block but it would feel like a misfire but I'm lost I checked the spark and it's good.
Any advice thank you
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Old 01-16-2017, 12:24 AM   #2
scicala
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Default Re: Flathead v8 rough idle

It sounds like maybe the carb is running out of fuel, or low on fuel. Maybe disconnect the fuel line at the carb and crank it over to check for fuel flow (into a jar or bottle). Possible the float is set too low after the rebuild also.

Sal
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Old 01-16-2017, 12:30 AM   #3
santino2010
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Default Re: Flathead v8 rough idle

Hello sal thanks for the reply, and I think there is fuel flow
Because I have a fuel filter that's going after the fuel pump to the carb Soni can see fuel flow going just fine unless I can still go that route you suggest thanks
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Old 01-16-2017, 01:11 AM   #4
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Default Re: Flathead v8 rough idle

Mechanical or electric fuel pump??? Have you checked the fuel pressure? Also, the flex fuel line between fuel pump and gas line from tank........
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Old 01-16-2017, 01:12 AM   #5
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Default Re: Flathead v8 rough idle

It's a mechanical fuel pump sir
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Old 01-16-2017, 07:48 AM   #6
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Default Re: Flathead v8 rough idle

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There is a process of elimination to follow even if we "think" something is right. Disconnect the fuel line from the carb and check the fuel flow as suggested by Sal. If it squirts out well you can move on to the next thing in line, the carb. If it doesn't you go the other direction and check the fuel supply line. Even that inline filter car receive fuel and slow the flow.
These folks will walk you through the adventure. Welcome aboard and enjoy the challenge.
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Old 01-16-2017, 07:50 AM   #7
Terry,OH
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Default Re: Flathead v8 rough idle

If one side is spraying strong and the other side is not then it is still a Carb. issue. Looks like one side of the nozzle is blocked. Compressed air and soak in alcohol to clean.
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Old 01-16-2017, 08:58 AM   #8
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Default Re: Flathead v8 rough idle

I had trouble with my carb on a 51 pickup. I tweaked it , rebuilt it twice after soaking it in different cleaners and blowing through compressed air. Finally I bought a new carb and it ran great. Best $300 I've spent. Good luck
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Old 01-16-2017, 07:13 PM   #9
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Default Re: Flathead v8 rough idle

Thank u I will check on those steps and see how it works
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Old 01-17-2017, 07:39 AM   #10
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Default Re: Flathead v8 rough idle

You may have sticky valves. Before tearing into thing put a pint of
MMO in the fuel tank. Shake or drive the car a little to mix it with
the gas. While running slowly drizzle MMO down both sides of the
carb. Drive about 30 miles and see how it is. Sticky valve can been
diagnosed by going below 10 MPH in high gear and SLOWLY push
the gas pedal and if it bucks a little it can be sticky valves. When
not sticking the car will pick up smoothly if everything else is in
good order. Take the test before you add the MMO and after. G.M.
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Old 01-17-2017, 09:35 AM   #11
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Default Re: Flathead v8 rough idle

a little hard to help you with so little information. what kind of motor/carb/ignition??

is it a rough idle or only when you give it gas after startup??

I had a flathead that would start and idle but give it gas and it would pop and fart horribly and it was a bad condensor.

if you have a stock 180 degree type intake manifold you may have a bad cylinder. as the venturi works on vacuum it will draw less on one venturi. do a compression test to check for this.

if it is a 97 you may have a blocked emulsion tube. these can be a real pain to remove as you have to tap them and make a puller to get them out. they can be cleaned and reinstalled afterwards or buy new from stromberg.
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Old 01-17-2017, 11:03 AM   #12
santino2010
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Default Re: Flathead v8 rough idle

It has a 239 flathead with original equipment
Ignition, and 94 holley
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Old 01-17-2017, 11:09 AM   #13
santino2010
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Default Re: Flathead v8 rough idle

Hello GM
It's Kinda difficult to keep the car to stay running, I try and give it gas but it won't stay on it feels when I give it gas it feels like it wants to die off. I rebuilt the carb and replaced the fuel filter so fuel is going through fine so now I'm guessing it might be a ignition problem now,
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Old 01-17-2017, 11:21 AM   #14
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Default Re: Flathead v8 rough idle

A real easy way to check the spark is put a timing light on any cylinder and watch the light pulses. If they are not even you have a problem and you know where to look! Gary
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Old 01-17-2017, 11:26 AM   #15
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Default Re: Flathead v8 rough idle

Alrighty Gary thanks for that info,
Thank u all for the help I'll be needing it, anymore info will help thank you
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Old 01-17-2017, 12:23 PM   #16
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Default Re: Flathead v8 rough idle

Santino-

I know you said you've rebuilt the carb. If you have any question as to how well you rebuilt it, I would strongly recommend the rebuild services of Charlie Schwendler (Charlie NY here on the forum). I just had him rebuild my carb and it made a world of difference. Went from not starting and/or stumbling to smooth running. He turned it around in about two weeks as promised and his rates are a bargain.
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