Flathead doesn’t idle right

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Flathead86

Junior Member
Flathead doesn’t idle right

Hi guys, I am lost, I’ve tried everything and can’t get my flathead to idle right, it’s spitting from the exhaust, like a soft back fire, I’ve tried Adjusting my timing, can’t really adjust my dual carbs bs of this issue, what you think might be the problem, any advice would be great? Thanks
 
Re: Flathead doesn’t idle right

Sticking valves....Drizzle some MMO down the carb at fast idle (out in the sticks someplace) and add some to the gas tank....
 
Re: Flathead doesn’t idle right

It could still be a valve hanging up or maybe its that nasty cam you put in it....;)
 
Re: Flathead doesn’t idle right

"race cam"? Race cams don't idle like a stock cam....they don't idle so smooth
Tell us about the build and the cam....
 
Re: Flathead doesn’t idle right

petehoovie said:
"race cam"? Race cams don't idle like a stock cam....they don't idle so smooth
Tell us about the build and the cam....
Click to expand...

It’s 80 over, Navarro heads, bubbas gmc distributor, dual 97, adjustable lifters, what else would you like to know, the cam is 3/4
 
Re: Flathead doesn’t idle right

We need to know exactly the specs of the cam . Just a race cam from H&H is not sufficient info. How does it sound when sped up to say 1800 rpm??
 
Re: Flathead doesn’t idle right

my4dv8 said:
We need to know exactly the specs of the cam . Just a race cam from H&H is not sufficient info. How does it sound when sped up to say 1800 rpm??
Click to expand...
I can’t really hear the engine right with it spitting like that, but it’s sounds nice,
 
Re: Flathead doesn’t idle right

I suggest a leak down test or at least a compression test. Have you double checked valve lash.
 
Re: Flathead doesn’t idle right

Look at plugs if they are black & sooty that will cause your issue. Carbs or too much fuel pressure could cause plugs to be this way.
Have you asked Mike at H&H for his opinion.
 
Re: Flathead doesn’t idle right

KiWinUS said:
Look at plugs if they are black & sooty that will cause your issue. Carbs or too much fuel pressure could cause plugs to be this way.
Have you asked Mike at H&H for his opinion.
Click to expand...

My plugs are black, but I can’t adjust my carbs with this problems,
 
Re: Flathead doesn’t idle right

Okay if plugs are black there’s a carb issue but there’s no adjusting of idle screws that will fix it. Carbs build correctly with correct fuel pressure should not soot plugs no matter where idle screws are. Start idle screws 3/4 to 1 1/4 turns out both same. Them black plugs won’t fix themselves. Need to glass bead or replace or will continue to misfire.
 
Re: Flathead doesn’t idle right

I would close down one carb totally and see how it runs on one carb. Then get a uni-sync and go through the dual carb sequence. Worked for me years ago with a 3/4 cam, dual 94's. Chap
 
Re: Flathead doesn’t idle right

On a modified engine, I use a vacuum gauge to set initial timing. Get it as close as you can, and then adjust the timing until you get the highest vacuum reading at idle. Then retard it just a small amount and you should be all set.

You're not done yet. This will produce the correct timing at idle, but really has nothing to do with timing at higher rpm's. That depends on the advance curve in the distributor. That is another subject entirely.
 
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