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Swampthang

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So, I got the spark issue fixed... it was indeed the coil, had no spark at all! Now my problem is this: I put fresh alky in it, fire it up. It will idle fine, but if I bump the throttle a bit, instead of returning to idle it tries to idle so fast it’s almost out of control. Even if I grab the throttle control arm on the carb and hold it in the idle position it does the same thing. Any thoughts?

sorry if I’m asking dumb questions, since I got out of karting and focused on tractor pulling, most of my flathead engine knowledge has been Replaced with v-twins!
 
it may have an air leak somewhere either at the carb to tank gasket or the intake gasket. I would check there first with some carb cleaner or brake kleen. If you don’t want the mess use a propane torch and just let the propane leak out unlit.
 
You adjusted the idle speed screw ?
Needle valve 1.5 turns out ?
48-52 jet?
Air leak is possible .
Throttle shaft not loose/wobbly ?
Did you take the butterfly out?
Is it a standard briggs carb ?
 
Idle speed is set the best I can set it.
Needle is roughly 1.5 turns out, it likes slightly more.
Not sure if jet... need to check that out.
Throttle shaft has a tiny bit of wobble, very tiny.
Have not had butterfly out, not had the carb off at all as a matter of fact.
It is a standard Briggs carb blueprinted on alcohol. This is an old retired racer... it has set for a few years so I’m trying to get it back up and running.
 
Did you replace the diaphragm?

Could be leaking there.
Both fuel and air.

Alky will generally let you be rich without problems at idle.
 
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Any one ever see were you turn the idle speed screw in a bunch and then idle comes down .
I seem too remember this happening on one of my engines .
It dosent seem possible , i know but am relativly sure it did maybe got the butterfly far enough away from the fuel outlet that it didnt draw fuel .
Or im completly wrong.
 
If you flatten the butterfly, the idle would change a bunch

A penny for throttle blade was difficult to get to idle. No venturi.
 
Update: new gaskets, new diagram, cleaned out all passages I could find, 48 jet, needle turned out 1 1/2 turns, now can’t get it to idle unless it’s idling fast enough to engage the clutch. If I turn it down it won’t idle. On the other hand, it does rev good now! Any thoughts now gents?
 
Wow total opposite .
Your sure the snake eyes under the jet are clear ? Thats where i would look .
1/2 inch wrench unscrew the whole thing . Pull jet . Look in there .
 
I pulled the jet and blew compressed air in the holes, they seemed clear as did the jet itself.
flattop1 said:
Wow total opposite .
Your sure the snake eyes under the jet are clear ? Thats where i would look .
1/2 inch wrench unscrew the whole thing . Pull jet . Look in there .
Click to expand...
 
Swampthang said:
Update: new gaskets, new diagram, cleaned out all passages I could find, 48 jet, needle turned out 1 1/2 turns, now can’t get it to idle unless it’s idling fast enough to engage the clutch. If I turn it down it won’t idle. On the other hand, it does rev good now! Any thoughts now gents?
Click to expand...
See post 2
 
Be careful poking anything in there -- The casting is already very thin behind the metering holes, and that small (idle) hole is only .026" or smaller. If you enlarge it at all, your engine likely will not run correctly for your current build.
 
How exactly do you do that? I’ve never done anything like that before!
OVALTECH1 said:
it may have an air leak somewhere either at the carb to tank gasket or the intake gasket. I would check there first with some carb cleaner or brake kleen. If you don’t want the mess use a propane torch and just let the propane leak out unlit.
Click to expand...
 
turn on the propane don’t light it just let it bleed out the nozzle. Fire your engine up put the nozzle around all the gasket surfaces. You’ll know it when you find your leak it will pick up rpm.
 
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