3hp Briggs won't run unless choke is on?

[Clayon]

Hi there guys, I got a 3hp Briggs that has me stumped. It will only run with the choke on, and it runs poorly even then. It will rev up, then almost die, then rev back up. It has a pulsa jet carb, and I checked the gaskets, all new, no leaks. The tube from the breather to the carb isn't blocked, the breather gaskets are new and the 2 holes in the bottom are lined up and not blocked, the carb was cleaned. I played with the jet, but that doesn't help. I'm not really sure what else I should do? :shrug:

Thanks for any help. :thumbsup:

 

[minibikin']

Fuel cap? Pick up tube could have a hairline crack?

 

[creia]

If it is an old carb, it could be an excessively worn throttle shaft. The shaft, and the carb body where it passes through, will become worn to the point it will pull air through the (now) oversize/oblong hole, making for a "lean" condition. Check to see if your throttle plate/shaft wobbles a lot. One of the worst things to do, and really contributes to wearing out the throttle shaft is by hooking up the throttle grip/cable return spring directly to the throttle plate. It puts too much side stress on the throttle shaft.
Michael

 

[Clayon]

Okay I'll check that Michael, I'll check the cap as well, it is a newer, maybe '98-ish briggs I/C and it is one an aerator so is has linkage, so it is not hooked direct. Thanks I'll let you know. :thumbsup:

 

[Clayon]

Still nothing, I took a look at the cap and actually took it right off, and it didn't change. The throttle shaft was pretty good, but maybe that's the issue? I'm going to try running the carb/tank on another motor tomorrow to see. :shrug:

 

[metal man]

sounds like there is something messing with a jet or in a port someplace . maybe some crap got loose from the screen and pluged it . maybe re clean and blow air in the ports . check the screen real good .

 

[txAggie]

You already checked for air leaks, but I'd do it again. To me it sounds like you have one somewhere. So it runs too lean when you turn off the choke, but the air leak is making it run closer to normal when choked. Doesn't sound to me like a fuel delivery issue, just air getting in somewhere. Have you pulled out the air/mixture adjustment screw? I have seen the little o-ring in there get boogered up and sit crossways so you feel like you have it set right but it is letting a little extra air in.

 

[Cubenzo]

compression?


leaking crank seals will make an engine do funny things.....

 

[Clayon]

Thanks metal man, I'll go through it again. And thanks txAggie, I will check that o-ring, I never thought of that. :thumbsup:


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[old-timer]

Clay did you replace the diaphragm ? Even if you did, i've had bad ones right out of the box. If you have an extra one, you may want to try swapping it just to be sure :shrug:

Just a thought

 

[Clayon]

I'll try that Vic, I did put a new one in, but like you said they aren't always good so I'll try a different one. :thumbsup:

 

[minibikin']

I'll try that Vic, I did put a new one in, but like you said they aren't always good so I'll try a different one. :thumbsup:

Make sure to check the diaphragm cover is flat/true also...

 

[Clayon]

I did trued the diaphragm cover when I put the new diaphragm in. Just a quick question, there should be a small o-ring inside the mixture needle hole on these carbs right? :shrug:

Because there isn't.

 

[old-timer]

Yes there should be Clay. Make sure it's not twisted or munged up.

 

[txAggie]

Yes, there should be an o-ring in there. I'm pretty sure the 3.5 also has a brass ring in there, so the oring might jsut be pressed back up in there behind that. When you look in it looks solid.

If you backed the screw out and then had slight resistance when actually pulling the mixture screw out, the O-ring is in there. Be careful when spraying cleaner through that, that stuff is tough on rubber.

 

[jim210]

Fixed jet carbs don't have orings or rings on the idle mixture screw. It is just the screw and spring.
Do you have foam in your tank?

Sounds like the idle circuit isnt working properly. Did you check the transitional holes behind the welch plug? Checked the air bleed? You can try checking and cleaning them without removing the welch plugs by using a small wire and carb clean. I poke all the holes with the wire then spray carb clean through the circuit to make sure the holes are clear. After seeing the carb clean flow threw each hole I blow compressed air through the circuit to make sure it completely clean.You have to know how the carb works though. If you still can't get it to work then you might have to knock out the welch plugsand give it a real good cleaning.

Check to make sure the long pickup isn't bottomed out on the tank by using a bent hanger. If the hanger can't go completely under the pick up it should atleast be able to move it.

 

[buckeye]

Thqt's good advice.:thumbsup:

 

[Clayon]

Thanks Jim and everybody else who helped out. :thumbsup: I did everything you guys said and it works good now. Thanks again.


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[Gocarman]

Did you find something? or did it just get fixed by doing everything.

 

[Clayon]

I just did everything. I never really found anything specific. When I rebuilt these motors I did 4 of them at once, so it's possible I just forgot to do something. :shrug: