Briggs 11.5hp tuning help?

[Kaptain Krunch]

Just got my briggs 11.5hp goin today (28 CID, same as 12hp) and its running funny, i completely cleaned out the carb, fresh gas, had a new plug, good spark, and it starts right up. It idles fine but when i open it up it starts to rev then back off then rev up again then back off and it keeps doing that till i let off the throttle. I've tried messing with the mixture screw (just one...) but it doesnt affect anything and i dont know carbs too well. any help would be great.

 

[EagleTalons]

Sounds like the governor is pulling on the throttle. Did you mess with the screw on the bottom of the bowl?

 

[Affair_driven]

It idles fine but when i open it up it starts to rev then back off then rev up again then back off and it keeps doing that

Called surging.
To prove it out, partially block intake (when surging) and see if smooths out.

 

[Rotore]

Sounds like the governor is pulling on the throttle. Did you mess with the screw on the bottom of the bowl?

thats kinda of whats happening to mine but mine has the rough idle then dies and it sputters wildly on open throttle

 

[Kaptain Krunch]

There is no adjustment screw on the bowl, its a pretty new engine.

Affair_driven, I'll check that out tomarrow or wednesday and let you know what happens. The airfilter is pretty filthy also.

 

[EagleTalons]

Is it a flathead?

 

[Kaptain Krunch]

Yup model 28d707-0025-01

 

[Kaptain Krunch]

Ok well im not going to be able to start it till tomorrow when i can use my moms car to jump it.

The engine was made in 94', and has only one adjustment needle. I have only messed with the engines that use high and low speed, needles, so what does this one do and how should i adjust it? Right now it starts easy and idles fine but its surging like affair_driven said.

 

[Affair_driven]

Did you try what I suggested yet (post 3) ?

 

[Kaptain Krunch]

No, im sick and i have no way of starting it until tomarrow.

 

[Kenny_McCormic]

There is no high speed adjustment, you only have idle adjustment. File out the main jet a little at a time. Dont use it like that, they tend to spit exhaust valves running lean.

 

[Kaptain Krunch]

Ok, well if its running lean now, and it wasnt 4 years ago before it sat, is there something i missed while cleaning? i didnt take the main jet out or anything (not sure if you can), Its not surging so bad, but its noticeable and the whole thing jerks a little as i ride.

Also i just noticed that my go kart surges a lot at idle, its got a tec 5.5 (yea i know its a piece), anyways when i went to look for idle adjustment i didnt see one, i didnt see any adjustments at all, its a pretty new engine also. Its annoying because when i start it, the surging causes it to idle a bit high (on the up surge) and the clutch engages a little.

 

[Affair_driven]

Fuel injector cleaner (added to fuel) sometimes cures leaning probs.
Check intake gaskets for leaks and that all carb mounting hardware is snug.

 

[Kaptain Krunch]

all the gaskets are a little stiff, maybe some permatex? all bolts and nuts and snug, the only other thing is the bowl had like 20 holes in it that i soldered up, but its not leaking gas so im not sure that has anything to do with anything.

Also, it definitely stops surging when i choke it. And it only surges after 1/2 throttle, before that it runs like a dream.

And lastely, if i were to switch for a mikuni, what size would be right for it? its got 28 ci displacement, not sure of displacement but its model 28d707-0025-01