Topic: need help setting up this motor for GP, USLMRA

[Hondo_k19]

i picked up a briggs model 31 ,avs version, 20hp,  plan on putting the motor on a mower i am building. This is my first year racing. But i have been reading a lot of negative things on the nikki carb.(which of course came on the motor i bought) I have been hearing a lot of good things about the Walbro. Can i replace the Nikki with a Walbro and if so what model/part #? i was also planning on stripping the motor down and checking the motor out before i continue with the motor. I know the motor runs but it flood....probably a carb issue. I am just ocd about motors and want to make sure everything is fine with it. I know the GP class the governed class, what legal modifications, if any, are allowed. Thank you guys.

[Hondo_k19]

well that was easy enough...do nothing...got it...Done. Just kidding guys. I'm sure i asked something that has already been answered already somewhere. Or the fact that i asked what can be done to a "stock motor" rubbed some people the wrong way. I was simply asking because ive seen some "stock machines with aftermarket air filters that's all. From my understanding the motor has to be completely stock as delivered from the factory right. so where does everyone get their advantage the gearing?Pulleys? Weight?All of the above?

[Eric (Moose) Mossow]

if it needs to remain stock than that's what it needs to b. you will want to use a aftermarket filter on it just for the flow. now you are gonna want to mess with your gearing to get speed im not very familiar with this class.

[Hondo_k19]

Is that allowed? An adapter and a filter in the gp class in LSMRA? I have a Briggs model 31 avs motor . Do I have to leave that plastic shroud? can it be replaced with a metal shroud, does it fit?

[MATCODUDE]

Stock means stock from factory as delivered to customer. No modifications to air boxes or carb, no adapters or brackets. you can use a FACTORY (oem) replacement air filter and spark plug. Meaning a k&n air filter that is for that motor and a ngk spark plug. The set up of the chassis and the gearing is wear you will get the advantage in g/p class.

[George Herrin]

after market filters and filter adapters are allowed that's the only modification that is

[cycloneracer]

after market filters and filter adapters are allowed that's the only modification that is

Not in USLMRA.  There was some confusion of this rule last year.  You can run an aftermarket filter as long as it is a stock replacement.   You MUST run the entire stock filter adapter.   Cover included.   

[George Herrin]

WELL THAT SUCKS AFTER MARKET IS A LOT CHEAPER AND LAST ALOT LONGER BUT HEY ITS THEIR RULES. ALL OTHER GROUPS ALLOW IT. MY MISUNDERSTANDING

[cycloneracer]

Many were under the same impression at the Iowa national.   

Stock is stock.   

If I build one I'm going to run a muffler!!!!

[Hondo_k19]

Ok, stock is stock. Fair enough, I want to race in the gp class to get my feet wet. What is a good starting point for pulleys and sprockets for tranny and axle. Sorry so many questions but I don't want to completely miss the mark because of inexperience .

[Conductor 81]

I also ran into an issue with the carb and had to order a new carb. When I got the carb it was a walbro carb. Engine came from a john deere mower and I ordered new carb from deere.

[Hondo_k19]

I would like to replace it but every part number I have in the manuals is for a nikki carb. I'll keep looking but am I correct in saying it is a lmt 56?

[Conductor 81]

According to the parts look up that is close to what they sent me. It's just a walbro that handles a fuel pump instead of gravity fed.

[Hondo_k19]

If I'm correct I think the only difference between a gravity fed and a pump fed carb is the float valve seats. Does anyone know the part number for a walbro carb for a stock Briggs 31avs. I don't wanna buy one unless I'm sure it's the right one. I see quite a bit of them on eBay but again I'd hate to spend $60-100 and find out it won't fit or it's too small for the application. Thank you guys.

[Hondo_k19]

quick question for you guys in LSMRA, USMRA. for the GP class. Do i have to use the factory exhaust or is open to customize?