Heymow - Lawnmower Racing Forum

Engine Help => Briggs OHV & Vanguard => Topic started by: cable1981 on June 21, 2020, 02:23:06 pm

Title: GP fell flat on its face!
Post by: cable1981 on June 21, 2020, 02:23:06 pm

So at the race this weekend, went thru tech with my GP, everything went perfect as planned. Tach checked at 3540 where I had it set at. Got out on to the track and it was wet, ran really poorly, so I went down gears. Second heat race ran equally as poorly. I was able to watch my tach the entire race, 2950. Got back to the pits, put the clutch in grabbed a handful of throttle, 3540!!! What could cause the mower to bog down so much??? I never once got close to running a governed speed, but it rolled around like I was just out on a Sunday stroll thru the park! Any ideas much welcomed!

Title: Re: GP fell flat on its face!
Post by: cycloneracer on June 21, 2020, 05:30:34 pm

You might have something starting to seize.  Creating drag.

Did it improve when you dropped gears?

Title: Re: GP fell flat on its face!
Post by: cable1981 on June 22, 2020, 09:14:12 am

It honestly didn’t help changing gears. I also thought about anything that might be locked up or rubbing, everything moves around freely.
One idea I had was when my transmission was put together possibly gears were not put in order, but wouldn’t the engine still want to get up to governed speed?

Title: Re: GP fell flat on its face!
Post by: cycloneracer on June 22, 2020, 12:36:36 pm

Were you lifting for the corners?    Or were you holding it wide open all the way around the track?  Did you lift while it was still pulling?   

Title: Re: GP fell flat on its face!
Post by: cable1981 on June 22, 2020, 03:18:17 pm

I never lifted once. Full pull on the throttle the entire 10 laps.

Title: Re: GP fell flat on its face!
Post by: cycloneracer on June 23, 2020, 03:53:59 pm

Too high of gear.   

Title: Re: GP fell flat on its face!
Post by: PPRINT on June 24, 2020, 10:15:48 pm

A carb running to rich or to lean will also do this.  A motor reving under no load has a different jetting requirement once under load.

I found this document on a FB group for calibrating the low speed side of the carb.  I couldn't get my wife's GP/T mower to come off the corner clean and it would pop and shart all the way down the straight and never reach full sing.  The tuning instructions at the bottom of that page led me to realize my idle jet was too lean and once resolved I could get it to the governor no problem.  Now to learn more about main jets.

Your results may very.

Rob

Title: Re: GP fell flat on its face!
Post by: Wade1978 on June 25, 2020, 02:18:04 pm

A worn throttle shaft and bushings in the carb will cause it to do that under load too

Title: Re: GP fell flat on its face!
Post by: cable1981 on June 26, 2020, 08:43:58 am

I did think about carb setup as a potential problem, but had never adjusted anything from last season, so didn’t look too far into it. I now have a good deal of time to look deeper into both the carb and the tranny. I want to think carb since I watched the tach never move for 7 laps