Briggs 3.5 wont start.

[Hspolenske]

My daughters gokart has a briggs 3.5hp. She was driving it the other day and it just shut off.
I checked the fuel, yes had fuel, checked the kill switch and that was good, checked for spark and has spark, put a couple drops of gas in the cylinder and it sputtered, tank was half full so filled it all the way incase the pick up tube extention was cracked pulling air into the fuel. I ordered a new diaphragm kit for it and installed it. Just tried starting it and it sputtered a bit and died. I cant get it to fire. Checked the compression and it has 85psi cold closed throttle.
Any ideas on what I can check or what the reason for no start is?
How many turns out is the air fuel needle screw supposed to be?

 

[Bird Brain]

That compression seems kinda on the low side. Pull the case breather off and make sure you didn't lose any valve spring keepers and check all that looks intact. Good luck.

 

[massacre]

Is the spark plug wet with fuel?

 

[Minimichael]

Clean the carb? About 1 1/4 turns on that air screw.

 

[creia]

85 PSI compression is fine and plenty to start and run. By the way, when you check compression you always do it with the throttle held wide OPEN, not closed. Your compression might even be a little bit higher with it held open.
Michael

 

[sparkwizard]

Try a new spark plug before you do anything else. Did you check for spark with the plug wire to the head, or did you remove the plug and check the plug for spark? A cracked porcelain insulator in your plug could act like this.

 

[Thepaetsguy]

You take the gas cap off and make sure it’s venting? I don’t understand why I didn’t film it but I had a 3hp you could fire up and the second you screwed the cap on it died. you could just set the cap on and take it back off and almost make the engine stall.

 

[Jim Donovan]

Just one more thing to look at, take off the side cover and remove the flywheel and make sure the woodruff key (half moon key) didn't shear. This will throw off the timing and it will not start or run. While you are in there check out the points and make sure it is still good and gapped correctly. The other thing to check out is remove the carb from the top of the fuel tank and check out the intake line and make sure the filter on the end is not plugged. It doesn't take much to plug the screen. We take the screen off when we race but are very careful when pour gas in to have a fine filter on the funnel to make sure no 'crap' gets into the tank.

It is a good little engine and it will turn out to be something simple to fix. You already have several suggestions to follow up on and one of them will be the correct fix.

 

[cl350rr]

Partially stuck exhaust valve? I have had a few briggs show up with exhaust valves that would not close all the way.

Put your thumb over the exhaust and pull it over a few times to see if it is blowing out through the exhaust on the compression stroke.

 

[Hspolenske]

Try a new spark plug before you do anything else. Did you check for spark with the plug wire to the head, or did you remove the plug and check the plug for spark? A cracked porcelain insulator in your plug could act like this.

I checked spark with the plug out and thru the plug

 

[Hspolenske]

Thanks everyone. I'll try and get another look at it in a couple of days.

 

[pomfish]

Partially stuck exhaust valve? I have had a few briggs show up with exhaust valves that would not close all the way.

Put your thumb over the exhaust and pull it over a few times to see if it is blowing out through the exhaust on the compression stroke.

THIS^
Friend had a riding mower that would shut off random and he rode it one day and when it shut off a few minutes later he heard a faint click. It was stuck exhaust valve. Added Marvel Mystery oil to gas and oil and never had problem again.
I use that stuff on my old Cub Cadets with Kohler engines and swear by it. Was designed for aircraft engines and it just works for top cylinder lubrication. And is a good fuel stabilizer to boot.