Export thread

3.5 HP. Started with Black smoke and slow or rough idle for a few months but just keep using it. Finally more black smoke then would not start. Some things I did. Replaced head gasket. Checked spark. New fuel non ethanol. New oil made for small engines. Cleaned magneto etc. Finally decided to tackle carburetor. Yea should have started there maybe. Took all screws out but would not disconnect from intake or lift up from gas tank so I sprayed cleaner in many places and put back together. It won’t start. It seems like no gas so put some down air intake and it started and ran great then died like out of fuel. Put more fuel in air again and after a few pulls ran again for 15 seconds then stopped. I’m guessing I have a fuel problem. Anyones thought on the best way to tackle this issue. Did I not go far enough pulling the carburetor off and checking the fuel pick ups into the gas tank? Thanks for any advice.

I would say YES. You carb has a pump diaphragm which does go bad.

Rivets said:

I would say YES. You carb has a pump diaphragm which does go bad.

Click to expand...

Thanks. So I guess I need to try and disconnect the piece from the intake tube and pull it up and away from the tank with the tube/pipe attached and look for an issue. It seemed hard to disconnect the intake.

You must remove the tank and carburetor together then separate them. Only two screws (bolts) holding the assembly on and of course the throttle linkage must be be undone as you the the tank.carb assembly. Once the two screws things just slide off the intake tube.

Ah, I saw a video of someone doing just that. Thanks for the confirmation sir!!

Well I took the carburetor off cleaned it and put it back together but can’t get it to run still. The gasket thing was in good shape so cleaned it and put it back. There was a part I put in wrong so took it apart and fixed it but still no luck. The second time I unscrewed the carb adjustment and sprayed inside but didn’t know exactly how I should return the screw. I finally decided to screw in all the way then backed it out two turns and tried several pulls. I kept repeating this with a half turn about 4 more times and have given up for the day. Going to have a Manhattan and ponder if I should purchase a carb repair kit. Any thoughts?

Did you preload the pump diaphragm and follow the tightening sequence when you reinstalled the carb? Second, these diaphragms may look good, but no long have the flexibility to pump properly, cheap part to replace. This manual may also be of some help. https://vdocuments.mx/briggs-stratton-service-manual-l-head.html?page=47

Thanks again. I found ~ $50 for a rebuild kit online. I’m going to visit a local parts store to see if they might have anything.

Normally don’t need a rebuild kit, just a new diaphragm.

That was my first thought too. a lot of my parts that are included in the kit AAA look fine on my machine

Remove the mixture needle and seat. Check for clogging there. According to the IPL you this type of carburetor.

This is instruction on removal of the part.


Reassemble by reversing the directions.

Star, here’s where we disagree again, as I come up with this carb. https://www.partstree.com/models/92...-vertical-engine/pulsa-prm-pulsa-jet-carbs-7/

Rivets if you look at the picture of 681 (pn 395508) you see that I am right about the part.

Now there are two version the mixture screw setup but IPL indicates it is Fig 21 setup.

And there are three choke systems that could be used. See figures B,C, and D. In this case it is either B or C.

I’ve been talking and think about the pump diaphragm, now I see your post is really talking about the same carb, but different part.

I took out screw with spring and washer but that’s all that would
come out. After attempting to pull out any other parts and not wanting to damage anything I use my high pressure to blow out. Put washer spring then screw and tighten until spring started to compress. I pulled several times with no luck. I’m getting a workout. Next I added gas down choke/air intake and after a couple pulls it ran fine for 10 seconds then stopped as it seems out of gas. Yea the tank is full. My local hardware had the diaphragm so will replace and more to come.

I used the new diaphragm but no luck. It will only run the few seconds of gas I put in the air/choke. I was able to remove the plastic piece with a rubber washer where the screw etc is. I couldn’t remove what looked to be a screw head but it seemed to have a few holes that were clear. I’ll need to research if this unscrews out and if so will replace. I blew out all the other pieces and they seemed clear. I’m getting closer to looking at electric mowers. Good thing I have a rider but it doesn’t cut as nice as the hi-vac does.

Latest. Well I can get the engine to run for more than a minute at times which is more than any gas I put in the air intake so I believe the engine is getting gas. So now I’m playing with the carb adj screw. The engine has a cutoff unless you hold on the safety bar so im going to rig it so I won’t need to hold it once running and try adjusting the screw slowly. Sometimes when the engine runs at high it seems to get starved for fuel and cuts out. Seems odd. I’m hoping I can correct this with the screw. Hate to give up on this but I’m also looking at those eGO mowers.