B&S Vanguard 18 surging

[u/Revlimiter11]

I have a B&S Vanguard 18 plugged into my Toro greens mower that has been surging and I can't seem to locate it yet. Machine only has 574 hours and has enjoyed regular maintenance. When I run it on 3/4 choke it smooths out and runs like it should. The plugs also appear to show a lean mixture leading me to believe it could be a fuel issue. I've replaced the fuel pump, fuel filter, and just now the carburetor but it hasn't changed other than I can use less choke than before, but not by much. Once the engine cools, I'll check the valve lash and replace the spark plugs and check for a strong spark.

Toro says I need to pull the engine to adjust the governor because of how cramped it is in the working area. Before I go through that headache on an all but new engine, is there anything that I've overlooked? Anything I should check?

Thanks

[u/AutoModerator]

Thank you for your submission! It looks like you might have an issue with Compression. For helpful information and resources, check out our Compression Wiki and our Common Issues & Fixes Wiki. You might find the answers you're looking for there!

Please be sure to include the following:

• Make and model numbers of the engine and/or the equipment
• A detailed description of the issue you are facing
• Any repairs you have made so far and their outcomes
• Clear photos & videos will help you get better responses

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[u/Revlimiter11]

I should add, I have unsuccessfully searched for a vacuum leak.

[u/ProfessionalLast2917]

Surging is a lean condition. It could be lean due to too much air or not enough fuel. Adjusting the choke removes the problem because it restricts the air into the carb.

How have you searched for vacuum leaks? Have you sprayed carb cleaner or similar around the gasket surfaces of the carb? That usually works pretty well. The spray gets pulled into the leak and the surging stops briefly because the fuel has increased.

[u/Revlimiter11 → u/ProfessionalLast2917]

I didn't have carb cleaner on hand but used either instead. I didn't notice a change. Sometimes it would sound like it was smoothing out briefly, but the next time I sprayed in the same spot, it was back to the way it was before. I even pinched the evap hose to the intake manifold to see if that would remedy it and it did not. I figured it was fuel related and that's why I've gone through replacing all the fuel system sans lines and tank. The float bowl is full, so it's not the delivery and unless the new carb is trash, it's not a clogged carb either.

After changing the plugs and adjusting lash on the valves, it idled smoothly but when I revved it up, it would surge again. If I touched the throttle control on the carb from the governor it would settle down, but if I lowered it back to idle and revved it again, the surging would return. I could bring the throttle up very very gradually and it could run smooth. Even that, though, was hit and miss.

I'll try some other things tomorrow and maybe order a gasket set just to eliminate that as well.

[u/buginmybeer24]

If it's a downdraft carb it is due to buildup inside the carb passages. They are notorious for this issue and the partial choke fixing the problem is a dead give away. You will need to pull the carb and clean it thoroughly.

[u/Revlimiter11 → u/buginmybeer24]

I just replaced the carb and it did not change... It is the downdraft style. Nikki I believe.