Briggs 10.5 surging. About to pull my **** hair out

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2,370
Location
Texas
So weird thing... went to start it today and it yanked the cord back. Checked the valves and the intake was off at .009... it was set at .003-.004. Now this could be coincidental since I just adjusted them and maybe it went out some. Adjusted it but it seems the compression release(when the intake valve bumps off during the compression stroke) bumped off fairly early in the compression stroke. Maybe it's just me? Could it be a timing issue?

Anyways got it started and sprayed carb cleaner from the head where the intake tube is to the carb. Sometimes it seems like it helped a little others not. Kinda confusing. So I can't say I definitely have an intake leak.
I did replace the fuel filter with a disc style and I noticed when it ran on the high side it ran a little better, but didn't solve the problem (maybe making up for a lean issue but still surging/waffling)
I also tried above with over riding the governor with no success.

So as if now I'm calling it a carb or timing issue.

So ill start with the carb and get an Amazon job to see if there is a difference. That brings me back to the walbro/nikki question.

And thanks so much fellas for the help so far. Really appreciated
If it pulled the starter rope out of your hand you might have a sheared flywheel key. It also won't run right.
 

sh40674

Thread starter
Messages
155
Location
iowa
I think I got the carb part figured out.. if I type the nikki number into Amazon, it comes up with different knock off brands.

If I type in "walbro lmt 4993" it comes up with even different brands but from what I can tell the exact same carburetor. Ordered a Nikki knockoff since I felt better about matching at least 1 part number lol. I should get it on Friday. Will update!
 
Messages
363
Location
Maryland
Good luck! Be sure and add a few ounces of Berryman B-12 to the gas tank every so often to minimize dirty carbs. I do that with all my outdoor equipment small engines and I rarely have fuel related issues.
 
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2,019
Location
Northeast Nebraska
OP you said it doesn't surge under load, just my two cents but my 5 hp Tecumseh on my 1996 snowblower has what I call a stumble when not under load at higher RPM's about every five seconds or so, but once it's under load and throwing snow it doesn't miss a beat. I always just figured it was somewhat normal.
 
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638
Location
WV
Surging can also be caused by a partially sheared flywheel key. Had you hit anything mowing before? This is the same as the post earlier that mentioned timing. If the key is worn or partially sheared it will throw the timing off and surge. Been there done that.
 

sh40674

Thread starter
Messages
155
Location
iowa
Surging can also be caused by a partially sheared flywheel key. Had you hit anything mowing before? This is the same as the post earlier that mentioned timing. If the key is worn or partially sheared it will throw the timing off and surge. Been there done that.
No, thought I had everything squared away, that was due to recoil backlash and the flywheel key is 100 percent. I have an Amazon carb coming friday.. so if its not that I'm suspecting timing somehow... maybe a tooth is broke off on the gear or something. Not even going to think about it until I get this carb on.
 

sh40674

Thread starter
Messages
155
Location
iowa
Good luck! Be sure and add a few ounces of Berryman B-12 to the gas tank every so often to minimize dirty carbs. I do that with all my outdoor equipment small engines and I rarely have fuel related issues.
I have a 5 gallon gas can I use for my small engines and it gets seafoam dumped in it. Im a firm believer in that stuff. My boat has an 84 evinrude, old man I got it from that bought it new said he's put seafoam in every tank of gas its ever seen and the carbs have never been off. I do the same thing and it runs like a brand new engine. Never tried b12 though, ill look into it!
 
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1,455
Location
Sask, Canada
I am not a firm believer in ultrasonic cleaning carbs. Use a strong solution and let the thing do its magic. I had hand cleaned carbs before with little or no luck but 30 minutes in the cleaner and they come out factory fresh and working like a top.
 
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13,251
Location
North Carolina
Even though you can see through the jets just fine, There is a residue from old fuel that makes them smaller. Get yourself a tool that welders use for gas welding. It has many size fine wires that you can push through the jet. You will be surprised at what you see.
I have some .014 stainless stylets that i use to run through every orifice of a carb. Will not go around corners, but cleans jets and tubes. That with carb cleaner , gets most carbs running decent
 
Messages
1,282
Location
Pacific Northwest
I am not a firm believer in ultrasonic cleaning carbs. Use a strong solution and let the thing do its magic. I had hand cleaned carbs before with little or no luck but 30 minutes in the cleaner and they come out factory fresh and working like a top.
I put small engine carbs in a peanut butter jar and fill it up with Berryman's carb cleaner and put the lid on. Then I put the jar in the ultrasonic cleaner full of hot water. Best of both worlds. You can see the crud just come flying out.
 
Messages
363
Location
Maryland
I have a 5 gallon gas can I use for my small engines and it gets seafoam dumped in it. Im a firm believer in that stuff. My boat has an 84 evinrude, old man I got it from that bought it new said he's put seafoam in every tank of gas its ever seen and the carbs have never been off. I do the same thing and it runs like a brand new engine. Never tried b12 though, ill look into it!
Berryman B-12 is much more potent than Seafoam. I've compared the Technical Data Sheets for both, and Berryman B-12 contains much stronger varnish and dirt "cutters" than Seafoam.
 

sh40674

Thread starter
Messages
155
Location
iowa
Well got the new carb on, ran it for 5 minutes and that seems to have solved the issue. A little popping out of the exhaust but I think that's the gaskets since either had to remove the muffler before (new gaskets in the mail tomorrow)
A few slight differences in this new carb... the mixture screw is different than the briggs replacement at least for the walbro, but I set it a turn and a half out and it seemed to run decent so I'm going to stick the cap on it. The fuel tube is bent instead of straight but the most noticeable is the choke is set up for a cable not a manual like my old one and can't be switched. I was able to hold the choke a bit and pull enough to get it started so it'll work. I'll do more this weekend as far as marking oil level and letting it run for a while and see if any gas makes its way into the crank case and check plug after a good run. But so far so good.

Thanks to everyone for your input!
 
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