Briggs 625EXI rpm surging

[bertsmobile1]

So, Bert, what would you say is the OSHA approved alternative method for finding vacuum leaks, hmm?

Like scrubby,
I use either wd40 or inox from a trigger pack depending upon which is closer at the time
No idea is it is OH&S compliant but a lot safer and cheaper than anything from a pressure can

 

[DOB]

Hello folks,
so one of those engines with the plastic carbs without a primer bulb, with the white "cartridge" in it, a 625EXI engine has issues with the RPM/throttle surging up and down.
Before this happend, the engine refused to run properly at all, so I took the carb apart, cleaned it, the ports too, replaced spark plug, placed a new filter and it run great. But after a hour or so after mowing, it started surging heavily, no matter if there's a filter on or not. Only thing I noticed is that the carb bowl is very oily/wet overall.
Not sure what to try since the carb has been cleaned already. No way to tune it or anything, so I'm out of ideas.

Video and image: (don't forget to turn sound on)

https://imgur.com/a/X6fmTR5

Thanks anyone in advance for any help given!

Low speed orfice restriction clean it with a piece of fishing line

 

[artemjemmy]

Low speed orfice restriction clean it with a piece of fishing line

Typically I would suggest exactly the same thing, it is the cause of probably 75% of surging problems, but I believe these carbs do not have a low speed circuit. There is a plastic piece for an idle fuel pickup in the carb and a cast depression for a welch plug on the side like an emulsion well, but it isn't drilled out. Seems like briggs added it as an afterthought if they wanted to add an idle circuit.

 

[Hammermechanicman]

This carb would have to go down in history as being the absolute worse design ever made

I'll second that. There is a term for designs like this. It is called SFB engineering ($h!t for brains). I wonder what moron dreamed it up.

 

[artemjemmy]

I'll second that. There is a term for designs like this. It is called SFB engineering ($h!t for brains). I wonder what moron dreamed it up.

Personally I don't find them too bad. Aside for the throttle shaft breaking because its thin plastic, I love how you can remove the carb jet and emulsion tube easily to really clean it out. When I do a carb clean it is almost always like back to new on these carbs.

 

[Hammermechanicman]

The brake kleen i use is non flammable. Works great to find air leaks. Engine wants to die if it gets in.
And i have 2 fire extinguishers in the shop. If you ever have an experience where you really needed a fire extinguisher it will make you a believer in having 2. A small one you can keep handy and a larger one hanging by the door. Trust me on this one.

 

[Hammermechanicman]

Personally I don't find them too bad. Aside for the throttle shaft breaking because its thin plastic, I love how you can remove the carb jet and emulsion tube easily to really clean it out. When I do a carb clean it is almost always like back to new on these carbs.

Every one of these customers bring in are either hard to start and/or surging.

 

[artemjemmy]

Every one of these customers bring in are either hard to start and/or surging.

I have found these carbs to surge far less than any of the previous briggs aluminum vertical shaft engine carbs, just my personal experience. If they are hard to start that pretty much just comes down to the autochoke not functioning. I have noticed that sometimes it will stick open when the choke opens all the way because the choke shaft gets wedged against the left steel support piece that the air filter backing cover screws to. I end up just trimming the choke shaft piece with side cutters and it works fine.

 

[bertsmobile1]

I'll second that. There is a term for designs like this. It is called SFB engineering ($h!t for brains). I wonder what moron dreamed it up.

And what is even worse is when Briggs took over Victa they got the rights to the LM plastic carb that never clogs, rarely ever floods and in many cases has run for better than 40 years on customers mowers without a single problem save perishing of the primer bulb if left in the sunlight all day every day.
It had been modified to make it teir II & III EPA compliant ( We have just gone to tier II ) for 2 strokes so should have been fine for 4 strokes.
But they ignored it in favour of the horrid POS currently fitted in all 4 variations.
They are the only carbs I regularly throw away as down here the bodies continually warp .
Don't know if B & S sent all of the trash ones down here but just about every one I have worked on required the choke spring to be shortened because it would flutter,
Bodies warp and cause the butterflys to stick either fully open or fully closed

 

[Hammermechanicman]

Another shop i know won't even work on them. They just replace them. At $75/hr owner says cheaper for customers to just put on a new carb and HOPE it work better than the POS they took off than try to fix the old one. Of course these are on engines you don't change oil in. Too bad i can't fit a Chonda chineesium $10 carb. They work fine.