Briggs 625EXI rpm surging

[XGamer223]

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!

 

[bertsmobile1]

Pull the breather tube off the back or the airbox and see if it runs better and how strongly the gasses come out of the breather ty=ube
The breather could be faulty or the head gasket could be blown.

 

[XGamer223]

Pull the breather tube off the back or the airbox and see if it runs better and how strongly the gasses come out of the breather ty=ube
The breather could be faulty or the head gasket could be blown.

Hi and thanks for your reply.
So, pulled off the breather tube and it ran actually good for a minute or so. Next start, and it ran bad (still, better a bit) yet again. It definetly did help, but not for too long, I imagine until it warmed up fully.

Nothing can be noticed to be coming out of the tube, even though the old filter was very oily, just like the whole air filter casing.

Suddenly, it started running okay-ish again (it still was surging, but a lot less, more like the surging everyone complains about on these engines, not even close as shown in my video), and it ran great until fully warmed when it started surging/bogging down again. So I went out and cleaned the outter carburetor casing and I noticed some grass stuck on the end of the choke lever. Afterwards, it ran good, even under load. It starts surging randomly (doesn't matter anymore if the breather tube is on or not), or when I go uphill with it. But I think it starts going bad again when it gets fully, like fully warmed up, when the choke is fully off.

But I'll try to check my fuel line and the in-tank fuel filter, as the randomess of the issue has given me suspicion on the filter. Next I'll probably re-try cleaning the carb.
Any more tips? It's giving me a headache.

 

[bertsmobile1]

I have needed to tighten the choke return spring on a few of these engines because it would flutter every now & then.
This carb would have to go down in history as being the absolute worse design ever made
The choke lever can foul on the side so not fully open and this gets worse with age as the plastic gets soft from heat and slumps a bit

 

[XGamer223]

I have needed to tighten the choke return spring on a few of these engines because it would flutter every now & then.
This carb would have to go down in history as being the absolute worse design ever made
The choke lever can foul on the side so not fully open and this gets worse with age as the plastic gets soft from heat and slumps a bit

Hi once again.
So I tried a different tank, w/o the fuel filter and the same issue. It starts running nice up until fully warm or put slightly uphill.
Currently I'm cleaning the carb, once again. I'll see if that helps anyhow.
Can you also please explain how you managed to get the choke return spring to be tighter, and which spring it is exactly?
Also, can the governor be bad, or out of tune? Thanks in advance for any tips!

 

[bertsmobile1]

Snip off one end then bend down the next 2 turns to make the mounting ring

 

[artemjemmy]

Hi once again.
So I tried a different tank, w/o the fuel filter and the same issue. It starts running nice up until fully warm or put slightly uphill.
Currently I'm cleaning the carb, once again. I'll see if that helps anyhow.
Can you also please explain how you managed to get the choke return spring to be tighter, and which spring it is exactly?
Also, can the governor be bad, or out of tune? Thanks in advance for any tips!

Since it runs well until it is fully warm on an auto choke model, that would mean that the carb is definitely running lean, and the period while the choke is still partially closed is compensating for this problem. Make sure the carb is clean, clean, clean. Then, I would check for vacuum leaks around the carb with brake or carb clean (safety nazis hate this), and if you still have the problem I would get carburetor drill bits and drill out the main jet roughly 1 or 2 thousandths. On these carbs the jet is brass and is cast into plastic, the jet and emulsion tube assembly can actually be removed from the carb body with a prying tool.

 

[bertsmobile1]

(safety nazis hate this)

OK in the states where there is next to no social security so stupidity is largely at costto the stupid.
however I work hard for my money so the idea of the government using it to support a blithering idiot for the next 40 years because a flashover blinded them is one of the few things that makes me cranky .
I am all for letting idiots chop their fingers / feet off in fact I would like to see it happen more often then perhaps the brain dead might come to the understanding that mowers are dangerous
But I just don't want it to cost me money

 

[artemjemmy]

OK in the states where there is next to no social security so stupidity is largely at costto the stupid.
however I work hard for my money so the idea of the government using it to support a blithering idiot for the next 40 years because a flashover blinded them is one of the few things that makes me cranky .
I am all for letting idiots chop their fingers / feet off in fact I would like to see it happen more often then perhaps the brain dead might come to the understanding that mowers are dangerous
But I just don't want it to cost me money

Found the safety nazi, lol. But have you actually done the spray test for vacuum leaks before? I have never had anything catch fire and it generally works very well. The only alternative is propane, which is still dangerous. Being a mechanic is a dangerous job man. Besides the occupational hazards, you work with dozens of chemicals that cause cancer.

 

[Richard Milhous]

OK in the states where there is next to no social security so stupidity is largely at costto the stupid.
however I work hard for my money so the idea of the government using it to support a blithering idiot for the next 40 years because a flashover blinded them is one of the few things that makes me cranky .
I am all for letting idiots chop their fingers / feet off in fact I would like to see it happen more often then perhaps the brain dead might come to the understanding that mowers are dangerous
But I just don't want it to cost me money

What about smoking? Obesity? Alcohol? Type II Diabetes? Motorcycles? Skateboards? Soda pop? Roundup? Carpet cleaner?

I can sympathize, but if you make society collectively responsible for health, you have to accept that some people are going to do stupid things that might cost you money. Otherwise every vestige of freedom is directly erased.