MTD Engine

[JandL]

I know some of you have had these engines in your shops already and now I have one that is being a pest. It is on a MTD Gold snow blower 24 inch clearing width. Model #: 31BM62KE704, Serial #: 1G229B86228, engine S/N 365-SUB0905264A0185. The problem; Engine will not operate smoothly with choke wide open, it hunts or surges if you will, it will run fine at one click of choke closed. I have cleaned the carb and made sure I can squirt carb cleaner in the vent, low speed idle port, main jet and needle seat. Removed old gas (looked fine) and put fresh 91 octane gas with Briggs and Stratton stabilizer in it (can't be too careful). Also installed new spark plug, after all that I started it and it runs the same as before! With the engine running I sprayed carb cleaner around all mating surfaces, no change in engine operation. I was going to check the valves but can find no spec on them. I took off the valve cover and checked to see if anything was obviously wrong but see no problems, valve lash is not what would be considered too loose or too tight. Accomplished a leak down test and found no problem. With all that said..er typed, any further ideas? Or is time for a new carb?

[bgsengine]

New carb. Valve clearance is unlikely to be the issue unless excessive (Intake 0.10mm or about .004" , Exhaust 0.15mm, or about .005") - We keep carbs in stock for them - they are VERY hard to get clean, once contaminated, and no real service parts to speak of other than gaskets, gasket kits, floats, etc. They are really finicky about it - we had one last year that had the exact same problem, customer did not want to get a new carb, in and out of several competitor shops, came back last week finally and coughed up for a new carb, slapped it on, fire it up, run it til engine is warm and it runs fine with choke wide open - They DO need to run at part choke until they get good and warmed up.

Also tweak the spark plug gap and make sure you get exactly the right plug (Champions don't work in them worth a damn, in my experience - Any type or heat range we tried.) - Put in an OE Plug MTD # 951-10292, or NGK BPR6ES are the only 2 plugs we have seen consistently work well in these (Not even a BPR5ES or BPR7ES - tried them both as an experiment on one engine, it would only run right on the BPR6ES. Keep in mind though, one engine does not a pattern make.) and the gap spec from MTD is .020 - .030 , and we've had success with tweaking the gap sometimes, .020, .025, .030 gaps - depending on the engine/machine have made a difference. No rhyme or reason we can find why one engine works great at .025 gap and stumbles or surges at .030 , while another one works best at .020 , and others run great at .030 Have not really had a big enough group of them to find any sort of consistency in what engines run best at what gap, but changing gaps did help in some cases, (changing plug heat ranges did not) , and other than that, carburetor usually solves the remainder of it.

[Roy_N]

Does this carb have a foam bushing or washer on the throttle shaft, on top of the carb? Reason I ask is that I had a hunting/surging problem on a small engine and the cause was the foam bushing had deteriorated which allowed some air down the shaft into the carb. I replaced the foam and then it ran nice and steady

[JandL]

Does this carb have a foam bushing or washer on the throttle shaft, on top of the carb? Reason I ask is that I had a hunting/surging problem on a small engine and the cause was the foam bushing had deteriorated which allowed some air down the shaft into the carb.

This engine only has around 2 hrs on it and is only 1 year old.

After I posted this thread yes another snow blower is suppose to come in tomorrow with the exact same problem! What the heck, it all pays the same...

[KE4AVB]

After I posted this thread yes another snow blower is suppose to come in tomorrow with the exact same problem! What the heck, it all pays the same...

That the way things goes sometimes in batches. I have worked 2 cycles for 5 years and never had a leaking needle seat problem then I got 2 in least a month this year. They were leaking around the outside mating area.

Please let us know of the solution as we will most likely run into same problem later.

[JandL]

New carb installed, engine runs like a top. Now I will see how long it lasts.

[Skywatcher]

Hi J & L

My experience with these Chinese carburetors is the idle jet usually seems to be the main culprit. The idle jet is the plastic one with the brass insert that's held in place by the idle speed adjusting screw. When ever I clean one of these carburetors, I run a #78 (.016") drill through the jet to make sure it's clean and haven't had a surging engine since (except the one with the plugged fuel cap vent). All the best,

Sky

[TK4619]

I have the same model, had it for about 2 or 3 years now and when I took it out of storage in the fall it gave me a similar issue, I always use startron in my fuel and have never had an issue with it going bad, but my neighbor used it last year when I was out of town and put some untreated gas in it, I decided to try something that a friend used on his generator during hurricane sandy. I put the correct amount of a product called Seafoam into the fuel tank, ran a full tank through the machine and the problem has gone away.