Snowblower Surging Until Warmed UP

[bob]

I have a MTD Yardman snowblower with the Powermore engine(357cc). Everything works OK except that it hunts or surges until it is warmed up. When I start it and slowly take the choke off and go to run postion it will quit if I do not turn it back one notch, Then when I can leave it in run postion it will surge until I give up waiting and start using it. The surging will soon go away and run good. Is this a problem with Powermore engine or do you think it is the carb. I have cleaned the carb.Thanks

Blair

[Skywatcher]

Hi Bob

This is a fairly common issue with these Chinese built engines and their carburetors. The description of your problem indicates a restriction in fuel supply or an air leak into the pilot circuit. When you cleaned the carburetor, did you extract the pilot jet from the top of the carburetor just under idle speed screw? If so, were both O-rings present and in good condition, and was the orifice in the brass insert clear? The normal size of this orifice on these engine is around .016". Hope this points you in the right direction,

Sky

[Arkie]

Is this a new to you snow blower?
Do you know if it ever operated normal during cold weather is why I ask.

Reason I ask is I've seen some small engines during cold weather hunt and surge even when new from the factory because of using low emission non-adjustable carbs. (have to run them on part choke for sometimes 2 min's before they would get warm enough.
I've also had to enrichen the L jet area just slightly.
Like skywatcher says the issue is usually because the low jet circuit is lean in the carb or a slight air leak.

[bob]

Thanks for answers. Bought snowblower used so I do not know if it ran perfect from factory or not. I did remove and clean the pilot jet and both O rings were there but the one nearest to the top was in rough shape. Maybe I will try to enlarge the pilot jet hole slightly. Do not have any small drill bits so I will have to do a little filing. I did notice it was very difficult to push pilot jet back into carb with O rings on. May be one O ring was swelled but I really had to push hard to get it back in far enough so that I could get idle screw back in

[38racing]

recently worked on 2 for friends. one sat for period and carb was gummed up. after cleaning it ran fine but flooded. couldn't stop the flooding so replaced with china carb. cold surge very short. second one was normal use but again it would only run on choke. added my homemade carb cleaner to the gas. she reported an improvement but I have checked it myself.

[Arkie]

Bob:

Just some hints
IMHO: and what I do before doing any mod to a carb.
I first check and see if I can get a replacement carb at a reasonable price and if so I install and test before trying a mod to the OEM carb. If the replacement carb operates ok I know then that I have a OEM carb that needs attention. If the replacement carb has same symptoms I need to look further as to why.

You do need to think about getting them O rings corrected first and look carefully at a emulsion tube, sometimes their are some very small holes that can be overlooked if the brass tube is not shiny that needs cleaning.
If I'm going to do a slight enrichment to a carb I check and see if a replacement jet or part that I'm going to mod is available as a replacement, if not I know then that the mod is permanent.
I do not know how a file could be used for a SLIGHT MOD?

What I've done for some of my own eq. (especially the low emission 8-10hp Tecumsehs used on emergency gens where surging is not a good thing and with fixed jet carbs)
I'm talking about doing the idle circuit on a small engine. Engine normally idles good but surges cold or when throttle up and know that it's carb issue.
I first use a micro bit and gauge the existing jet then start going oversize in steps.
I use a set of micro drill bits and a hand operated chuck. Have to be very careful and constantly back off the bit/clean and another careful turn. (if a bit breaks in the jet you are SOL and they are wimpy. (keep the bits in order because they are so small that if they get mixed up you have another mess)
You can find the micro type twist drill bits with chuck on flea bay for around $15 or less.
I'm indicating hand enlarging a brass jet, not steel.
If you know the starting size and enlarging don't work you can sometimes restore with solder and then resize a jet but not an emulsion tube.