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Craftsman snowblower surges on high speed only

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24K views 4 replies 3 participants last post by  paulr44  
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#1 ·
I have a Craftsman snowblower that surges only when the throttle is on full open. It's model number is 247 888160. It has a Tecumseh 6.5hp OHV engine.

More details about the problem:

Starts on the first or second pull always.
Idle is smooth.
No signs of overheating
With the throttle in the fast position (full throttle) the engine surges, unless there is alot of snow going into it, then it will smooth out at high speed, but as soon as the load is off, it will start surging soon or immediately.

Returning the throttle to low idle will smooth out the surge.

Last year I replaced the carburetor with a new one from sears parts, checked for intake leaks as well. Installed a new plug, drained and cleaned the fuel tank
 
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#3 · (Edited)
it is surging basically across it's whole RPM range. I also found today that if I hold the govenor arm steady while it is set to high speed, eventually it will stop hunting. But if I idle down, then go full throttle, or put a load on the engine then remove the load, it will hunt again.

The carb replacement was done after it started surging. Replacing the carb was an attempt to make it stop surging.

it almost seems to me that something in the Govenor assembly is sticking. As in the govenor is not moving quick enough to respond properly to changes in speed, and then needs to overcorrect.

Also changing where the spring is connected on the throttle (there are 5 numbered holes to choose from) changes the speed at which the surge happens.
 
#5 ·
If a spankin' new carb. didn't stop the surge then the surge is obviously due to another issue.

But I would suggest you review static governor adjustment first. Go to this thread, http://www.hobbytalk.com/bbs1/showthread.php?t=383991 and look down to usmcgrunt's post with the repair manual link, which will guide you in that adjustment.

There are two things I usually check for when an engine surges. One is a too-lean mixture. This can often be checked by partially choking the engine if it has a choke plate, or by partially blocking off the carb. intake with your finger. If the engine cleans up and stops surging, then it's often a carb. related or vacuum leak issue.

Holding the governor arm steady often gives you insight too. If it cleans up, then it's often a governor issue. Re-setting the governor static adjustment is a start. Moving the gov. spring in the various holes will change a couple things. One is RPM. The other is governor droop as the mechanical advantage relative to the arm has changed.

We have on occasion seen engines surge from valves needing adjustment. Although a rare cause, it does happen so perhaps you should check them too.
 
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