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Discussion Starter #1
Just noticed that I posted this to the wrong board so I am reposting here.

Hi, I have a Craftsman blower model 358798980 which is built by Poulan.
Couple of weeks ago it quit running on high speed. As I had noticed that the carb diaphragm was leaking I decided to rebuild the carb. After finding that a new carb was just slightly higher than a kit I opted for that. I also replaced all the fuel lines(correctly routed.) New primer bulb and new spark plug. (RCJ8Y) what manual called for. All happy with what I had done, yank the cord, starts right up,same problem , runs while choked but take it off choke and it dies at full throttle. Okay, after a little web research I see that these are prone to the cylinder bolts coming loose, check that, all tight. I now do a compression check, 95 pounds, fine, right? Also checked the muffler and port, all clear.The only part not replaced was the gasket under the carb as one was not supplied, old one seemed intact. The primer bulb is staying full of fuel when it is running also. Any ideas at all greatly appreciated. The wife swears that I will throw it in the trash and buy a new one so I wanna prove her wrong, please help a brother out.
P.S. Also has fresh 40:1 fuel
 

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You might lightly seat the H (hi-speed) needle, then turn out 1 1/4 turn.
There are lots of posts on this forum on how to tune the engine with the H and L needles.
hope this helps,
thanks,
 

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Discussion Starter #3
Thanks, carb does have the "tamper" proof plugs on it, hate to mess with those right out of the box unless neccesary.
 

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While it is running spray carb/brake parts cleaner along all the mating surfaces behind the carb and along the crankcase, if the engine tempo changes you have found a leak and can take the appropriate action. Have a good one. Geo
 

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Discussion Starter #6
I just cracked the plastic case (again) gettin' real good at that, and tried the carb cleaner trick around the base, no change in speed at all. Vent in cap huh? Should I blow it out? Take it off?
Thanks for all the suggestions thus far, open to all and any.
Thanks!!!
 

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high speed

I just cracked the plastic case (again) gettin' real good at that, and tried the carb cleaner trick around the base, no change in speed at all. Vent in cap huh? Should I blow it out? Take it off?
Thanks for all the suggestions thus far, open to all and any.
Thanks!!!
the cap has to vent to allow fuel to flow freely start engine and loosen cap after starting it sounds as though the carb. is running out of fuel.:)
 

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Possible air leak between the carburetor base and the crankcase or lower crankshaft seal. If lower seal is leaking, there may be wear in the support bearings on the crankshaft.
 

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agree with the air leak ideas. will it idle on full choke? did you check the screen in the muffler? being a new carb i would not suspect that. on the gaskets behind the carb make sure all the holes line up. how about the fuel filter?
 

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Discussion Starter #10
Yes, it will idle at full choke with the accelerator locked down. No I did not replace the fuel filter. Is the 95psi sufficient for the compression.
Have gotten sidetracked so I have not been able to look at the vent in the fuel cap either. Thanks again for all the help folks.
As far as a screen in the muffler, i have had the muffler off and have not seen a "screen", what am I looking for?
 

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There is usually a spark arrestor screen in the muffler that can become clogged with carbon build up. The fuel cap vent is not likely the issue if the problem is immediate, if it will run for awhile alright before the problem starts, then it could be the vent in the cap.
 

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Discussion Starter #12 (Edited)
Update

Got to have a little garage time today so here is the latest:

Checked the muffler screen and all clear, got a better compression gauge and after 5 pulls reading 125psi.
Same thing, starts on choke, runs strong til warm then dies when taking choke off or giving gas via throttle.
Vent in gas cap clean. New fuel filter.
Decided to tear down completely. Rubber gasket under the plastic carb holder,/manifold a little rough, possible air leak?
Took off the cylinder jug, seemed as if the gasket under the cylinder may have had a small leak as it seems as if there was an oil trail from inside to outside. Maybe when it starts to get warm the compression drops. The piston was very clean with very little carbon and no heat scoring on the piston or cylinder walls. I did manage to break the rings while checking to see if they were stuck, or maybe they were already cracked, is that a common thing?
Anyhow it looks as if the gaskets and rings are cheap enough so wadda ya guys think?
P.S. When I took out the spark plug I noticed that it was wet so I know that it is getting fuel when it dies.
Also the oil that was leaking was running down on the pickups? on the coil as it, and the rotating pickups? were oil coated.
 

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If there is a leak in the cylinder gasket then it could be sucking air there. A leak in this gasket will not affect the compression. It could also be the lower crankshaft seal, but it does sound like an air leak causing your problem
 

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Discussion Starter #15
Well, the fact that the plug was wet leads me to believe that it is getting sufficient fuel. It always starts right up when cold on the first pull but as it starts to warm up the problem arises.
At this point I have two choices, 1. pitch it and give away the new carb or 2, spend a few more bucks and put it back together one more time.
Everyone on here has sure been helpful and it is much appreciated.
Are any of you guys in the parts sales end of this business or have any reccomendations?
If I do throw in the towel does anyone here want the carb?

I will keep you posted.
 

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Take a look at the crankshaft seal underneath the flywheel. This seal could be leaking after the engine warms up a bit. If it is, there is likely oil residue around this area, and it should be clean and dry if the seal is good. Also check for play around the crankshaft in this area, as wear on the bearings could also cause a leak.
 
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