Poulan XXV Problem Increase RPM When Tilted Forward and Dies

[Degull]

Hi everyone. I have a Poulan Micro XXV that I bolted on a cylinder/piston from a Poulan 180 Pro. It bolted right up and fits very well (the 180 is a two ring design so I thought I see how well it would work). I'm have a strange problem. The saw runs well when it is on the ground level but if I tilt it forward the RPMs increase then when I bring it back level it cuts off and dies? This is only happens while the engine is idling. I tried a different carb and the same thing happens. At first I thought I had a vac leak somewhere, so I inspected it pretty close and could not find a problem. Anyone heard of this before?

 

[Lakeside53]

You may well have a vac leak - hard to find one by inspection - you need to pressure /Vac test. Look for something that "Flexes".

I see many saw that slow down when tilted forward or sideways. This is due to the L being too rich a fuel puddling in the bottom of the crankcase or carb boot. Tilt forward and the excess fuel changes the mixture.

Tilt your saw forward, gun the throttle with it tilted. Does stay higher RPM or drop back to idle?

 

[Degull]

I got a chance to play with the saw again today. It only acts up when it is idling. You tilt it forward while idling it increases rpms then starts bog and if you bring it level again it dies. If you hold the throttle open it runs with lots of power no matter what position it is in. I noticed the reason it is increasing power then dying is not because of a air leak, it is getting too much fuel. After it dies, it's hard to start as if it is flooded. I pulled the plug and sure enough it was soaked with fuel. Somehow fuel is pouring into the cylinder when it is tilted forward. The cylinder from the 180 Pro I put on it was a little different design and I wondering if that's my problem.

 

[Kneejerk Bombas]

It sound like your low speed jet (L) is set too rich. Try turning it in (clockwise) an 1/8 turn at a time and retry it.

 

[Degull]

Mike you were absolutely correct. I turned the low screw in 1/8 turn and kept trying until it stopped increasing rpm and dying when tilted forward. Thanks so much!!

I'm pretty new at setting up these little two strokes as you can see by my questions. I got a couple of question about setting up this carb so this saw screams and acts predictably when started and operated.

1) the adjustment that controls throttle valve stop, should the screw be adjusted so it stops when the valve is completely closed or should it be adjusted to stop the valve not closed completely allowing a little air to pass by when idling?

2) how is the high screw adjusted, and if I play with the high do I have to go back and adjust the low?

It's running pretty well now with lot's of fiddling but it's been done by trial and error instead using a proper carb setup method.

 

[TimberPig]

Carburetor adjustment has been well covered on here. If you use the search and look around, you will soon find many threads on how to set up the carb adjustments properly. There was even one a couple days ago. If you go search, advanced search, then type in carburetor tuning (or something similar) and search only the chainsaw forum and only for titles, I'm sure you will be able to read for days on how to set that carb up.

 

[Cut4fun]

carb tuning

Two links for carb tuning.
http://www.madsens1.com/sawtune.htm
http://ilvirtualforest.nres.uiuc.edu/harvest/timstips/sawburetor.htm

 

[Kneejerk Bombas]

The Madsens site is the best reference I've seen for tuning a saw.
The butterfly plate stop screw should be set so the saw idles high enough it doesn't stall but slow enough the chain isn't spinning.
THe high speed controls the maximum RPM. If it's too lean, the saw will rev too fast and blow up. If it's too rich, it will loose power, suck gas, carbon up the motor, and smoke a lot.

 

[Fish]

How bout that fuel line?

 

[Degull]

I have been following the instructions above and I have the saw running pretty well now. I was more concerned with getting the high adjustment correct because I didn't want to burn the saw. One last question. The funny thing about the carb in use (Walbro WT20) and the spare I have tried, when the throttle is wide open the fuel that is being sprayed above the butterfly valve goes all over the place. It's like a little fountain that kind of sprays upwards? Is this normal? When carb cover is installed it doesn't seem to make a difference because fuel is still all over the little compartment. You would think that the vacumm created by the engine would suck the fuel into the carb, but it looks like more fuel is being sprayed outside the carb than in. Many thanks to everyone for the help.

 

[Degull]

Anyone have any idea why my carb is spraying fuel like a fountain. It's looks as though more fuel is being sprayed outside the carb than inside. I've tried a different carb and it does the same thing. Is this normal?