Poulan Runs Strong but Dies At Idle

[Loggerhead]

I'm still attempting to solve the "NO IDLE" problem with this saw but reaching the end of prossibilities that I'm familiar with. So Far, I have performed the following:
Replaced the fuel line and tank filter
Total and complete overhaul of carburetor
Checked muffler and screen for blockage
Removed and checked reed valve
Cleaned and gapped spark plug
Performed three compression tests with a range of 135 to 140PSI

This Poulan 2300AV starts on about the fifth pull of rope when cold and fully choked and the first pull when warmed up. It dies at low speed and will not reach a point of "4 cycling" and my attempts to adjust the low speed mixture do not eliminate the problem. At WOT, a fair amount of fuel vapor or droplets are emitted from the top of the carburetor and I assume this is simply reed valve flutter but it doesn't seem to have an affect on the engine as it is responsive and doesn't bog at hard throttle. Overall, I have to say that it performs well except for the no idle condition. The only other thing that I can think of that may be causing the problem is weak spark at low RPM...any suggestions would be gratly appreciated...

 

[1Alpha1]

Might be a simplistic suggestion, but have you checked to make sure the idle screw is turned in far enough?

I'm not talking about mixture screws, but the actual screw that holds the carb butterfly open.

A friend of mine had a similar problem on a saw of his a few years ago. His idle screw had somehow backed off, allowing the butterlfly to close up.

 

[Loggerhead]

Hey Dano...good point but yepper, Ive adjusted it in my attempts to keep it from dieing long enough to adjust the low speed fuel mixture...It certainly seems like it's not getting fuel through the idle circuit of the carburetor but it wasn't dirty or gummed up when I took it apart and I cleaned it thourougly...all the way down to sticking small wire in all of the orifices to make sure there were no obstructions and blasting air through them as well...air leaks would cause it to run at a high idle and even surge or run erratically so I know the unit is tight...I'm stumped on this one...

 

[begleytree]

impulse line OK?

 

[Kneejerk Bombas]

A saw with a lean condition may also have an air leak. Impulse line, intake boot, crank seals.

 

[Crofter]

does it make any difference whether the lo speed mixture screw is one turn or 5 turns out I see the possibility of some of the internal passages in the carb being plugged somehow and not even letting fuel to the lo speed screw. Seems you have covered most of the bases but should really pressure test the saw for leaks. A small leak is much more harmfull to lo speed idling than it is to high speed, tho that usually leads to a higher idle speed.

 

[Loggerhead]

This saw doesn't incorporate an external impulse line but has a small hole in the carb base/reed valve assembly that aligns with a hole in the carburetor itself...it seems to pull adequate fuel from the tank with each yank of the rope as you can view it when the line is empty. I forgot to mention that I did check the cylinder to crankcase mounting bolts for tightness and they were fine. I don't have a way of pressure testing the case but assume that most of the "good reputation" small engine shops have this ability as I'm sure the crankshaft seals would be a more likely candidate to cause my problem. Turning the low speed mixture screw does have an affect on the running of the engine but not enough to allow it to idle low enough without dieing...

 

[Crofter]

low speed mixture screw does have an affect on the running of the engine but not enough to allow it to idle low enough without dieing...

That, along with not being able to get it to 4 stroke at WOT, I think would warrant a crank case pressure and vacum check. Let us know how you make out

 

[Loggerhead]

That, along with not being able to get it to 4 stroke at WOT, I think would warrant a crank case pressure and vacum check. Let us know how you make out

Crofter, could a guy perform his own vacuum and pressure test if he blocked off the intake and exhaust ports correctly and included a schrader valve in the process?...of course, I wouldn't know how much air pressure to put in the case or what kind of tolerances would be acceptable as far as bleed down time goes. I guess most legitimate shops can do it...you have any idea what the charge is to do it?

 

[whatsnext]

You mentioned reed flutter. I'm not familiar with your saw buy if the reed, if you have one, is not sealing well it can cause a poor idle.

 

[Loggerhead]

Sure did...have the results in my original post...135 to 140 out of three tests...should be adequate compression for this saw.

 

[Crofter]

Loggerhead, you should be able to rig up something. about 5 psi max and listen for leaks if you have pressure drop. Soap and bubbles? behind the flywheel is trickier. Stripping the saw down and blocking off carb and exhaust is the biggest part of the job. You can pressurise either here or plug hole. A repair shop might have a minimum labour charge so I would expect to pay at least $30 as a guess.

 

[Lakeside53]

Adding to all the above...

Unless really bad (and then the saw usually won't start) seals tend to fail under vacuum rather than pressure. Pressure test a good indicator for other problems, but you'll also need to vaccuum test. I see many saws that hold pressure all day, but the seals leak like a sieve under 5-7lb of vacuum.

Generally, if a saw slowly dies at idle it's choking up with gas. If it speeds up even a little then dies, it's leaning out. The problem is that most guys tune to get around the leaking seal so the basic setting is rich, and when the seal varies it's effectiveness (we're talking about a slightly faulty seal, which is where they all start getting bad), the saw can suddenly become too rich and choke. The problem with a marginal seal, it that it affects both air volume in the mix AND impulse pumping... Above idle, it's often not a problem as the tiny leak from seal is only a small proportion of the total volume.

Without a pressure and vacuum test, the hardest part is to figure out where to start.

One way to guess at your seals and other leaks is to look at your carb settings with respect to standard (I assume that's one turn out, but you'lll need to check)? If it idles "better" at say 1.5 turns, then that a pretty good indicator that you have an leak somewhere, as you're now compensating for the additional air creeping in around the seal or whenever. If it idles better at say .6 turn out, then you are much too rich somewhere.

You can remove the seal and impulse issue from the variables completely by simply connecting up an external fuel tank (like a coffee can) to the carb and hanging it about 2 feet above the saw (be careful). I use a small weedeater tank, but a coffee can with a small hole that pinches the hose where it enter the tank and a few of feet of fuel hose works also. Start the saw and tune for a reliable idle. Varying impulse pressure will now have no effect on pumping gas, and any small leak, even varying, can be tuned out of L end. Look at your settings and see where they vary from "basic".

 

[Loggerhead]

That's a great suggestion Lakeside and I appreciate you sharing the idea...I have something I can use for a fuel reservoir and "gravity" feed the fuel to the carburetor...will I need to "block off" the impulse orifice under the carburetor base to do this since the pump will still be activated by the vaccum and pressure of the engine?

 

[Lakeside53]

That's a great suggestion Lakeside and I appreciate you sharing the idea...I have something I can use for a fuel reservoir and "gravity" feed the fuel to the carburetor...will I need to "block off" the impulse orifice under the carburetor base to do this since the pump will still be activated by the vaccum and pressure of the engine?

Probably not... but it might remove any possible conflict. I'd just try it without touching anything, then change one variable at a time.

 

[Loggerhead]

You mentioned reed flutter. I'm not familiar with your saw buy if the reed, if you have one, is not sealing well it can cause a poor idle.

"Flutter" was the only word I could come up with and I was hoping somone would respond with some kind of theory based on the description I gave...I didn't think it should do it but let's say at wide open throttle, a fuel vapor or fuel mist is forced out the top of the carburetor...I assumed that it was because the RPM's were so high that the reed valve vibrated out of sync or "bounced" so to speak...How is the best way to check the reed valve for sealing or can it be done?...it's never been tampered with but I guess it doesn't matter if the sealing ability is affected by age or use. Wouldn't the saw be hard to start if it was not sealing properly or not?

 

[scottr]

Setting & clearance

Lh , the initial settings for the carb adjustment is one turn out from lightly seated . The maximum gap between tip of reed petal and seating surface is 0.010" .