Poulan 451 Going lean in cut

[exenos]

I have an old Poulan 451 I picked up from the side of the road a while ago. Put it in the shed until now. Pulled it out checked the fuel lines, spark plug ect and started it up. Compression is good @160psi. Idles great after a slight tune and ran great for the first tank of gas. I absolutely love the saw, tons of torque and an amazing sound. However near the end of the first tank it started to die under full throttle in the cut. It would rev out for a second then die. Felt lean and the plug confirmed it went lean for a second. Made sure the tank was venting and the fuel filter was clean and tired again. Same result, goes lean after a few seconds of cutting. I'm thinking its the fuel pump and have a carb kit on order but I'm wondering if its anything else that I could be missing?

Pictures of the saw cause every one likes pictures.

 

[hotshot]

Sounds like the fine inlet screen on the fuel pump side of the carb is clogged up, but you'll know soon enough when you put the kit in.

The crap that was left in the fuel line & pump side probably got strained out.

Those are neat old saws, look alot like the smaller 60cc Poulan 361.

 

[Westboastfaller]

So you cracked open the gas cap to test vent? Did it start to race and then it starve out?

 

[rd35]

If it only does this near the end of a tank of fuel....It's probably running out of fuel. The pick-up will start to take little gulps of air as it begins to come out of the fuel and when it takes in enough air to lose its ability to supply enough fuel for the carb it will begin to lean out. Sometimes a dying/stiff/distorted fuel pump diaphragm will exaggerate this problem as it will not be able to pump air as well as a good/new one does.

 

[exenos]

If it only does this near the end of a tank of fuel....It's probably running out of fuel. The pick-up will start to take little gulps of air as it begins to come out of the fuel and when it takes in enough air to lose its ability to supply enough fuel for the carb it will begin to lean out. Sometimes a dying/stiff/distorted fuel pump diaphragm will exaggerate this problem as it will not be able to pump air as well as a good/new one does.

Sorry I should have mentioned that I had filled the tank up as well. So it's not for lack of fuel in the tank. After it happened I undid the cap and heard a small woosh from the tank but couldn't tell if it was pressure escaping or from a VA ume being drawn inside so I left the cap cracked open for the next try. Didn't help.

 

[rd35]

Then, I'd say a carb rebuild should do the trick. Check your fuel line to make sure it has not become soft. I have seen those lines collapse under fuel pressure builds up in the tank. Either way, a rebuild kit is always a "plus" for an old carb!!! For now, you might want to try removing the H and L needles and blow out the seats with air to be sure there is nothing blocking those ports. That H needle can sometimes get some grungies in there that will also impede fuel flow causing a lean run at high revs under load.

 

[exenos]

So I took the carb apart today to see if there as any blockages and the only thing there was some gunk in the mesh filter like hotshot said. Cleaned it all out and checked the needles while i was at it and put it back together. Still dies when loaded up even with the high screw 1.5 turns out. It will rev out a little longer than before before it dies so it is getting more fuel but I don't want to keep turning up the high speed screw cause thats just masking the problem. Guess I'm just waiting on the carb kit then.
Thanks guys

 

[Greenerpastures]

If the saw is cold, will it start up, run well for a time and then die.
They do this if they were run on straight fuel.
I hope this is not the case though and your new carb kit sorts the issue.

Regards, john

 

[exenos]

No it will idle for ever if I let it. It only dies at full throttle cold or hot. Really hoping its just a fuel issue because i cant find any parts at all to rebuild this.

 

[rmh3481]

The diaphragms in the carb have probably hardened off from time and the alcohol in our gas. Those hard carb diaphragms are probably causing your starving issue. You could raise the carb lever a hair but dont go too high or it will flood. Best bet would be to replace the diaphragms and the fuel lines. On the metering side of the carb the gasket goes below the diaphragm and on the pump side the gasket goes above. I mention this because if you get the order mixed up it wont work.

I would also take a look at the crank seals they could be seeping a little air. A light psi pressure test of the case will tell you, no more than 4-5psi is necessary. If you need replacement seals, you can get a set at a bearing supplier but you will need to take the old ones with you for measurement. Baileys may also have a set of seals for that engine, they were a Poulan dealer when they made real saws. I didnt look at the IPL, but Im thinking that engine will have a needle bearing on the output side so you will have one ball bearing on the ignition side, one needle bearing at the connecting rod and one needle bearing on the output side. Use bearing grease to set the needle bearings if you take it apart. Replacement gaskets can be cut easily out of a brown paper bag with a little grease.

Good luck with it, its nice to see a real Poulan because they were a fine saw.

 

[exenos]

So the carb kit finally arrived. I started to tear into the carb and noticed that the mesh screen was partly clogged up again. Poked around the fuel system and it looks like the old filter in there was shedding stuff into the fuel lines even though it looked clean as could be. flushed the fuel lines and replaced that, finished rebuilding it and it runs good now. Not sure if it was the filter or rebuild that did it but I turned the high out 1.5 turns to be safe and the plug came out black after a few test cuts. Definitely need to lean it out.
Now all I need to do is decide whether I'm going to run a 16" or 20" bar on this. Thanks guys