Pioneer 1074 carburator problems

[rtw_travel]

I am trying to restart a pioneer 1074 chainsaw after many years of not running. It is probably 25 years old and has been empty of oil & gas for the last 6 years.

I found the elec specs on another thread, and it now has a good spark after a cleanup.

Hwoever there is no fuel getting into the engine.

Fuel is getting as far as the carburator. I thought something was plugged so I bought a gasket kit for the Walbro 22A carburator and a can of carb cleaner.

All passageways are now clean. But it still doesn't work. If I blow gently from the fuel pump section down toward the metering section, it seems blocked. If I manually push the needle valve then I do get air flow from the fuel pump section through to the rest of the carb. hmmmm.

Would there something with the metering diaphragm that is wrong to cause this? I have not taken apart a carb on a small engine before. I realize after reading the carb thread that I put the gasket and diagraphm the wrong way around on the fuel pump side (the parts diagram I found on the internet shows it the opposite way)... maybe that'll fix everything, but somehow I don't think so.

I'd appreciate any words of wisdom on how the fuel pump and metering diephragms are supposed to work... because it seems like black magic to me. I think if I understood what was supposed to happen then it would help me troubleshoot it.

Thanks in advance!
David

 

[PES+]

The carb is working properly from what you describe. Check the impulse hole and/or impulse line that feeds back to the metering chamber. Also check for broken or missing reeds......if you have a large enough hole in the reeds or if the reeds are stuck shut you will have no pulse and no fuel pumping

 

[rtw_travel]

Tx Pest. I am lost... can you tell me where I should look for the impulse hole ... or the reeds? (reed = needle valve?)

Here is the mfg dwg of the carb.

http://wem.walbro.com/walbro/productprint.asp?CategoryName=1074&Series=WA&partnum=WA%2D22%2D1&GroupName=Chain%20Saw&FamilyName=EMAB

 

[PES+]

I have a Farmsaw version that I will tear apart sometime this week and post pics.

 

[pioneerman]

If I remember correctly the 1074 does not use reeds. It just has an insulating block between the carb and the body. Make sure that the gaskets are sealing properly around this block. Check your metering lever for the proper height. The tip should be flush with the carb chamber floor. If not adjust by bending the lever slightly in the proper direction. Make sure that your initial idle mixture screw is turned out 1 1/4 turns. High speed mixture can not be adjusted. Did you take out the welch plugs and clean in behind them. If not there could still be dirt blocking some of the small holes. The farmsaw is a mid size saw and does not share much with the small series saws such as the 1074, P20, P26, and P28's.

 

[PES+]

http://www.acresinternet.com/cscc.n...6cb8b65e3260962688256b00001a7609?OpenDocument

 

[PES+]

I could very well have it wrong in memory but I am pretty sure I sleeved a 1074 to get it precisely to 3 cubic inch for a guy.....I could be wrong and often am...perhaps the owner could post a pic with the air cleaner removed to clear my memory

 

[rtw_travel]

Here are two pics:
1) chainsaw (carb removed)
2) carb (from choke end... choke removed)

If you need photos from other angles or pieces removed, let me know.

P.S. What is a welch plug? I did not remove any plugs.

 

[PES+]

I did not have a 1074 it appears the saw I modded may have had just the 1074 side cover. You do have the gasket that goes between the carb and that white plastic block right? look at the plastic block and see the small hole next to the larger one. That is the impulse hole that drives the pump and metering in teh carb. You have to make sure the gasket is good and that it is not installed upside down which will block the hole and no pumping action hence no fuel. If the plastic block that the carb screws to is a reed cage I doubt it would give you trouble as the reeds do not stick to the plastic cages. Look in the hole in the plastic block and if it has reeds you will see them.

 

[rtw_travel]

The existing gasket between carb & block came to pieces when I took the carb off yesterday. It was not in the rebuild kit, so I'll have to go back to the parts store or make my own.

So the impulse line brings pressure back from the engine, and this pressure provides the force to pump the fuel? This is all starting to make sense.

I found the impulse line. I'll remove the block from the saw later tonight and make sure that the impulse hole is clear... and also clean the mating hole in the carb because I know I didn't do it before.

Other things on my list of things to do: check metering lever height; look for welch plug that I might have missed.

Thanks!

P.S. no reeds in sight in the block

 

[PES+]

Wait!

Don't remove the plastic block because then you will have to get another gasketfor the other side of the block. I did indeed have the wrong saw in my head. A new gasket should get you set...

 

[rtw_travel]

too late! but luckily that one came off in one piece

 

[rtw_travel]

A new gasket should get you set...

exactly right... new gasket and it runs like a champ, or at least a champ that smokes 3 packs a day. I'd forgotten how smoky 24:1 engines are.

Thanks very much for your help. I can retire my crosscut again!

 

[TimberPig]

exactly right... new gasket and it runs like a champ, or at least a champ that smokes 3 packs a day. I'd forgotten how smoky 24:1 engines are.

Thanks very much for your help. I can retire my crosscut again!

With modern oils, there's no need to use 24:1.

40:1 to 50;1 will be just fine with any decent modern oil, and will reduce the smoke. You might need a little carb adjustment as well to get it running perfectly.