372xp won’t start.

[Craigb]

Touch wood, the saw runs. A different carb that was billed as a copy of a walbro hd12 b arrived today. It was unfortunately another c3m. But the saw runs and idles. They are a pig to tune and this one was loading the saw up with too much fuel on 1 1/2 turns L. One turn got it running and sounding good. I will be seeking a proper walbro when I can get my mits on one.

[spudulike]

That's good, pretty much what I found when tuning many of these carb copies.

The standard H&L screw settings are 1 turn on each. I suggested 1.5 as it will definitely work and be safe to the machine but as you have found, it is a bit rich on a carb that works OK. 

[Craigb]

Thank you very much to everyone that has contributed to this thread.

[Craigb]

Proper walbro carb on. The only problem now is a poor idle. Cuts fine but bogs a bit in the cut. Also the saw is very easy to pull over. I’ve capped off the decomp. Pressure and vac is good. Is the bogging in the cut and a poor idle symptoms of bad compression?

[adw]

Certainly low compression will affect the idle greatly, if you think it has low compression then it most probably has., compression test should tell us, or just pull the cylinder off and see what sort of ring end gap we have,

[Craigb]

20 thou. I reckon the cylinder I tried to get the  scoring out of is knackered.

[adw]

The cylinder will not wear as such, if you have shaded areas around the inlet or exhaust port then the nikasil lining has worn through, it sounds more like the piston ring has dust worn.

[spudulike]

A bit high at 20 thou but not massively bad. If you have been rubbing small areas of the bore with wet and dry, you can cause small cavities that can kill the compression. You should be 150-170 PSI on a decent 372XP. 

You can drop the base gasket and seal with liquid gasket. It is a simple performance enhancement and you will maintain enough squish clearance.

It won't sort the issue but it may make the saw usable.

 

[Craigb]

Put it back together and now it won’t pressurize. Lathered it leak detector but no bubbles. Sounds like it’s coming from the impulse line area but could be under the carb tray on the case gasket. Back to bits.

[Craigb]

41 minutes ago, spudulike said:

A bit high at 20 thou but not massively bad. If you have been rubbing small areas of the bore with wet and dry, you can cause small cavities that can kill the compression. You should be 150-170 PSI on a decent 372XP. 

You can drop the base gasket and seal with liquid gasket. It is a simple performance enhancement and you will maintain enough squish clearance.

It won't sort the issue but it may make the saw usable.

 

 
I might drop the cylinder later but I want to sort the problem out first.