372xp won’t start.

[Craigb]

So, she does indeed run but slowly dies at idle. Bouts of sputtering until it stops. It also stops dead after a boot full of throttle. I’ve had the L at everything from one turn to two turns out and it does last longer at idle in a lean position. The carb pressure test slowly dropped off and I put that down to a dry gasket. The carb was rebuilt as per the instructions from spud, metering lever level gaskets and diaphragms in correct order. We did deduce this carb wasn’t actually THE carb for the saw. Do I need a proper carb or am I missing something else?

[Craigb]

And if that is the case does anyone have a carb they are selling? L and s are out of stock and I know nothing about after market carbs.

[spudulike]

On the L screw...get the saw running with an idle speed that will hold for long enough to adjust the carb but not so the chain spins or the idle seems too fast.

Turn the L screw in and the idle should speed up and then the idle will begin to splutter and die, turn the screw back out, past the point when the revs were at their peak and then turn it out to a point the revs are less even and become very slightly uneven.

Then adjust the idle speed to go with this. Adjust the H screw to around 1 1/4 and try it again.

If the saw continues to cut out and play up....swap the carb out.

I have no experience of aftermarket carbs for this particular saw but ADW may be able to help on the Walbro carb to replace the Zama one.

Usually if you can't dial in a decent stable idle after a minute or two on a newly rebuilt carb, the thing is scrap.

[Craigb]

Tank vents fine. The saw it’s self is solid apart from the previously mentioned issues. Out in the rain for a good half hour adjusting the carb and the same results.

[Craigb]

More fun and games. I got a new carb but it is a spurious one. It holds pressure and nothing seems a miss. Saw fires and almost runs with choke but then runs two fast on the next pull and dies. Opening the throttle makes it instantly die. Different symptoms but ultimately the same outcome, a saw that doesn’t run. Altering the L jet from shut to four turns open and the usual 1 1/2 turns yelds the same result. 

Edited July 31, 2023 by Craigb

[spudulike]

What exactly is "a new carb"

Your symptoms are of the carb not delivering enough fuel so the carb is pulling fuel through on full choke enough to fire and then the revs increase because of lack of fuel and if you open the throttle, lack of fuel, kills the engine.

If the L speed circuit was OK, the machine would idle, especially on a richer setting. If the H speed circuit was OK, the saw would rev flat out but die on idle. 

It sounds like a blockage in the supply of fuel or the carb isn't pumping enough up from the tank.

If the carb is a brand new OEM Walbro then check that fuel line, tank breather and fuel filter again.

If the carb is secondhand, strip it down and check out the gaskets and diaphragms are in the right place and that the metering arm is set OK, the gauze strainer is unblocked etc etc...normal MO!

[Craigb]

New as in brand new, aftermarket but not branded. The fuel line is brand new and so is the filter. I’ll pull the top off it and check the arm is at the correct height.

[spudulike]

Mmmm aftermarket...some are good, my blower is testament to that and some are far less then good.

Up to you if you send it back or see if it has a blockage somewhere. 

[Craigb]

It unfortunately is another 365 c3m. I’ll strip the thing and see if anything is blocked. The proper 372 walbro is out of stock. 

[bmp01]

Impulse line, no pulse arriving at the carb ?

On choke the engine sucks fuel from tank because the jets in the carb are down stream from choke plate, so big vacuum. As soon as you open choke you loose that 'direct' suction and rely on the pump in the carb to deliver fuel from tank to metering side of carb. If you can repeat the - runs on choke, runs for a handful of seconds after choke and then dies out - it suggests the pump in the carb is not working. It may not even be connected with wrong carb ???

It might run on wide open throttle, may be enough vacuum to pull fuel directly from jets ....

 

Apologies if this has been checked already...its a long thread.

Edited August 2, 2023 by bmp01