Blower non start

[openspaceman]

I've had a message from an old friend who I haven't seen since he moved further south some 30 years ago that his McCulloch GBV 345 blower stopped and will not restart:

 

"My leaf blower stopped and refused to start, so did all the usual's, still no go, long story short. Good blue spark on new plug, flywheel off, check knib key all o.k. mainshaft oil seal is just a sealed ball race, compression 140 psi, whole engine in good condition and low hours. changed carb for known good one, still nada. The engine wont even fire with a squirt of petrol in the intake or the plug hole. "

 

He's well up on engines, great and small, and has done all the checks I would have done except check the piston rings through the exhaust so I cannot think what else to do and it's a bit far to go and look.

 

Any ideas?

[AHPP]

I’d have said fuel until you said it didn’t work with fuel down the bore. Air filter?

[Paddy1000111]

If it has compression then it has air, if you put fuel in the intake and it still won't fire then it's definitely spark. I would be looking at a dodgy coil that won't fire under compression, sounds dumb but possible. New coil and HT lead would be my go to with that. I think spud had a saw that wouldn't fire under compression but fired fine with the plug out.

[Stubby]

Also 140psi is not huge

[openspaceman]

17 minutes ago, Paddy1000111 said:

If it has compression then it has air, if you put fuel in the intake and it still won't fire then it's definitely spark. I would be looking at a dodgy coil that won't fire under compression, sounds dumb but possible. New coil and HT lead would be my go to with that. I think spud had a saw that wouldn't fire under compression but fired fine with the plug out.

Yes I've had this in the past. Also most electronic ignition systems need to turn over at 400rpm before they will produce a spark and this may be easy if the plug is out but if the motor is nipped up not possible with the plug in. I have a neon telltale which fits between the plug cap and plug which I use to see if any current is running in the HT circuit.

[openspaceman]

10 minutes ago, Stubby said:

Also 140psi is not huge

No it's not. Since I stopped work I have no access to meters for compression or air leaks so no longer any feel for this.

[Khriss]

Peel off the McCulloch sticker put a Stihl sticker  on and fresh mix and yr off . K

[GLynch]

Definitely try a new plug I do a lot of small mower repairs and servicing and I did one the other day, great spark on the plug when it was out of the engine but put it back in and engine wouldn't start.

New plug fitted and ran perfect 

[openspaceman]

1 hour ago, GLynch said:

Definitely try a new plug I do a lot of small mower repairs and servicing and I did one the other day, great spark on the plug when it was out of the engine but put it back in and engine wouldn't start.

New plug fitted and ran perfect 

I've had a message exchange with the owner and on re testing the compression once the oil was blown off the bore it was dropping to less than 100psi so he took the cylinder off and the piston showed definite signs of blackening by blow by so he has concluded it was too worn to be worth bothering with.

 

If it were a decent saw with a nikasil bore I would have popped a new ring in but a cheap blower...

Edited May 31, 2021 by openspaceman
grammar

[spudulike]

Have you checked the ring is loose in the groove? I had one once where the ring was a bit stuck. I just freed it up carefully and it was enough to make it run again.