This maybe useful?
litl
litl
Mcculloch ProMac 3600 Brush Cutter Problem
- Thread starter Dave54
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- brush cutter engine problems
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Thanks for that. Always useful to have something to refer to.
It was looking a bit on the white side the other day, but today it was looking a lot darker. Typical 2 stroke colour.
It's a weird fault. Last time I had anything similar was nearly 40 years ago with a Mini estate. The short pieces of pipe on the fuel pump on the rear subframe had perished and were blocking the fuel flow. That one really had me going!
It's a weird fault. Last time I had anything similar was nearly 40 years ago with a Mini estate. The short pieces of pipe on the fuel pump on the rear subframe had perished and were blocking the fuel flow. That one really had me going!
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Always best to have a spare plug standing by - and in the Mini situation, giving the SU fuel pump a clout would often get it clicking again 
Do check the fuel pipe from the tank for splits.....Stihl pipes are almost indestructible, other makes can have problems with the pipes hardening.
John
Do check the fuel pipe from the tank for splits.....Stihl pipes are almost indestructible, other makes can have problems with the pipes hardening.
John
I've had a quick look at the pipes, but I'm going to have a proper look at everything I reckon. It's certainly nothing obvious.
That Mini. I'd rebuilt the pump thinking that was the problem! Wasn't it those that you had to turn the threaded diaphragm "stalk" a certain number of turns to set it right?
Anyway, the pump was running lovely, but there was about a 2mm hole through the perished rubber tubing!
That Mini. I'd rebuilt the pump thinking that was the problem! Wasn't it those that you had to turn the threaded diaphragm "stalk" a certain number of turns to set it right?
Anyway, the pump was running lovely, but there was about a 2mm hole through the perished rubber tubing!
Have you had the muffler off to check for carbon build up and scoring of piston?
litl
litl
Not yet, that'll be the next move, after the carb / fuel thing is exhausted (no pun intended)
It runs lovely for some minutes until it stops doing so!It's not that Dave, but thanks for the input.
It was more or less the first thing I tried as it was the classic symptoms, and I tried it again yesterday with the cap loose on the bench. Still the same!Why did I say that? Long ago I was taught industrial electrical fault finding. The first thing we learned was to look for the obvious things first. . .
Jumping to the brush cutter, it seems that they generally run much better with fresh fuel in them.
The fuel I was using was old. I'd made some up fairly recently, but that was in the other can!The stuff I was using was probably two years old. . .
It's running fine now with fresh fuel in it. Warmed up properly and adjusted the L / H and tickover.
I feel a right twit!
Thanks for all the help!
C'mon Dave, at least blame the garage for flogging you dud gas......
Seriously if the engine ran for 20 mins or whatever I reckon the fuel is ok. I've had machines stored with juice in them for nigh on two years and they have still started and run well.
No worries, happy strimming!
John
Seriously if the engine ran for 20 mins or whatever I reckon the fuel is ok. I've had machines stored with juice in them for nigh on two years and they have still started and run well.
No worries, happy strimming!
John
It's weird I agree John. Nothing obvious wrong with the fuel. No water etc. Wonder if I loosened a bit of carp yesterday.
As you say, I've had no problem with oldish fuel stored in the machine (s) in the past. Although this had been stored in a plastic can, with a bigger surface area. Could have lost "something" I suppose.
Anyway, it seems OK now, it was dying when revved after a few minutes ticking over on the bench yesterday, today I ran it until it was nice and warm, including some revving sessions, and it was fine.
The real proof will come when I use it properly, but it's too wet today!
As you say, I've had no problem with oldish fuel stored in the machine (s) in the past. Although this had been stored in a plastic can, with a bigger surface area. Could have lost "something" I suppose.
Anyway, it seems OK now, it was dying when revved after a few minutes ticking over on the bench yesterday, today I ran it until it was nice and warm, including some revving sessions, and it was fine.
The real proof will come when I use it properly, but it's too wet today!
I would have thought that starting the thing up would be a problem if the fuel was duff....and reckon there was a carb problem all along.
The carb drillings on these are so fine there's no way you can see any grot.
John
The carb drillings on these are so fine there's no way you can see any grot.
John
I've been using it for nearly an hour this afternoon Slight carb readjustment once it had settled, but nothing really.
It's been fine.
I suppose I've been messing about with engines on and off for nearly 50 years now, and that's only the third or fourth time I can remember something similar, that is an engine that seems to start and run OK but stops after a while.
Had a couple of blocked fuel cap vents, that Mini thing with the fuel pipe, and a duff coil (on a Mini again IIRC) that was failing when warm.
I wonder if this time it's our "old" friend ethanol. Here's my theory. Ethanol had evaporated, leaving 10% less fuel thus making the oil mix more than it should be. Hence causing the engine to run weak until it overheated and stopped due to fuel vaporisation.
I thought (with hindsight) that it was smokier than usual.
John might remember the dire warnings in "Motorcycle Mechanics" back in the day, about using richer oil mixtures than recommended in pre-mix 2 strokes due to the engine running weak.
If it was that, then it confirms my feelings about pretty well all the "green" solutions on offer. I'd rather use vehicles etc. 10% less than have something added to the fuel that causes all sorts of problems.
It's been fine.
I suppose I've been messing about with engines on and off for nearly 50 years now, and that's only the third or fourth time I can remember something similar, that is an engine that seems to start and run OK but stops after a while.
Had a couple of blocked fuel cap vents, that Mini thing with the fuel pipe, and a duff coil (on a Mini again IIRC) that was failing when warm.
I wonder if this time it's our "old" friend ethanol. Here's my theory. Ethanol had evaporated, leaving 10% less fuel thus making the oil mix more than it should be. Hence causing the engine to run weak until it overheated and stopped due to fuel vaporisation.
I thought (with hindsight) that it was smokier than usual.
John might remember the dire warnings in "Motorcycle Mechanics" back in the day, about using richer oil mixtures than recommended in pre-mix 2 strokes due to the engine running weak.
If it was that, then it confirms my feelings about pretty well all the "green" solutions on offer. I'd rather use vehicles etc. 10% less than have something added to the fuel that causes all sorts of problems.
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