I have a kit but cleaned carb and all looked good.
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McCulloch Chain Saws
- Thread starter Bruce Hopf
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Put the kit in.
So worked on the 790 tonight. I can't get it to even pop off. I've got bright beautiful spark. I could only get about 115 lbs on my compression gauge, but think it's a notoriously low gauge. My buddy's 562 only pulled 118 lbs on this gauge and that saw ran great.
Cylinder and piston look fantastic through exhaust. However when I got this saw it was completely pickled in oil....like the cylinder was completely filled with oil. I drained that off but I'm wondering if it made rings sticky and it's just not pulling enough compression to fire. Maybe residual oil making it too rich to fire over. I know that compression seems a bit low but figured it would at least fire off for a second.
Cylinder and piston look fantastic through exhaust. However when I got this saw it was completely pickled in oil....like the cylinder was completely filled with oil. I drained that off but I'm wondering if it made rings sticky and it's just not pulling enough compression to fire. Maybe residual oil making it too rich to fire over. I know that compression seems a bit low but figured it would at least fire off for a second.
Try flushing it with fuel and letting it dry, also acetone and atf 50,50 makes a good unsticker for things
Points
I already cleaned and adjusted points. Spark is strong.
Give it a healthy prime with mixed fuel right down the throat of the carburetor then crank it over WOT.
Mark
Mark
Already primed it several times directly down throat of carb. I even squirted some directly in plug hole while I had it out checking for spark. Nothing, not even a slight pop.
Only thing I can think is compression is too low to fire, however seems as though it should at least try to fire on anything over 100psi?
On vintage sleds I've very rarely seen great spark tested outta the hole, but then spark seems to be killed when fired under compression. Any chance of that? I've got unfired mix running out of the muffler. I've wiped it up with a rag and noticed it doesn't have a strong gas smell. Smells more like oil. Is there still just too much oil in crankcase that's atomizing under compression with fuel and just unable to fire?
Only thing I can think is compression is too low to fire, however seems as though it should at least try to fire on anything over 100psi?
On vintage sleds I've very rarely seen great spark tested outta the hole, but then spark seems to be killed when fired under compression. Any chance of that? I've got unfired mix running out of the muffler. I've wiped it up with a rag and noticed it doesn't have a strong gas smell. Smells more like oil. Is there still just too much oil in crankcase that's atomizing under compression with fuel and just unable to fire?
Tried this morning but now won't bust off. Getting fire and fuel compression is like 135 now but just won run. Getting discouraged. Any ideas will be appreciated.
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I had the same problem with a 790. Mine had great spark but no pop, with a swift down the carb or in the cylinder. It seemed like may be compression was blowing the spark out? after fighting it a couple of days, I changed the condensor and bingo, I got it running easily. This didn't make sense to me but worked. 135 should get you a pop as a 795 with DSP valve open doesn't develop any more compression than that. Check your flywheel timing again, though I doubt that's it.
Try another plug. Those rare things still happen now and then.
Ron
Ron
That actually brings up a good point. According to what I found online the 790 needs a Champion DJ8. Saw currently has a Champion J8. What is the difference between the 2?
The D indicates it's a "Bantam" height plug. Same reach and heat range but shorter than the J8.
Is the tank vent in the cap? And is this possibly the reason it keeps flooding [emoji35]Ok I pulled the carb put my extra kit in and the tank had pressure in it . All this while I was rebuilding the carb???????
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Each atmosphere of compression you add makes it more difficult for the spark to make it across the electrodes. The denser the air, the more resistance there is. I've had one plug fail under compression.
I have come across several bad plug wires on 10 series MAC's. Insulation cuts and degradation. You might try pulling it over in a dark room to see if the spark is jumping to ground somewhere along the plug wire.
Where it exits the starter cover is a good possibility.
Electricity always takes the path of least resistance.
I have come across several bad plug wires on 10 series MAC's. Insulation cuts and degradation. You might try pulling it over in a dark room to see if the spark is jumping to ground somewhere along the plug wire.
Where it exits the starter cover is a good possibility.
Electricity always takes the path of least resistance.
The vent in the cap only lets air in when it's under vacuum so it does build pressure when when it gets warm. Sometimes enough to spray fuel all over when opened.
Was the metering diaphragm hooked into the metering needle and is the metering lever set level with the metering chamber floor?
Are both the pump and check valve diaphragms installed on the pump side? I'm assuming it has an SDC 44 carb.
Yes on the carb. Getting fire. Just won't bust off. Could my coil be weak and if so how to check that.
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