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3rd cylinder not firing 1985 70hp

T

turfdogg

New member
Hey everybody hope you all can help. I have a 1985 70 hp J70elcos that sat for two or three years. It is pretty clean. My problem is the third cylinder will not run. Compression is good I do not have a gauge but the intakes have good vacuum while engine is running. I have rebuilt the cab and paid special attention to the main jet and all the others but it was pretty clean. The float is properly adjusted also. I replaced a couple fuel lines. I am using a clean portable tank with a new line assembly. The plug is wet so it is getting fuel. The spark is very good and jumps a 7/16" plug tester gap I saw mentioned in the forum. Replaced plugs and wires. When the engine is running and I remove the plug wire on the cylinder there is no loss of rpms when I take the others off it dies. Please let me know what you think and thanks in advance to all the pros who share their experience and the amateurs like me who keep the pros in business.
 
Maybe there is a hole in the fuel pump diaphragm and it is flooding the bottom cylinder.-------Repair kits are available and easy to install.
 
Thanks Racerone I figured out it is not the cylinder. I switcheb the top and bottom carbs and it does the same thing on the top cylinder now. I have been thru this carb twice with a rebuild kit, the jets are open the float is properly adjusted the carb is just not that complex. Does anyone know of any secrets about rebuilding these carbs?
 
Simplest carburetors in the world !--------Remove the high speed jet in the bottom of the bowl and clean it.-------There are no secrets to them , none at all.
 
I agree, cleaned it twice can see right thru it must be some other port or passageway are there any others that might keep it from getting fuel? Thanks
 
There must be some blockage somewhere !---------- Blockage before the float valve ????----------------And you need to be very careful running this motor with suspect carburetion.-------------No fuel means ---NO OIL either.-------With the plug out of the bowl , will fuel pour out when you squeeze the bulb ??
 
It might not be a blockage but an air leakage.
1 Does it run on idle?
If running on idle but not when giving throttle, most likely the small center gasket has been 'compressed' and not sealing.
Use carb cleaner in a spray can and blow all channels.
 
Hey guys thanks for the replies. Plenty of flow at the bowl plug. Motor runs at idle but rough, checked the center gasket looks good. Went thru everything for the third time. Pulled the top metal plug out checked the ports they were clear replaced with new plug. I did try one thing I misted some 2 cycle fuel in the carb while the motor was running and it did not seem to fire. Double checked the spark and it was strong on the tester. This is crazy, it's spotless and still wont provide fuel to the cylinder. I'm in the small engine business I think I know what I'm doin maybe not! Looking on Craigslist and ebay for used carb. Any last suggestions I am open.
 
Did you use a screw driver to remove the jet in the bottom of the float bowl.----------It is not 100% clear that you did that.
 
Have you checked that the cylinder is firing at the correct time?
It might be a case where 2 cylinders are firing at the SAME time, but in fact the no 3 is 'dead'.
Mark the flywheel 1-2-3 when at TDC, then use a timing light to identify that you only get a reading when respective cyl is at TDC!
A spark tester with 3 connections might give a similar indication, it should spark 1-2-3 and not 2 cyls at the same time.
 
Ok, been away enjoying my motor running like a scared cheeta. I rebuilt the priming solenoid and made sure the red lever was in the proper position (which may have been the problem all along, I hate to admit) and all is well with my Johnson so to speak. Thanks to those who replied and good luck to everyone else. This is a great forum.
 
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