1993 70 tlrr

[grouper sandwich]

I have a 1993 Yamaha 70 TLRR that is a giving my father and I fits. He recently rebuilt the carbs and we've replaced the entire fuel system from the gas tank to the fuel pump. After a long run across the flats last Friday we were stopped for a license and bag check by the FWC. After a friendly chat we went to get going and it was difficult to start and would only run on 2 cylinders. We determined the bottom cylinder was not firing. We changed the plugs and took it out today and ran if off of an auxiliary tank to try and eliminate a fuel restriction and the same issue existed. Back to the ramp we went. When we got home we pulled the plugs and did a compression check. Top = 115, Middle = 118, Bottom = 107. After inspecting the plugs it appears as if the bottom plug is not firing at all as it was clean and bright as brand new while the other two showed obvious signs combustion. We also did a crude test on the coils and all 3 appear to be functioning. Also tested the fuel pump for leaks. Any ideas?

[jb123]

do you use a water separator?
sounds like you may need to redo/clean carb
also if you still have the quick disconnect @ the motor, personally, id remove it

[grouper sandwich]

Yes, a Yamaha mini-10. It has about an hour on it, same as the freshly rebuilt carbs.

[99yam40]

Unless you do some testing that will give measurable results and let us know what they were, you and all of us are just guessing at your problems.
Test spark with spark tester and measure peak voltage to coil to see if it is getting spark.
If it is then go through carbs again

[grouper sandwich]

Unless you do some testing that will give measurable results and let us know what they were, you and all of us are just guessing at your problems.
Test spark with spark tester and measure peak voltage to coil to see if it is getting spark.
If it is then go through carbs again

Thanks, will do!

[grouper sandwich]

Spark tested out fine. Didn't test the peak voltage, but my father did notice gas running out of the exhaust when the motor was tilted down. We removed the bottom carb and discovered that the needle valve assembly was not tightened properly which I suppose was allowing gas to flow freely into the bowl and flooding it out. Anyway, we tightened that up, reassembled everything and fired it up and she purred like a kitten on the hose. I guess it's time to haul it to the coast and test it under a load again. Thanks for the help. This our first time exploring the carbs on our own so I guess a something as silly as not properly tightening that valve should not be totally unexpected.