Yamaha 40tlrc wont idle. Timing troublei think.

TBTech24

Seaman
Joined
May 3, 2011
Messages
56
The motor runs great above 1200 rpm. Anything below she pops like back pressure in the exhaust and then she dies. Kind of a pain to start have to use the warm up lever to start then quickly back off before the rpms jump up. The gas tank had water in the fuel. So it was drained cleaned and filled with fresh gas. The fuel filter pump and lines where purged till fresh fuel came out of the three hoses where the carbs hook up to the fuel lines. The sync part of the overhaul was adjusted to correct specs. Now with the timing. On this model it says its controlled by the cdi module and mechanical linkage. The setting in the book are 6-8 deg atdc for full retard. The full advance was 24-28 deg atdc I believe. Book says to move linkage to full retard and check if in spec. Same with full advanced. My knowledge of checking timing degrees is to run the motor an hit the flywheel to read the number. Motor wont run anywhere close to idle so I cant check full retard. And there is no way to check full advanced on a water hose. Am I an idiot or is there a different way to time this motor. I'm almost betting that its timing. Gaskets look fine. Fuel filter is new. No water fuel separator yet. Spark plugs look black and some times wet. Little bit of oil on the outside of the plugs seat ring. After I tried figuring out the timing and didn't think I got anywhere, I put the boat in the water to see how she ran under load. Same results nothing under 1200rpm. Smooth above. Pulled the plugs out before flushing the motor and they where dry and nice and tan. Looked like they where burning clean. Piston head looked drier and not so black and wet. the cylinder walls nice and shiny lubed and cleaned. Anyone Have Any Suggestions!
 

99yam40

Fleet Admiral
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Sep 7, 2008
Messages
8,851
Re: Yamaha 40tlrc wont idle. Timing troublei think.

sounds like a lean sneeze.
Do a better cleaning job on carbs sounds like pilot jet/passages are still plugged.

I take it this has the prime start system, need to make sure it is all clean and functioning properly also.
Timing can be seen with a timing light on hose if you disconnect the linkage and move wiper to the different positions by hand.
Just make sure to mark where it goes with throttle before disconnecting linkage.

Timing should be advanced some at start and then retard to normal once motor has warmed up
 

TBTech24

Seaman
Joined
May 3, 2011
Messages
56
Re: Yamaha 40tlrc wont idle. Timing troublei think.

sounds like a lean sneeze.
Do a better cleaning job on carbs sounds like pilot jet/passages are still plugged.

I take it this has the prime start system, need to make sure it is all clean and functioning properly also.
Timing can be seen with a timing light on hose if you disconnect the linkage and move wiper to the different positions by hand.
Just make sure to mark where it goes with throttle before disconnecting linkage.

Timing should be advanced some at start and then retard to normal once motor has warmed up


Thanks i drilled and pulled the plugs for the pilot screws and cleaned them. New better digital timing light arrives friday so i can verify correct timing. Do new plugs have to be installed or is the pilot screws ok in the open?
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
Re: Yamaha 40tlrc wont idle. Timing troublei think.

plugs are there to keep people that do not know what they are doing from messing with adjustments(EPA stuff), should be OK without them in place as long as the EPA police do not see it and will make it easier next time
 
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