2003 Yamaha 90HP Misses intermittently with Hard Stall

[agm2003]

I recently got a 2003 Yamaha 90HP 2-Stroke Engine; Model TLRB 3 Cylinders 1140cc that had sat for 2-1/2 or 3 years. It cranks easily and runs at idle (with earmuffs) but after warming up will miss with a HARD STALL.

BEFORE attempting to start, we drained the old fuel, oil, carburetor drain plugs, replaced fuel lines and main oil line. Spray cleaned (carburetor cleaner) the carbs and fuel pump. Using a concentrated cleaning mix of Seafoam (1 can in 5 gallons of gas) and 2 cycle oil mix (not knowing status of the oil injection system) in High Test NON-ethanol fuel in a clean gas can and a new gas supply line.

It cranked up fast and easily the first (and subsequent times), but after warming up missed with a HARD STALL every few minutes. After a while we thought it was too much oil and discontinued the gas-oil mix allowing the oil injector system to supply.

We changed spark plugs, but it continued the same even after running for over an hour (multiple stalls and restarts).

• Cylinder Compression 110, 108, 108
• I could see spark on all 3 plugs / cylinders from the console (working by myself); but can't attest to quality/brightess of spark beyond that.
• HOWEVER-when pulling PLUG Wires while motor running--NO Decrease in rpm on cylinder #2

Thinking it might not be getting gas to Cylinder 2 (since plug was sparking) and seeing Seafoam cleaning recommendations I added 1 part Seafoam to 2 parts gas (actually was probably closer to 3 parts fuel, but it already had the Seafoam in it from earlier). I ran that in for 15 minutes, turned off and allowed to Hot Soak~22 hours. NOTE: It now actually will run ~10-15 minutes at idle before it stalls.

After clearing the SF Cleaning (using the regular [ 1 can Seafoam / 5 gallons) concentration] I cranked again.

• It again idles 10 - 15 minutes before stalling.
• When increasing engine speed, the misfires become more apparent and shakes harder even at the times it doesn't stall
• STILL NO decrease RPMs when unplugging Cyl 2 plug

Any help will be appreciated.

Art

 

[99yam40]

I would pull the carbs and clean properly, hard stall sounds like a lean sneeze to me

 

[agm2003]

Thanks for your reply. Should I clean all 3 carbs, or just Cylinder 2 carb since it's the one that doesn't seem to be working??

 

[99yam40]

Myself I would do all of them so you have nothing to worry about

 

[agm2003]

Thanks for the input. I take it that I seem to be on the right track that it's lack of fuel to cylinder 2....

Thanks again

 

[racerone]

No fuel / weak spark / bad reed valve could be the problem.

 

[agm2003]

Racerone, Thanks for the reply.
Which order would you check these?
How do I quantify / test for weak spark ?

 

[racerone]

See if spark will jump a gap of 3/8" or more in air outside of the cylinder.----Reed valves can be inspected when carburetors are off.

 

[agm2003]

Air Gap spark is 1/2" consistently, but seems a little erratic above that.

In taking off carbs--on right (looking at carbs) of the middle carb is is oil injector-Do I detach the 2 screws holding plunger? I don't see any other way to get it off.

 

[agm2003]

Carbs are pulled. Reed valves LOOK ok. Should I press them to see if they move ????
Do I need to pull them out to check if they look ok from outside?

 

[agm2003]

I've cleaned carbs, replaced o-rings/gaskets, etc. The middle carb's o-rings were in pieces--I thought for sure that would be the culprit.

However, although it seems to run a little better (although seems to have slightly different sound)--still seems to have same issue when increasing rpms slightly.

--I did try the propane to find possible vacuum leaks, but can't tell any difference anywhere.

 

[agm2003]

That "different sound" seems to be air leak---possible vacuum leak?? Any suggestions?