1993 Yamaha 85 HP C85TLRR rough idling before quiting
On muffs, the engine will start but will idle very rough for a few minutes then die. Can re-start and keep running rough with throttle input. The remaining throttle positions will increase rpm but its not normal (very rough.
Actions taken:
Rebuild carbs but was not done by experienced mechanic.
Spark test – good spark on all three
Ran new gas/oil from surrogate tank
Compression readings #1 100 psi #2 90psi #3 95 psi
Replaced spark plugs with correct gap
After all of this, problem was the same.
Items that were not done yet:
Fuel pump replacement
Tear down the carbs again and give a good soak, spray, poke, making sure floats & seats are adjusted.
De-carb piston rings.
I am travleling down this week to see if I can help these folks and I’m requesting some of the pro’s to give me some thoughts on where to start. I am thinking either carbs again or puel pump.
Advice from experts??
Re: 1993 Yamaha 85 HP C85TLRR rough idling before quiting
No feedback yet.....any pros out there that can give me a place to start. Going down to Melbourne tomorrow to try and figure this out. I'm convinced it is a fuel problem but wanted some feedback. If i can provide any additional information, please ask. Thank you
Re: 1993 Yamaha 85 HP C85TLRR rough idling before quiting
Troubleshooting update
Here is what was done so far:
1. Very maticulous carb re-build.
2. Replaced fuel tubing from tank to carbs.
3. Checked fuel pressure from fuel pump....good.
4. Checked all linkage.
5. Compression test 100, 92, 95.
6. Bypassed fuel in tank using fresh gas & oil.
7. Swapped coils.
8. Spark test...all three good.
All of this had no change in rough idling and/or operation.
One wierd factor that may point directly to the problem is the fact that...while running (large throttle input needed to keep running), pull the bottom plug wire off (motor dies). pull the middle plug off (motor rpm drops but does not die), pull the top plug off (no...or very little effect at all).
Question - if i have good carbs, good compression, good fuel pressure and good spark.....is this a timing component failure...and if so, which part??
Re: 1993 Yamaha 85 HP C85TLRR rough idling before quiting
Timing is easy to check on all 3 with a timing light, but it still sounds like a fuel problem if it is not affecting all 3 cylinders the same.
Spray some fuel mix into the different carbs while running and see if it causes the dead cylinders to fire.
If no difference then start testing the electronic components like the manual says
Re: 1993 Yamaha 85 HP C85TLRR rough idling before quiting
are there any signs of rodent activity?
you could have some blocked, cracked, or stuck reeds.
if you have a good blue spark that jumps the correct gap (sorry not sure how big a gap for a yamaha) then your problem is in the fuel delivery..... since your comp is good.
as said above spray some pre-mix into each carb... or at least the top 2 since the bottom cyl is obviously dragging the other 2. if you have noticeable difference and you are certain your carbs are clean i would look for an air leak around the intake...... your carbs get fuel from suction if you have an air leak the eng wont be able to suck fuel through the jets.
to test for an air leak i usually spray carb cleaner around the carb to intake and intake to block gaskets.... if its leaking air you will know it.
did you do the carb cleaning like in the faq section on this site?
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1993 Yamaha 85 HP C85TLRR rough idling before quiting
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