carb or coil?

[clawless]

Hi All - Im working with a 1990 175, it wasn't running well at low speed and was very sluggish on take off earlier in the season. I checked the plugs and the top two were a little wet (with fuel) the middle two were dry and looked normal, and the bottom two were very wet (again fuel), it has sat for a little bit so I changed the plugs, cleaned the carbs and rebuilt the fuel pumps, that made some difference, however it was acting up again at low speed today, barely running, and at full throttle it was missing at-least 1 cylinder as it did not hit max RPM. When I checked the plugs, they were the same - top two wet, middle two dry, bottom two very wet. Could it be the top and bottom carbs or the 21 year old coils? thoughts?

--clawless

[99yam40]

Why not test to see if you have a spark problem?

As always my recommendation is to test compression, spark, timing, and fuel pressure/vacuum. If all that is good the you work on the fuel/air mix (carbs)

A Yamaha service manual for your motor and the proper test equipment are worth the money spent

[clawless]

more info

I tested the spark and all is good there, however what i found seems odd, compression was 95 across the board, however I was running it with the carb cover off, you could feel air being sucked in on the middle 2 cylinders, however there was barely any air being sucked in on the top or bottom sets.

with it running, if I pull a plug wire from a middle set, it dies, if I pull a plug wire from the top or bottom, no noticeable change in running.

how can it have 95psi compression yet not suck any air in while running?


--clawless

[jb123]

check fuel pumps
clean/rebuild carbs

[mitch]

check fuel pumps like jb said

[DRV90_175]

Mitch,
I have the same 1990 175ETXD twins and would like to test the fuel pressure on both Yamahas. Could you tell me what the numbers on both the high and low sides? I would also like some advice on what manuals I should have for these engines. Can I buy them online somewhere?

[clawless]

Reed valves?

So its been a while, I have been running it. I have cleaned the carbs and checked the fuel pumps, all seem OK. Could the reed valves be bad? I still have 95PSi compression across the board but poor idle and no intake suction on 4 of the 6 cylinders.