Yamaha F90TLRB (03) Carb synchronization?

[TroubleCode300]

I have ordered the shop manual for this wonderful F90 outboard. My customer is pushing to get this finished ASAP!

I have completed a 100 hour service on this engine.
Found: Carbs #1-#3 were varnished up and overflowing with fuel. I disassembled, soaked, cleaned, adjusted floats on all carbs... reassembled them put new o-rings on everything and torqued to specs.

Although...
The engine continues to fluctuate at idle and sneezes every once in a while. I was wondering if anyone has a sync and link adjustment procedure thread link that I might be able to go through and see if I can work through this...

If any other information is needed about this challenge, please let me know and I will post it also.

Thank You
TroubleCode300
(No running on all cylinders)

 

[Capt Ken]

Re: Yamaha F90TLRB (03) Carb synchronization?

Do you have a Vacu-mate to balance the intake vacuum? There is no sinc and link adjustments like a two stroke.

 

[Don S]

Re: Yamaha F90TLRB (03) Carb synchronization?

You can do it with four very accurate vacuum gauges and some needle valves to kill the rapid fluctuation of the gauges before they beat themselves to death, but it's a pain. Been there, done that.
Then you adjust the rest of the carbs to the base carb to get it just right. And they will idle perfect, as long as the carbs are cleaned perfectly.
Depending on rather your carbs have solid or wire links between carbs, you may have a stepped vacuum adjustment or equal.
Best to get the OEM manual, and the Vacu-Mate Capt Ken mentioned if you want to get the job done quickly and accurately.

You aren't in the adjust by ear motors anymore.

 

[Capt Ken]

Re: Yamaha F90TLRB (03) Carb synchronization?

Did you remove the plugs covering the low speed adjustments?

 

[TroubleCode300]

Re: Yamaha F90TLRB (03) Carb synchronization?

Thanks Capt. Ken & Don,
I have access to the low speed needles.
I do not have a Vacu-Mate at this time.

Update; I removed the carbs once again to check the float height. According to the manual, Yamaha recommends the level to be at .055. The carbs were all at the recommended height.

I also performed a cylinder leak down test on the four cylinders. All results were 20-25%. all within the acceptable range.

I will be checking the TPS tomorrow for the proper voltage and position.

Still trying to see if I can narrow it down to a vacu-mate investment

Any more ideas?

TroubleCode300

 

[Capt Ken]

Re: Yamaha F90TLRB (03) Carb synchronization?

Until you balance the intake vacuum, the engine will not idle or run smoothly.

 

[TroubleCode300]

Re: Yamaha F90TLRB (03) Carb synchronization?

I was afraid you might say that...:facepalm:

 

[bitsy4643]

Just Bought a carbtune pro, 100 dollars. unbeleivable results. Hook up and instruction could not be simpler. 50hp 4 stroke , 2001 Mercury. A 10 year old could synchronize with this tool. Basically, just assures all carbs getting equal amount of air and fuel. Repeat, this is not carb tuning, but synchynization.

 

[GA_Boater]

Just Bought a carbtune pro, 100 dollars. unbeleivable results. Hook up and instruction could not be simpler. 50hp 4 stroke , 2001 Mercury. A 10 year old could synchronize with this tool. Basically, just assures all carbs getting equal amount of air and fuel. Repeat, this is not carb tuning, but synchynization.

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