Yamaha 50hp 4stroke circa 1999

[morimaro]

Is there a modification that Yamaha recommend on the fuel pump for my engine that cures overheating which causes fuel vaporisation in the fuel pump. I have been told this mod (new pump assembly with an added water cooling line, taken off the engine water cooling system) should cure problem and applies to al Yamaha power heads.

 

[seamule1]

Re: Yamaha 50hp 4stroke circa 1999

Unless your engine has a serious overheating problem, and I mean boiling hot, I doubt that the recommended running temperature of your engine has enough heat to "vaporize" the fuel in the pump prior to it reaching the carbs. This is almost what a fuel injected engine does on purpose to increase hp and fuel efficency.

 

[rodbolt]

Re: Yamaha 50hp 4stroke circa 1999

you were told wrong.
certain fuel injected motors did have a fuel percolation issue that lead to an over rich fuel mix in the intake causeing a hard hot restart.
your 99 carb version is not one of them.

what is your motor doing or failing to do ?

 

[morimaro]

Re: Yamaha 50hp 4stroke circa 1999

Thanks for replies, the story so far.
When I leave my mooring I have a 15-20 min run at idle or low speed (900-1200rpm) to harbour entrance, at which point I usually find the engine misfiring or even dropping out. If I then apply more revs it usually coughs kicks in and seems OK at the higher speed (2000-3000 rpm) From then on it is generally OK but sometimes missfires at higher revs too.
First time out this season it dropped out at low speed in the harbour, then about half an hour or so later after some high speed running (3000 rpm), we were then at WOT for 5-10mins and the engine started missfiring and stopped.
We could not then restart the engine and got a tow back towards harbour. After a 30 min tow we tried the engine again and it started but was still not running without the occasional misfire.
This has been an ongoing problem from last season (misfiring) and my mechanic now reckons it is overheating and there is the mod mentioned by him that should fix it!
Hence the question and the replies I got, that overheating is highly unlikely and there is no mod as such for this engine.
I have tried going out again this weekend but the misfiring started just outside the harbour again so we returned and I informed the mechanic and he is now not pursuing the overheating prognosis but more a fuel mixture or timing problem from the ECU!
Cheers
Morris

 

[rodbolt]

Re: Yamaha 50hp 4stroke circa 1999

first we want a leakdown test run, not a compression test, next test spark with a 7/16ths gap tester, if both pass then you have two paths to persue, either its a high speed ign circuit failure or carbs are dirty.
use test wheel YB1611(F50) or YB1620(T50) and then you can fully load the engine while tied to the dock and check WOT timing as well as primary coil input and secondary ign coil output.
if all ign system tests check out as per the tuneup spec guide you now will know its a carb issue.
are you using a factory trained technician? if so look for the 4 stroke and fuel systems certs on the dealership wall.
the electrical cert would be a bonus.

 

[morimaro]

Re: Yamaha 50hp 4stroke circa 1999

Rodbolt,tks for msgs, as my original mechanic was on vacation another guy looked at the OB and found gunge in the No.4 carb due to water in gas. Cleaned out all carbs and jets, setup again and got rid of contaminated gas. To prevent any future problems I fitted a large Quicksilver fuel/water filter in gas line. All going great now.
Tks again for help
Morris