prov 150 help needed

[Bamamark]

I have a 1990 prov 150LD. Last time out it was running great and then lost power. Did a compression test and all were 105-110. Did a spark test with a spark tester and all were firing. Assumed carbs were stopped up so I tore the top carb down. It looked brand new, obviously it had been cleaned recently.(I've had the boat 6 mos) Bought 2 new yamaha fuel pumps and installed today. Cranked the engine on muffs and put me hand over each carb. Top and middle carb responded but bottom carb did not. Fuel was leaking out of it a little though. The engine smoked alot and I've ran it on muffs before and it didn't do this. I'm thinking now that the smoke is from raw fuel running through the bottom cylinders and that they must have week spark or no spark while running. I don't really know which direction to go with this now because I don't know alot about outboard ignition systems. Any input or thoughts would be appreciated.

[jb123]

fuel leak then why do you want to blame ignition ?

[99yam40]

you can test voltages to see that they are withing specs with the proper equipment and a service manual, but to little fuel or too much will not let a cylinder fire properly even if you have good spark

[Bamamark]

Just looking for answers jb, that's why I posted here. There wasn't alot of fuel leaking, just a few drips out of the carb. That combined with the smoke led me to believe that it was possibly a spark issue. Anyway, I tore the carb apart and it looks clean. I sprayed it out with carb cleaner and blew air through all the passages and everything is clean. BTW, I have cleaned outboard carbs on numerous occasions and they have all worked fine so far. Now I have ordered new orings for the carb because the old ones broke when I took it apart.
As far as testing the ignition parts, I would like to do that but I don't have a manual so I don't know what to test or what the specs should be. Anywhere I could get that info other than purchasing a manual? Thanks again.

[jb123]

i have an 89 pro and i have had to clean the carbs up to 3x to get them right.....
the only electrical issue i ever had was the coil leads bleeding out, i just shrink wrapped each one

if you feather the choke and it helps.... youll know real quick

[Bamamark]

Ok, while I am waiting on my carb parts, the thing that I can't quit thinking about is why this carb wasn't sucking air. The other 2 were sucking air just fine but this one not at all. No air blowing out either which I took as a good sign. Even compression on all cylinders too. What could be the causes of this carb not sucking air???

[99yam40]

You never said anything about not having suction on bottom carb all you said was "Cranked the engine on muffs and put me hand over each carb. Top and middle carb responded but bottom carb did not."
Even that does not say anything about what happened when you did it.
Are you sure the throttle butterfly was open

No suction could be a hole in crankcase or a major air leak. The cylinders/ crankcase have to be getting air from somewhere to form the compression

A manual and test equipment would be cheap compared to paying to have the motor worked on by a trained tech, but at least he would know what to look for

[Bamamark]

Yeah, sorry, I could have been more clear there. The bottom carb was not sucking at all but the cylinders did have good compression. Are you saying I am looking at catastrophic failure here? I agree a manual and test equipment would be the way to go but if I'm looking at something major here then I don't want to waste my money. I'f it is possible that it could be something minor then sure, I will order a manual. I consider major to be tearing into the crankcase...

[99yam40]

I have never seen a motor that had no suction on a carb throat but showed good compression on all cylinders, so you may need to wait for someone to give some advice or take it to a good Yamaha shop to see what they say is the problem.
The only thing i was thinking was if it cannot suck any air into the crankcase then it would not have anything to compress.

[Bamamark]

Ok, I get what you are saying now and I agree. Like I said, I did a compression test first thing but I will do another and see if I can feel it sucking air.