View Full Version : 92 ProV 175 dead cylinder tried everything Help

07-31-2009, 12:31 PM
"We have a 92 Yamaha ProV 175 on a 21' Grady. Ran fine for years. Suddenly it lacked the power to get up on plane. So the investigation started:

Compression is good on all cylinders, 115-125.

We pulled each plug wire off under load and found that the bottom left cylinder is not contributing. All others had a noticeable slowdown and speed up as we pulled the wires off and put them back on.

We checked that the plug was firing, it was, but we tried replacing it any how. No-change.
Swapped coils, no change. Same cylinder bad.
Note, that one plug from the bad cylinder was shinny and spotless clean like new, while the other 5 were a little dark and a little oily. (they are relatively new as well since we replace them two weeks ago and only ran a little bit.)

Removed that carburator and took out all jets and pretty much any brass parts and although they looked spotless clean, blew them out with carb cleaner. All ports seemed to blow through. Ran it again and no change, cylinder still not contributing.
Checked that that float bowl on that carb was full of gas, it was. Cleaned carb again, out of desperation, no change.
Clear bowl on engine always had plenty of fuel in it and other 5 cylinders run fine.

I have pretty much used up my limited knowledge of boat engines so if anyone has any suggestions, please, please help!


08-01-2009, 10:54 AM
"I had the same problem with my VMax 150. Replaced all plugs and bottom left coil (this coil was not firing) Had spark at the plug, went to the water and same problem again. Found a loose ground wire (not on the coil) that supports this coil, fixed the problem after that. Been about a year with no problems.
Hard to find but seemed to be the problem. This is what it would due before fixed. Boat would run fine until we hit waves or drove down rough road in route to lake, then it would start again, loose one cylinder.
Check this item just to make sure.
Good luck"

08-01-2009, 11:44 AM
"Thanks, I'll take a look. At this point when I am starting to suspect a crankcase pressure/vacuum issue I would welcome a possibility like this.


08-02-2009, 07:03 PM
"I know you said that you cleaned the carbs twice, but it still sounds like a carb or fuel restriction issue. Also, is the pilot screw setting correct?

I had a similar issue with my 150 VMAX. My problem turned out to be a piece of gasket material restricting the flow of fuel into the carb. I could still pump fuel into the bowl by manually pumping the ball, it just wouldn't pull by itself. Good Luck."

08-03-2009, 08:51 AM
"I'll take another look and also check the pilot screw setting. I don't think anyone touched it but maybe it moved by itself. Also, there is fuel in the bowl when I check it so I know I am getting fuel at least that far. There is also no effect of spraying carb cleaner or ether in that carburator when the engine is running so I am not sure what that indicates??
The boat had been running earlier this season and while running this sudden loss of power problem cropped up.


08-03-2009, 12:55 PM
"well you know you have spark and your timing hasn't changed, and you have good compression, so it has to be restricted fuel to that specific cylinder,so maybe a plugged carb jet that you may have missed when you were cleaning them? maybe the blow out with the air hose not getting it...maybe a piece of fine wire, then the hose. keep us posted with what you find and good luck!"

08-04-2009, 11:18 AM
"While under load, and air baffle removed, look into carb throats and make sure all butterflys are open fully. Look for equal gas spray from all main jets. Put palm of hand over bad cylinder and check if it is spitting back (bad reed?)

Once, I put my hand over a carb, and the additional vacuum must have sucked out whatever was clogging something up. Ran fine for years after that."

08-08-2009, 08:40 AM
"Well, a couple of you guys were right. 3rd time was a charm with cleaning the carb. There is a bolt in the float bowl that looks like it is just to drain the bowl but it also has a hole in it and allows the fuel into a central boss in the bowl that the main jet sits in. A piece of guitar string wire cleaned it out and all is well! Thank you all for the tips.