1988 Yamaha 175 - Bogging down after running

Rich · #1 07-01-2008, 03:15 PM

I bought a 20' MA from Honeyhole off this site last year. It has a 1988 Yamaha 175 that has been acting funny. It needed a new steering arm and while I was having that done I had the carbs rebuilt. When I picked it up it ran great until I put it in the water. There was a lot of water in the tank and I had to flush out the fuel water separator a bunch of times. During last season it would always bog down while opening the throttle and could never reach higher RPM's. Originally I thought it was water in the fuel. Over the winter I had the tank drained and a new water separator installed. While staring it up first time this year it ran great, that’s until I put it in the water. The problem still exists. Usually the symptoms are such that when I first drop it in the water and am running out it usually gets up to 4800 - 5000 rpm’s if I’m lucky. After running for awhile it struggles to get past 3900 rpm. While running like this and with the throttle open all of a sudden it may jump up to 4700 again for a brief time. It kind of feels like not all cylinders are firing and if I hit a wave correctly all of a sudden it boosts back up for a brief time.

I have a buddy who has worked on many different OB engines; he has a little marine shop. He has had it and tested everything he knows to test. Decent compression, spark is good, he had it on the muffs for 15 minutes today and it was purring like a kitten, all cylinders firing etc. The last time I was out with it a new problem occurred. While at idol it would suddenly cough and die. Most of the time it would start up again but a couple of times i had to use starting fluid. It still has the issue of reaching higher RPM’s. The oil line was disconnected before I bought the boat and I premix the oil into the tank when I fill up.

Is it possible that there is some sort of electrical issue going on that causes some of the cylinders to stop firing? The cowling has a couple of cracks in the back that could allow a little water in. I have noticed the clips that hold the spark plug wires on the bottom two cylinders are a bit corroded, probably from saltwater getting in through these holes. Could this be a contributing factor? I’m at a loss mainly because my knowledge engine as a whole is not that good.

Any suggestions would be appreciated.

Thanks,

Rich

76Red18 · #2 07-01-2008, 03:26 PM

Sounds like there could be gunk in your tank getting sucked up into your fuel pick up tube and restricting flow. Gotta love that ethenol!

76Red18 · #3 07-01-2008, 03:37 PM

You could check it out by using a portable tank.

76Red18 · #4 07-01-2008, 04:41 PM

Another thought for testing would be to put a vacuum gauge between the fuel/water seperator and motor. I think I'm gonna do that with mine just to keep an eye on filter flow effiency. There should be very little vacuum. Anyone know the correct number?

Fr. Frank · #5 07-01-2008, 07:00 PM

I strongly second the idea of using a portable tank with new, clean fuel. That can isolate the problem to the engine or the boat.

skipjake04 · #6 07-04-2008, 06:13 PM

Does the bulb stay hard and how old is your fuel line?

another thought, I have only owned one Yamaha and is was only for a short time. Mine was shutting down almost to 1500-2000 rpms, no buzzer and it was a water issue. It was getting hot and the pistons were swelling.????? was told it was a safety issue to keep the motor from locking up.
Replaced all water components and ran fine. Atleast until I sucked up an ice bag and finished it off about two months later.

Ed · #7 07-06-2008, 10:44 AM

Does a 1988 175 Yammie have a VST tank? If so, you may want to check the filter on it. Dirty VST filters cause the engines to bog down in the mid rpm range.