I'm stumped.
My boat has twin 1989 Yamaha 200 HP outboards. When running in the Ocean I go through two rips that make the ocean violent and when I go through them one motor bogs down, I loose RPM but never stalls. I slow down from 4000 to 2500 for 15 seconds then get back up to 4000. This may happen two or three times.I believe it's a fuel issue.
Once out of the rips and into the smooth it does not happen.
I've already looked into the filters/fuel tank/anit-S valve and all looked good
Could a carb float or fuel pump do this?
Thanks!
I'm not expert on anything and certainly not a marine mechanic. I'm mechanical in nature, working on cars since the age of 10 but fairly new to the boating world.
That being said, I fought a VERY similar issue to yours, unfortunately, for a couple of years, before it took a turn for the worse and I found a good Yamaha mech that actually knew what he was doing, instead of just sounding like he did.
So, My engine and boat is a 1992 Yam 250 TXRQ on a 21ft Aquasport Walk-Around. I run mine primarily in a bay, but it's quite busy on the weekends, lots of large wake. Mine would run great until the boat started bouncing or having to plow through some larger wakes. the RPM would go up and down with each wave or bounce. Went back and forth to the shop, lost the better part of two seasons with it being at the shop. I kept asking the shop to check the carbs and pumps, and every time, they'd tell me it wasn't the carbs and pumps, that they "looked good".
2 seasons ago, I replaced alot of the original stuff myself including new fuel tank, fuel lines, sender, filters, everything fuel related up to the fuel pumps.
I replaced that stuff because it needed it. The original tank had too many holes to be fixed. It was after this that issues with the boat really started, which really through off the trouble shooting for me. I followed the advice of a lot of other folks from various sources telling me to check this, that and the other.
At the beginning of this season to make a long story short, The boat wouldn't run at all off idle. It would start fine, then as soon as I put it in gear, it would die.
I replaced the plugs, found one bad plug wire and replaced that by replacing the entire coil and went out and ran it. It seemed to run great, but was down about 10mph slower off WOT normal top speed. Wierd, but lots of possibilities as to the cause so I wasn't immediately overly concerned. But then upon returning, I throttled down to idle in the "No Wake" zone, and the engine took an immediate turn, and began running pretty badly. Bad vibration, smoky as hell. Engine had a BAD miss. At least one cylinder wasn't firing. Whole back of the boat was sooted up.
I pulled the plugs, and found that there were two of my 6 cylinders that hadn't fired at all on the entire 45 minute run. The 2 plugs looked brand new.
I took it to a new shop, and within 24 hours sent me pictures of two green carbs. Those carbs had to be in rough shape for the last 2-3 years at least. They looked ridiculously bad.
So, That's MY experience with your symptoms. Take it for what it's worth.
It cost me $2k to get the carbs and pumps rebuilt, all new fuel line on the engine side, new oil injection line, new carb linkage that the previous shop cracked and jimmy-rigged with a cable tie (no joke), etc.
But the boat hasn't given me any issues ever since. It's been used nearly every weekend, hard, for the last 8 or 9 weeks now, and it's been great.
