150 ETXD rough over 700RPM

[LastCast]

1990 150ETXD
Ran Great Last Year
Replaced all fuel Lines, Replaced priming electric Fuel Pump, water separator
Starts OK but shutters over 700 RPM sounds like a few cylinders are dropping.
Replaced plugs, same problem. Plugs seems wet with fuel. Fuel bowl full and clean.

Hints, expert advice, all appreciated

[zenoahphobic]

1990 150ETXD
Ran Great Last Year
Replaced all fuel Lines, Replaced priming electric Fuel Pump, water separator
Starts OK but shutters over 700 RPM sounds like a few cylinders are dropping.
Replaced plugs, same problem. Plugs seems wet with fuel. Fuel bowl full and clean.

Hints, expert advice, all appreciated

"shutters over 700RPM" does that mean it does run over 700RPM (idle) but has some shudder?
Without knowing more sounds like floats in carbies, I'd hazard a guess they(one or more) are overfilling as pump pressure increases because the float valve stuck or floats not "floating".
Because it readily starts I would rule out ignition at this stage.
It could also mean your engine is jamming through lack of lubrication (or corrosion).
Only you know the extent of the shudder, but one would be tempted to rev the engine to cleanout the "cobwebs?"; that is run it for a while at some throttle so that all is lubricated and up to temperature.(I presume you have checked oil etc etc.)

[LastCast]

Thanks,
It runs over 700 RPM but bogs down and runs real rough. I revved the engine with no load and it got worse.
I'll check the carb floats. I am having a tech come over and do a tune up.
Please explain jamming.. Oil pump works and it seems to be getting fuel and oil on the plugs.
I am curious in what a reed valve failure looks like? I suspected this and a friend said probably not since they don't break much and when they do gas spews out of the exhaust. Which is not happening.

[zenoahphobic]

What I meant by jamming is does the motor turn freely, not partially seized.
Doesn't sound like it is.
Reed valve failure rare but they can loose their efficiency. This would cause your symptoms, but you would get spitting out of the respective carby.
Someone one might recommend ringfree if your compression measurements are low.
Lets see what the mechanic finds.

[LastCast]

Tech checked it out and found fouled carbs. One boat buck later ($1000) seems to do good but WOT is only 4900 RPM. Folks are saying it should be 5500.
What do you think?
Thanks

[zenoahphobic]

Great to hear going OK ($1000 not so great).

Your max revs seem a bit low. What did you get last year before the problem?

This would normally be tackled by putting on a lower pitch propeller.

Roughly what is the size of the boat and the size of the prop?

[99yam40]

If it had more RPM before this then there is a good chance you still are not getting all cylinders hitting properly.
If that guy charged you $1K what all did he do?
Seems for that money he would have made sure all was well with all cylinders
Compression, spark, timing, and carberation

[TownsendsFJR1300]

i was going to say varnished up carbs.

$1,000 for a mulit-carb cleaning (I gather no re-build kits) is pretty steep.

YOU may want to drain the float bowls again (and catch what comes out) looking for any crap. You could have some crap come loose and still floating around clogging a main jet..

How old is the fuel your using???


BTW, now that is running, Yamaha's "RINGFREE" is highly recommended to help keep your carbs clean. Not cheap but ALOT cheaper than $1,000. A fuel stabilizer is also a necessity as well. I pay the extra $ for NON-Ethonol fuel as well. IMO, its worth it in the long run.

The Ringfree, run on the heavy side, will help clear out any still clogged orifices that may not be fully cleaned.. I run it in EVERY GAS ENGINE(SUV included) I own...

[LastCast]

Thanks for the input everyone.
Says he rebuilt the carbs and charged me for a kit (185$)
Can Ringfree and Stabil live together..might have to leave room for fuel..Yes I use 92 unleaded Premium fuel is new..one month. Fuel lines are brand new.
I have a GW Gulfstream with M17 props 1990 and twin Yami 150ETXD rebuilt in 2012 a tuna, salmon, and occasionally Lingcod out of Newport ,Or. fishin machine.
Something I discovered is that I had a priming pump failure and replaced with a supposedly marine pump, but I am thinking go with a bulb as it sometimes "surges" at 4600 RPM. This is after the carb rebuild. Will do that this weekend.

I may look around for a pair of lower pitched props but sounds expensive.

Thanks again.

[zenoahphobic]

Only go the route of buying lower pitch props if you are absolutely certain that engine (s) are running correctly and that you only ever achieved those revs in the past (never exceeded 4900?)

Thanks for the input everyone.
Says he rebuilt the carbs and charged me for a kit (185$)
Can Ringfree and Stabil live together..might have to leave room for fuel..Yes I use 92 unleaded Premium fuel is new..one month. Fuel lines are brand new.
I have a GW Gulfstream with M17 props 1990 and twin Yami 150ETXD rebuilt in 2012 a tuna, salmon, and occasiond 4900lly Lingcod out of Newport ,Or. fishin machine.
Something I discovered is that I had a priming pump failure and replaced with a supposedly marine pump, but I am thinking go with a bulb as it sometimes "surges" at 4600 RPM. This is after the carb rebuild. Will do that this weekend.

I may look around for a pair of lower pitched props but sounds expensive.

Thanks again.

[TownsendsFJR1300]

RingFree and Stabil will work fine together. I'd run the Ringfree on the heavy side initially...(won't hurt anything-2 x').

Ethanol free fuel is MUCH better than 10% ethonol crap.

You also want to make sure there are absolutely NO air leaks in the fuel line, primer bulb, under cowl filter, etc.

Re the bulb, any doubts get a genuine Yamaha bulb. Yes its a little more expensive but you can literally feel the difference between it and a cheaper one..

And as posted above, if you got 5,500 RPMs, WOT, prior to issues, leave the prop alone.

I would still drain the carbs, ONE screw for each side of the bowl, just to make sure there's no crap in there..

[rodbolt17]

leave the 92 octane out.
its designed to run on regular 87 octane.
92 octane can produce more carbon and lower top engine RPM. that and it costs more to do less.