150 VMAX carb gets on plane and then loses power

[bassinman215]

Motor: 150 VMAX Carb V150TLR manufactured in 2007

Motor starts and idles fine. Boat gets up on plane, will accelerate, and then loses speed. I have changed the fuel water separator and the plugs, an it still has the same symptoms. The fuel lines look fine, but there was some blackness left on the fuel water separator fitting. Also had a ring of what looked like oxidation where the fuel water separator gasket would fit against the bracket.

Tested the fuel pumps according to the Yamaha service manual. They hold pressure and vacuum.

I last ran the motor in the water in mid October. I've started it in the yard about every three weeks. Sta-Bil and Ring Free in the gas. Ran the motor on the water over Memorial Day weekend as well as yesterday. Compression was fine as of Memorial Day.

Fuel bulb, anti siphon valve, fuel lines are all original. Fuel strainer on the motor appears debris free but the cup is stained brown.

Suggestions on where to look next? Time to get into the carbs? All insight is appreciated - haven't had time to fish since last October and really looking forward to getting to learn the Chickahominy.

[headhigh]

I had the same issues on a older Yamaha 150 carb motor. I had to tear the carbs down completely, clean them THOROUGLY and put them back together. Best way to tell if its your carbs, when it starts losing speed hit your choke on the key. If it starts to accelerate and run better it is a fuel issue and 99% likely the carbs. Good luck. They are pretty easy to clean and rebuild.

[bassinman215]

With the Yamaha carbs, does it matter that it uses a true choke rather than a primer to increase the richness of the mixture?

As far as cleaning the carbs, as I read the manual, the pilot jets are adjustable but the high speed jet is fixed, correct? As far as cleaning, what (if any solvent) should I use? Do I need to get the rebuild kit, or is acceptable to disassemble, clean, and then reassemble?

[allen656]

I went through all the same last fall...hose,ball,filter,plugs...ended up being fuel pump.....I had REALLY bad cold start issues for past few seasons...all gone now with the new fuel pumps

[headhigh]

With the Yamaha carbs, does it matter that it uses a true choke rather than a primer to increase the richness of the mixture?

As far as cleaning the carbs, as I read the manual, the pilot jets are adjustable but the high speed jet is fixed, correct? As far as cleaning, what (if any solvent) should I use? Do I need to get the rebuild kit, or is acceptable to disassemble, clean, and then reassemble?

If I recall, pushing in on the key will trigger your "mechanical" choke. Try that. It should help if your carbs are the problem. I'm not sure about the jets. My old Yamaha was quite a bit older and had fixed jets. The only thing adjustable was the idle air screws on top of the carbs. I would go ahead and get the rebuild kit (with floats if they come that way). That will have all of your little o-rings and new bowl gaskets. Just get yourself one of the 1 gallon cans of carburetor cleaner and soak the parts overnight for best results. Disassemble, clean, replace floats, needles and gaskets as required, reassemble and reinstall.

[headhigh]

Looking at boats.net, the carbs are basically identical to the ones on my old ProV150

http://www.boats.net/parts/search/Ya...TOR/parts.html

Item 21 from the link below is the carb repair kit you'll need (IF THE CARBS ARE THE PROBLEM). One for each of your 3 carbs.

http://www.boats.net/parts/search/Ya...201/parts.html

[bassinman215]

I went through all the same last fall...hose,ball,filter,plugs...ended up being fuel pump.....I had REALLY bad cold start issues for past few seasons...all gone now with the new fuel pumps

It acts like my GT150 did when the VRO went. But, I removed the pumps and checked the pressure and vacuum via the manual. Both passed. I was surprised.

[bassinman215]

Looking at boats.net, the carbs are basically identical to the ones on my old ProV150

http://www.boats.net/parts/search/Ya...TOR/parts.html

Item 21 from the link below is the carb repair kit you'll need (IF THE CARBS ARE THE PROBLEM). One for each of your 3 carbs.

http://www.boats.net/parts/search/Ya...201/parts.html

Thanks for the input. I'll get the kits. Anything on them that is hard to set up? I screwed up the floats when I tried a carb job on my old GT-150, but that's because I didn't set them correctly.

I've heard rumors that carb cleaner can hurt the finish on these carbs. Any truth to that? Am I safe to get the big can of Berryman B 12?

[headhigh]

Don't buy the kits until you're sure that's the problem. The running choke trick will tell you for sure. Carb cleaner won't hurt those carburetors. This Gunk carb cleaner kit is what I used.

https://shop.advanceautoparts.com/p/...cc3k/7040709-P

The big can of Berryman should work too.

The floats on your carb are very easy to set. With the bowls off they should hang level. Your service manual should show a picture of that. If you don't have an OEM Yamaha service manual for your motor, I'd get one before you start. I think they can be had for $30 on E-bay or Amazon.

[bassinman215]

Don't buy the kits until you're sure that's the problem. The running choke trick will tell you for sure. Carb cleaner won't hurt those carburetors. This Gunk carb cleaner kit is what I used.

https://shop.advanceautoparts.com/p/...cc3k/7040709-P

The big can of Berryman should work too.

The floats on your carb are very easy to set. With the bowls off they should hang level. Your service manual should show a picture of that. If you don't have an OEM Yamaha service manual for your motor, I'd get one before you start. I think they can be had for $30 on E-bay or Amazon.

Thanks for the info. I did press in the choke the first time I ran it and it changed the way it ran, but I don't know if it made it better. I'm the type of person where if the engine is not running right, I don't continue to run it.

I have the shop manual. The Yamaha one.

If not the carbs, any other things to check or diagnose? Its about 40 minutes for me to drive to the lake, so if something else I'm overlooking is easy to check, I'd like to do it before I get there.

[Charles Prestridge]

I do not see where you have checked fuel pumps.

Unbolt fuel pumps, squeeze fuel ball several times and see if any fuel leaks on back of pumps.

If so, replace pumps. Rebuild kits are about the same price as entire fuel pump.

If not, replace spark plugs, if they are anywhere close to a year old. Spark plugs that look good can still be an issue.

[bassinman215]

I do not see where you have checked fuel pumps.

Unbolt fuel pumps, squeeze fuel ball several times and see if any fuel leaks on back of pumps.

If so, replace pumps. Rebuild kits are about the same price as entire fuel pump.

If not, replace spark plugs, if they are anywhere close to a year old. Spark plugs that look good can still be an issue.

I checked the fuel pumps with a vacuum pump per the service manual. They held pressure and vacuum according to the specs.

Plugs are brand new.

[Greenwing1]

Thanks for the info. I did press in the choke the first time I ran it and it changed the way it ran, but I don't know if it made it better. I'm the type of person where if the engine is not running right, I don't continue to run it.

I have the shop manual. The Yamaha one.

If not the carbs, any other things to check or diagnose? Its about 40 minutes for me to drive to the lake, so if something else I'm overlooking is easy to check, I'd like to do it before I get there.

I had a bad set of reeds in my 225 Vmax, after 3 mechanics, cleaned carbs, replaced fuel pumps, plugs and thermostats the last guy I took it to actually ran it long enough on the water to diagnose the problem. Motor would run great under 4000 rpms after that it would randomly drop 5-800 rpms then never pick back up. Probably not your problem but something to check.

[bassinman215]

I had a bad set of reeds in my 225 Vmax, after 3 mechanics, cleaned carbs, replaced fuel pumps, plugs and thermostats the last guy I took it to actually ran it long enough on the water to diagnose the problem. Motor would run great under 4000 rpms after that it would randomly drop 5-800 rpms then never pick back up. Probably not your problem but something to check.

Thanks for the idea. I'll shine a light through the intake manifold to take a look at the reeds when I pull the carbs.

[secdawgs]

I had the same issues on a older Yamaha 150 carb motor. I had to tear the carbs down completely, clean them THOROUGLY and put them back together. Best way to tell if its your carbs, when it starts losing speed hit your choke on the key. If it starts to accelerate and run better it is a fuel issue and 99% likely the carbs. Good luck. They are pretty easy to clean and rebuild.

THIS, I have an 08 and motor would blast out and then not carry the RPMs I normally do, press choke and bam RPMs shoot up and then falls right back off. I took my carbs off and cleaned with carb cleaner re-install and runs like new money.

[cwilt]

update?

[bassinman215]

No updates yet. Haven't had any time to test it - moving into a new house. Will update as soon as I can. Planning on tearing into the carbs in mid July.

[cwilt]

No updates yet. Haven't had any time to test it - moving into a new house. Will update as soon as I can. Planning on tearing into the carbs in mid July.

good luck, i am getting ready to replace mine with 200 carbs.

[Charles Prestridge]

good luck, i am getting ready to replace mine with 200 carbs.

What gains do you think you will see with the 200 carbs? Are you going to also install composite reeds at the same time?

[cwilt]

pm sent.