NEED HELP PLEASE! Diagnosing Issue with 1994 Yamaha ProV 150

[texahomankid]

Okay so I have a 1994 ProV 150 on an old sprint boat, the motor cranks every time I take it out and runs for a few seconds, but then at idle it slowly droppers from 700 to 600 to 500 to coughing and dying. Every time I start it I choke it and it fires immediately but it won't idle, last weekend when I was trying to adjust the idle it would sit at 600 and idle for hours but if i tried to turn the idle up it would either die as soon as I started adjusting or it would rev up and idle around 1k to 1200, no in-between. I have cleaned the carbs thoroughly and am running real gas in it. Also when I start it out on the water and put it in gear sometimes when I roll in to the throttle it revs up for a second and then just bogs out and dies. It also doesn't seem to want to run any faster than 40 mph which is about 3300 rpms just just seem to drop off and plateau right there. Its only a 17.5ft boat and I feel this size motor should push me at least 50-60mph. Any help would be much obliged. Thank you.

[Bamaman]

When my Yamaha 115 2 stroke ran a little rough, I'd first change spark plugs. Then I'd make sure the needle valves would be doing their job--visibly looking for the old drip, drip, drip. I'd also make sure the fuel line, bulb and the filter on the power head are without stoppages. Then, I'd inspect the siphon hose in the fuel tank--in case it has a filter on the end (again looking for obstructions.) I would also make sure the fuel cap is letting air into the gas tank.

Have you changed the membrane in the fuel pump lately? It's rubber, and we know how 90/10 affects anything rubber in a fuel system.

Since you've cleaned the carbs., at that point I'd be stumped.

[texahomankid]

Im pretty mechanically inclined but when you say "needle valves" what are you referring too?
Also if it is a "membrane" on the fuel pump should I just replace the entire fuel pump or just the gasket on it?
My uncle whom I inherited it from did run the ethanol gas in it and the carbs were all gummed up but the lines seem to be alright because gas flows through them. and I ran some sea foam through it hoping that would clear them up more, I'm really suspicious that it is the fuel pumps because when I put it in the water and let it run I can see fuel sitting on top of the water around the motor. Thanks for the hasty reply.

[hawgherder]

Rather than choke it try pumping the bulb. If it picks up rpms it`s the pump or lines from the tank.

[headhigh]

I had to pull my carbs off three times before I got them to run right....so they may need to come off again. Break them down to parade rest and let them soak overnight in carb cleaner. Make sure your floats are set correctly also! BTW, are you running a 10 micron fuel/water separator filter on that?

[Charlie206]

Sounds like the air/fuel ratio is way off. The engine should turn about 5800 rpm's at WOT, you're not getting anywhere near that. Did you remove and completely dismantle the carbs? Did you install new base gaskets under the carbs. Did you set the air screws per the manual?

[texahomankid]

Air fuel is set to what the manual says or at least what I believe I screwed them all in until it began to stick (felt like if I screwed it in any tighter it may damage them however they will screw in more) then unscrewed the starboard 3/4 and the port 1 1/4 like the manual says. Ill take it out and pump the bulb and see if that works, it acts completely different in the drive way compared to when its in the water. No I am not running a water/fuel separator I read on a thread where they are not necessary unless you are running it every day. Yes I did remove the carbs and dismantle them and cleaned them out completely to what I would clean one of my bikes carbs too (race and work on dirt bikes both 2 and 4 stroke these motors really aren't that much different than bikes other than having multiple carbs and cylinders). On the middle carb I had to make a gasket out of rubber gasket making material because it was deteriorated completely. This was to be only a temporary fix but I figured it would work for the time being. All other gaskets on the carbs were like new only the middle carb gasket was bad.
I feel like I'm on the verge of getting it right its just not running 100%, I mean when its running past an idle it seems to run strong just won't hit the high rpms..

[Charlie206]

It's hard to diagnose an engine over a computer, but the failure to idle correctly coupled with an inability to set the idle generally means there is too much air in the ratio. You would see the same thing with a vacuum leak on a 4 stroke, you will never get it to idle correctly. I've also run into that problem when the flywheel was removed and not tightened enough when put back on the engine and the key got sheared, throwing the engine out of time.

[texahomankid]

Do you by chance know the proper air/fuel settings? also how would I check the fly wheel? just take the cover off the top and see if its tightened down or not?

[Charlie206]

If no one pulled the flywheel since it ran good the last time, that is most likely not the problem. If someone did pull it recently - you have to remove the flywheel to check the key. You listed the proper air/fuel idle settings above. I suspect that gasket you made is not working correctly....Not running past 3300 and not able to control the idle means you are Not close to having it running correctly. Did you soak the carbs overnight and blow out with compressed air?

[texahomankid]

Okay guys so I replaced the fuel pumps and am currently redoing the carbs, on the air/fuel screw how tight are you supposed to tighten it down as a starting point? Now that I have the carbs off I realized I can tighten them all down 1/4 turn tighter but any further than that I feel like I could damage the needle??? Maybe not, I just don't want to mess something up while I'm trying to fix it. Thanks all.

[cbailey]

Does it sound like its missing when it does idle? What do the reeds look like? Since u have the carbs off, go ahead and pull the reed blocks off and take a good look at the reeds. Make sure there isnt any broken. Make sure you cant see light between seats and reeds. After you eliminate that, i would replace fuel lines just because and the bulb. I sure its time. I cant remember if its got a filter inline or not, if it does change it. If the keyway has broke under the flywheel, which is unlikely but possible, it will be running extremely rough, i know because i forgot to tighten mine after rebuild and as soon as i chopped the throttle, it sheared the key way. Put a timing light on it and see where it is set at idle and WOT. Just listening to you, it sounds like a fuel problem to me but i would eliminate everything that didnt cost money first or at least the cheap items. Take this time to replace all the little things so you can enjoy years of service from the yammi. Make sure your choke isnt hung shut. Check for fire on all cylinders, if its missing. Make sure your plugs are in good shape. Make sure all linkage is connected and not binding. Ohm the plug wires. Check the fuel pumps that u installed, make sure all lines are connected and secured. Check the compression on cylinders. Make sure to let us know what u find.

[texahomankid]

When I had them off I did inspect the reeds, no kidding for a 20 yr old motor they look brand new, like I said before I have a lot of experience with 2 strokes with racing motocross and all and I've seen some reeds that you wouldn't imagine would even allow a motor to run but these look darn near perfect. I changed all the gaskets on it and reassembled the carbs. No it does not miss when I have it in the drive way idling, sounds like a perfectly running motor, no funny noises, no issues. I did change the fuel filter thats mounted on the motor but it looks like theres a second inline filter just past that one that I have not changed. Will probably do that tomorrow. Im taking it out to the lake tomorrow to test all I've done and see if it has helped, I checked all the plugs last weekend, they are all new and gapped properly. Compression is something I have not check but when it runs it doesn't sound like theres a dropped cylinder and no odd vibrations, We have a Willys jeep that had dropped a cylinder and you could tell something was wrong with it even when it ran, vibrated and sounded sick. Not saying that a 55 willys has anything to do with a 2 stroke outboard.. but other than not idling and not wanting to run in the high rpms it acts like a motor should run. I do believe I did not have the air/fuel mixture screws right because before when id take it out it would put out a thick blue cloud after starting and running for 10secs before dying, and when I say thick I mean like a diesel rolling coal thick.

[cbailey]

Just out curosity, are you mixing your fuel/oil or does it have an injection pump on it? Is there any chance that you pouted way to much oil in gas if you are mixing? If its got an injection pump, make sure the linkage arm is hooked up. If it has come off, pump is spring loaded to go to WOT meaning all the pump has to offer. I would for sure check the air mixture screws in carbs, seeing how you may have had them set wrong. If all is fine , i imagine you have a low cylinder or two. Mine was acting similar after i broke a ring on a cylinder port. I hope you find something simple. Keep us posted.

[texahomankid]

Took it out today, new fuel pumps, rebuilt carbs and fuel air screw set. Ran awesome for the first 30 seconds, then it plateaued at 40-43mph and about 3700 rpms (if I remember correctly) it starts now with out choking it too. After this run, I stopped to fish. When I got back to the helm, it started with no choke, but now wouldn't run like it did before, now leveling off at about 3300rpm. After plaining like this the motor just lost power and slowly died out. It now idles for about 15secs at 1300rpm and then coughs every few seconds and slowly loses rpms before dying. When I finally got it to plain again running about 3200rpms I choked it and after I let off the choke for a split second the motor revs up and sounds good before setting back to how it acts. To me it sounds like its bogging but it wouldn't explain how choking it would make it run better.. Any thoughts?

[texahomankid]

Also it has the injection pump, I don't mix the gas. When it plateaus like it does, can put it on the floor and there isn't a change in it at all.

[texahomankid]

Checked the fly wheel also, I saw someone said to check that, it looks new and is secure, no teeth missing on it or the starter. Im really stumped right now as to what it is, will buy a compression gauge tomorrow and check the compression.

[Brianmoore25]

If choke helps it run better then your not getting enough fuel or its getting to much air.

[texahomankid]

Only momentarily tapping the choke helps, if I hold it down it just bogs and dies. Something else for all that are following this post is that when I went to the pump today to fill it up, it was not venting properly I could only pump about 2seconds before I needed to stop so the air could escape so its not venting properly. Could this have anything to do with it?

[BuzzB8]

Bamaman suggested checking the fuel line in the fuel tank. Did you check there? It sounds like you aren't getting enough fuel.