Rodbolt and Ray- please help my '91 yamaha 150

[Johnshan1]

1991 Yamaha 150 hp Pro V

Brand new NGK plugs were installed during the problems- no change.

Also every single electrical connection has been cleaned and checked- throughout. I have 2 new batterys and all new wiring in the boat.

My engine will not spin higher than 4200 rpms, the entire fuel system has been replaced right down to the tank and lines. I have had people pump the primer bulb with no change- it is hard at all times. If I hit the choke while the boat is at 4200 rpms the boat almost stops dead- I assume I do not have a fuel issue. I have pulled and cleaned the carbs 3 times now, each time they are clean and I note no difference in performance.

I have adjusted the timing, no change except a better idle.

I sometimes get a surging while underway, as if I am losing a cylinder or 2. At the dock, it sometimes will not even idle. When this happens I have my idle screw maxed out and push 600 rpms- I am not running on all cylinders. I appear to drop 2 cylinders here and there. When I regain them the idle jumps to 2200 rpms or so and I re-adjust to 800-1000 rpms with the idle speed screw.

My "manual" analog teleflex (non yamaha) tach comes and goes- pointing to a rectifier issue, but what feeds the rectifier? Would the source for the rectifier also feed the ignition? I have ohm'd out the high and low speed stator and they are within spec- but who knows if they are good while under load.

I have checked the ohm's on the CDI pulser output and get some really really high values, not anywhere near spec.

I am about to buy a used CDI as I feel that is my issue, since the pulser test failed on the cdi end- before I do so, Rodbolt and Ray- what do you think?

There must be a connection to the tach dropping to zero and the lack of cylinders firing? Please help!

Thank you for all the help you provide us.

-John

 

[Johnshan1]

Re: Rodbolt and Ray- please help my '91 yamaha 150

or anyone- please help!

 

[Johnshan1]

Re: Rodbolt and Ray- please help my '91 yamaha 150

Did some looking at the scematic and the only 3 things that would generate my issue is the pulsar coils, the stator, or the cdi. The stator tested out fine so I rule that out. The pulsar coils would be shutting down cylinders on both banks, I only have issues on the one bank. I rule this out for now. That leaves the CDI- I ordered one, I hope it resolves the problem- we shall see.

 

[Ray Neudecker]

Re: Rodbolt and Ray- please help my '91 yamaha 150

Try eliminating the fuel disconnect and the engine mounted filter and bypassing them. It still sounds fuel related.

 

[Johnshan1]

Re: Rodbolt and Ray- please help my '91 yamaha 150

I actually did both of those things- no change. Thank you for your input Ray- I just cant imagine its a fuel issue after all the carb cleanings and other work thats been done to the fuel system? I will cross my fingers it is the CDI, the motor was submerged a year ago but has over 100 hours on it since then.

 

[Johnshan1]

Re: Rodbolt and Ray- please help my '91 yamaha 150

Well Ray, your problably right as always, but I cannot find any issues with the fuel system.

I took the new micro-cdi-computer box and installed it, still the same deal.

I took the fuel pumps off the engine, checked checked the diaphrams and they are fine, everything looks brand new there.

I also took the carbs apart, everything looked spotless but I let them soak overnight and blew compressed air through everything, got them back together and will goto the marina in a bit to install.

I bypassed all filters as well to eliminate them as problems for the moment.

Just dont know where to go from here...... im at a loss

 

[rodbolt]

Re: Rodbolt and Ray- please help my '91 yamaha 150

ok, the money you spent on that CDI would have been better spent on test equipment.
but to test the CDI output you will need a DVM with a DVA adapter, or a CD-77, fairly pricy or the mecury 91-99750A1 or its equivalant is availible from Sierra at most any NAPA store. setthe meter on the 400V scale and test each coil primary lead for proper voltage, also index the flywheel and check for cross fireing,rare on a yamaha. about as rare as CDI failures.
if your model 150 has a crank position sensor monitor it carefully as models with crank position sensors use two pulser coils and the other two ign coils are triggeredby the CDI using input from the Crank position sender.
about the only way to actually test yamaha electronics is to usethe DVA meter and actually test each subsystem,under load, atthe problem RPM.
use a logical approach and dont splatter gun it andI bet it takes less than 2 hours to confirm or elminate the ign system.

 

[Johnshan1]

Re: Rodbolt and Ray- please help my '91 yamaha 150

Thanks so much Rodbolt. I assumed the cdi was the problem when it metered out way off base with the ohm tests, I ran with that and purchased a used one off ebay for real cheap money- it was a gamble for sure and a mistake on my part.

I installed the carbs again, and surprise surprise, it runs very very well now. I still only see 4700 ish RPMS but thats good enough for me.

So I assume that I need a better filter system to make sure this doesnt happen again- even though they looked spotless to begin with?

Maybe this is a fluke but its working at the moment.

 

[rodbolt]

Re: Rodbolt and Ray- please help my '91 yamaha 150

4700 is almost lugging the engine. it may be over propped.
have it run on the test wheel or a dyno to insure the engine is making power.
if its not and you try to run it it will die, take it to the bank.
if its overpropped then you will need to reprop it to turn 5500-5600 with a normal load.

 

[Johnshan1]

Re: Rodbolt and Ray- please help my '91 yamaha 150

Thanks, the engine used to turn 5500 rpms so I know the prop is right. I will try some decarb and run it a bit to see if it improves. I only run it at 4000 rpms max anyways.

 

[rodbolt]

Re: Rodbolt and Ray- please help my '91 yamaha 150

doesnt matter that you only run 4K, if the motor is down almost 1K its telling you its sick. 2 strokes wont complain about being sick long, they tend to die suddenly.
if no hull or prop changes have been made and its 800 RPM down you have a serious,potentially engine killing issue going on.
my advice is to fix it or have it fixed before it gets expensive.

 

[Ray Neudecker]

Re: Rodbolt and Ray- please help my '91 yamaha 150

Have you tried running on a seperate small tank to help isolate whether your problem may be from the boat tank or the engine fuel system?
That model was pre the seperate crank sensor.
Like Rodbolt, I don't belive the results show the problem to be eliminated yet.
Sure is great to have Rodbolts knowledge and willingness to help back on board.

 

[Johnshan1]

Re: Rodbolt and Ray- please help my '91 yamaha 150

Thanks guys, I had it out this morning and had a chance to get into the throttle, its going past 5,000 RPMS now with ease- didnt get a chance to run it this way for long, small craft advisory made that a rough ride- I think all is well at this point. I had a charter captain with me who runs a '93 Yamaha 250 he commented on how nice the boat/motor ran, thats a big change from 2 days ago for sure.