yamaha 70 1995 BETO won't go above 3000 RPM

[sasko1980]

Hi all ,
Yamaha 70 1995 , 2 stroke BETO
Is I was advised - I'm starting a new thread.

as my trim was leaking, i took the boat out and replaced the trim seals.
All went ok, no modifications to the engine were made.
I took the boat after a month in water and i noticed that won't go above 22000-2500 RPM - 2 person on baord. With me only it came to 3000-3200 RPM.

I thought that may be starving for fuel, so i changed the hoses, primer bulb, new tank. With this nothing resolved, stil wont go above 3000 RPM (my onla onboard)

I bought new spark plugs, instaled them, all the same -same problem.

Then i took the carbs off, and toght that maybe was a problem with jets - all was ok, the carb is clean, the jets are clean -the carbs are like new.

What could be the problem ???

It idles fine, it goes to 3000 RPM very nice, just when you press the lever to go above 3k, it sounds buaaaaaa, then you put the lever back it cames back to 3k.

I wil try to test the coils for continuity with a ohmmeter and see that.

Please help

P.S. The primer bulb is ok even on 3000 RPM , the fuels goes fine.

[TownsendsFJR1300]

Did you pull ALL the jets in the carb and literally look thru them? Sounds like its still clogged.

Jets will varnish up without stabilizer and sitting with today's crappy fuel

[sasko1980]

Jeys small, and big all clear as a day.
I was looking to find a clogged jet, but no all are cleat, and all carb holes.
Even the fuel in bowls were clean, no gel or jelly like deposits

Im gonna check the spark cables and coils

It seems, as i read about the carb system that this problem occurs when the
retard-throttle system kicks in.

Any ideas, im new to this

[99yam40]

Looks like a strange language you are writing,
but probably just the auto correct is helping you out

checkto make sure timing is in spec and advancing as it should

[sasko1980]

1995 70 BETO - problem 3k

After cleaning the carbs the problem was gone.

Now it came back again.Wont go over 3k RPM.
I took the coils down and tested them.
These are the tests.
Upper Cyl coil : 60kohms(b/w - to spark connector), b/w-black = continuity
Middle Cyl coil : 49kohms(b/w - to spark connector), b/w-black = continuity
Lower cyl coil : 4.5kohms(b/w - to spark connector), b/w-black = continuity

My opinion is that the lower coil is OK, and the upper and middle are gone.
Is this right??

But why the motor sill works "fine" to from 800 to 3000RPMs?


Could the CDI unit be the guilty one for upper and middle coil going bad??

Any advice??

ThX for all your help in advance

BR sasko

[99yam40]

monitoring the peak voltages into and out of the CDI as service manual says to will tell you if any of that is out of spec when the problem shows up.
Monitoring the high voltage output to plugs would tell if coils were a problem.
Timing light should show if timing is out of spec when problem shows up also

If spark/timing is not the problem then you are left with a fuel issue again

[sasko1980]

I think that will be a hard job to test all those things with boat in the water., because i have to mesure at 1500rpms and 3500 rpms witch i can, t achive only around 3000rpms.
Are there some tests that could be done outside the manual, on minimum like 800rpms or some resistance tests like in my post for the coils????

Again thx for answers, and help


Or i could take the prop down and try to test it that way???

[sasko1980]

When this problem occurs i can see that around 1500rpms starts to sound like a missfire, like a repetitive automatic gunshot. (no that loud)! That is hapening even around that 3000 rpms. Sometimes after few atempts starts to take the rpms to 4000-4200 like no problem, and then when i put the lewer back to stop and try again it starts to missfire sounds again.

The carbs are clean, very clean like new one, from tank to the fuel line to the carbs are ok.

[pstephens46]

Still sounds like a fuel problem

[TownsendsFJR1300]

Did you EVER RUN the OLD fuel thru your cleaned carbs??? If so, you get to do a "do over"...

You may also want to simply drain the carbs (with the drain screw on each bowl) and catch what comes out... Maybe prime the bulb a couple of times to flush.. All fuel filters are clean?

Still sounds like crap in a main jet..

[99yam40]

OP may be talking about a lean sneeze with the gunshot description.

But with the proper test equipment (peak reading voltmeter built for these ignition systems ) you can monitor the voltages while running at different RPMs to see if one is going out of spec.
If it will not get to 3500 do to missing then you should be able to see if voltages are still in spec when the probelm is happening

[TownsendsFJR1300]

If it really needed to be at 3,500 RPM's, you could probably keep the boat strapped to the trailer, and back into the water on the ramp.

Then start the engine, put it in gear and run it up to 3500 using tilt as needed to get some slippage at the prop...

You'd still have a fair amount of load on the engine.

[RayBersch]

If it really needed to be at 3,500 RPM's, you could probably keep the boat strapped to the trailer, and back into the water on the ramp.

Then start the engine, put it in gear and run it up to 3500 using tilt as needed to get some slippage at the prop...

You'd still have a fair amount of load on the engine.

Getting a little hot down there in Florida, is it??

[TownsendsFJR1300]

Getting a little hot down there in Florida, is it??

Not anymore than usual(abut 85F right now).

Its usually hotter up north during summer... Just NO snow!

[sasko1980]

OP may be talking about a lean sneeze with the gunshot description.

But with the proper test equipment (peak reading voltmeter built for these ignition systems ) you can monitor the voltages while running at different RPMs to see if one is going out of spec.
If it will not get to 3500 do to missing then you should be able to see if voltages are still in spec when the probelm is happening

Will the multimeter set on to mesure AC voltage do the job. The read value then had to be multiply by 1.42 to get the peak??

So if the value must be around 145 Vpeak by manual , then is to expect a multimeter reading of 100V

Right or not???
Only the freq of these 145 V is not known!, at least i dont know it