85 Yammie jerking at high revs

[dadsandlads.co.za]

Hi guys. I am fairly new to the forum. I have a issue on my 85Hp Yamaha 3 cilinder.
Symptoms

She idles fine, but when I accelerate the motor does a jerking motion as the revs pickup and drop, pick up and drop.

What I have checked so far.
1. Drained all my fuel from the build -in tanks. Cleaned the tanks.
2. Let fuel hang for 4 weeks due to dirty fuel.
3. Take new fuel into tanks and problem still persists.
4. Took it to the a reputable boat mechanic and they cleaned the carbs, replaced the inlet manifold gaskets(they were dry and hard and leaking, tested by myself and the mech)
4. Replaced the fuel pump diaphragm.
5. Replaced sparkplugs and set the plug gap to 1mm as per manual.

The mechanic is of the opinion that the CDI is faulty?My question is why would the CDI be faulty at constant high revs but delivers the initial power to get the revs to maximum, should it not fail sooner?

My observation;

1.When I rev the motor and kill it at the key the primer bulb is soft, when she idles the primer bulb stays hard. When pumping the primer bulb she does not stop when it should it is as if one carb is still taking fuel in, now this is where I say the one carb is running empty while the other two stay filled, does it make sense. The carbs have been serviced so why would one become empty and make the engine pulse at high revs.

2. I removed the number 1 spark plug and checked for spark at high revs and the spark stays constant with no visible loss of fire. The spark is the same when the same routine is done on all three plugs.


Please help. I cannot afford to replace a CDI and then the problem still persists after the cdi replacement.

regards

www.dadsandlads.co.za

Lukas

 

[w2much]

Re: 85 Yammie jerking at high revs

Get a NEW fuel line and try it again. Also bypass the water seperater if you have one. CHeck out my old post. Went through all of the same issues as you. Turned out to be a hairline crack in the fuel fitting( fuel line from tank to engine). Good luck. Probably not electrical. If you still have problems get a manual and run the electronics test they are not too difficult. Messed with mine all summer ,buy a new fuel line.

 

[BruceAML]

Re: 85 Yammie jerking at high revs

Have you changed the fuel filter? Get a genuine Yamaha fuel line. They are superior to anything out there.

 

[rodbolt]

Re: 85 Yammie jerking at high revs

use a peak reading meter,check for about 100V on each coil primary. if its there and steady fix the fuel system.
attach a vacum gauge at the fuel pump inlet,system vacum should be 1/2"Hg to 4"HG. less go look for air leaks,more go find the restriction.
the bulb cannot stay hard as its on the suction side.

 

[dadsandlads.co.za]

Re: 85 Yammie jerking at high revs

Thanks for all the help guys.

Rodbolt, I do have a multimeter, will this be sufficient it does have a peak Voltage setting. If this meter is fine, between which points do I measure, the black wire entering the coil from the cdi and the plug wire? Or between Plug tip and common on the engin? This sound like a stupid question but I am new to proving voltage over a coil.:redface:

 

[rodbolt]

Re: 85 Yammie jerking at high revs

no
your proving not only are you clueless you wont read a manual.
however I will still try.
what we are looking for is a Peak reading.
not a volt or RMS reading.
however if you set a dvm on AC then what your looking for is all 3 are about equal.
an analog meter is better for this.
your gonna read between the coil primary and grond.
RMS is NOT peak reading
dont care what ya read on the net
however in this case we have 3 coil primaries to compare. if all are close then ign is most likly ok.
ya have to remember, that even though we may be looking at a DC signal its very rapid and will act almost like an AC signal.
its why we have diagnostic equipment. run it up on the test wheel with a stevens CD-77 atached to all 3 coil primaries and in 3 minutes I can tell ya if the ign system is at fault.
does your guessing tech have a CD-77 and a YB1620?
if not find a real tech
but ya really have to educate yourself on primary and secondary sides of an inductive coil.

 

[drewmitch44]

Re: 85 Yammie jerking at high revs

man this repair is getting cut throat, as far as if you dont know something. Im going to have bad dreams about that and fear posting. Just joking. I would be ignorant as well when it comes to electrical system. At least you got your answer. Rod is the best but its like the soup nazi of sienfield. "No tech for you" if you say the wrong thing. LOL Rod i love ya man. LOL

 

[rodbolt]

Re: 85 Yammie jerking at high revs

sorry if I sounded nasty. was not the intent.
it was a rather maddening day at work, I deal with this on a daily basis.
I love helping the DIY's, however they also need to take some time to study the systems they are working with and try to understand how each engine subsystem interacts with the next.
then life would go a lot smoother.
you would not believe how many coil,CDI and ECU sales I blow off, cause its rarely the failure.
If I sell it, its sold, no returns and the customer usually ends up with a broke motor and spare parts.
some of those parts are a tad pricey.
last ECU I sold for a 200 OX66, the guy tried to return it. its his for almost 1200 dollars.
the problem,once he brought it in, was a loose throttle shutter sync screw.
took about 10 mins to find/correct it.
so take no offense as I try not to be mean, however I am human

 

[dadsandlads.co.za]

Re: 85 Yammie jerking at high revs

Rodbolt, don't worry mate no offence taken. I am just extremely busy at work and only got to read all the great advice and "rodbolt chirps: about now. I am exactly the DYI person that cramps up your live. I would ask question no matter how stupid.

Thanks for all the guys with advice but I can only test and try the enjin later this week. I basically left my house on Friday afternoon and arrived back from work at this moment. So I need some sleep. Thanks again and for the banta about dyis...well bring it on... Atleast it will get my boat sorted.

Enjoy.

Lukas.
www.dadsandlads.co.za

 

[dadsandlads.co.za]

Re: 85 Yammie jerking at high revs

Hi guys,

I finally got to test my cdi and the puls to the coils. Man was I disappointed. I took a scope from work, connected it to the black of coil one and to common. I could see the 100V wave pulse away at idle. As soon as I opened the throttle the pulse died completely. I mean it drops like a stone from the air. Did it to all three coil feeds and the same result. I recon my mechanic might be right. I will take it to another boat mechanic for a second opinion before I spend my cash on the boat.

Thanks to all of you and your advice. I really appreciate the help and I have learned how to test the pulse from my cdi. I am one step closer to understand the working of my boat engin.

I will feedback on the second opinion.

 

[dadsandlads.co.za]

Re: 85 Yammie jerking at high revs

Hi guys, I resolved the issue or should I say I was guided to use a bypass way of getting my Yammie to rev.

Spoke to a JP at King Marine and he suggested to remove the rev limit wire from the CDI. I did and am a releved to say my motor revs like it should. Goes to show one might just get the right advice from people by asking.

Thanks again to Rodbolt for guiding me to use a meter to test the coils and cdi feeds. Thanks I am forever gratefull.