Video of Rough Idling Yamaha 40hp 2 Stroke

[Ruggybuggy]

This is a continuation of a previous post. The motor is a '04 Yamaha 40hp 2 stroke which I bought this spring. It has around 30-40 hours on it . This is the idle after I have done the following which didn't really seam to help much. I replace the spark plugs with NGK's, all the carbs were removed and cleaned (very little if anything in them), check the fuel pump to make sure fuel wasn't entering the crank (good), vacuum check the enrichment diaphragm (good), tried to adjust the idle mixture screw the best I could and didn't make a difference (I don't have a manometer) so i returned them back to their original factory position (had the "do not tamper" plugs). I haven't check the ignition timing or did a link and sync.

I was suspecting a rich condition because when it's running above 1500 rpm it starts to smooth out and at WOT it runs well. It will idle like this all day long and after it it tuned off fires up right away. I did notice that if I shut the motor off after it's been running and restart it the rpm's rise to about 1200 rpm's and stay there for about 30 seconds then the idle will immediately drop to 800 rpm's. Is this normal?

So is this idle how most of the Yamaha 40hp 2 strokes run? It's kind of annoying when your trolling and I was hoping I could make it somewhat better.

In the video you can hear the idle rising. That was me tuning up the throttle a tad to around 1200 rpm's to demonstrate how the motor smooths out a little.

Sorry for the long post.

http://s392.photobucket.com/albums/pp10/Ruggybuggy/?action=view&current=SDV_0019.mp4

 

[99yam40]

Re: Video of Rough Idling Yamaha 40hp 2 Stroke

it is would be best to keep all under one thread instead of multiple ones

Do the link and sync. it is necessary every time you pull the carbs and reinstall.
Would not hurt to check compression just to be sure.
Timing is a simple thing to check and mine was retarded twice as far as normal, 14 ATDC instead of the 7 ATDC at idle. I ended up having to replace CDI to fix that on mine. made a big difference with the carb adjustment while idleing
How did you clean?
Hopefully you did completely disassemble and used carb cleaner and compressed air to get the stuff out of the passages. They say it takes 2 or 3 times sometimes to get it done completely.

Does not look like it is jerking around very much in the video and I did not see the pee stream. but the camera angle was not right for that. Mine shoots out far and hard at idle so I thought I would be able to see in you video

 

[Bob Gilvary]

Re: Video of Rough Idling Yamaha 40hp 2 Stroke

Try pulling off one plug wire at a time, replace it then pull off the next one. Note the running after you pull each wire. It could give you an indication of which carb or cylinder is causing this condition.

Did you adjust the carbs on the water, in gear, and at idle?

Revving up like that could be coming from a lean condition.

 

[rodbolt]

Re: Video of Rough Idling Yamaha 40hp 2 Stroke

that revving up is normal.
its part of the start cycle.
timing gets held advanced for a warmup period.
its part of the prime start system which has no choke.
turn the key to start.

 

[Ruggybuggy]

Re: Video of Rough Idling Yamaha 40hp 2 Stroke

Sorry I should have kept it under one post but thought that mentioning in the heading about the video would draw more attention to it. I will do the link and sync and adjust timing. What did you think about the restart and the idle running up then after about 30 seconds dropping to 800 rpm's? Is that how your motor acts? The carbs were completely disassembled and cleaned with carb cleaner and compressed air. There really wasn't much to speak of in terms of contamination. I did try disconnecting one spark plug wire at a time and rpm's dropped on each one I did. I will do a compression check tonight but didn't suspect a problem because of the low hours on the motor.

Strong pee stream from the motor. I put in a new impeller on it in the spring. Someone at work who has a 50hp Yami 2 stroke says his shakes in a similar way but his is an older motor with quite a bit off abuse. Just want to make sure I'm not chasing my tail and trying to repair something that's "normal".

 

[Ruggybuggy]

Re: Video of Rough Idling Yamaha 40hp 2 Stroke

Did a compression check and read 134 psi on all three cylinders with good strong needle sweeps. This was done on a cold motor. I didn't have time to run it on the hose then test.

Rodbolt, from the all the 40hp Yamaha's you've work on do you think that the idle can be improved on this motor or am I chasing me tail?