96 Yamaha 200 couple of issues

[Curious]

I was finally able to get my boat (78 22 FF) in the water yesterday for a shakedown cruise.  Ran great other than the following:

At 2,700/2,800 rpms the boat was running at 21 to 22 mph.  Ran great at that speed with no issues and idled great.  WOT was only 4,600 rpms at around 35 mph.  The prop that's on it is junk anyways but I'm pretty sure I need to re-prop based on those numbers.  I'll post the results in the prop forum when I do.  

After about 3,000 rpms the motor started to run funny.  It would be running evenly and then start to surge (the best way to describe it) kind of like it was only running on 5 cylinders and the other one would kick in and out every few seconds.  Or it might be a fuel issue.  Any thoughts?  I just changed all the plugs and I'm running it temporarily on a 12 gallon portable tank through a racor filter.  It's a 1996 Yamaha 200 Saltwater Series (carb).
Thanks, Dan

[fitz73222]

Sounds like a coil; try to establish which cylinder is acting up by pulling each plug wire; (leave the sparkplug in).  One at a time and isolating the plug wire away from its spark plug and try to get the wire grounded with a another donor sparkplug or some means of grounding that wire against the block. Run the engine and repeat this with all 6 cylinders until the miss goes away (water test). When the miss goes away you found the cylinder. Next, you can swap coils with a known good cylinder and see if the miss follows the coil. The other option is to take it to a shop; say fix it and write a check.

[Curious]

Thanks fitz.  I knew the coil pack was one option.  I'm going to try to get the mechanic out on the boat to listen to what it's doing.  He's wicked smaht and he'll probably be able to diagnose it pretty quick so I can then decide to troubleshoot it as you stated or have him do the work.  I know a little about the motor, but just enough to get myself into trouble so if I can get a second opinion I can do some of the work myself if its as simple as replacing a coil.

On that note, a big thank you to Roger (and Patti and Tracy) at Glyn's Marine (www.glynsmarine.com).  These guys really helped me out and got me to this point.  Great, professionally run boatyard.

[seabob4]

Thanks fitz.  I knew the coil pack was one option.  I'm going to try to get the mechanic out on the boat to listen to what it's doing.  He's wicked smaht and he'll probably be able to diagnose it pretty quick so I can then decide to troubleshoot it as you stated or have him do the work.  I know a little about the motor, but just enough to get myself into trouble so if I can get a second opinion I can do some of the work myself if its as simple as replacing a coil.

On that note, a big thank you to Roger (and Patti and Tracy) at Glyn's Marine (http://www.glynsmarine.com).  These guys really helped me out and got me to this point.  Great, professionally run boatyard.

That's a nice change of pace these days!!!

[Curious]

So I finally got the boat back on the water today.  Engine ran great, no problems.  No surging as reported earlier.  WOT on the maiden voyage a couple of weeks ago was 4600, today I buried the throttle and got 5000.  Again, the prop is junk, but useable.  I don't have any speed numbers to offer as today was a family day so I really didn't spend a ton of time playing around but it ran great!  Thanks for all the advice but for now it seems good.  I plan on running it as often as I can and seeing how things go.
Thanks again, Dan

[Curious]

I considered not posting this due to the embarassment factor but then I realized it might save someone the same headache.  I started to encounter the same problem again so, after a thorough check and inspection of all engine systems, I finally diagnosed the problem, (I think).  Are you ready?  Loose plug wire.....  I did a compression test the other day and when I was taking a couple of the wires off they felt like they came off too easy.  When I put everything back together I made sure to "click" them all on.  Ran it the next day and it ran flawlessly at all RPM ranges and I couldn't get it to do the same surging thing that it was doing before.  So just something to consider-  start with the small, obvious stuff!!!!  Thanks again for the replies.

[Curious]

By the way, the compression was all 125 except for two cylinders which were around 119 and 120.  That's pretty normal for a 96 motor right?

[flounderpounder225]

By the way, the compression was all 125 except for two cylinders which were around 119 and 120.  That's pretty normal for a 96 motor right?

Great numbers, that 96 V-76 is one great motor... did you have the throttle plates all the way open during the compression test?

[RickK]

I know my '91 250 v76 is still running great.  Had a few hiccups with trim and tilt but engine is solid (knocking on wood).

[Curious]

By the way, the compression was all 125 except for two cylinders which were around 119 and 120.  That's pretty normal for a 96 motor right?

Great numbers, that 96 V-76 is one great motor... did you have the throttle plates all the way open during the compression test?

Shoot, didn't think of that.  Do you mean just open the throttle all the way?

[fitz73222]

By the way, the compression was all 125 except for two cylinders which were around 119 and 120.  That's pretty normal for a 96 motor right?

Great numbers, that 96 V-76 is one great motor... did you have the throttle plates all the way open during the compression test?

Shoot, didn't think of that.  Do you mean just open the throttle all the way?

Compression is really a test of how well the engine exchanges air and how well the rings are doing their job of sealing against the cylinder walls.(Air volume = horsepower). Holding the throttle butterflies wide open allows the engine to gulp the maximum amount of air, compress it and expel it. The additional way to accurately measure compression is to turn the engine over through 4 compression strokes only (gauge needle pulses). A healthy engine will obtain a maximum compression reading in 4 compression strokes. If you just crank the engine until the needle stops moving it will eventually show a higher compression number even if the cylinder is sick. The goal is to understand the efficiency of the cylinder. Your cylinder compression you've shown is very good and well within the 10% variance allowed between cylinders. If you really want to understand the health of your powerhead, try what Mark and I have suggested.