90 Yamaha 115

[Bozo]

I have a 90 Yamaha 115 that is extremely hard to start and is only hitting good on one cylinder, #3. I know this because once I get it started, I can remove all of the other plug wires and it makes little or know difference on how it is running. If I unplug the #3 wire with all others connected, the motor dies. I have rebuilt the carbs earlier this year, recently replaced the plugs, and have switched the coils around and the problem does not move with a specific coil so, I believe the coils are good.<br /><br />I am thinking it may be the CDI but, I want some others opinion before I take the risk of buying such an expensive part. I did have a bunch of crud in the tank at one time that could have gotten past the fuel filter and clogged the carbs back up but I don't think that is the problem because the plugs are wet with gas/oil mixture on the cylinders that don't seem to be firing properly.

 

[Bozo]

Re: 90 Yamaha 115

any suggestions?

 

[Reel Appeal]

Re: 90 Yamaha 115

Hi Bozo,<br /> Here's an idea.Get a competant helper,then remove one of those plugs that is gas soaked.With the plug out,hold the BOOT part of the spark plug wire(you may want to wear a leather glove too)with the plug and ground it to the motor.Have your helper crank the motor.While cranking,take a look to see if there is any spark on that plug.(shade the spark area to make it easier to see).No spark,white or gold spark are no good obviously.Should be blue in color.If nothing,then definitly ignition.Whether CDI or Stator remains to be seen.It's best to get the motor tested at a Yamaha dealer.They can test both components.<br />NOTEisconnect/disable working plug(s) so motor will not start.Also,keep your other hand Clear of that flywheel!!Good luck and post back...

 

[Trent]

Re: 90 Yamaha 115

First you need to do a compression check! Have you checked the spark on the wires?

 

[Reel Appeal]

Re: 90 Yamaha 115

Ahh yes,Trent brings up a VERY important thing I overlooked Your motor must have adequate compression to fire..Do you have a compression tester or can you borrow one?

 

[Bozo]

Re: 90 Yamaha 115

Yes all four cylinders have good compession.<br /><br />I haven't looked at the plug out of the cylinder but when I was checking to see which one was hitting good and which ones weren't, I could hear the spark arching from the plug wire to the plug tip when removing and replacing each of the wires.<br /><br />I have replaced all of the plugs (twice) just to make sure that I didn't crack one when installing them.

 

[Capt Ken]

Re: 90 Yamaha 115

Trent has a point there, but if he wears a hat, no one will notice. The 115 Yamaha is the only Yamaha that I've ever had problems with the CDI. But then they only lose one cylinder when they go bad. As for fire, get your wife/girlfriend to hold the wire as you spin the engine. If beats you over the head with the boat paddle, the fire is fair. If stands there just shaking, the fire is great.

 

[Bozo]

Re: 90 Yamaha 115

Thanks for the assistance guys....I called the parts house and found out the CDI was $400. I decided that I had make sure that was the problem before I bought that part. I figured it would be pricey but I had no idea that it would be that much....well to make a long story short, I took the carbs back off, tore them down and soaked them overnight and hit every nook and crany with carb cleaner and assy all back...went to the lake this afternoon and it ran perfectly. I had just done that and replaced all of the gaskets and needles early this summer. I didn't see any sign of crud or varnish in the carbs but I must of fixed something.<br /><br />Thanks again for your 2 cents about the CDI usually not going out except for one cylinder...that saved me a big mistake.