70 Yamaha with idle issues

[Ken Buke]

Took the boat to NC and (I think) ran it on bad? gas. It has been having idle issues since. Before I ask the shop to look at it...

When idling it will backfire (pop) that will cause it to stall or almost stall. I can increase the idle to keep the engine running. The engine was perfect (2 Years old) prior to the NC trip.

I changed the plugs after the trip and it helped a little (prior to that it wouldn't idle at all...)

I think the carb is fouled.

Any suggestions would be appreciated...

[fatkenny]

sounds like the new gas gummed up your carbs. Not sure about the backfires, but the rough idle sounds right. The other sign is that I lost about 2000 rpm on my WOT, and had a tough time getting up on a plane.

[Kuskus68]

It sounds like you need to clean out the carbs,the same thing happend to my merc,I had to have the carbs rebuilt.

[tommat]

Try This first. It's what I did to my 1992 ,130 Yamaha and it worked like a charm.. Engine has never idled better. It's pretty easy to do as well.

I've got the same motor but newer, 2003, I had a similar problem with the E10 crap this spring and the motor wouildnt idle....After doing all the obvious with filters and stuff it still wouldn't idle.
I drained my bowls, there will be 4 of them, one on each carb. It is a 10 or 12mm screw on the bottom side of each carb. Crack one at a time and drain the bowls. Spray some high pressure carb cleaner in each opening and reseat the nut.
Now find the idle adjustment screw. It is the one with the spring on the needle valve. Seat the screw *clockwise* until it stops. Count the turns in quarters and remember how many turns it takes from it's present location until it stops. Now take it out all the way. Using the red high pressure attachment on the carb cleaner, spray into the opening hood and hard. Insert it all the way in and out and keep spraying. Now reseat the needle valve all the way down and turn back out the appropriate number of turns. Do this on all 4 carbs. I bet you $$ She fires back up and idles.
Before you do all this I would change the racor, inline motor filter and plugs. Plugs even fairly new ones can have some mysterious failures on 2 strokes from my experience. I would definently get to the problem NOW before spring....
Good luck!

[RogerStg]

Poor idle and backfiring sounds more like carbon buildup in the motor. Even without the backfiring symptom, I solve 50% of my idle issues by simply decarbing the motor. For carbureted engines I use Deep Creep. It's the aerosol version of Seafoam.

There's a seafoam routine on the internet that involves using a small gas tank with seafoam. It works well too, with the added benefit that it cleans the carburetor as well.

Decarbing should always be done before adjusting the carburetor. It's best to start with a clean combustion chamber. If that does not solve it, the next step is to do what tommat wrote.

[Ken Buke]

Very cool. Thanks for the info.

I hope to be Cod fishing soon and then down to Daytona for a week... --127-3-