Yamaha C40TLRX main jet sizes

[99yam40]

Well, I just got a new #115 main jet from the Yamaha shop here, that they had to order one for me just to see if I was correct on how to check the orifice size on these Yamaha jets since no one could give me any info on how to check them.

I was correct in thinking that someone had drilled out the main jets or at least the top and bottom ones. The new jet will not allow me to insert the 1.18 mm rod into the orifice on the #115 like I could on the ones in my motor. So apparently some one has tried/done some modifications.

Can someone tell me if I am correct in thinking that this motor has a #118 jet in the middle carb and #115 jets in the top and bottom carb?
The manual lists them as : 115 118(M) for the 40hp.
I take it the (M) stands for middle.
Looking on line for parts, I do not find a listing for a #115 main jet for the C40TLRX.

If I am correct then I will order new ones for all carbs and try them out and see if the WOT cutout will go away.

 

[99yam40]

Re: Yamaha C40TLRX main jet sizes

I finally got the new jets and the 1.18mm rod would not fit into any of the new jets I bought, not even the #118 jet.
So, my thought on measuring the jets does not hold water, someone definitely has been trying to modifying this thing to try to beef up the HP I guess.

I ran the motor yesterday and every thing seems to be normal. No miss at WOT even with the silencer on. Hopefully this will stop the fuel/oil residue from dripping out of the lower unit side water drains while it sits in the driveway after running every so often. Hopefully I will get even better fuel economy and I sure hope I do not find anything else the previous owners did to this thing.

This is just to show you when you buy used you never know what you will run into and never rule anything out when you are trouble shooting. It only took me a little over a year to find the solution.
The thing that gets me is it did not seem that bad until I cleaned the carbs real good and that is when it started with the WOT miss, but I guess I finally got things clean enough for the problem to show up. Who runs WOT enough to see what kind of problem you have at that RPM.

 

[polar05]

Re: Yamaha C40TLRX main jet sizes

Are those the hp ones? Where is middle texas coast at?

 

[99yam40]

Re: Yamaha C40TLRX main jet sizes

Main jets were replaced, people need to realize you can not just put more fuel in to increase the hp. From what I have read the air jets and exhaust are different also.

Clute Tx around Freeport