'99 C40TLRX, 2-strk - Fresh Powerhead - Missing throughout RPM range after < 10 Hours

[a387673]

After the installation of a new powerhead by an allegedly reputable Yamaha mechanic, the performance of my C40TLRX has deteriorated steadily to the point that it is now rough throughout the power band, after less than ten hours running on the re-build. I am afraid I know the answer to this question but will ask it anyway. If the engine was link/synch'ed with the Prime Start in the "Open" or "Closed" position, instead of "Normal", does it need to be totally re-done (timing and all....) with Prime Start set to Normal?

I think it was set Open, it was definitely not on Normal. I discovered this when investigating the cause of hard starting, and set it back to Normal. It will start OK, just runs rough, won't hold WOT, discernible missing at all speeds. Performance was not bad initially, but has steadily deteriorated, with most of that continued deterioration after I re-set the Prime Start to Normal. Thanks for feedback.

[99yam40]

Prime start in the normal position only allows more fuel during warm up if it is working properly and has nothing to do with the link and sync procedure.
do you know if the prime start system is working as it should?

have you tried to turn it back to open to see if that helps?

If it does the the carbs are running too lean and the extra fuel is making it run better.

what does the Yamaha guy that installed the new power head have to say about the power loss?

Hopefully it is not running too lean and hurting the pistons/cylinders.

Where you using extra oil for the break in?

did the fuel pump and carbs get reworked when put on the new power head?

[a387673]

Response

Responses "in-line":

do you know if the prime start system is working as it should? Appears to be, increases RPMs on Cold Start, reduces after warming period.

have you tried to turn it back to open to see if that helps? Not yet.

If it does the the carbs are running too lean and the extra fuel is making it run better.

what does the Yamaha guy that installed the new power head have to say about the power loss? Gathering info, checked fuel lines, etc., before making that call.

Hopefully it is not running too lean and hurting the pistons/cylinders. For sure, that's why it needed the new powerhead.

Where you using extra oil for the break in? Yes

did the fuel pump and carbs get reworked when put on the new power head? ]Yes, but a carb cleaning was forthcoming as standard response to the issue. I examined every drop of fuel in the tank, and went toward the motor, confirmed all is well as far as the fuel pump. I was a little suspicious of a clamp that I snugged up, but I doubt I',m lucky enough to have fixed it there (haven't yet re-tested). Checked bowls for presence of fuel on the other end, looked OK, so I've basically surrounded the carbs on the fuel side of the equation.

[a387673]

Thanks

Thanks 99, for the info on how the enrichment works after warm-up, I was concerned that there was more to be re-done. I will try running it briefly set back to Open.

[a387673]

Update

As indicated, I checked out the gas lines, snugging up one fitting in the process, and I also put fresh plugs in although the old ones did not appear bad, maybe a little dry fouling. With it idling in the driveway, I flipped the Prime Start to open and it immediately shut down.

Set back to Normal, took it for a spin, and symptoms were improved, to about the point where it started. An occasional "bobble" at WOT. One of those things that's difficult to isolate, but always in the back of the mind........ If the pattern repeats, though, it will deteriorate again soon.......

[99yam40]

It took me close to a year to finally figure out someone had drilled out the main jets on mine.
put in new ones and it has been running well since.

I found out with the cowling and silencer off I could run into the wind and it would run fine. turn around and go with the wind and it would have the high speed miss.

did you get new crankcase recirculation valves when the new power head was installed?
I found only 1 on mine that was good when I tested them during a crankshaft replacement

fuel pump leaking into #3 crankcase can also cause some problems
not sure how many times I pulled and cleaned the carbs looking for something.

Oh yea.
the timing is advanced during warm up along with extra fuel.
when the temp switch that tell it is warmed up says it is warmed up the CDI changes the timing(RPM).
but the heater unit has to also warm up and close of the extra fuel.
research that or get the service manual and follow the procedure for measuring the unit to make sure it is moving to close off the extra fuel