yamaha 9.9 ELRX won't idle

[micmor64]

A lot of searching and reading old posts and haven't found an answer that worked for me... So thought I'd post a new thread.

1999 - 9.9 high thrust 4 stroke - motor has 22 actual run time hours on it and it ran fine the last couple of years until an intake valve bent. Just finished a valve job and it starts and runs great at mid to high speed, but will not keep running under (i'm guessing) 1500ish rpm (no tach to measure actual). I have gone through the carb having just replaced the main needle, diaphragm and bowl gasket. cleaned the entire carb pulling both main and idle jets, removed the cover and cleaned the ports in the throat from the Air/fuel Mix screw.
I've spent hours trying air/fuel needle mix settings from 1/2 to 4-1/2 turns open in 1/4 turn increments. Every time i drop the throttle below 1500ish (guessing) the engine drops off and dies acting as if it's out of fuel. A couple pumps of the diaphragm and throttle reset to mid range and it comes right back and runs great but only at mid to high throttle settings. I'm and old JhonnyRude 2 stroke and am new to Yamaha 4 strokes. What am I missing to get this motor to idle?

 

[99yam40]

have you checked compression to make sure the cylinders are sealing well?

I have no clue how an intake valve could get bent, except hitting the piston or some other hard object.
are you sure the timing is all set up properly

 

[micmor64]

have you checked compression to make sure the cylinders are sealing well?

I have no clue how an intake valve could get bent, except hitting the piston or some other hard object.
are you sure the timing is all set up properly

I too was stumped on a bent intake valve. Still am. There was no indication of hitting the piston. When the engine ran last, a fgew minutes after I pulled the fuel line to let the carb "run dry" the engine coughed hard and stopped (it was ideling fine after a few hours run time, and stopped hard, not the typical running out of fuel) and didn't run after. I'm assuming a backfire, causing the problem. Thats when I did a compression check and identified the valve problem. Upon completing the valve job (replaced all 4 valves, lapping them in, and seals) I checked both compression and timing and both are fine.

Upon initial start up (after the valve job) I could only get it t to start by making a choke plate with a 3/8" hole to cover the intake (never had to do this before). Without the plate it wouldn't start or run. I pulled the carb apart again this time removing the cover to the 4 ports from the air/fuel mix screw, found two of them blocked. Cleared the blockage, Pulled both jets again and went through everything again, replaced The diaphragm, needle and bowl gasket. Now it starts and runs great at mid/high throttle, but I can't get it to idle. If I turn down the throttle, it'll slow and stop like it's running out of fuel. To get it running again I sply "pump the accellorator" a couple time, set it to mid throttle setting and it fires right up (no choke plate).

Scratching my brain not sure what part of the circuit is causing the problem. I've been working on 2 stroke carbs for near 50 years now so I'm no stranger to a rebuild, but I've obviously missed something. Local shops don't want to touch anything older than 10years, and this is a 1999 with only 22 hour run time, go figure.

 

[99yam40]

If the compression ,valve timing, and ignition timing are all in spec, You might need to get these carb parts into a heated sonic cleaner to help get rid of some stuff you have not been able to get out already,

I would still like to know what bent the valves.
Something had to hit to cause that in my opinion.

 

[micmor64]

If the compression ,valve timing, and ignition timing are all in spec, You might need to get these carb parts into a heated sonic cleaner to help get rid of some stuff you have not been able to get out already,

I would still like to know what bent the valves.
Something had to hit to cause that in my opinion.

My task today is to "once again" remove the carb, and go through it again. I will search to try and find someone with a heated sonic cleaner that will run my parts through. None of the local shops want to touch these parts as they're "too old now".

I agree, I'd love to know what bent the valve, but my forensic skills (reads more like crystal ball) are insufficient.

Any suggestions as to where the air/fuel mixture screw should be set initially? I read in a post somewhere it should be 3 turns open from lightly seated. Mine was 1-1/4 before all this happened.

 

[micmor64]

My task today is to "once again" remove the carb, and go through it again. I will search to try and find someone with a heated sonic cleaner that will run my parts through. None of the local shops want to touch these parts as they're "too old now".

I agree, I'd love to know what bent the valve, but my forensic skills (reads more like crystal ball) are insufficient.

Any suggestions as to where the air/fuel mixture screw should be set initially? I read in a post somewhere it should be 3 turns open from lightly seated. Mine was 1-1/4 before all this happened.

I have done some looking at engine diagrams and have found that whiole the engine is labled F9.9 ELRX (which is 1999), the carb matches F9.9 ELRW (which is 1998). The difference is that in the 1998, the air mixture screw is accessible where as the 1999 it is Under a cover plate and in-accessible.

I'm guessing my motor was a very early 1999 model using an "older" 1998 carb. As far as I'm concerned, that's good news for me.

 

[micmor64]

My task today is to "once again" remove the carb, and go through it again. I will search to try and find someone with a heated sonic cleaner that will run my parts through. None of the local shops want to touch these parts as they're "too old now".

I agree, I'd love to know what bent the valve, but my forensic skills (reads more like crystal ball) are insufficient.

Any suggestions as to where the air/fuel mixture screw should be set initially? I read in a post somewhere it should be 3 turns open from lightly seated. Mine was 1-1/4 before all this happened.

IT RUNS. FINALLY!
My daughter and son in law were here for the weekend and with a couple of sets of hands and eyes and some much needed extra brain power, We have the motor running really well.

We took the carb apart several times without much success and after a lot of head scratching we went back to basics. With each successive find/fix we got better and better results, until it's finally done. What we found were the following: 1) one of the four micro ports from the air/fuel mix valve into the throat was not completely cleared, 2) one of the factory seals on a croww drill port in the idle circut was leaking, 3) one of the two brand new NGK plugs was not functioning well, each o fthese finds mad improvements but it still was a little off, what finally fixed it all was Rory (son on law) noticed there was a slight misalignment to the intake to head gasket.

After a couple days off and on several removals/replacements of carb, all of these issues combined resolved the low speed performance issues and the old motor is readt to reinstall in the boat.

It's amazing what a fresh 2 pairs of eyes and a couple of sharp young brains (daughter and son in law both) can do to help an old frustrated guy like myself to muddle through.

I would still like to know what bent the valve to begin with, but for now I'm content with just adjusting the air/fuel mix valve and idle stop and doing a little fishing.

 

[99yam40]

thanks for the update, let us know if you even figure out what bent those valves