Yam FT9.9EXH barely starts, stalls with throttle increase

[murphyjh]

I can get this 1988 motor to idle only by reducing the idle speed setting, and even then, it idles roughly. It will turn the prop at idle in a tank. However any attempt to speed it up causes it to stall immediately. Even in neutral, any slight opening of the throttle butterfly makes it stall. Compression is good (130-135), but the plugs are wet with gasoline.<br /><br />I have taken the carb apart, and found the main jet completely clogged. Fixed it. Everything else looked good. The float is at the right level, and I ran wires through all orifices.<br /><br />It appears to be running rich, which could cause the idle to be rough. When I open the throttle, I don't know whether it stays too rich or suddenly becomes lean.<br /><br />This leads me to the mysterious Bimetallic Vacuum Switching (BVS) valve system on this motor, which is a starting enrichment system that senses block temperature and sends vacuum signals to the carb. The Seloc manual has a general description, but no real details (I suspect that they don't understand it either).<br /><br />Has anyone experienced this problem? Is the BVS valve in the block bad? Anything else I can look for in the carb?<br /><br />Jack Murphy

 

[murphyjh]

Re: Yam FT9.9EXH barely starts, stalls with throttle increase

Followup: I found the problem. The pilot jet became clogged again. This jet feeds the two small ports thst become exposed as the throttle plate opens, accounting for my symptoms.

 

[ST]

Re: Yam FT9.9EXH barely starts, stalls with throttle increase

Hi murphyjh;<br />Was it complicated to take apart the carb? Do you need to replace anything? I might be doing my 86 9.9 carb cleaning before too long myself.

 

[murphyjh]

Re: Yam FT9.9EXH barely starts, stalls with throttle increase

ST:<br />It wasn't difficult using the Seloc manual. I didn't replace anything.<br />I found that removing the items on the top of the carb involved many steps that were unnecessary because my problems were in the bottom of the fuel bowl. When I finished, I wrote myself a 5-step mini procedure for my use if the problems return. Here it is, condensed (Seloc item numbers):<br />1. Undo throttle link and remove small hoses marked A and C (marked on hoses and carb).<br />2. Remove the two manifold mounting nuts and washers. Then move the carb so you can remove the fuel line.<br />16A. With the carb out,loosen the large brass drain valve and drain the fuel.<br />12. Drop the bowl (4 screws).<br />13. Watch for the starter nozzle that will fall out of a well in the bowl.<br />17. Pry up the white plastic cap. Use a suitable screwdriver to unscrew the pilot jet in that hole. Also unscrew the main jet next door.<br />That's it. Use fine wires to clean the jet bores. Scrape off any crud; blow through them with air or solvent; and reassemble.

 

[SamalotCj]

Re: Yam FT9.9EXH barely starts, stalls with throttle increase

Originally posted by murphyjh:<br /> Followup: I found the problem. The pilot jet became clogged again. This jet feeds the two small ports thst become exposed as the throttle plate opens, accounting for my symptoms.

I can't tell you how many carburetors I've cleaned due to dirty fuel only to have them return with the same problem. I recommend to every victim of a dirty carb to ditch their remaining fuel and refill. Also make sure to purge the fuel line of any remaining gas as well. In a small outboard it's VERY easy to clog those tiny fuel jets.

 

[ST]

Re: Yam FT9.9EXH barely starts, stalls with throttle increase

Murphyjh;<br />Thanks for your step-by-step procedures; I saved that for my future reference!<br /><br />If these small outboards are so susceptible to dirty fuel; you think it's a good idea to install an in-line fuel filter on them?

 

[ST]

Re: Yam FT9.9EXH barely starts, stalls with throttle increase

Murphyjh;<br />I followed your step-by-step yesterday. Did everything as your post, but I was not able to do step 17: couldn't pry up the white plastic cap! <br /><br />In fact, I might have ruined it now: using a pair of cutter, instead of pulling it out, I cut the cap! Tried to look for part replacement at BOAT.NET or Yamaha website; but unable to determine which part I need; hard to read those parts drawing! <br /><br />How did you remove that plastic cap? You think I should just leave the cap alone?<br /><br />1986 Yamaha FT9.9ELJ

 

[murphyjh]

Re: Yam FT9.9EXH barely starts, stalls with throttle increase

Sam:<br />Mine came out easily. Here are the part numbers for the plug and its o-ring:<br />6G8-14345-00-00 PLUG,MAIN NOZZLE $1.77<br />654-14198-00-00 GASKET $1.92<br />You can probably drill the piece (less than 1/4" long) out. Use a small bit and drill at an angle to avoid drilling through the hole in the jet. It makes me wonder why Yamaha didn't tap the hole and screw a plug into it.

 

[ST]

Re: Yam FT9.9EXH barely starts, stalls with throttle increase

Murphyjh;<br />Just wanted to follow up: even though my engine model year was 1986; but my carb looks like 1987 model year! The parts you listed is for 1987 and later model year I believe; so I got them ordered (along with other part I needed) from boat.net and already put them back together. Thanks again!