93 C85 Yamaha Rough Idle

[bproctor123]

Idle is rough when in gear until about 1500 rpm. This is a low time, all original motor. I have carefully disassembled and cleaned carbs, and have adjusted idle mixture screws several times, but can't smooth out. Plugs are correct and new, and all bolts carbs and intake are tight.<br />Compression is within 5 psi. Previous owner has screwed around with timing screw on control link(other timing at factory settings), but I have set it back to where the factory tamper paint matches, and to Clymer manual's preliminary length adjustment. Runs great otherwise. It is hard to start in cold weather, but starts on a dime when warm. <br />Thx<br />Salty Bob

 

[ob]

Re: 93 C85 Yamaha Rough Idle

Sounds like your carb linkage could be out of adjustment.If motor runs good otherwise including WOT I wouldn't mess with timing.

 

[rudeafrican]

Re: 93 C85 Yamaha Rough Idle

Might help to check out your thermostat. It could be stuck in the open position. You won't believe the difference it makes to cold and slow running.

 

[Capt Ken]

Re: 93 C85 Yamaha Rough Idle

True, a cold engine will idle rougher that one at the proper temp. But be sure you set the linkage on the carb up properly. Just a hair off will do what you are describing. Back the idle adjustment screw off where its not touching, loosen the screw on the top and bottom carb's arm. Remember these are lefty tighty, righty loosey, not righty tighty, lefty loosey. Be sure all butterflys are fully closed and tightened the top and bottom screws, then reset the idle screw back in place.

 

[bproctor123]

Re: 93 C85 Yamaha Rough Idle

Thanks to all. I like the idea of not messing with the timing too. I have felt the head when running and temp seems right, but hard to really tell I agree. I will try the linkage check in the am. South Africa????? It's a small world.

 

[bproctor123]

Re: 93 C85 Yamaha Rough Idle

I reset the throttle linkage on top and bottom carbs, while the center carb linkage was firmly held closed. Also verified the thermostat was closed. Test run did not show much improvement, but there was a slight improvement. Any more ideas?

 

[Capt Ken]

Re: 93 C85 Yamaha Rough Idle

Time to start a ground zero. Remove the carbs again and really be sure they are clean. Especially the low speed circuit. Be sure the floats are set at the same level as each other. Then just check and recheck everything and try again. If you run the engine with the carb cover off, does any of the carbs try to blow a fuel mist back out the front?

 

[bproctor123]

Re: 93 C85 Yamaha Rough Idle

Last time I ran it with the carb covers off, it did not spit back. FYI:<br /><br />I did note that when starting cold (the hard start is getting better, I just needed more choke and more throttle than I have ever experienced on any other outboard)I do see a slight fuel/oil film on the water as I let it warm up. (to give you a reference, outside temps in the 40-60 range). Aside from slow speed operation, performance is perfect. The reason I went through the carbs initially was that it sat up with stale gas from previous owner, and would barely run.