Ready to shoot 1992 Yamaha 40... HELP!

Boat_Boy!

Seaman Apprentice
Joined
Jul 29, 2001
Messages
34
Okay guys... I disassembled the carbs and cleaned them really well. I inspected each part and they were all in good shape, well within spec on all measurements. No wear on the idle screws or the needle valve. I set the idle screw to 1.75 turns out from seated. The engine starts fine, but runs fast.<br /><br />The manual says that the idle screws should be no more than .25 turns + or - from the set position. I can't get this thing to idle down! The throttle screw is not even touching the plate. I.E. it is not affecting the idle speed whatsoever. When I try to adjust the idle screws in to slow down the idle, I go past the .25 turns (somewhere around a full turn) and then it runs like a bag of hammers, and eventually dies.<br /><br />I don't have a tach so I can't give you any specific numbers, but when I engage the forward gears, I get a bit of a crunch. Not good I assume. The original problem was a rough idle. Where should I look now, or how do I properly adjust these carbs? Do I start with the top carb, or bottom carb? Should I look at timing or electrical?<br /><br />I'm a newbie, but I video taped the disassembly, and I am very meticulous. I am absolutely certain I got it back together correctly.
 

kev_79

Petty Officer 1st Class
Joined
Aug 5, 2001
Messages
355
Re: Ready to shoot 1992 Yamaha 40... HELP!

Boat boy, check your idle timing. I am not too fimiliar with Yamaha, but on my merc, when you push the throttle forward, the first thing it does is advance the timing, making it run a little faster, without giveing more fuel mixture. I bet this is you prob if your motor is running fine. I thing idle timing should be around 2 to 4 degreees before top dead center. Check manual, or call your wrench to validate. Good luck, and let me know what you find.
 

hohmanj

Cadet
Joined
Mar 22, 2001
Messages
12
Re: Ready to shoot 1992 Yamaha 40... HELP!

I had a 2 cycle engine that behaved this way because of an air leak at a gasket @ the base of the engine....??????
 

Boat_Boy!

Seaman Apprentice
Joined
Jul 29, 2001
Messages
34
Re: Ready to shoot 1992 Yamaha 40... HELP!

I will check the engine timing and the look for any leaks. The manual describes a way of checking the timing without a light. I'll look into this.<br /><br />Does anyone have any recommendations on how I could get a tach onto this engine inexpensively? Even if it's just an analytical tool, and not permanent. I have a dwell/tach meter that is designed for autos, if I could only find a signal wire, I think it might work...
 

kev_79

Petty Officer 1st Class
Joined
Aug 5, 2001
Messages
355
Re: Ready to shoot 1992 Yamaha 40... HELP!

If you know any mechanics or race car enthusiast, you might want to ask them if they have a timing light that will read the tach. One like that will cost about 300 dollars, but those guys like expensive tools with flashy lights and buttons...they might let you borrow it if your nice. Good luck
 

norman158

Petty Officer 1st Class
Joined
Jun 29, 2001
Messages
329
Re: Ready to shoot 1992 Yamaha 40... HELP!

i have a tiny tach its digital and has a built in hour meter very easy to hook up cilp 1 lead on the number 1 plug wire ground the other works on multi cylinders and 2 and 4 stroke engines i got it through a briggs and stratton dealer cost was about 50 bucks hope this helps Rick
 
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