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Author Topic:   70HP Yamaha cold start problem
bloller posted 07-28-2003 12:11 PM ET (US)   Profile for bloller   Send Email to bloller  
What could be causing my new engine to idle rough and stall out when first starting it? Once it warms up it seems to run fine.
Peter posted 07-28-2003 03:07 PM ET (US)     Profile for Peter  Send Email to Peter     
Try putting in some new spark plugs and see if that makes any difference.
Jamie 20 outrage posted 07-28-2003 09:09 PM ET (US)     Profile for Jamie 20 outrage  Send Email to Jamie 20 outrage     
Plugs are the first step, then either adjust the carbs, or take them apart and clean them.
Clark Roberts posted 07-28-2003 09:12 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Each of the engines three carbs has an idle air mixture needle valve. These need to be adjusted slightly on the rich side and a shop manual will give you the drill for adjustment. Sounds like these need adjustment? Basically you need boat tied to dock and engine in gear at idle: in sequence adjust each carb's needle valve by turning clockwise (leaner) until engine runs rough, then turn it CCW until same and then try to get somewhere in between. Once engine runs smoothly go back and turn each needle valve counter clockwise (CCW = richer) very, very slightly. Shift to neutral and to fwd several times to confirm no stall and adjust idle-in-gear to about 700rpm via the single throttle arm stop screw on (as I recall) center carb... Happy Whalin'... Clark... Spruce Creek Navy
PS> haven't adjusted a Yamaha in a while and hope above is half way correct
jimh posted 07-29-2003 08:18 AM ET (US)     Profile for jimh  Send Email to jimh     
Are you using the idle throttle levers (on remote control) to increase the idle speed during warm up? I have a 70-HP Yamaha and it needs a few minutes of running at about 1100-1200 RPM before it will be able to idle at 600 RPM without stalling.
Peter posted 07-29-2003 09:07 AM ET (US)     Profile for Peter  Send Email to Peter     
The new 70 hp Yamaha has what they call "Prime Start" or something like that. It is an automatic enrichment system.

Starting a new 70 hp, at least mine, from a cold start doesn't require any lifting of the neutral throttle lever on the remote control. Once started, the motor holds the idle speed higher (about 1000-1100 rpm) until the motor has properly warmed up (in the opinion of the motor's control system). Once it has warmed up, the motor's idle speed slows down (about 700-800 rpm). This usually takes not more than about 1 to 2 minutes from the cold start.

If your motor is having difficulty going through that procedure, you may have a problem with the "Prime Start" system operating properly. After you change spark plugs (properly gapped) and you still have a problem, I would take it back to the dealer and let them fix it since it should be under warranty.

Follow up questions:

If you have a vent on your fuel tank, is it open?

How many hours on your new 70?

Have you passed the break-in point where you are using fuel without oil and just oil from the oil injection system?

bloller posted 07-29-2003 09:43 AM ET (US)     Profile for bloller  Send Email to bloller     
The motor has passed the break in period and has about 16 hours on it. I'm running straight gas now. The problem came not to long after getting it back from the dealer after the 10 hour service, before that everything was fine. When i first start it up it idles rough and stalls but it also revs rough in nuetral. The problem goes away once on plane and does not reoccur when I bring it down to idle. It reoccurs only after the motor sits overnight and I start it up the next day.
Peter posted 07-29-2003 09:46 AM ET (US)     Profile for Peter  Send Email to Peter     
Does it go through the Prime Start procedure?
bloller posted 07-29-2003 10:18 AM ET (US)     Profile for bloller  Send Email to bloller     
When you first start it, it revs high and then drops down like it should but once I put it in gear to leave the dock, that when it begins to act up.
Peter posted 07-29-2003 10:34 AM ET (US)     Profile for Peter  Send Email to Peter     
What rpm does the engine idle at once it has run through the prime start procedure but before you have engaged forward or reverse for the first time?

What rpm does the engine idle at once you have run it around for a while where you say it is OK?

bloller posted 07-29-2003 10:42 AM ET (US)     Profile for bloller  Send Email to bloller     
It idles at 7or8 after first idling around 12 when i first start it but then drops down to 3or4 then stalls once i put it in gear. It idles at 7or8 once warmed up and in gear it idles around 6. I'm not sure but I think it would even idle rough and stall in neutral after putting it into gear than dropping back to neutral
Peter posted 07-29-2003 01:03 PM ET (US)     Profile for Peter  Send Email to Peter     
The operator's manual says to allow three minutes for warm up. Are you following that recommendation?

In any case, since the problem appeared after it was serviced and only when cold, I would check some simple things, namely make sure the spark plugs are clean, properly gapped and tightend to specification and I would also check to see whether the motor's fuel filter assembly is tight to specification. I believe that the 10 hour service calls for a change of plugs and a cleaning or at least an inspection of the fuel filter, among other things.

Your best bet is to take it back to the dealer that serviced it and complain about what it is doing since you got it back from them.

bloller posted 07-29-2003 01:25 PM ET (US)     Profile for bloller  Send Email to bloller     
I'm going to take it out tonight and check the things mentioned. Hopefully I will have no problems. I sure would hate to have to take it back to the dealer. Those people take forever.
bloller posted 07-30-2003 04:06 PM ET (US)     Profile for bloller  Send Email to bloller     
Added new gas, replaced in-line fuel filter and pointed primer bulb upward by relocating it closer to engine and there was a noticable improvement in performance. Don't know if any of this helped but fortunately I wont have to be taking it to the dealer and they won't be getting any more of my money.
John Bocskay posted 08-04-2003 10:07 PM ET (US)     Profile for John Bocskay  Send Email to John Bocskay     
Bring it back to the Dealer, IT"S UNDER WARRANTY!!!!

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