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Author Topic:   Yamaha Coils
hardensheetmetal posted 05-14-2001 05:38 PM ET (US)   Profile for hardensheetmetal   Send Email to hardensheetmetal  
I have a 1988 225 Yamaha on my 22R W/T. The motor starts, idles and seems to run fine in the slip. When I take the boat out and get up on plane, after several minutes (1-2) at 3000-3600 the motor drops back to almost nothing. I replaced the fuel filter, thinking it was not getting enough fuel at speed, but that did not have any effect. I have been told by several people that it could be the coils that are attached to each cylinder. I've checked these out, and they seem to be easily removed, my qustion is; is there a way for me to test these and determine if one or more may be bad? Anyone have an idea on how much one of these cost? Any other theories on why the motor might be doing this?.
Unfortunately, I don't have a Yam. dealer located anywhere near me, so I would like to rule out all of the easy stuff before I haul the boat and trailer it to a dealer to get it looked at.

Thanks for any input,

rsess1 posted 05-14-2001 06:39 PM ET (US)     Profile for rsess1  Send Email to rsess1     
I just had the same thing on my merc outboard. First disconnect gas. Take all six spark plugs out. Attach to spark plug leads and position each near block. Crank engine for one or two seconds. Check which plug(s) don't fire. Swap one coil that works for one that doesn't. Repeat. If bad plug has moved you need coil. If bad plug in original place, look for bad wire leading to coil from power pack. I had cracked internal wire at powerpack. just put on new crimped connector and fixed everything.
carlz posted 05-14-2001 07:55 PM ET (US)     Profile for carlz  Send Email to carlz     
The yamaha manual calls for an impedence check on the coils. If it is burnt out it will likely have a very high impedence. The spark plug test described above is also suitable. However, a coil failure should be solid, not kicking in after warmup. If you stop for a minute do you go back to normal? Or do you have to wait until the engine goes cold? If the later, I would consider the possibility of an air leak into the crankcase which only occurs when the engine gets warm (ecpansion opening up some crack). I had a torn crank seal which had the same end result, although I didn't have to wait for the engine to warm up for the problem to manifest itself.
hardensheetmetal posted 05-14-2001 10:18 PM ET (US)     Profile for hardensheetmetal  Send Email to hardensheetmetal     
Thanks, both, for the input,

I'm going to see if I can test them tomorrow, and well see.

Carl, once the RPMs drop off, I can almost immediately push the throttle back up and get the boat up to planing speed, so it does not seem to matter if the motor is cold or hot, more if it has a load on it or not. I can not make the RPMs drop of if I fast idle it in the slip.


DIVE 1 posted 05-14-2001 10:26 PM ET (US)     Profile for DIVE 1    
Check your entire fuel system. It sounds like you have a pump going bad or a fuel line collapsing.
lhg posted 05-14-2001 10:30 PM ET (US)     Profile for lhg    
Could it be the low speed (1000 - 3000 rpm range) stator?
carlz posted 05-14-2001 10:42 PM ET (US)     Profile for carlz  Send Email to carlz     
If when back off the throttle for a while and they you once again have full power, that is consistent with fuel starvation. In that case you are sucking fuel out of the carb bowls faster than they are being supplied; back off until they refill and power is restored.
I like the fuel pump theory. Don't try to rebuid it, rather replace it. I went down this road. Yamaha has superceded the partno's on the carb diaphram so many times with incompatible parts that you cannot rebuild. And the pump is only $35 or so, anyway.
carlz posted 05-14-2001 10:47 PM ET (US)     Profile for carlz  Send Email to carlz     
btw, I noticed you live in northern NY metro. If you give up on the self-cure, I had good luck with Catalano & Sons in Greenich, Connenticut. That was after $1200 of incompetent work from my NJ Yamaha dealer. Rob Catalano is the mechanic; very competent and not a gouger.
Tom W Clark posted 05-14-2001 10:48 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
I'm no engine mechanic, but I suspect a fuel starvation problem in some form and it may not be the motor. I would start with the boats fuel system and verify that the gas can get to the engine without impediment before digging into the motor itself.

There was quite a discussion of fuel check valves here:

lhg posted 05-14-2001 11:21 PM ET (US)     Profile for lhg    
If it's a fuel delivery problem, you can tell a lot by inspection of, or squeezing, the primer bulb. If it's collapsed, it's the boat system. If you can keep the engine running by forcing fuel through the bulb, it's probably the engine fuel pump. If the bulb stays firm, and no more fuel can be pumped in, it's something else. You can also disconnect the fuel hose from the engine, and look at the volume of gas you can squeeze into a container. If plenty of gas flows freely, then you know it's not the boat or filter, and definitely the fuel pump if squeezing keeps it running.

I watched a mechanic diagnose an only slightly bad fuel pump for me this way.

hardensheetmetal posted 05-15-2001 12:45 PM ET (US)     Profile for hardensheetmetal  Send Email to hardensheetmetal     
Carl, yes, I have seen Catalano's add in the back of Soundings, I will give them a call if all else fails.

As far as the fuel system goes, wouldn't I experience the loss of RPMs at the dock when I run the motor up in neutral, or is it that the motor is using that much more fuel to get the boat up on plane. I could see that it may be starving one or two minutes after the boat is up because it is burning whatever fuel is left in the motor.

I,ll let you know what I find,
Thanks all


Whaletosh posted 05-15-2001 01:30 PM ET (US)     Profile for Whaletosh    

No, you wouldn't just burn up the fuel in the carbs. Flow capacity (vol/time) is the question here. Your fuel system could very well have enough flow capacity to keep the motor running at displacement speeds. And the carb bowls might very well have enough in them to get the boat on plane. Then when you are forced to slow down what flow capacity there is catches up.

Your problem sounds very similar to what happens when the vent on a portable tank is not open.


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