Yamaha two stroke ignition help

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Old 09-06-10, 07:30 PM
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Yamaha two stroke ignition help

This story is a little convoluted and the engine has been transplanted so numbers might not be readily available. So here goes.

An older Yamaha snowmobile in really poor condition was getting scrapped but the engine still ran. It was removed from the snowmobile and in the course of two weeks was transplanted on to an equally old Polaris ATV. Before anyone realized that the engine would not start in the Polaris, the snowmobile had been scrapped. The engine lacks spark, has good compression, and fuel.

So what I am hoping for is some general guidance on where to begin tracking down why there is no spark.

The best guess on the motor is that it is in the 400cc range and a two stoke engine. It came off of a 20+ year old Yamaha snowmobile.

Steve
 
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Old 09-08-10, 02:44 AM
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What parts for the ignition did you move over - CDI stuff?
 
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Old 09-08-10, 08:31 PM
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Is it likely that there was an external CDI responsible for the generation of the spark for the plugs? I would have thought that a twenty five year old snowmobile would not have had a CDI ignition. But I know so little about such equipment that it would not fill a thimble, so that is just a question.

The ATV vehicle is not mine but I am often asked to help out on this stuff. It is my first venture into a larger two stroke engine. If the old snowmobile had an external CDI unit I am willing to bet that it did not make the trip with the engine to the ATV.

Do you have a basic electrical chart to show how the various components of such an ignition system are connected?

Steve
 
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Old 09-08-10, 09:28 PM
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Anything specific you'd have to have the model/serial numbers to work with.

About 1986 is when a lot of the small engines went to the modules which used capacitors. It was likely different with the snowmobiles but I would think about those years. The high energy systems in automobiles came in about 1978.

If the sled engine doesn't have/need the CDI box, it would be a lot easier to rig up an ignition system for it. Does it have an electric start on it, or just pull?
 
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Old 09-09-10, 06:51 PM
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It is a pull only start system.

I could check the engine for numbers - would that help? I could check the block on Saturday when I am up at the house where the ATV is located.

Steve
 
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Old 09-10-10, 03:16 AM
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I thought maybe everything would point toward a point/coil setup, but going to Yammer Hammer parts, even the '80 has the CDI. With that in mind the CDI stuff is likely what you're missing. You would need to nail down the year/cc of the sled and get replacements for the ignition parts. With that information and parts you could move forward on getting a manual for the wiring schematics.

The engine numbers aren't as handy as the the sled id stuff. Then you can go through on line sites to pick up diagrams and components.
 
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Old 09-10-10, 11:32 AM
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Thanks, and I was afraid that is what you might say. The snowmobile was scrapped and no longer around.

Do you think it might be possible to rig up any old Yamaha CDI box to serve the function or is it fairly specific to the engine?

Steve
 
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Old 09-10-10, 11:40 AM
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It's certainly application specific = that same engine could have been used in a different application and with it a different CDI for a number of different reasons = up grading, timing advance to control output of the engine, fuel quality changes, etc.

However, that's not to imply, in the time frame of say five years encompassing that engine/sled, there were hundreds of different CDI boxes put out. If you had the same size engine in a sled within a year or so of the manufacture of that sled, the CDI could very well be the same. Still there could be a couple of different wiring schemes for, say, grounding variances, accessories, etc.
 
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Old 09-13-10, 09:29 PM
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Funny that you mentioned "grounding". That was the issue. While all of the wiring was transferred to the ATV - at least as best as I could tell - not all of the harness was hocked back up. Two different grounds were hanging loose. It does not run well yet but it does start. Thanks.

The remaining issue is fuel delivery and should be easy to fix.

Steve



Originally Posted by marbobj View Post
It's certainly application specific = that same engine could have been used in a different application and with it a different CDI for a number of different reasons = up grading, timing advance to control output of the engine, fuel quality changes, etc.

However, that's not to imply, in the time frame of say five years encompassing that engine/sled, there were hundreds of different CDI boxes put out. If you had the same size engine in a sled within a year or so of the manufacture of that sled, the CDI could very well be the same. Still there could be a couple of different wiring schemes for, say, grounding variances, accessories, etc.
 
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