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Discussion Starter #1
New to this forum, glad to see active threads.

2012 90 will start sometimes with no issue. Other times it just turns over and over but won’t crank. When it does start it runs fine, idle may be up to high as it wants to go with choke on but without choke it idles fine.

The other day it had issues starting, I charged up the battery for awhile and it fired right up. Had same issue yesterday, charged up battery and still wouldn't crank. Pulled plug cleaned it off, reinstalled and it fired right up. My son rode around for half hour and parked it. I cut if off and restarted like five times just fine. It sat for 20 minutes then back to not starting.

Any ideas?
 

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Is it slow cranking at all? The bigger ones need 100% battery to function properly but they are also fuel injected. When it wont start, can you jump start it from a car? If not, id think it could only be spark or fuel related...

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Is it slow cranking at all? The bigger ones need 100% battery to function properly but they are also fuel injected. When it wont start, can you jump start it from a car? If not, id think it could only be spark or fuel related...

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Doesn’t seem to be slow cranking at all. Also haven’t tried to jumpstart it from a car yet. Maybe next time it won’t crank I’ll try to jumpstart it. This is a carbureted yamaha raptor 90.

Going to pull the gas line off the carb later and see if fuel flows out
 

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Turns over fast after charging four hours but still wont crank. Pulled plug and theres spark. Pulled gas line off carb and the carb is getting gas. Out of ideas on this thing.
 

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No I don’t have a tool to check it. Was running fine just a few days ago though
Doesn't matter, some engines run great, then seize. Others, gradually lose compression until it gets hard to start, then they won't start.
It's not that common, but I've see it happen to 2 and 4 strokes.
You can rent a compression tester at most auto-parts stores, and just match the threaded end to the sparkplug threads(there will be several sizes with the tester).
Compression can be good today, and bad tomorrow. I'm not saying you 100% have low compression, just process of elimination and worth checking.
 

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Discussion Starter #9
Doesn't matter, some engines run great, then seize. Others, gradually lose compression until it gets hard to start, then they won't start.
It's not that common, but I've see it happen to 2 and 4 strokes.
You can rent a compression tester at most auto-parts stores, and just match the threaded end to the sparkplug threads(there will be several sizes with the tester).
Compression can be good today, and bad tomorrow. I'm not saying you 100% have low compression, just process of elimination and worth checking.
I’m probably just going to take it to the dealer service and get a diagnostic and hope they know what they are doing. Probably beyond my mechanical ability at this point. Sucks the guy that sold it to me told me it was alright. Dont really have the time to be fixing a lot or the knowhow.
 

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Discussion Starter #10
If I can find someone local that rents a compression tester for cheap, what compression should I be looking for on this yamaha raptor 90? Probably a good idea to test it before taking it somewhere anyway if possible even though I wouldn't be able to fix a compression issue myself.
 

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Discussion Starter #11
Went ahead and bought compression tool, figure it will help if I ever buy something questionable. Looks like 182 or so for compression and from the manual that is in the standard range.

Went ahead and replaced plug and it fired right up. Plug spark area is a little black looking though after one start, like oily.
 

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If the spark plug is "oily" Is it smoking at all?

Hard starts, especially when hot, can be tight valves, as said above.
You can buy a feeler gage set at an autoparts store for $5 and the valves are simple to check and adjust.
I would do that next vs paying anyone.
 

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It sounds like the valve adjustment is off. If it starts hard when cold, but OK when hot, sounds like tight valves, especially the intake. If you have the manual, it's easy to check, and we can help with adjusting.
 
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Discussion Starter #14
When I cranked it up today with the new plug, it had some transparent white smoke but not much. Just a little.

Since I recently acquired it Im gonna go ahead and do an oil change first being that I really have no idea of prior maintenance.

While I’m at the store I’ll pick up a feeler gauge. I have the manual that I suppose came with it but not a shop manual if thats what you mean. If you have a good one let me know so I can look into ordering one. Also if you have any links to adjusting valves that would b great.
 

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Discussion Starter #16
So same thing this weekend, went to start and no dice. Bought a new plug and it ran fine. Parked it for a day, no start. New plug, ran fine.

So something is definitely fouling those plugs.
 

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It sounds like the valve adjustment is off. If it starts hard when cold, but OK when hot, sounds like tight valves, especially the intake. If you have the manual, it's easy to check, and we can help with adjusting.
What happened with the valve adjustment? The spec's may be on your air box cover.
 
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Discussion Starter #19
What happened with the valve adjustment? The spec's may be on your air box cover.
Eh I never got ahold of a 90 shop manual that shows me step by step directions for doing it. I’d prefer having it to know exactly what needs to come off to get to them and how to check everything and reassemble.

I’ll try getting a picture of the carb later. It looked like a place for a hose on the bottom and nothing attached to it.
 

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Did you PM Morphrider for a manual? Should be YouTube videos. Any video from any motor will give you a general instruction, the difference would be if you have to remove plastic body panels for access.
 
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