'89 Yamaha Big Bear timing? - Yamaha ATV Forum
 
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post #1 of 8 Old 05-18-2016, 08:58 PM Thread Starter
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'89 Yamaha Big Bear timing?

Hey everyone,
I had my big bear bored out 83mm to 84mm. Assembled everything. Started right up. However I believe my timing might be off. The T on is visible on the timing, the lines match on the upper head, however it stalls out very easy. That being said I havnt actually ran it for a decent period of time. Other repairs to the front end and tires have made me unable to drive it at this time. however I hope to have it rolling in the next few days.

I am wondering if anyone has had a problem similar to this before.

It has sat a while, Im not sure if it just needs to be run and blow all the junk out or what.

A friend of mine says the timing might be a tooth off on the cam. He was going to look at it but hasnt had time yet.

Thanks in advance,
M
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post #2 of 8 Old 05-19-2016, 07:51 PM
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it will take some time to seat the rings and break in the new parts, check the timing for sure but I would bet on bad gas due to sitting or just not broke in yet
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post #3 of 8 Old 05-21-2016, 10:23 AM Thread Starter
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I drained the gas tank a while ago and put new gas in it, so I dont think its that. While it will take time to break everything in it should still not run as rough as it is.

I finally got it rolling today. While it runs and drives it seems to heat up extremely quickly. Also, when I push the throttle it makes a low pitch almost popping sound, not the normal revving sound. This in turn causes it to lose power and almost want to stall out.

I know some adjusting to the gas/air/exhaust flow needs to be done still (again, my friend has not had time to look at it yet), but I wouldnt think that would cause it to not want to rev correctly - meaning it would expect it to want to go faster than it is currently.

I did check the timing, everything lines up as the manual says it should (I have the actual mechanic's version, not just the owners). I know cars wont run worth a dookie if the cam is off by even one tooth. Just am not sure exactly whats going on with the quad.
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post #4 of 8 Old 05-21-2016, 02:41 PM
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since the timing is good and it is heating look for something causing a lean condition. vacuum leak between the carb and the head, main jet is to small or plugged, air mix screw in to far. check your compression
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post #5 of 8 Old 05-23-2016, 06:31 PM Thread Starter
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Well I adjusted the air intake and exhaust and it ran great! I started driving it down the road a bit and it overheated rather quickly. The engine is air cooled so i checked the oil cooler and the lines going to it and there was oil in it, so the lines and such werent plugged (which is good . I cranked it over a few times and no oil pumped out, so I started thinking it was the oil pump. Then I remembered... awhile ago I pulled off the crankcase to replace it and the gear that controls the oil pump was laying in the bottom of the case... so I am going to replace that.

The only thing I am struggling with now is since it overheated the bike wont start. It cranks just fine and is getting good spark, but it wont fire up. Any ideas?
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post #6 of 8 Old 05-24-2016, 12:10 AM
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i would start with a compression test to make sure you did not hurt anything when it got hot. do you see fuel spraying out if you crank it with the plug out
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post #7 of 8 Old 05-24-2016, 12:02 PM Thread Starter
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Well I popped the spark plug out and had a friend turn the motor while my finger was over the hole (where the spark plug was). I had done this when we first put the head and such back together to make sure the compression was there as well. It felt the same this time as it did the first time. So I do not believe I damaged anything when it overheated.

I am going to check the valves and see if maybe one didnt get stuck open or closed or something? I assume if they are not moving at all (either way, open or closed) the bike would not start up.

I will also check for fuel spraying out when I crank it with the plug out.
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post #8 of 8 Old 05-24-2016, 09:55 PM Thread Starter
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I checked the valves earlier. Apparently when adjusting them I did not tighten the locknut enough. The exhaust was super loose and the intake was tighter than... well... you know.

Once I adjusted them the bike started right up and ran well. I did not keep it running long due to the fact that I need to install a new oil pump.

Hopefully that will be the last thing I need for it to run well :)
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