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Old 05-30-2014, 09:04 AM   #1
2stroke1971 OP
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yz465...knocking, etc...

I know this has been done to death. I have an '81 YZ465.

The bike had been entirely rebuilt by a friend of mine who lost interest in it shortly thereafter. I spent a few rides getting the jetting where I wanted it.

Generally speaking, from what Ive read and what Ive experienced, to get the throttle response clean and free of blubbering, you have to lean the thing out. Problem is, it has a tendency to knock anyway. So, by the time I got the throttle barking like it should...it would start knocking badly after 1 lap.

Octane boosters are crap in my book, never helped any of my stuff over the last 20 years or so all though I did try some in the YZ twice.. I tried adding an extra head gasket, and the knocking was almost bearable...It still happened after two laps, and it wasnt as bad, but I lost alot of low end, and the power took too long to come on=bad starts, etc.



So Im back to one head gasket. So far I have been running 93 octane from the pump. I want to try some race gas but I have no experience whatsoever with it....what should I try in the YZ, and do you think it will help? I have also thought about retarding the timing a bit.....

My brother said I should fatten it up a bit but then I will lose the response I have now....right now I have a 370 main in it...and a 45 pilot....and I did the slide mod...3.5 or so. and besides back when i first rode it and the jetting was fat and the throttle response was blubbery, it still knocked a bit.

also thought about running my hone through the bore but I dunno....

thanks in advance for any ideas or recommendations on fuel etc...

2stroke1971 screwed with this post 05-30-2014 at 09:24 AM
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Old 05-30-2014, 02:39 PM   #2
Mr. Carts
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Have you checked the timing?
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Old 05-31-2014, 03:03 PM   #3
2stroke1971 OP
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Originally Posted by Mr. Carts View Post
Have you checked the timing?
Nope. I could put my timing light on it I suppose.. The worst thing is I can't really work on it where I live...well I can work on it but testing it--nope.
The guy who put it together used hex bolts for the stator---no getting a 10mm socket in there or else I would have been adjusting it at the track a few weeks back. I'm going to pull the flywheel and put some small button heads on it so I can get in there with a number 4 T handle while the flywheel is on.

Makes for a frustrating routine, race it, agonize over what to change before next race....hope it works, etc.....

I really need to take it out to some pay-to-ride place with a bunch of tools and spares and just wrench on it all day long.

Overall, it's one of many indulgences that I don't really have the time or money for, so it's not like I get to play with it that much. I race it maybe 5 or 6 times a year and thats about it.
Thanks for the reply!
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Old 05-31-2014, 03:52 PM   #4
Toddv
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Check timing, if that's not it you either have a compression ratio problem or somethi g else causing the preignition. Too hot a plug would be an easy one but could be some sharp edges somewhere in the combustion chamber that is getting hot and lighting off the fuel before the plug does.
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Old 06-01-2014, 08:18 PM   #5
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Agreed. Check timing. Here is what I went through:

http://www.advrider.com/forums/showp...5&postcount=74
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Old 06-03-2014, 09:44 AM   #6
mtbdemon
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My experience is that either the squish band and/Or very high octane fuel will cure the problem. I raced IT's and YZ 490's and those two things were the only things I could find to help with the pinging...
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Old 06-03-2014, 06:49 PM   #7
2stroke1971 OP
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Originally Posted by mtbdemon View Post
My experience is that either the squish band and/Or very high octane fuel will cure the problem. I raced IT's and YZ 490's and those two things were the only things I could find to help with the pinging...
So did you find that the ITs pinged as well? I actually have an IT jug that I could use, but sounds like Id be in for more of the same.


There is a drag strip not too far away where I can get some high octane gas...not sure exactly what they have. Gonna check the timing first and foremost, as soon as I get a spare moment.

Im tempted to go back to a second head gasket, and drop down one on the counter shaft to try to recover some grunt, and STILL use some high octane or leaded fuel.

Thanks for the replies!
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Old 06-04-2014, 04:01 AM   #8
anotherguy
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Check timing. Look for air leak. Confirm jetting. Do not confuse the antics of the 490s with the 465. For some reason they are totally different in execution.

My YZ has pinged when I ran the ragged edge but generally runs well and is a 3-4 kick starter. And I've had it for decades. Race fuel isn't necessary but does give a consistency unobtainable with nasty ass pump gas.

Are you sure it's a 465? What are the first 3 digits in the VIN?
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Old 06-04-2014, 04:46 PM   #9
Andyinhilo
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Go to your nearest general aviation airport and buy some 100LL. That should solve it, unless something is wrong with the timing.
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Old 06-11-2014, 04:29 AM   #10
buls4evr
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Back in the day.....they used to reshape the heads and play with timing on that bike. People like DG made a good living doing that. Maybe ProCircuit could fix you up on that or direct you to someone who can. Really hard on rods when they rattle also you know....
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Old 06-12-2014, 08:26 AM   #11
jub jub
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I had a YZ465 that I got to run smoothly by adding Boyesen Reeds and a boost bottle from a YZ490. The pilot jet was stock and I had dropped the needle to the highest notch. I miss that bike.
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