compression release on 1980 motor

schlakeandbake308

schlakeandbake308

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I'm looking to install the old compression release on my 1980 motor. i ended up with the rocker that went with the compression release on accident and its conveniently already installed. so I'm just checking, can i just throw that compression release cover on it and have it work? anything else that has to happen?
 
thanks fred, further though... my motor is rephrased with a high compression head. I'm just trying to get it to the point that my lady has the ability to maybe have a chance, at possibly kicking it over haha. will it do anything on the rephrased motor?
 
schlakeandbake308 said:
thanks fred, further though... my motor is rephrased with a high compression head. I'm just trying to get it to the point that my lady has the ability to maybe have a chance, at possibly kicking it over haha. will it do anything on the rephrased motor?
Click to expand...

Hi s&b,
firstly, this one ain't a Doherty but it costs far less:-
http://www.feked.com/decompression-lever-7-8-ball-end.html
But I don't see why a compression release will not work just as well on a rephased motor as on a 360º motor.
But here's a way to kick-start that may be helpful. It's a version of the ol' "HTF do I start my Velocette without breaking my leg?" trick modified to suit a bike that has a compression release but don't have a manual spark control.
Put bike in 1st or 2nd gear.
Pull comp release.
Pull bike backwards until the engine comes up against compression.
Click gear into neutral.
Turn on ignition.
Keep decompressor pulled.
Kick with right foot while standing beside bike.
Repeat as needed.
 
I used a brake lever from a child's push bike. The XT/TT/SR decom levers were too expensive.
I don't use it and have no problem starting the bike, which is rephased (277) using a Mikes XS bike fin barrel and piston combo. Compression ratio around 9:1.
See how she goes starting without the lever, its an easy addition if she needs an easier kick.
 

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On an 80 I don't think it will work. To work the rocker arm needs the nub. hump whatever you may call it on it. The shaft in the cover has a flat sot on one side. When not pulling the lever this flat spot rides over the nub. When you pull the lever the shaft rotates so the round side presses on the nub, opening the exhaust valve a bit.
I don't know just what year they quit making the rocker arms with the nub, my 75 has them. My 81 doesn't.
Replacing the stock exhaust rocker arm on you 80 with one with the nub is not hard to do, you just need to pull the head.
If this is on your wife's bike, I might suggest putting the E-start back on.
Leo
 
First of all, I have no experience whatsoever with the XS2 compression release, but have been pondering this issue myself, as my spare engine is an XS2.
Now, being a 4-stroke twin (360, 277, 270, even 180 crank does not really matter), one cylinder at a time will be at the compression stroke.
So even with a decompressor arrangement on the left cylinder, the right cylinder will be just as hard to bring over TDC anyway.
I guess if one can first bring the right cylinder just past TDC on its compression stroke, like Fredintoon suggests, then the decompression lever will help build more momentum before hitting compression on the right cylinder again. This may or may not be sufficient for making kickstart a good option for a lady.

With TCI or any other crank triggered ignition, it should be fairly easy to build some kind of TDC indicator setup at the end of the camshaft, like on the XT/TT/SR 500. This would then ensure the engine is in the optimum position for kickstarting.
 
Last edited:
I believe the following to be true:
The whole intention of the decomp is to make the ELECTRIC start easier. I don't think Yamaha was convinced that their after-thought electric motor was capable of turning both cylinders through the compression stroke. The XS1 had no electric start and no decomp. They added the decomp lever when they added the electric starter, and they coupled the starter motor switch to the decomp lever so that you had no choice but to electrically start the engine on only one cylinder. They abandoned the decomp lever when they realized that the starter motor really was capable of turning both cylinders unaided.
 
Leo, s&b sez his '80 did acquire the appropriate rocker arm.
And arctic, it depends on the lady, dunnit?
And her knowledge of the appropriate kicking technique?
And the power of her thighs?
Betcha the average ballet dancer could kick your teeth through the back of your head.
 
The decomp lever DOES NOT come into play when you kick start an XS650 so fitted. If you try to use the decomp lever when kick starting, you will engage the starter motor! The decomp lever contains the electric starter motor contact!

As fredintoon suggests, any normal, able-bodied adult should be able to kick a properly tuned stock XS650 with the correct technique.
 
Thanks for all the input guys I really appreciate it. By sheer happenstance... I needed to buy new rocker arms. I went to a local salvage yard and he only had two rockers, both brand new, that both had the nub. I wasn't even thinking about a decompression lever back then and I put them on my exhaust valves. I remember thinking something wasn't right when I put them in, but they work just fine. I could kick this bike over just fine before I rebuilt the motor, but after the rephase and a 700 kit, it got kind of tough. Couple that with my kicker lever being bent to get around the rearsets, it gets really hard. I can do it, but I'm 6'5" and 225 lbs. she's 125... Surprisingly, this bike doesn't scare her and my norton terrifies her. So if we both go out, I have to start it for her. She doesn't ride it often, but it'd be nice if it would help. There is no starter anymore, it's gone as are all of the gears associated with it. Putting it back would mean splitting the cases again. I was thinking of doing the bicycle lever idea if it would help her at all. I know it's a little unorthodox, but we all like to have fun here, plus it's about to get too cold to ride. I just figured if it would work, it might be worth a shot haha
 
well.... i opened up my tappet covers and wouldn't you know it! Both of those nubbed rockers are on the intakes!!! looks like i might be pulling the head. you'd think that once in a while you might get lucky with SOMETHING on these bikes haha
 
DogBunny said:
The decomp lever DOES NOT come into play when you kick start an XS650 so fitted. If you try to use the decomp lever when kick starting, you will engage the starter motor! The decomp lever contains the electric starter motor contact!
Click to expand...

There is electrical and manual component to the decompression lever. Do not connect the starter motor through the decompression lever, just use the decompression lever connected to the rocker cover and then kick it over or use the electric starter through the right handle bar switch as per the 80 model.

If you don't have a electric starter motor then it will work the same using the decompression lever and kick starting

Some have used the electric starter in conjunction with kicking over high compression motors to make it easier to start, without the decompression lever
 
well i stopped by A and A cycle today in Oklahoma City and he traded me a bunch of scrap for the decompressor. it was froze up but after a four hour soak and a wire wheel it was working again. just finished polishing her up. ill let everyone know how it goes
 
well guys, for those who wondered, i got it working great, but the cable from mikes isnt very good. it sticks pretty badly, even after being soaked in oil. but what can you do, we have a local cable maker getting on one for me. we will see how it goes
 

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