Can I eliminate my 72 compression realese.

[CalsXS2]

I just read the guys tappet cover thread and it got me to thinking.

I have a 72 that I want to put either 75 carbs that came on the 75 motor that I'll be using, or the EX 500 carbs. The 75 carbs and the EX500 carbs both use a single throttle cable I think. It's been awhile since I looked at them.

You guys said in the other thread that Yamaha figured out the compression release wasn't even needed. So could I eliminate mine and use my 75 carbs with 75 handle bar switch for the stater button. I wonder if the wiring will work.

 

[fredintoon]

Hi Cal,
does the bike still have the c/r handlebar fitting?
Do the '75 engine's rocker arms have the end nibs the c/r needs?
If so, I'd opt to keep the c/r feature just for it's cuteness factor.
But sure you can eliminate the c/r system and most likely the wiring will work with the '75 bar switch.

 

[5twins]

'76 carbs were the first with the linkage and a single throttle cable. '75 carbs would still be separate units (not bolted together as a "bank") and use two throttle cables. I'm sure you could adapt the '75 switch housing w/ the starter button. It will probably require changing or re-wiring some plugs, either the one on the handlebar switch or the one (or ones) in the headlight bucket.

 

[CalsXS2]

Hi Cal,
does the bike still have the c/r handlebar fitting?
Do the '75 engine's rocker arms have the end nibs the c/r needs?
If so, I'd opt to keep the c/r feature just for it's cuteness factor.
But sure you can eliminate the c/r system and most likely the wiring will work with the '75 bar switch.

The 72 has all of the original parts.

The 75 engine does have the notch in the rocker arm I got lucky there.

The only reason I waould want to eliminate it is because of the throttle cable situation. But maybe I can just make one a dummy cable for looks.

 

[CalsXS2]

'76 carbs were the first with the linkage and a single throttle cable. '75 carbs would still be separate units (not bolted together as a "bank") and use two throttle cables. I'm sure you could adapt the '75 switch housing w/ the starter button. It will probably require changing or re-wiring some plugs, either the one on the handlebar switch or the one (or ones) in the headlight bucket.

Truthfully I'm unsure of what year the motor is. I looked up the vin and some sources say 75, some say 76.

I do know that the carbs I have that came on that motor is linked together. I don't know if it takes 1 or 2 cables. I'll have to look. But it sounds like if it's linked it takes 1. And that might be an indicater that this motor is a 76. Right?

The motor does have the proper rocker arm for the compression release. I thought you, or maybe it was Gary had said that they stopped that in 75. What year did they stop that.

I got this motor in a pile of part's and I do have a single throttle cable set up. But the guy didn't know if it was right for these carbs.

 

[5twins]

Well, all the carb sets were somewhat linked together what with crossover hoses and choke linkages, but the sets that were bolted together solid as a "bank" didn't come along until '76. There would be an angle iron bracket connecting the lower fronts of the carbs. Older carb sets don't have the casting or tapped holes for that bracket.

A newer carb "bank" could be an indication of motor year but the way parts get swapped around on these bikes, I wouldn't take that or use that as my only I.D. factor. A better indicator might be the cam chain adjuster. I don't think those were as prone to being swapped around.

 

[CalsXS2]

Well, all the carb sets were somewhat linked together what with crossover hoses and choke linkages, but the sets that were bolted together solid as a "bank" didn't come along until '76. There would be an angle iron bracket connecting the lower fronts of the carbs. Older carb sets don't have the casting or tapped holes for that bracket.

A newer carb "bank" could be an indication of motor year but the way parts get swapped around on these bikes, I wouldn't take that or use that as my only I.D. factor. A better indicator might be the cam chain adjuster. I don't think those were as prone to being swapped around.

These carbs are bolted together with the angle iron bracket.

I'll take some pics later.

Is the rocker arm bieng notched an indicater. Do you know what year they stopped that.

 

[CalsXS2]

Here's the pics of the what has to be 76 carbs and the starter lever wiring. Does the wiring the same as the later years.

I appear to have a choice. I can keep the starter lever set up and hope the end of the throttle cable will work with the other carbs. And I'll jut have one dummy cable. Or I can use the later single throttle cable and hope the wiring is the same.

What sounds the best. Seems like 6 one way and a half a dozen the other to me.

 

[5twins]

That's a '78-'79 carb set you've got there. That could indicate you have an even newer motor than you think but like I said, carb sets are easily swapped. That carb set is missing the crossover hose (the two capped nipples) below the fuel line nipples. You should put that back on if you intend to run those carbs. It balances the fuel feed and keeps one carb from running out of gas if the side of the fuel tank it's fed by runs out.

I don't know when Yamaha stopped installing the compression release type rocker arms. I'm thinking they had a ton made and just kept using them until the supply ran out. People owning '73s, '74s, and '75s will just have to chime in here and tell us.

 

[XSLeo]

My 75 has the Compression release rocker arms. The 81 and 82 engines I have don't have the C/R rockers.
So somewhere in between these years.
Leo

 

[CalsXS2]

That's a '78-'79 carb set you've got there. That could indicate you have an even newer motor than you think but like I said, carb sets are easily swapped. That carb set is missing the crossover hose (the two capped nipples) below the fuel line nipples. You should put that back on if you intend to run those carbs. It balances the fuel feed and keeps one carb from running out of gas if the side of the fuel tank it's fed by runs out.

I don't know when Yamaha stopped installing the compression release type rocker arms. I'm thinking they had a ton made and just kept using them until the supply ran out. People owning '73s, '74s, and '75s will just have to chime in here and tell us.[/QUOT]

I think the carbs may have been swapped.

I could have sworn I looked up the vin and it said 75 or 76. I'll have to dig the motor and a check the vin again.

 

[joebgd]

Does the compression release make it easier to kick? I have the opposite ? if so. Can I put one on my 80?

 

[5twins]

The compression release wasn't used for or activated during kicking, only when using the electric start.

 

[XSLeo]

You can buy all the parts but to install the rocker arm you would have to pull the engine, pull off the rocker box, remove the tubes that run up into the rocker box so you can remove the plugs that let you remove the rocker arm so you can swap in the C/R rocker arm.
Seems a lot of work. There is a certain knack to kicking a bike over. Start with the key off, turn the engine over slowly to get one cylinder just past TDC.
Now let the kicker return to the top of stroke, now give it a good kick. No half hearted attempts, kick like you mean it.
Use your weight as well as your leg.
Once you get that down, do the 750 kit. This ups the compression from 8.4 -1 to about 9.5 -1, around 165 lbs. to 195 lbs. of compression.
On my 75 I rebuilt it as a second over and on the stand with engine full of assembly lube, cranked with starter. The 165 lbs. When I built the 750 engine under the same conditions I got 195 lbs.
A bit more to kick. Lots of fun though.
Leo

 

[CalsXS2]

That's a '78-'79 carb set you've got there. That could indicate you have an even newer motor than you think but like I said, carb sets are easily swapped. That carb set is missing the crossover hose (the two capped nipples) below the fuel line nipples. You should put that back on if you intend to run those carbs. It balances the fuel feed and keeps one carb from running out of gas if the side of the fuel tank it's fed by runs out.

I don't know when Yamaha stopped installing the compression release type rocker arms. I'm thinking they had a ton made and just kept using them until the supply ran out. People owning '73s, '74s, and '75s will just have to chime in here and tell us.

I've determined it's a 76 motor.

What are you going by to say they are 78-79 carbs.

According to the boats.net fiche the 76 carbs are linked with the angle iron. So what are you seeing.

Did the 76 have angled boots. These carbs have angled boots.

Whats the name of that website that sells good boots.

http://www.boats.net/parts/search/Yamaha/Motorcycle/1976/XS650C/CARBURETOR%20XS650C/parts.html

 

[5twins]

Referring to your pic #4, the external "tells" for the '78-'79 carb set are the two larger round holes at 3 and 9 o'clock on the intake bell and the absence of hose nipples on the float bowl bottoms for drain hoses from a bowl overflow pipe. The '78-'79 carbs had no bowl overflow pipe, hence no drain nipple for it. This change went hand in hand with the installation of vacuum petcocks. I guess Yamaha figured the vacuum petcocks would never allow the carbs to overfill so an overflow tube was no longer needed.

 

[CalsXS2]

Thanks for the education.

So the million dollar question is will they work on my 76 motor.

Here's an odd thing. The guy I got the motor from said when he bought it it was not in a running bike. So he rigged it in a stand to fire it up. He said when it started gas came pouring out of the carbs. Where could of the gas been coming from. Does this sound like a stuck float or what. Got any incite on that.

 

[5twins]

They would work on any 650 motor, properly cleaned and re-jetted if need be of course. Actually, I consider that set the best of the 38s. It was the last and most modern set produced. It has a new slide design with a spring-loaded needle which gives smoother running, especially in the lower RPM range. The '77 and older sets had a rather loose fitting and somewhat hard mounted needle. A large plastic disc simply sat on top of the needle and clip, holding it down into the slide by pressure from the slide return spring. As I said, it was a loose fit. With that plastic disc seated, the needle still has about 1/2mm of up and down play. That's half of what a clip slot adjustment does to your needle height. That means the needle is free to bounce around through half a clip slot range of adjustment during operation. Obviously, that's not going to make for very precise fuel metering. It is most noticeable from idle up into the lower RPM range. These older carb sets run rougher through that range than the '78-'79 set.

Yes, it sounds like a stuck or bad float needle and seat. Gas comes pouring out the carb throat because the overflow tubes in the bowls are gone. Instead of coming through those and out the drain nipples on the bowl bottoms (also missing), the fuel has no where else to go but up into the main bore of the carb, gurgling up through and out of the needle jet. It can (and sometimes does) also come flowing out the two little air jets on the intake bell.

 

[CalsXS2]

Hey 5twins. I.m getting ready to polish my hubs and wand to paint the middle black like you have done. Can you point me to the thread where you talk about it. Thanks

 

[5twins]

That wasn't me. I leave mine natural aluminum, just bead blasted to clean them up.