1978 XS750 high speed problems

[DGXSER]

Yep, if those diaphrams can not draw a vacuum, then your needle jets will never open up and you will starve for fuel no matter what jets you put in there.

I highly recommend going to cap screws if your keeping the carbs. Go to ebay and look up stainless steel cap screws. You can get a set for abou $16 for the tops and the float bowls.

[IanDMacDonald]

Looking for good diaphragms

Looking for good diaphragms for my '78 XS750. Looking for a decent price. Thank you.

Mac
IanDMacDonald@Live.com

[IanDMacDonald]

Just bought a set of "used" diaphragms off ebay. God, I hope they are in decent condition!

Mac

[cywelchjr]

Good luck. Those things if their out of the carb for any time tend to shrink, and getting them back in can be a chore. And new ones IF you can find them are often pricey, and in some cases ONLY come with the pistons. I'm glad mine are good, cause I hate to spend that kind of money.

[DGXSER]

I'm convinced they used a different material for these in the 80-81 carbs. I have worked on four or five sets now of the newer style and NEVER had a problem with shrinking diaphrams. However, the 78-79 set I am currently cleaning up, those were all messed up due to someone putitng the caps on with them not in the slots. They should straighten out, but I do notice the shrinking issue in these.

[IanDMacDonald]

Cam Chain Tensioner Help

Fellas-

I screwed up big! So, got the diaphragms today and got them to seat properly. Before I put the carbs back on, I decided to "mess" with the cam chain tensioner. Followed the book exactly. Found that I was unable to tighten the bolt properly. Figured something was stripped, pulled the bolt out and found metal shavings from where the case threads were stripped. Stupidly, I unscrewed the two screws holding the cam chain tensioner case, and pulled that off carefully. I re-threaded the case, and tried sticking it back on the bike, but now the shaft and spring will not go back in.
I need help, as I think this is my only obstacle to getting this bike going again. How do I get this back together? After I get in back on, will the bike have to be re-timed, etc.? I need a play by play on this one, as I am close to admitting defeat!

Thanks fellas,

Mac

[IanDMacDonald]

P.S. I have a shop manual to aid me in this process. I took off the valve cover and I am ready to put everything in it's respective place. Pretty sure I am just supposed to follow what the book says. But, that's what I did with attempting to adjust the cam chain tensioner and that flopped horribly. I am not that smart, so I plan on waiting for my buddy to help me out tomorrow while I am at work.
Any advice is much appreciated.

Thanks,

Mac

[cywelchjr]

If those on the 750's are at all like the 1100 ones, they are really easy to strip out. Make sure you don't have anything (I'm assuming you used a helicoil to fix the threads) going into the area of the shaft as that would keep it from going in. If you get that fixed up, then just following the book carefully should get it to work properly.

[Ken Talbot]

To reinstall on an 11, you loosen the locknut and plunger bolt, depress the plunger, snug the plunger bolt, reinstall the unit, release the plunger bolt, torque the plunger bolt to spec, torque the locknut to spec.

Any chance you were trying to reinstall it with the plunger extended?

[IanDMacDonald]

Of course Ken, otherwise the plunger not being extended would not coincide with my luck! Little things to learn before you go touching stuff that you have no clue about. I'm pretty sure after reading the book I have it figured out. I have to remove the camchain, make sure everything is lined up, reinstall the plunger, reinstall the chain, then readjust the tensioner. My next door neighbor is old school and knows about all of this (without a book), so he will be helping to make sure I don't bend a valve, etc.
Thanks fellas.

[DGXSER]

FYI, there is absolutely NO reason you NEED to remove the cam chain to reinstall the tensioner.

Now, you DO want to make sure all the dots on the cams line up with the arrows on the bearing pillow blocks at the same time the line on the timing pointer is aligned with the T mark on the timing plate. If those are off, you want to adjust and ensure you have all the slack out of the back side of the chain.

And BTW, I would not go turning the engine without the CCT in place, or pushing with your finger nice and tight on the guide the tensioner pushes against.

[IanDMacDonald]

Okay, DGXER, you were right, did not have to remove the chain, as it did not come totally off sprocket. I was able to get a long handled screwdriver and push on the chain and put it back on sprocket. However, my buddy has no faith in my re-threading of the cam chain tensioner case (I did not use a heli coil), so he told me to wrap a hose clamp around the tensioner bolt until I order another one. Make sense?

[DGXSER]

Okay, now I get it, the bolt you stripped the hole out of is the one in the side of the cam chain tensioner, the bolt that holds the slide in place. For some reason I thought you said case you were referring to the bolt hole in the engine that the tensioner mounts to.

If you do not feel the threads will hold, I would not even start the engine. If the bolt loosens, then the tension will not be applied to the cam chain and it can/will slip a tooth on the crank or the cams and you can very easily end up with a bunch of bent valves.

If it were my bike, I'd look for one of the automatic cam chain tensioner options like one form a V-Max, or a Venture and a few other models and put that on instead.

[IanDMacDonald]

Possibly bent valves

Man!!!!
Started the bike up tonight and I heard the clanking of either the valves or the cam chain. I'm not a mechanic, so I am not sure, but my buddy thinks I may have bent my valves when I ran the engine after I screwed with the cam chain tensioner. Is there an easy way to find out if I bent the valves?

[DGXSER]

Well, First, pull the valve cover off, and then the timing cover and manually turn the engine until the T mark lines up with the timing pointer mark. Then look to see if the dots on the cams line up with the markings on the pillow blocks.

IF they do, then you may not have bent valves. If they do not, chances are really good you do. From there, try a compression check if all lines up. A bent valve will not seal and you will see it in the compression check.