[nhps]

Hello All,

I have tried other forums and have not yet found much luck. Did a quick google search and found this forum hoping for some help from everyone!! So i got a 1977 XR75 for free that supposedly ran when i was parked. Ya ya ya we've all heard that one before. Well is sat for idk i think they said 10 years? Motor was not seized though. Let me tell you what i have done and please advise me on what else i should try. Compression was a solid 35!!! so i did a top end rebuild and had the cylinders honed and purchased new pistons and new rings. Installed and psi is roughly 130 good now it will run right? still no luck. I have ultra sonic cleaned the carb three times now completely diasembling it and ensuring all passages are clear. I have tried start with an air pod and with OEM air box and still nothing. I have checked valves and set them to .002 which is what i read somewhere on this thread. I have ensure that it is top dead center. O on cam sprocket is at 12 o clock piston is all the way up. I have gone as far as removing the advance timing lobe from the inside of the fly wheel and moving it 180 to see if for some reason previous owner has done this. It basically will just act like it wants to start but never get there. It will back fire out of carb at times and it will fire out exhaust at times. Any thoughts?

Thanks alot,
Dylan.

 

[nhps]

Oh also the points and condenser are brand new.

 

[nhps]

Oh and i have good spark and fuel flow aswell.

 

[johndjmix]

Backfiring out the carb should *never* happen.

Timing is off. Either cam or ignition somehow.

You positive it's not 180 deg off?

--John

 

[rm25088]

Sounds like a timing issue.

 

[nhps]

A timing issue is what i have come up with to. Idk if its the advanced timing or just regular timing. tomorrow im gonna hit it with a timing light again and see where its lighting up. Where exactly on the flywheel should it be lighting at? And like i said i flipped the advanced timing 180 on the advanced timing lobe and i went 180 out on the cam to. Maybe im wrong and i didnt and it is 180. But when i have the O at 12 o clock the piston is at the top and the lobes of the cam are facing down with no tension on the rockers. Isnt this right?

 

[elixur]

U sure ur points are set right?

 

[nhps]

My father installed the points and condenser. Im not really sure what there is to do with them except for what the manual says. I verified it opened at the marking it suggest and that it closes at the correct position per the book I also checked the gap of the points at its widest points. I will double check the tomorrow as well. Is there anything else about the points i should check?

 

[my67xr]

My father installed the points and condenser. Im not really sure what there is to do with them except for what the manual says. I verified it opened at the marking it suggest and that it closes at the correct position per the book I also checked the gap of the points at its widest points. I will double check the tomorrow as well. Is there anything else about the points i should check?

With the timing,
was the cam 0 marking lined up at 12 o'clock when the T marking on the flywheel was lined up with the marking in the case ?
Then you tightened the cam chain tensioner, next start the engine and readjust the tensioner

 

[nhps]

I will also check the flywheel marking with the 0 at 12 o clock. But I can't do the next part cause the bike won't start yet. Thanks you again for all the relies. I'll report back with more information in a few hours

 

[nhps]

So it is top dead center and the calves are set to .002 but on my flywheel my is nowhere near the mark on the case. Is this my problem? How do I fix this?

 

[nhps]

Okay so i realize that i messed up when putting the motor back together and this will most likely cause te timing to be completely wrong. Disclaimer this is the first motorcycle that ive completely tore down as i wanted to learn. So i took the cam sprocket off and re adjusted so 0 is at 12 o clock, piston is all the way at the top, the T mark is lining up with the case marking. I go to turn the flywheel by hand and it opens the exhaust port first and then once it gets to the intake port right before it hits the peak of the intake lobe it stops. It is deffanatly hitting something. there is no turning it. What do you guys think?

 

[spiz5]

Dont force it, the piston is hitting the intake valve and will bend if you force it. I see one of 3 scenarios:
1. You already bent the valve from your prior mistiming it, and its hanging open and piston is hitting it.
2. Your flywheel key is sheared and its not clocked correctly on your crank.
3. You still dont have it timed correctly.

 

[nhps]

Im praying number one isnt the issue. I dont think its number 2 as i just installed a new flywheel key yesterday as the last one was shear. Im hoping that the timing is just off slighty. Tomorrow i am going to remove the top end so i can take a look at the valves. Unless there is another way to check?

 

[nhps]

I believe i know why it was hitting but it makes absoluetly no sense to me. Maybe someone here can enlighten me. i tried playing with the tension and moving he chain one tooth in both directions to see if that would help and all it did was change where the motor would jam. Took the top of he motor of and could see that when i turn my engine to TDC it does not fall on the T sign but instead is like 2 inches to the right of the T. My woodruff key is in good shape. For giggles i tried adjusting the cam to go along with the new mark i made on the flywheel for true TDC. The engine was no longer hitting anywhere through cam motion.

 

[spiz5]

Pull the flywheel and check key again, thats the only thing it can be.

 

[GSjimmy]

OK, your way off the timing mark. It is at the 2 O'clock, small triangle cast into the case.

So assuming that you didn't bend a valve, you have to reset manual timing on the engine. Start by removing the upper (cam) sprocket and setting the "T" onto the timing mark cast into the case. Next, reset the cam position to the lobes up position (no valves open). Install the cam chain and sprocket onto the cam. The bolts will be parallel to the head surface and the "O" mark will be straight up. Torque to spec using loc-tite blue. (Guess what happens when a bolt backs out!)

Set the chain tensioner to remove any slack in the chain.

Rotate the engine over by hand. If you get any binding stop and track it down.
If everything lines up with the marks, you can start thebike. Leave the flywheel cover off to verify timing & points.


Points

You can remove the timing advance from the flywheel andinstall it to the crank to set the points with a feeler gauge. Or go thru thewindow of the flywheel if you grind down the correct gauge to fit into thewindow. Just rotate the flywheel untilyou can see the points open.

 

[nhps]

Okay so update. Pulled top of motor and the valves are deff not bent. Reinstalled and re timed the engine again. Fooled around with it for a while kicking and its started for like 2 seconds then died. Went to kick it over again and I hear a loud pop. It shot a piece of my head gasket out the side. Compression must be good. This is most likely due to the gaskets being home made sense both of the gasket kits I purchase did not line up even close. Doesn't anyone have a for sure good gasket set that works for a 77 xr75

 

[spiz5]

This changes everything. You cannot use a home made paper head gasket, most other paper gaskets sure, but not a head gasket.

 

[nhps]

First engine rebuild. My mistake makes sense now. Bought two kits that would not fit. Any links for a correct kit?