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Bike will not start for nothing! Help please.

5538 Views 22 Replies 8 Participants Last post by  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,
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Oh also the points and condenser are brand new.
Oh and i have good spark and fuel flow aswell.
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?
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?
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
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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?
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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?
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?
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.
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
First engine rebuild. My mistake makes sense now. Bought two kits that would not fit. Any links for a correct kit?
Honestly i am unsure i could dig them up and take pictures. Father purchase and just threw them in a box with the bike. They seemed original like from the 70s so maybe they shrunk. Im gonna purchase new gasket set and tear apart and rebuild with proper gaskets in like a week in a half. Moving onto base and will finally have a garage.
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