Project thread 81 XJ650 -750 motor

Got the bike from my other post for 200$ and have done alot to it.

I Stripped it down to frame, noticed a lot of missing bolts, and other stuff. Painted the frame and swing arm. (not takeing the swing arm off next time). Put it back together. made my own wiring harness, because the original was cut up by the P.O. got the head light, tail light and blinkers working with indicator lights. got the coils and pickups working with the TCI box.

The exhaust is a pain to put back together, never separating header pipes from collector again. Still not fully together, but all of them are in about 1/8".

I didnt have an air box, was thinking of going with a manifold than pods out the sides, but my buddy just happen to steel mine durring transport. so now that the bike is fully together, i have an air box... lovely. but even without the airbox in the carb boots should alow the bike to start?

The carbs that i have are jetted for a 650 bike. i know i need to jet them for a 750. but the bike should at least run with the 650 jets. Right?? I cant get it to run. i got the motor turning over, i can feel suction and pressure. I can get it to start up but not stay running with starter fluid. (it sounds beautiful with new oil and clean exhaust.) all the valves are in spec!!! (so happy about that)

Tl;dr; 750 motor, with 650 carbs. no air box. cant get to stay running. only revs with starter fluid than dies. what should i look for? and if i need to put the airbox in, it is going to get cut than "welded" back together. im NOT taking this bike back apart for atleast a cupple hundred miles.

 

If it runs on spray, but then dies........you're not getting fuel through the carbs.

Is:
there gas in the tank?
the petcock vacuum line hooked up the petcock?
the vacuum line hooked up to the vac. port on the intake boot?

Have:
you TOTALLY gone through the carbs?
wet-set the floats?
checked the fuel rail for clogs?
totally cleaned the enricher circuit?

Open the bowl-drain screws and see if there's gas in the bowls. If not, you're not getting fuel. If there is, you're not getting any through the starting circuit

Airbox:

Don't cut it...........get a heat-gun, slowly and carefully soften the sides and the bottom. then fold it up enough to slip into place. Heat it back up and straighten it out. Put the filter back in, put the lid on...Finish closing her up.

Exhaust:

If it's that difficult to get the pipes back in.....

did you:

loosen the bolts for each pipe collar on the collector box?
replace the exhaust pipe gaskets at the bottom?
clean the pipe inlets to the collector box?
replace the muffler gaskets?
clean the collector box outlets?

If you haven't cleaned everything, you're going to have rust and dirt in the way. If the pipes and inlets are clean, then new gaskets will slide right in and the pipes will slide right in..

An 1/8" inch is NOT very much.

Now, if you HAVE done all that, and you STILL only get 1/8" in, then my next question would be----do you have the right pipes? If they are literally too short, you may have an issue with trying to put 650 pipes on the 750 engine. They'll fit at each end, but may not be long enough overall. The 750 engine is slightly taller, so the pipes are slightly longer.
The 650 maxim did not have a collector box.....two pipes went to each side, there is a "2-into-1 end" on each muffler assembly, and there is a cross-over pipe between the two. The 750 maxim has an actual collector box. The leading edges of the box may also be at a slightly different point than the leading edges of the 650 unions, too. So in short, 750 engine, 750 collector box, 750 pipes, 750 mufflers....THAT should all fit together.

Dave Fox

 

OK, whent down your checklist. my buddy "said" he cleaned and prepped my carbs (we switched cabs (i dont remember agreeing but anyway)) i cleaned and preped his carbs, set the floats, bench sync etc. and he did a half ass job on mine.

So that was step 1. still didnt start, i did manage to squeeze the airbox into place, the heat gun trick worked nicely, thank you. and still didnt start. to get to the point, i forgot to put in the gaskets behind the carb to motor boots and tighten them down.

got the motor running !!! now i am trying to figure out the throttle responce. once the bike warmed up i tried the throttle and it revved up and stayed there for a while than came down, altho i only hit the throttle for a little bit.

the exaust i had the left and right sides swapped. once i swapped thoes, it went on pretty easy. still not drop on, they needed a little work, but they are in!!

all thats left to do is fix up the breaks, and figure out the throttle issue.
Can the rear break piviot go in when the swing arm is in?
What would cause the throttle to "Stick" for s little?

 

ok update... Thottle Sticks still. When i blip the throttle it revs for longer. i am going to blame proper cable routing. testing that soon. thought of that while typing this.

No Rear Break. Is it Possible to put the pivot in with the rear swing arm?

and Clutch sticky...up on center stand, in gear with clutch fully pulled tire spins. thought i wasnt getting enough pull, so i tried putting a wrench right to the lever at the case. and that didnt help. i am running 20w50 conventional.

 

ok fixed my clutch, didnt have good oil... i guess when i porred the new oil in it cleaned out everything and the oil picked up a bunch of crap. so i needed a second oil change.

i took the bike out for a 1 mile trip to see if i could figure everything out. it helped. needed air in my suspension. and have a vacuum leak. fixing the vacuum leak tonight, and fixed the suspention yesterday.

i found out my transmission is backwards... Its 1 up and 5 down. so it took a little to get used to that.

 

got new intake gaskets and air jets in on the bike. runs so much better. dont know why it didnt start after 15 minutes of being on prime. but the next afternoon it started right up. It was a great ride for what it is. for the first 25 miles, no new problems. than my front break locked up on me.

Why would my front break lock up? i fixed it by cracking the bleeder for a second, and than closing it, and it was fine.

still need new roller bearings to make the steering strengthen up. every bump would try to rip the handlebars from my hands. the exaust sounded great.

Why would my bike loose a lot of power and die out for a tenth of a mile. than run normal?

Still need to vacuum sync my carbs, hopeing that will fix most of my issues? slo what size bolts are the drains in the carb?

 

BECAUSE IT NEEDS TO BE REBUILT. Like all of the other critical systems on a 30+ year old motorcycle.

It locked up because the caliper needs to be thoroughly cleaned and the seals replaced. The brake is dragging (because the caliper is not releasing fully) and as it gets hotter the fluid will expand (it's old and has air/moisture in it) making it drag even more and eventually lock up. All you did was momentarily alleviate the extra pressure.

RE: Transmission "drag" in a cold motor: the rear wheel WILL spin even if the bike is in neutral. And you cannot effectively "operate" the clutch with pliers on the throwout lever.

RE: Vacuum sync: not until you get the valve clearances in spec.

The idle is "hanging" because you're not in sync yet. Did you WET SET your float levels?

 

ok, Plan is to replace old rubber lines, with new stainless steel lines, rebuild the caliper, and master cylinder. I did put in fresh fluid before driving it.

The Transmission was dragging because of already burned oil. i was trying to drive my bike in 5th, wondering why i couldn't find neutral and why i had no real power. than realized that my shift pattern is upside down, 1up4down. i replaced the oil + filter and now it works well. (still alittle drag but not excessive.)

My valves are in spec, i was surprised when i opened it up. even on the old 650 motor they are in spec. so i have 2 motors ready.

The hanging idle was fixed by the correct intake gaskets + jets. was running WAY to Lean. now it is pretty snappy and responsive.

It doesnt look to hard rebuilding the MC, it just looks tedious. and replacing the lines is a good idea anyway.

I also am going to rebuild my petcock on the 750 gas tank, so that i can use it instead of my 550 tank. on the 650 frame. i already got offered 1000$ for the bike at the gas station. i bought it for 100$, friend went half of 2 of them + parts, 10$ in paint, 40$ in oil + filters, 80$ in gaskets and jets, 20$ misc. (carb cleaner, simple green, shop towles, acid, etc.) so i am doing pretty well, new break system will make it even better.

 

Ok, update on the bike. Rebuilt the Petcock. working really well. cleaned up the inside of the tank with bb's and tried using electricity. worked pretty well. I like the feel of this tank compared to the 550's. i need to repaint it thoe.

This winter is going to be an expensive one. (i already have to sell my 550) but that money is going into this project. I plan to powder-coat my frame + swing-arm. polish my suspension, new head bearings, new break system. and it is going to be mostly cosmetic work.

This bike has come along way and i couldn't have done it without this site, or Len, so thank you, not just this thread but all the people on this site.

to all in the NorthEast be careful out there, lots of leaves on the road, and they are Slippery.