my maxim "get her running right" thread

Hello gentlemans and the few,
New rider/bike owner here, so here goes nothing.

I bought this 1980 xj650 that was quite a handful (for me). I paid $1500, in the hole another $600 with titles, tags and parts. The bike wasn't without issues, classic "you'd rather it be running rich than it running lean", dead battery, and would die on idle. Original owner demoed the bike to me, showing me that it indeed runs and shifts, me looking for a challenge, that was good enough. The chrome was still chrome, the tank's paint was still good.

First thing I got it, I bought a new battery, and a carb rebuild kit. I think I messed up the brake light switch unloading the trailer, by using the front brakes, so I got that on order as well.

I went in and tore into the carb, rebuilding the whole thing. Float heights were set to 17.5mm from the lower lip of the carb housing, no gasket, and a bench sync was done with calipers. Vacuum gages are on the way, I intend to sync the carbs once I get the bike running somewhat right. Mixture screws were set to 2.5 turns out.

O'reillys seemed incapable of giving me the right battery, even though it was referenced by bike model. Got lazy and took the battery box out. Save it for the next owners I guess.

Then ran the bike off some non-eth in a water bottle. Cyl 3/4 (couldn't tell) backfired real good into the carbs, I blamed that on none of the clamps being tightened, backed the mixture screws out half a turn, and moved on.

The next time I worked on the bike, I washed the whole thing with engine degreaser, put the gas tank on. Ever since then, on startup the bike would "idle" at 6krpm. Only today I found out the intake manifold boots had pieces of silicone falling out of it, pointing to someone had redneck fixed it before me, and the wash recreated the vacuum leak. I isolated the issue to not the petcock line, as it was clamped off, and the bike idled fine before I washed it. The thottle plates are also completely closed, I backed the idle screw all the way. Besides a leak, no idea how it would keep running.

I would appreciate any tips/tricks/pointers, and if I'm missing something important. Otherwise if the boots still doesn't fix it, next step would be valve clearances.

 

Considering the condition and the previous owner's fixes, I'd say the valves need to be checkd now. If the intake manifolds are really bad you probably will need to look for new ones. I think I saw one post where the boots were repaired with shrink tubing or tape. I'm sure someone will give you more info on that or a link to the site. Also check that the intake gaskets are good and not leaking air. (That was my problem.) If you took any short cuts on the carbs you probably didn't get them cleared and clean enough, especially the pilot circuit. (Learned from experience.) Syncing the carbs is also a must to get a good idle, and 2.5 turns out is just a starting point. I used a colortune plug and all of mine are less than 2.5. Every bike and every cylinder is different.

 

I have new intake boots on the way. Does the valvecover gasket need to be done when doing the clearances? Or is that reusable? Bike has 19xxx miles

 

You have a 1980 650 the mixture screw threads on those carbs mabye coarse threads and require less than two and a half turns out. Not sure exactly on the amount. But somebody will chime in and tell you. Did you replace the mixture screws with your rebuild kit?

 

If the gasket comes off clean and doesn't rip you can reuse it

 

Yeah I replaced the screws, threaded in fine. I doubt its the mixture, throttle plate is all the way closed and it still runs.

 

"Ya canny change the laws of physics cap'n...."
So, it needs air and fuel to run, it's getting both! So I would suggest mot all your butterflies/throttles are closed. Air/vacuum leaks alone won't do it.

 

Well darn. I got my wish.. kinda. I replaced the boots yesterday, went to fire it up and the battery was dead. Put it on the charger, and when I went to start it this morning, it doesn't run with the throttle plate fully closed, nor open. Very very light sputtering. I pulled the plugs, they left a light streak on my fingers when I rubbed against it, felt slightly moist. Out of ideas.
Should I increase the AFR and try again, or move directly into doing the valves? Kinda bummed because I'm getting my permit on Sunday, and am excited to take it out for a spin.

 

Yep, I checked today that the throttle was indeed all the way closed

 

ok I guess letting that full tank of gas from the old owner sit for a week was a bad idea. I fired her up off a bottle of non-eth and it ran an idled.

sarge, I guess I can.

It's time to do valves and tune the carbs. Throttle response is great with the choke slightly on, very sluggish with no choke. I guess I'll start from there. My plan is to stick an o2 sensor up the sniffer port and tune it that way. Colortunes are just so expensive, also I love my headaches.

 

O2 in end of the pipe will do you no good, your pipe is most likely a 4-2-2, in other words all the down tubes meet at a collector so your AFR readings will be a collective of all 4, and not individual cylinder readings, it would work only if it was all separate exhaust tubes, or a single carb.

 

if he has oem exhaust there are ports at the header pipes for each cylinder

 

Not large enough for an o2 sensor unfortunately..

 

The plan is to use the stock o2 ports. I'll make it work.