XJ650 with cracked airbox, mangled jets, Input needed

Hi there,

I am new the forum out here in the Berkeley, CA area. I could use some input about a 1982 XJ650 I purchased. I have to say this is an awesome forum with lots of info. So I picked my bike from some guy who worked on it quite a bit. He said it was running (but not well) before he started working on it. He went through process of changing Head gasket, new brakes, fixed the wiring, and pulled the carbs for cleaning. After that he said he never could get it to run right and it was really hard to start. I got it for 250 bucks and decided to see what I could do. I have done this before with a GS550 which I fixed up and ride everyday. Anyway this is what I found and think is happening. I would appreciate any other input you guys might have.

I now get it start quite easily (new battery, new plugs). Initially all 4 cylinders were firing and then it dropped to two sometimes 3, (cylinders 1-3). Plugs 1 and 2 are all fouled (Black and sooty so it’s running rich). Carbs 3 and 4 had some black on them but not much, probably because they weren’t really firing much. All plugs do get spark so it’s not the coils. Initially (when all 4 cylinders were running) the RPMS were sluggish to respond to the throttle. Meaning if I revved it up and then down, it would take a little while to come down. That implies to me some kind of air leak around the air box or carb boots. Is this correct? Now of course it won’t idle since only 2-3 cylinders are firing.

On further inspection I noticed the air box has several cracks in it. I think the previous owner may have cracked it while putting those carbs back in and not known it. I know from searching the forum that replacing the air box requires moving the engine (something I don’t think I want to do). If I take some JD Weld and patch it up do you think that will be sufficient? The cracks aren’t huge but they go all the way through the box. Am I corrected in thinking that the cracks will be very problematic and cause the delayed response to the throttle? The alternative would be to switch to pod filters but I know what a pain that can be.

I also did pull the carbs and carb 3 and 4 were pretty dirty and had some mangled jets. I saw someone post a pic of something similar with the heads chewed up. That could explain why they weren’t firing as well. I will be ordering new jets from sudco. Has anyone used these jets? Are they generally made correctly and perform well?

One last thing, I did experience (which many of you have) oil/gas mixture spitting out my air box. But it didn’t happen immediately. I did leave the prime switch on for a while and forgot and started the engine. Could this have caused that to happen or did a stuck float cause this. I checked the floats and they all seemed to move freely but maybe one wasn’t sitting right when assembled. I don’t think too much oil was in the crank-case since it didn’t happen the first few times I worked on the bike. I will be changing my oil soon. Sorry for the long post but I appreciate your input!

-skm599

 

I'd go back to basics starting with a compression test. No point in doing anything else if the PO screwed up the head gasket.

Next you need to fix your fuel valve. It should shut off the gasoline when the engine isn't running. Gas in the oil indicates that it's leaking (or you left it on PRI which is a no-no).

Change the oil and filter.

Clean the carbs and set the float levels.

I'd just patch the cracks in the air box so I wasn't getting unfiltered air.

I'm to the point with Hitachi carburetors (which you have) where I don't even bother trying to pull the jets with a screwdriver. I go straight for the vice grips.

 

Hello SKM, welcome to the forum.
I'll start off with your first question. A floating return to idle does signal a leak somewhere or messed up mixure setting (I'll lean toward the leak though). Use a can of WD-40 and spray the liquid around each of the carb joints, when the idle smooths out and the rpms climb slightly, you have found your leak. There are other methods to doing this but I think this is the cheapest and most available.
A cracked airbox is not all that uncommon and will lead to throttle response problems as you surmised. JB Weld should work just fine. Removal of the box requires the motor be out unless you hack the box up. I would personally avoid the pods as you would then have to go through the hurdles of rejetting and setting up the carbs for them. Then the real work of tuning for the pods begins. What a pain!
I cannot attest to the fit or finish of Sudco parts but they do enjoy a very good reputation concerning carbs. Do consider our very own Chacal for XJ specific parts, he is the resident parts guy.
Your blow-by in the airfilter could be as simple as leaving the prime on, which typically fills the crankcase as well. If you avoided that, you are blessed in life. If you had a bad valve seat, chances are you found the issue. Change the oil straight away.

 

Wow thanks for the quick replies! I will get to a compression check as soon as I find my tools (I just moved here) and go the patching route for the airbox. Thanks for pointing me in the direction for parts. As soon as I get everything back together I will post what happens.

skm599

 

Enjoy Bezerkly, I sure did! (Come to think of it, I loved Orinda, San Leandro, San Jose, well, just about everywhere but the 980/880/80 and Oakland). There are a few other XJbikes members out in the bay area. Be sure to look them up and get in touch with them for guidance/assistance.
If you are going to JB Weld your cracks, be sure to gently sand the area on either side of the crack to give the JB some "tooth" to hold onto for a solid repair. Best of luck to you!

 

Update:XJ650 with cracked airbox, mangled jets

Well thanks for all your suggestions. I ordered new pilot and air gets. Clean everything. Went through each hole using a guitar string. Checked floats, bench synched and put the bike back together.

The bike started right up with no effort and now all 4 cylinders are firing nicely. I took it out for a spin several times. It seems to get better and better each time I drive it. It does hesitate off the line. Once the rpms get up to 2500-3000 then it really wants to go. Seems to be fine at speeds (actually runs really nice). It is idling at 1100rpms. It some times is slow to return to idle but that hasn't been consistent. Also when I started it this morning the idle jumped up to 3000 rpms or a 15 seconds and then settled down I did check for boot leaks and have not found any. I believe the airbox is completely patched now as well.

However I do know that it is running rich on all cylinders (pilot screws are all out 2.75 turns and plugs have soot all over them) I haven't had a chance to sync it (hopefully tonight or tomorrow I will). Can the occasional slow return to idle be due to bad air mixture or do I have leak somewhere else? Would this problem go away if I sync and colortune? I am under the impression that if there is leak somewhere in the system, that syncing and colortuning cannot be done correctly. So my question boils down to, Besides air leaks, what else can cause a slow return to idle after opening up the throttle?

Appreciate your input!

-skm

 

Slow return to idle indicates an over-rich fuel mixture. Lean them out a tweak and check the plugs after an afternoon of riding. Tweak as needed until happiness is located.
Or do it the easy way and purchase/borrow a Color-tune and do it right the first time.
I do not believe your problem is an air leak.