85 XJ700 Maxim is now lurching and miss-firing

Hey guys, I’m new to the forum but will only be here a little while. I recently purchased a 2012 R1 so once I sell my ’85 Maxim I’ll be on my way.


So here’s what is going on: I have a 1985 XJ700 Maxim that I’ve had for about a year. It’s always run great with no problems whatsoever. The only things I could list as con’s would be that it has always been cold blooded and so I always warm it up good before I take off, and then the second thing is if I’m at a stop light I can tell it’s running a bit rich (you can smell the unburnt hydrocarbons) but it’s always run strong with no issues. Anyway, about two weeks ago I took it for a ride and at the beginning it was lurching and missing (after I came off the choke), but smoothed out at speed. Once the bike was warmed up, approximately 20 minutes, I had not further issues starting or during riding. Although I was worried because it never had done this before.


Well, this week I went to ride and the bike started normally on choke and I let it warm up as usual, but when I got on it, put it in gear and gassed it (choke was almost off at this point) it did the same lurching and missing only this time it back fired once or twice too. I tried riding it up and down the block (it stalled out a couple of times) and made sure the choke was completely off but this time it wouldn’t stop this issue like it did the week before. The funny thing is that it will sit there and idle normally, even if you rev it (not low revs, they are rough), but when you put it in gear and put a load on it she just bogs down and starts to lurching and missing.


Now all I’ve got is the XJ650 manual which is a little different, but I’m trying to use it to troubleshoot. First thing I did was assure I have fuel, check. The battery is kinda old so I replaced it with a brand new sealed Interstate battery ($110!!), check. Tried running the bike again: exact same issue. So I’ve verified the timing plate under the cover is not loose, check (the plate and pickups look like they’ve been replaced in the last few years as they are clean and shiny). I’ve verified that the choke is operating on all 4 carbs and that they release completely, check. And I verified there was no binding on the throttle linkage to the carbs, check. Still same issue. So next I’m going to check the timing and see if it is advancing correctly (I suspect that it will be fine at idle since the bike idles normally, one possibility is that it’s not advancing due to a bad TCI??) And I would have checked the timing first but my kid borrowed (took) my timing light so I had to buy a new one today.


So has anyone had this problem or can take a stab at what you think it might be?? Also, I know I can ohm out the coil primary and secondaries which I will also try.

 

Start with checking valve clearances.
http://xjbikes.com/forums/threads/airhead-valve-adjustment-with-pics.14827/

I wouldn't mess with any timing right now.

 

Time to clean the carbs. Don't think you can change the timing.

I have the same bike and except in cold weather or if it has set up for a week or so I don't have to use the "choke." Even when I use the choke, it comes off within a minute. My bike ran very rich when I got it--the plugs were black and it was hard to start. I cleaned the carbs really well--took a couple of efforts since I was new to bike-, adjusted the valves, used a colortune plug to set the pilot screws, installed new plugs and all's well. In addition to running well the mpg went up significantly. My bike is bone stock and your's appears to be, which is good and will make it much easier to get it running well.

 

You are right in that the timing can't be changed..., it's all controlled by the TCI. I suppose it could be the carbs because it just seems so weird that it idles well but then starts to cough up a fit when you put the gas to her. I probably won't get to this until Sunday at least but my plan will be to check the timing, install a new set of plugs (I have an extra set and remember I'm trying to sell the bike so I don't want to put too much work into it, but I also don't want to leave someone with a mess!) and then I'll try it one more time before I decide to rip the carbs out. Do you know it there is a drain plug in bottom of each carb? Maybe I can flush them out first. I'll keep checking back here but I'll also touch bases with the local Yamaha mechanic and see if he has any suggestions too. I guess if the timing is correct and seems to advance when rev'd then the carbs might be the next step.

My bike's the same way with the choke: I probably only move the lever 1/4 inch to start it then it will run there at a high idle for a minute or two and I can immediately bring it almost off..., I usually have it slightly open when I start riding and within a few blocks I take it off..., of course this was before all the latest BS.
Thanks

 

You can NOT properly tune your carbs, regardless of how clean they are (and replaced rubber components) without having your valve clearances in spec.

I recall backfiring being a symptom of out of spec valve clearance. . . . ?

If you want to sell the bike perhaps you would be doing the 'next in line' a favor by not rushing through things. You don't want to be dubbed The Dreaded PO, do you?

Or put it on Craigslist, be honest about its conditions and ask a fair price. That way you have more space in your garage, money in your pocket and the 'next guy' has a certified project bike that he/she can cut their teeth on (just remember to tell whomever you sell it to to come to this site).

 

Today I had a little extra time so I checked the timing: the bike idles just fine and timing was within the correct limits. When you use throttle the timing advances significantly so everything there is fine. When the bike is at idle there is no missing and everything sounds normal, but as soon as you crank on the gas it starts to miss and if you put it in gear and try to get going the bike has no power and sputters (lurching and missing). I tried moving the petcock to prime to see if that changed anything but still the exact same issue.

So do you guys agree that this may indicate a carb problem? Could the valves (one or more) go out of tolerance within a span of two weeks and would this give the same conditions as I'm seeing??

My next step will be to pull the tank and drain it to see if there are any contaminants or fuel feed blockages but the tank looks super clean. Then I'll drain out the carbs and shoot some carb cleaner into any openings I can access without pulling the carbs off: lube all linkages etc. and then with fresh petrol see if that changes anything.

My biggest question is do you guys think that the issue sounds like a carb problem or something in the ignition (like a weak spark)? And I agree that if the carbs come off I'll also check all the valve clearances.

 

Nice bike. Sounds like a issue that didn't get fixed then progressively got worse. Stump is right...the valve clearances must be in spec in order for it to run right. Are you sure there's spark on all four? How old are the plugs? Have you checked the gap on them? Has the clutch been rebuilt since you've had it?

Gary H.

 

hobojo, nice bike !!

just curious, you said you had the bike for a year, was there any maintenance done on it after you became the owner?
I see you are in Olympia, I used to live in Kent, just curious, how was it stored for the winter time?

@tabaka45 +1Time to clean the carbs
@Stumplifter +1 Start with checking valve clearances

and if you don't want to spend effort on it, do exactly what stumplifter said..... Or put it on Craigslist, be honest about its conditions and ask a fair price. That way you have more space in your garage, money in your pocket and the 'next guy' has a certified project bike that he/she can cut their teeth on (just remember to tell whomever you sell it to to come to this site).

Good luck

 

Uh.... Yeah---- that's why we've said that several times.

The shim clearances don't go out of spec in a week or two---- they continue towards going out of spec from the time they are installed. They WILL eventually be out of spec due to length of running and time. If you never checked yours, you have no idea when, if ever, they were done.... What the clearances were, what shims are in there now, etc...... So, you may very well be waaaay past due and you finally reached the wall.

But yeah, carbs gotta be done..... Shims need to be done FIRST, or else you won't get a correct sync.

Just on a lark, though, try simply new plugs AND a new fuel filter, along with a dose of seafoam.

Dave

 

Got it! I'll start by cleaning the carbs.

 

The only things I've done to the bike since I got it was oil/filter change, serviced the K&N air filter, and replaced the plugs. And I store the bike in my garage which is heated.

 

Um.... you missed the point. Start by checking and adjusting the valve clearances.
And ditch the K&N, they tend to make the bike run lean. Get a paper element filter. EMGO makes a quality direct fit air filter at a reasonable cost.

 

Re-read

 

Well..., let me tell you that the carbs haven't been taken off this bike in a while. Now since I'm planning on selling this bike I just pulled the carbs and flushed them out real good with carb cleaner and then gasoline. The only thing that was amiss was one of the boots had been improperly seated so it's always had an intake leak on #2 cylinder. On Wednesday I'll reinstall the whole mess, put the new plugs on and see if that fixed the problem. I hope I don't have to pull them again to rebuild them but I'm going to take a chance. I'll also clean all the molex connections before I reassemble the air box/battery box section as they are all kinda dirty.

The boots from the carbs to the airbox were a witch to get out: I hope they go in easier. Here are some pics of the mess...,

 

Well, I got the carbs back on. I did find two neat little tricks I should pass on: the first one is using a household vacuum cleaner to check the CV carbs…, you can hold the vacuum on the discharge of each carb and verify the main slide moves up freely without having to pull the top covers off and visually inspect the diaphragms. The second one is to lube the boots while they are still on the breather box and then shove them into the breather box…, this gives you just enough room to remove the carbs. I took all the boots off and they were a pain to put back…, in fact #3 has the choke cable going right past it and the only way to put the boot back on was to start with it pushed into the breather box.


Okay, so anyway I could find no issues with the carbs while they were off. I could shoot carb cleaner through all the orifices and there were no plugs whatsoever. But I cleaned them up real good and put them back. Then as I was reassembling the bike I cleaned all the electrical connections I could get to and then ohm’d out the coil packs. Remember that the bike idled good but had no power when you came on the throttle…, also the timing was correct so that is why I assumed it was a carb issue. So the #2/3 coil pack was fine (2 to 4 ohms in the primary, and 20K ohms on the secondary). When I went to pull the cap off #1 plug it came off in my hand. So I cut the wire a little shorter and tried to ohm it out and the primary was good but the secondary was open. So I have a new coil on order which should be here today and I’ll get it installed. I also replaced all the plugs and you could see it had fouled up #1 & 4. So I’ll wait until I run it to say it’s fixed but I believe the bad coil pack was the issue all the time. The dumb thing was $190 from Yamaha as I couldn’t find an aftermarket one.

 

How do you know the condition of the diaphragms, springs and air jets? My bike had a bent spring under one of the hats. $190 for a coil...ouch! Did you try Len?Did you remove both caps to ohm out the coil (it could be a bad resistor)?

Gary H.

 

1. Normal procedure is to push the boots into the airbox but glad you found out

2. Even easier than getting a vacuum...... Just blow air into the "Kidney bean" shaped orifice

 

Have you checked the resistance of plug caps should be 5k ohms. Common problem that is overlooked