XJ700x not starting - spark question

Hey all,

I recently acquired an 86 XJ700X that hasn’t ran in 8 years. After rebuilding the carbs, replacing the air filter, and changing the fluids i finally put a new battery in to see if it would start…. Which it did for about 10 seconds.

when it started on full choke, power seemed very low, reading just over 1k RPM before shutting off. When i tried to start it again,(on center stand and clutch engaged) the starter wouldn’t crank. It did however crank with the kill switch turned to off.

my question, could this be a spark issue? I am rather confused on how to test the plug when grounding to the bike. Am i supposed to do this while cranking in the RUN position? Also, will the plugs be wet when cranking with the kill switch flipped to off? I didn’t replace the spark plugs but rather i gently cleaned the carbon residue off(all 4 were black on the tip, insulator still white).

thanks in advance! And please go easy on me lol, this is my first post to the forum but i have already learned so much from you guys!

 

Welcome to the forum. If you have not ordered or downloaded a manual for your bike, I would. Just reading through some of the pages will help you get the mindset for working on your bike. The troubleshooting section will also help out a lot.

To get you stared. Yes, the kill switch needs to be in the "run" to make spark. Your battery has to be very good, some of the bikes will not throw spark if you have a weak battery. Removing the spark plug leads from the end of the wires to see if the copper part of the wire is green, white or looks like copper is a good idea. Trimming off a very small part of the end of each plug wire is a good idea, just don't go nuts, the wire needs to reach back onto the plugs.

If the bike has been sitting for 8 yrs, I would take the time to go through the wire connectors on the bike. Yes it is a pain but will remove a lot of electrical issue before you have to deal with them. One at a time remove the connectors and check to see how much chalk like stuff, white, green or just a lot of chalk like stuff there is. Clean off each side and then connect them again.

The "X" was the quick bike, has the 5 valve head from the FZ sport bikes if I remember. Good luck and keep us posted on your progress.

 

Hey Timbox, thanks for the quick response.

so i charged the battery up this morning (reading over 13v) and the starter turned over just fine with the kill switch turned to OFF. However, once I flipped it to run, i got nothing.

Tomorrow I’ll go out and try testing the starting circuit according to the troubleshooting guide. The hardest part of that will be locating the clutch and neutral switches. I’ll check back here with my findings.

i do have to a manual copy which i found on here though I’ll probably buy a hard copy from chacal eventually.

 

The output of the kill switch powers the starter relay (and ignition circuits) so with the kill switch off the bike will not crank - or run. So, either there is some operator error here, a faulty switch that somehow connects in the off position, some wiring changes by the PO, or a connector inadvertently connected incorrectly.

 

Hey Rooster, thanks for the reply but now my confusion has grown lol. The starter was definitely cranking in the off position (flipped down) but at that position i didn’t get any spark.

When i initially put the battery in yesterday, i flipped the kill switch to RUN and got nothing from the starter. After a few failed attempts (and jiggling some wires) i was able to get it to crank and start up for all of about 10 seconds. The bike wouldn’t start back up after that, but i was able to successfully test spark in cylinder one before it would not crank at all in the RUN position. instead, it crank’s beautifully and with ease in the OFF position.

I plan on checking connections tomorrow, but if anyone has an idea of where i should start that would be super helpful. I was able to get the starter to crank earlier in the run position by connecting a jumper lead to the negative battery terminal and the “L/W” wire on on the starter relay

 

That's encouraging for the starter and starter solenoid as it eliminates them from a no crank fault.

I would look at the relay assembly located to the right of the battery and look for wiring mods since the starter is cranking with the kill switch off. That relay is a combo relay containing the starter cutoff relay, fhe flasher unit, and the auto cancel unit.

Another really simple check is to check voltage on the R/W wires on the TCI, side stand relay, relay assembly, or ignition coils. That is the output side of the kill switch and should have 12V in the run position and zero in the off position.

 

So after some more testing i am now convinced that these stickers are in the wrong position. I was able to get the bike fired up numerous times today with it flipped down which appears to be the off position. (Unless im reading this wrong)

once started though, i wasn't able to get it to run smooth enough to perform a vacuum sync. I did follow the bench sync method i found in the “Information overload” but im wondering if i made an error?

Here’s what im experiencing when starting the bike:

with the choke on- low idle, have to open throttle to keep bike running.
i adjusted the idle screw so that i don’t have to hold the throttle and i closed the choke
At that point i get a ‘run away’ idle situation where the bike revs and revs upwards of 5000 RPM before i shut it off immediately.

If this is an air leak situation, could it be from poorly clamping the petcock vacuum hose? Where else should i check?

thanks in advance and apologies for any redundant questions that may have already been answered on other threads

 

Edit: i just pulled the plugs and they are all carbon fouled. Could this be caused by the Auxiliary tank constantly flowing?
also, could the high idle rev and the fouled plugs be caused by the same issue?

i plan to pull the carbs again to double check the fuel levels tomorrow.

 

Dang that's hard to read on that switch, but it should look like this:



If you pull the carbs be sure to double check the bench sync as that can cause runaway idle if they are not set correctly. You can use the paper clips as suggested or use the transfer port holes to make sure they are opening evenly. Hopefully the below pic applies to your bike as the photo is a set of Hitachi's from an XJ750RJ



The plugs are going to look very black if you are only running in the garage and using the choke a lot. However, if you have one fouled and not firing consistently then idle symptoms can be similar to what you are having. Be careful, but make sure all four pipes are heating to indicate all four cylinders are firing.

Church of clean? Did you break the rack? And the consensus is the stock paper filter works best on these bikes with the CV carbs.

 

yes and yes. I also bought the stock filter and carb rebuild kit from xj4ever, I’m determined to resurrect this beast and i want to do it right!

Also, thanks for the pic. My kill switch doesn’t have the engraved letters like shown in the image provided, but the stickers i have are definitely backwards…at least thats one less headache to worry about.

I’ll take the advice given so far and will check back once the carbs are reinstalled. Thank you so much for the guidance!

 

Hey so i pulled the carbs this morning and reset the fuel levels. I spent 3+ hours on the task, filling and draining and resetting the floats is very time consuming lol.

When i started the bike, same issue with the runaway idle, and i noticed the exhaust pipe for cylinder 3 was hot, but not as hot as the others.

also, and this may be user error, but ive been getting fuel leaking from the overflow tube between carbs 3&4. It happened before today and even though I reset the fuel levels and the needle is new, i am still experiencing this issue when I initially start up the bike.

probably gonna have to pull the carbs(again) but wanted to know if anything else could be causing the overflow besides the float height.

 

Hey wooly , just rebuilt a xj750 maxim x and had similar high idle issues. Did you replace the carb diaphragms ? If no did you check them for rips /tears ? Mine were in terrible shape and those along with a stuck needle ( even though they were from a new kit ) caused the idle and overflow leak. Very time consuming task to work on the carbs but that is where I would be looking again.

cheers !

 

Hey DC,

Thanks for the reply! I didn’t replace them but only because they were already in pretty good shape with no tears and holes. With that in mind, I pulled the carbs off today and upon removing the carb hat from carb#4 i noticed the vacuum diaphragm was not properly sealed! I guess not enough silicone lubricant was applied to hold it in place.

That explains the overflow problem (hopefully) but doesn’t explain the exhaust pipe on cylinder 3 not heating up in unison with the others. I trimmed the cabe lead for the spark plug cap but maybe its time for new plugs. I’ll probably end up replacing them this weekend after i reinstall the carbs, hopefully that does the trick!

 

I don't think the diaphragm will have anything to do with the overflow, perhaps others could weigh in here. Normally, an overflow condition is most likely a leaking float needle valve, or a misadjusted float.

Not sure you rechecked that bench sync as suggested so be sure you get that really close so the bike will idle better at the initial start.

if black and sooty I would agree just to be sure all is well there

 

Yes I believe the diaphragm issue would cause the high/inconsistent idle. The overflow leaking is forsure a pilot needle not seating correctly. Recheck again , if you have the carbs installed on the bike - while it’s leaking out the overflow if you take a small ( hitting tool lol I don’t wanna say hammer but ) and gently tap the carb bowls you may find the leak stops.

let us know what you find Wooly

 

I triple checked the bench sync and all is good on that front. I also rechecked the fuel levels and found out i was slightly too rich on carbs 3-4; after adjusting those levels i am now confident that i have the overflow problem situated.

with that in mind, i am still experiencing the runaway idle almost immediately after starting which is leading me to believe there is a vacuum leak somewhere. All boots to the manifold and the airbox are nice and snug, but upon further inspection I noticed that i may have installed the stock paper air filter backwards. Could that be my problem?

also, i realized i am missing the bolt that holds the airbox lid at the top, resulting in the lid not properly sealing on that end, closest to the carbs. Would this also be a potential area that could be causing my issue?

 

It could be yeah , is there a way to throw some duct tape on it and close it up to check if that helps ? It can be difficult to find a vacuum leak , you can try spritzing some brake clean around the intakes and carb lines while it’s running to find an idle spike and narrow it down.

 

Verify you throttle cable has a bit of slack so it is not pulling on the throttle plates with no throttle applied.

Are you sure the idle adjustment screw is backed out far enough? Start with it just touching (or not) and then push on the throttle linkage to make sure the throttle plates are closing all the way.

Not sure about the filter, but just put it in the right way and try the above. Normally, the bikes will idle OK even with the airbox boots not connected

 

Typically a runaway idle is due to an out-of-synch situation with the engine, although some other mechanical issue (such as a "stuck" throttle or choke cable, stuck or damaged choke plunger, or the idle-speed screw being grossly adjusted too far in, thus keeping the butterfly valves cracked open).

It's important to understand that a "bench synch" and a "vacuum (running-engine) synch" are two entirely different procedures, done for entirely different purposes, and besides the word "synch", have little in common with each other....and since the word "synch" (for synchronization) can have 2 different contextual meanings, things can become murky rather quickly if you don't understand the underlying concepts.

The "bench synch" procedure sets all of the butterfly valves open to a minimal and, importantly, an equal amount. The purpose of this process is to give you the best chance of getting an otherwise unadjusted / un-tuned engine to start and run under it's own power, no matter how well or poorly. Once the engine can run under it's own power, the entire bench-synch process and purpose has been accomplished and everything that was done to get it to that point needs to be forgotten, because......

The engine-running "vacuum synch" has an entirely different purpose, which is to equalize the power output (horsepower or torque, whatever measure you wish to focus on) of each cylinder, and to do so, each butterfly valve needs to (typically) be set at completely different openings (so that a "weaker" #2 cylinder, for example, gets a little more fuel because its butterfly valve gets adjusted to be a little more open than the others, so the power output of #2 goes up and equalizes with the power output of cylinders #1, #3, and #4......).

Engines (or more specifically, individual cylinders) which are "out-of-synch", power-output-wise, will create an internal power-struggle within themselves as each cylinder (or groups of cylinders) fight for control amongst each other, usually in a stair-step manner, ratcheting up the idle speed over and over until you get a "runaway idle speed" situation.

This is why the "vacuum-synch" (poorly named, but the concept is correct) uses some type of vacuum-gauge (flickering-needle type or sliding metal rod type) to measure the vacuum pull of each cylinder individually, as the strength of the vacuum signal is the simplest surrogate measure of how much power a cylinder is producing.

 

Thanks for replying everyone!

I backed the idle adjustment screw off and was able to get an idle at about 2k rpms. If i try to go lower than that, the bike tends to drop too low and wants to die.

i have a color tune plug along with the vacuum sync tool. Am i able to start the color tune and syncing process if the idle speed is not correct?

 

If it idles at 2000 you can hook up the synchronization and begin leveling them

 

thanks Simmy. I got all the carbs syncd, or really close to syncd at 2k rpms but i still cant get the bike to idle lower than that. I tried color tuning for cylinder one while idling at 2k rpms but with the mixture screw backed out 5turns im still getting a light blue color and i cant seem to achieve orange flames.

i know im looking for a bunsen blue color but wanted to see if i could use the orange as a baseline. I replaced all plugs too and all are pointing to signs of a lean condition.

after the color tune fail, i decided to gradually screw in all mixture screws until fully seated to see if it had any effect; the bike did bog down and die. This result leads me to believe that the pilot fuel circuit is in fact clean (took them to the church)

i then checked for vacuum leaks in all the obvious locations(manifold boots, throttle shaft seals, air box boots). I did this by spraying brake cleaner in all locations and did not experience any rpm increase. I’ll continue to check for vacuum leaks in the coming days, but anyone have any idea on what could be causing this high idle, lean condition?

 

Anyone have advice to share?

 

Are you sure that the brake cleaner you tested with was flammable? There are modern brake cleaner versions that are not flammable, so could mess up your results.

 

If you can't get a yellow/orange flame with the pilot screws wide open, you most probably have a partial blockage of the internal passage of the pilot fuel circuit......very common issue. A partial blockge will allow some fuel thru (but not enough), and of course you would still be able to kill the engine by screwing them all the way in (since that cuts off ALL fuel flow).

That, or something else is a problem within the pilot circuit (too small fuel jets, way too large an air jet).

 

hmm i thought i responded here already. So i pulled the carbs per your instruction and checked/cleaned the pilot circuit. I did this by removing the pilot jets and spraying fuel through the passage, with the idle mixture o ring removed and my finger blocking the main air jet.

Fuel forcefully sprayed out of all the tiny holes as a result and so i reinstalled the carbs. After experiencing the same issue, i decided to check the fuel level (again) with the carbs on the bike and below are my results. Would a fuel level this low cause my high idle issue? I guess i should've took Chacal’s advice to bribe someone to do this for me lol