XJ700N Spark Plugs

Happy Friday everybody!!

The attached images are from my 1985 XJ700N (airhead) plugs.

I just wanted to see if anybody could notice anything funky about these plugs. I know some people can look at plugs and diagnose problems - I'm not there yet.

Back story: The 700N I acquired this spring kind of runs like trash (especially compared to my 650J). Valve lash has been adjusted to spec. Carbs are on their way for a vacation in upstate New York with @hogfiddles. While the carbs are out for a little therapy I plan to install new intake boot gaskets, nipple covers, vacuum line, and fuel line. Intake boots seem to be OK - no cracks or anything.

The one thing that I noticed right away was that somebody numbered the plugs 1-4, but they were not installed in any particular order. That makes me think this bike has run like trash for a while and somebody was trying to troubleshoot it, got frustrated, and sold the bike to me. The plugs don't look all that much different to me - maybe somebody was expecting one of the cylinders to be way rich or lean and couldn't find it.

I'm kind of hoping @hogfiddles finds an old wasp nest or something in the carbs that explains why it wasn't running well - that would be the easy fix. Somebody has definitely been in the carbs before, so maybe they just plain f#$%d them up.

What exactly do I mean when I say it runs like trash? Here's what I notice:
1. Cold start is hard - enrichment circuit seems to do very little.
2. Random stalls at stoplights and such. Makes bike not so fun to ride since sometimes getting it started again is difficult. If your bike stalls at a busy intersection and you can't get it restarted, you're gonna have a bad time.
3. Some idle creep when hot

Any ideas for what to check/do while the carbs are on vacation would be appreciated.

 

I also have the 85 XJ700N. I had all the problems you mention. So here are my comments based on my experience and getting my bike to start, run and idle very well, not to mention a substantial increase in mgp.
1. Cold start problem was mostly solved by a full cleaning of the carbs. Hogfiddles will get that done for you. But after getting your carbs back it will still be up to you to fine tune the pilot screws. More on that latter.
2. I had the exact problem. It turned out that the alternator was not putting out enough voltage at idle, and often just hitting the brake light at idle would shut it down. Then it would really be hard to start if it started at all. I installed new brushes and the problem was solved along with the hard starting. Check your voltage at idle--should be in high 12's if not low 13's. At 3000 rpm you should see around 14 or better.
3. Idle creep when hot could be an air leak that opens when hot. Check around the intake boots and elsewhere for leaks. When you say idle creep, how high? in addition to valve adjustment you need to check your carb sync.

When you receive your carbs the pilot screws will probably be set at 2 1/2 turns open. Every engine is different, and every cylinder of every engine can be different--that's the reason for syncing the carbs. Here is how I got mine set as close to perfect and I can get without some very expensive equipment. Get the bike running and sync the carbs. Attach a colortune plug to one cylinder and get the bike at warm idle with no choke (or enrichment). Close the pilot screw until you see flashes of white indicating a lean setting. Open the screw until the white goes away. Repeat for every cylinder. Install new plugs and take a ride of 15-20 miles. Remove the plugs and see what they look like. You are looking for a light gray or brown on the porcelain. If a plug is all white open the pilot screw about the width of a dime. Repeat for all cylinders. Take another ride and repeat the process. Continue this process until all plugs have a nice light gray or brown color. Each cylinder can be different. My pilot screws settings range from a little more that 1 3/4 and a little over 2. It took me a couple of weeks and several rides to get all the screws set. If you do not have a colortune plug just start at about 1 1/2 turns open and adjust. Just not long high speed riding until the plugs look good. You will like the results.

Good luck.

 

Thanks @tabaka45 . Really appreciate it. I figured that I can't be the first one struggling with this.

I will definitely incorporate all that into my plan. I do have a colortune on my list of things to order from @chacal next week.

My idle creep goes up to about 3k. To be honest, I don't know if I'm just adjusting the idle too high so that cold starts don't suck so bad, or if there is an actual idle creep problem. Hopefully once the rack gets back from vacation and I replace anything that could be leaky in the intake side of the world, I can focus on tuning and synching.

I am also going to clean up the rotor surface and brushes with a little P1000 sandpaper. Hopefully I won't need to replace the brushes, but I will check voltages once the bike is back up and running. I should also assume that the battery is garbage and replace that.

 

Hello Dan They look a bit lean in the middle plugs.
I also sent my carbs to Hogfiddles and he is a very smart and capable guy. But I would check with him and ask if he Wet Sets the floats after he is done, I may be incorrect... but I believe that he doesn't. IF NOT YOU WILL NEED TO THAT... and to not understate this comment it will be the most critical adjustment you can make and biggest bang for you time on performance issues.
It gets a little tiring removing and reinstalling the carbs because you missed something and its not because we are stupid we just don't know any better.
My bike runs as good as it looks now but it wasn't easy... getting it to that that point, I had those carbs off and on at least... four times.

 

ohm out the ignition system. specs for that and charging system can be found here
The Ultimate Relay, Switch, Sensor, and Diodes Guide
if the caps are original check the screw inside the caps make sure they are tight. I would replace them with new ones.
get 4 new spark plugs why work with an unknown.

make sure you clean the rotor off after using sand paper some grit may remain I would use a hard eraser .
as far as the brushes dont sand them , go better to check lenght there is a wear mark on them , replace them too seeing you have opened the alternator up and have done the work.

 

The plot thickens. I followed @XJ550H 's advice and checked the resistance on coils and plug caps. I'm not 100% confident I measured everything correctly. For primary, I measured at the input connector for the coils, for secondary, I measured from the end of one plug wire to the other, with caps removed, and then measured the caps from the input to the plug connector.

Results are as follows:

LEFT SIDE (1-4 coil)
Primary: 3.8 Ohms
Secondary: 12.6K Ohms
Cap 1: 8K~9K Ohms, was hard to get a good read (This is a T-134 cap)
Cap 2: 8.5K Ohms, (This is a T-134 cap)

RIGHT SIDE (2-3 coil)
Primary: 4.0 Ohms
Secondary: 12.9K Ohms
Cap 1: could not get a read (This is a T-133 cap)
Cap 2: 4.5K Ohms, (This is a T-133 cap)

I may be losing my freaking marbles here, but it appears that somebody put on the wrong plug caps on cyl 1 and 4. Looks like they put on 10K Ohm caps instead of 5K.

Looks like the 1986 XJ700S would have used the 10K Ohm cap, but XJ700N is supposed to have a 5K Ohm cap.

And I have no idea what is going on with the cap that I could not get a read on. That one may be just plain borked.

May be a miracle this thing ran at all!!

I guess at the very least I will need to add new 5K Ohm caps to my shopping list.

 

if you put the spark plug back in the cap you can measure the resistance by using spark plug as conductor measure from wire end to tip of spark plug

 

I tried measuring the caps with a plug in - didn't change the result, still can't get a reading on one.

 

Does anybody know what would happen if one coil had the 10K caps and one coil had the 5K caps? Would that have an effect on tuning?

As @JCH noted, cyls 2 and 3 may have been running leaner, and those where the ones with the 5K caps. How does the resistance in the caps (or plugs, or wires) effect combustion?

Just to add another layer to the onion, looks like the battery is incorrect too.

 

Somewhere in the dark recesses of my brain I seem to remember that only two of the plug gaps had 5 K resistance--one for each coil. The other two had no resistance. Seems like I got that from Chacal--but maybe not.

 

You don't want to see the dark recesses of my brain. At best you'd find a howto for steering head bearings and wheel bearings.

 

Well, after reading my previous post, I see that I said "plug gaps" when I should have said "plug caps." I guess that's the dark side taking control!

 

Got the new plug caps and intake manifold gaskets installed on the XJ700N. OK, you can't see that gaskets, but trust me, they are there.

When cleaning up the old intake manifold gaskets, it looks like somebody may have been in there before and smeared them with gasket goo. More evidence that somebody has been down this road before of trying to make this thing run better.

Pretty much ready for when the carb rack gets back from vacation!

I also picked up a Colortune from @chacal when I got plug caps and gaskets. Started practicing with the Colortune on the XJ650J. I'm not confident that I'm doing it correctly just yet. I end up with the screws something like 5 turns out. I does seem to idle smoother though - used to have kind of a "cha-chunk cha-chunk cha-chunk" idle (almost sounded unbalanced like a Harley), that is better now.

 

If adjusting the mixture screw to 5 turns out is required to get to the transition point between blue and orange on the colortune, you've got other problems........most probably, the pilot mixture screw circuit is blocked (or something else involved with the pilot circuit).............

 

Perhaps the XJ650J carb rack needs an upstate NY spa vacation too. I'm going to try to Colortune it again and see if I can get any better at it before the XJ700N rack returns from vacation.

 

When I got my bike I had to open one of the pilot screws to about 5 to get a blue flame on the color tune plug and for the bike to run without a skip Turned out to be a badly torn intake gasket that was causing the cylinder to suck a lot of air . Replace that and the problem went away. I would check carefully for air leaks.

 

So curiosity got the best of me. I pulled the rack off the XJ650J to investigate what could be going on with the pilot circuit.

My understanding is that the pilot mixture screw should have the following parts in this order: o-ring, washer, spring, screw.

What I found was that all 4 carbs had the pilot screw and spring, as expected, however...

None of them had anything I could identify as a washer.

#1 and #2 had things that look like they may have started out life as o-rings, but are now just crusty crap. I didn't try too hard to fish them out because I'm sure they will just disintegrate:


#3 and #4 have nothing that looks like anything in there. Looks like bare seat to me:


So my best guess now is that the lack of proper sealing in the mixture screws is the reason why it takes 5 full turns to get to a rich state.

I'm trying to decide what my next move is. It wouldn't be too expensive to order some replacement o-rings and washers and see what happens.

 

Curiosity saved this cat!

Correct!

Yes!


And remember, when you go to re-installl, the washer is the lower "seat" for the spring............in other words, the o-ring goes into the hole first, then the washer, then the spring. The lack of the washer is why the o-rings got chewed up, since the sharp bottom edge of the spring was sitting on top of them........

In reality, you should assemble all of the components onto the mixture screw before installing into the carb body.......the o-ring is tight enough against the shaft of the screw that it holds the other components (washer, spring) in place during the install.

 

Thanks @chacal. I'm going to see if there is anything else I want to pick off of my wish list and then get stuff ordered.

Never a dull moment with these things! Never know what you're going to find! Who the heck put this rack back together and just left our a few parts??

I thought I has gotten through the period of atonement for prior sins with the XJ650J, I guess not quite yet.

 

The dreaded "PO" (previous owner) strikes again!

 

Somebody should confiscate PO's tools and never let him or her work on anything again.

I can ALMOST give PO the benefit of the doubt - they may have been a novice mechanic (like many of us here) and made mistakes. All of us noobs make mistakes and hopefully learn from them and move on.

To me, what is infuriating is that I suspect a lot of these "repairs" where made by "professional" mechanics - so some unsuspecting PO paid good money to have somebody completely cock up their stuff, leaving it running like crap and motivating the PO to sell.

I'm still waiting for an initial assessment from @hogfiddles on the XJ700N rack, but I wouldn't be surprised to find out that there is something equally whacked out on that rack.

For now, I will replace the missing pieces on the XJ650J rack and hope for the best. The weird thing is that the XJ650J actually runs pretty well. I really enjoy riding on a daily basis - no problems starting, dying, or anything. Maybe that's a testament to the engineering of these bikes in the first place. They can be pretty whacked out and yet still function. (the XL650J is the bike where I can't seem to get a reading on the secondary side of one of the coils, but it is still running strong, even with the whacked out pilot adjustment screws).

 

Hope everyone had a great 4th weekend!!

 

Dan, I’m finishing up two other racks in line..... one will be done in the next day or two, then yours gets torn down, too— then we’ll know

dfox

 

Not sure if its been covered on here or not yet, but when you do resistance testing, you first need to touch the probes together to find the resistance of the meter you are using, and subsequently subtract this reading from your test readings to get the actual true results. All meters are assembled with potentially different internal circuits, so will have a resistance of their own and do not pertain to your testing scale.

Ohh and all four plugs seem extremely lean, and gaps are inconsistent. I have not personally seen any of hogfiddles work, but I have bought a carb base from him, spoke a little and read a few of his posts, and I'm confident that you won't be disappointed.

Do you have a bore scope? You can get a better idea of how it has been running by looking into cylinders and checking the valve surface condition. Plugs can be cleaned and changed, not so easily done to valves. Inside view of the cylinders is like viewing a trees rings, the whole story is in there.

A cheap HD snake cam can be had from Amazon or ebay cheaply, and plugs into cell phone port. Some even have lights and pic capabilities.

 

I have a borescope somewhere. I'm sure I put it somewhere for safe keeping and now I can't find it. I've used it to look into the YICS port before, but not the cylinders.

 

Here's what remained of the XJ650J pilot mixture screw o-rings:


New o-rings and washers are on their way from @chacal, and the XJ700N carb rack is on vacation with @hogfiddles, so now that I have copious amounts of spare time on my hands I finished up my KV75 tank refinish project:

 

Looks good!

 

I got the new mixture screw o-rings and washers installed on the XJ650J this weekend. It's better, but it still takes 4~4.5 turns to get an orange flame on the colortune.

I did a leak check with carb cleaner spray - no leaks detected.

Must be something inside the carbs we can't see?

Maybe the wrong jets? Somebody could have re-jetted, but I don't know why they would. Still has stock airbox and exhaust.

Maybe float heights wrong? Would that effect the mixture that much?

 

Weak spark can still run a cylinder, and not produce... Get an adjustable spark tester and slowly adjust the gap. when it no longer jumps the gap, stop and count the #of turns or measure with a dial caliper. Do all 4, and compare.

 

Sounds about right. Now turn the mixture screw in until you get a nice Bunson burner blue.
Orange signifies a rich condition, 4-1/2 turns would definitely give you a rich condition.

 

Im sure @hogfiddles can confirm, but if you have the new o ring, washer, and spring in all 4, and you have to turn them out to 4+ turns, there is still some blockage, or fault internal in the carb base.

you ever put your thumb on a garden hose and use it to control the water spray?

thats similar to what the screws your adjusting do to the "Air" coning thorough the idle circuit. the farther you turn out the richer it makes the mixture, and vise versa for turning them in. @Simmy is correct in telling you your running rich.

if you have to turn them out that far something is wrong with that circuit. And, I highly doubt it is the same issue for all 4 carbs.

is it possible you have the jets in the wrong holes?

 

Yes, agreed. In my experience the only time I might possibly see turns that far out are on 550’s..... they’re a different animal.

double check to see if you haven’t mixed up the jets. Some of the manuals are incorrect. The air jets under the diaphragm belong in this position:
The bigger number goes toward the front of the bike
The smaller number goes toward the driver seat

If you are working with pods, all bets are off and you are basically on your own

 

I always thought that the idle mixture screws controls the amount of fuel and not air. Did I misunderstood or is it different on others carbs than my BS33's?

 

They control the MIXTURE.That means they are controlling both, in a sense. As you turn them out, more fuel is allowed through into the air stream.... as they are turned in less fuel is allowed into the airstream. You are adjusting the MIXTURE

 

Ok, so it works as I thought, thanks.

 

OK, I've definitely got more investigation to do with the XJ650J rack.

Definitely possible that there are misplaced jets. In this case at least it wouldn't be my fault.

I think I will wait until the XJ700N is back up and running so I have something to ride when I pull that 650 rack off again.

In the mean time, I may just get some clear tubing and get a read on where the float levels are set while the rack is still on the bike. I have a suspicion that the fuel levels may be low.

 

Why.... because THIS rack was SO Low?? Lol

 

Luckily (or unlucky, depending upon how you look at it), the two bikes came from different places. Maybe the same mechanic "serviced" both racks.

A couple of times on this XJ650J I've been riding down the road - say 55MPH - while also near the primary/reserve switch off points in the fuel tank. I've pulled up to stop at the stoplight, causing the fuel to slosh forward in the tank, then when I get to the light the engine dies. In other words, starving the carbs just long enough while braking to stop for a light was enough to drain the bowls. At least that's what it seems like. Maybe that's normal.

 

you should pull off the fuel line and see just how long it will idle on what's in the bowls.....quite a while
i think you have other problems

 

Yes, I have a lot of problems.

 

get off the highway and stalls at red light, is a classic valve adjustment problem

 

@Toyobaru866, he's right in saying it controls the "mixture"....the carb will either pull air or fuel in the pilot circuit automatically based on that cylinders vacume level,
but not both. So if the external "Pilot"adjuster is mounted "High" up on the carbe base, then it will adjust Air, for the mixture and carb will most likely be pulling fuel automatically if circuit is not clogged.

If the Pilot adjusting screw is mounted "Low" on the carb base, then it will adjust "fuel", For the mixture and pull air automatically.

thats typical for most bike carbs in general, however some models of carb have an external "Brass" tube running fuel from bowl to upper part of the carb, also some have accellerator pumps. so not all are alike but general function is common among all...

 

It can be a symptom..... But it can also be a symptom of too much fuel swamping everything.

Getting the carburetors cleaned out, rebuilt, and dialed back in, Removes them from the problem list

 

Yes I know he's right I don't doubt hogfiddles one minute! I didn't express myself good in my last post. But thanks for explaining in detail, always willing to learn!

 

Another proof of not expressing myself very good... Of course I meant 'for a second'....

 

I did a quick sample of #1 and #4 float heights on the XJ650J (which turned over to 30,000 miles today, just a fun fact).

Here's what I found:

#1 is AT LEAST 10mm below carb body:


#4 is better, but still at least 5mm below:


So I think the plan will be to pull the rack, verify the size and position of all fuel and air jets, and set float heights. Not sure when I will do it, would prefer to wait until I have XJ700N rideable again.

 

@Dan Gardner, when you pull the carbs take the floats off, and get a clear container full of water large enough not to allow the floats to touch anything.

stick each float in the water and see how far it sinks, place them in with pivot bracket down gently so as not to allow them to bob around.. the floats over alot of heat cycles can absorbe fuel like a sponge would. compare the amount of float above the water line to each other.. if you can get all 4 in one container at same time, that will be easier.

Also get a small kitchen scale to weigh them, these test will help you to determine if you need to replace one or two.
there is no set amounts here, but more a comparison between the 4.. this will also allow you to set float heights.

bet the manuals dont help anyone like that...lol

 

FWIW, I have NEVER seen an xj float absorb fuel

 

@hogfiddles, your way more familiar with the XJ's than I... but it can happen, I've seen it before. but not necessarly on any XJ's. so I will take your word for it.

float them next time you do a carb set, i would bet money you will see a difference on depths they sink across all carbs in the rack.

 

I have see it on other things, for sure.... never an xj though