Carboning on plug

This is an XJ700 Maxim-X with 9K miles. I've had lousy mileage since I bought it last year even though I rebuilt the carbs last fall, have Dynacoils, no resistor in line to the spark plugs. I found cyl 3 was fairly thick in carbon. Cylinder 4 was very thick in carbon. 1 & 2 were fine. Yesterday I pulled the carbs and reassessed the fuel level.

I assured all the fuel levels were at 3mm and colortuned/carbtuned it. When I rode it last night I found the engine was hanging at stops like it had done last fall; hangs at 2K and then drops down to normal. Keeping the brake on & partially engaging the clutch as to stall would bring it down and it did not try to speed up. The problem had disappeared this spring and after the fuel levels were adjusted it returned.

So today I took it for a 30 mile interstate excursion and gassed up and it took .9 gallons so I'm still at the same crappy mileage as before. Decided to go for a 10 mile run at 65MPH and do a plug chop and here are the results & I apologize for the blurriness I used my cell phone in foggy conditions & it's the best I could do.

#4 plug is on the left.






So obviously #4 is extremely carboned and 1,2,3 are too lean.

I exchanged plugs 1 & 4 and rode 6 miles home. I looked at the plug now in in cyl 1 that was carboned in #4 and it is now looking lean like the other three were. The lean plug that was in cyl 1 & now in cyl 4 has become carboned. That eliminates a bad plug/wiring as the problem.

So with all that, there's definitely a problem with the #4 side.

This might be important; before I removed the carbs yesterday, plug #3 was almost as carboned as #4 is in the photos and 4 was the worst yesterday. The carboning is not wet or oily, it's dry carbon powder and rubs off easily. Correcting the fuel levels and resyncing the bike fixed the issue with the carboning on #3 and in the photos you'd never know it was close to #4 yesterday.

Have Dynacoils - replaced all components of the the float valve assemblies last fall with new ones - Accel 8mm ignition wire - did the zero ohm mod on the plug caps - carb dipped everything overnight - replaced all the rubber in the carbs with new including throttle shaft seals - made sure the carb cleaner in a pressurized can went through the passageways in all the carbs - assured there are no air leaks around the carbs using starter fluid and propane - enrichment circuit is intact and working properly. There is no smoking from the exhaust, does smell a bit rich.

What would be good for me to consider doing at this point?

Thanks.

 

Based on the hanging idle my first inclination would be that the carb synch is off. I don't see anywhere in the list of things you did:

a) Valve clearance check
b) Bench synch (just a primer for...)
c) Dynamic synch

All of these can lead to one of more cylinders misbehaving. That said, a few other thoughts.

1) You mentioned replacing the ignition including caps. Have you tested you spark in each cylinder afterward? #4 might have weak or inconsistent spark causing it to load up.

2) Enrichment circuit - check the plunger on #4 to ensure it is functioning properly

One more thing - are those spark plugs gapped properly? It just might be the fuzzy photo but the gaps look too large to me.

 

I bet the enrichment circuit on that carb is not cutting off. Its the only thing on your list not mentioned. You might be able to remove the #4 carb bowl with the rack in place, if not pulling the carbs is next. I check mine with a 1/8 silicone tube from a model airplane. Slide the tube over the pick-up all the way on to the carb body and try to suck through it. Even a little air coming in means there is a leak.

 

@ Lanker; Bench synced and I used the carbtune to sync on the bike & the colortune to get the air/gas proper at idle. I didn't check the gaps as there are so few miles on the bike and the first valve check on this bike is at 25,000 miles, not the 5,000 of other XJs. Looked at the spark and it's hefty. I'm using the dynacoils which give 45KV. All the plugs are gapped equally, I don't recall the value but it's from the service manual specs. Lousy photos... see my comments to Mlew for more.

@ Mlew. Hi again & nice to hear from you. I found something today when I removed the diaphragm and that was the tiniest of pinholes which would never be seen unless you stretch it hard. I used liquid tape over that and am taking the bike out for a 10 mile run in a bit to see if that made any difference. I looked at the enrichment plunger when I had the carbs out a couple days ago (or was it yesterday?) and the plunger appeared to be in sync. I don't think I can get the one carb out, don't know how I'd break that from the rack in place. I have the original philips heads, not hex caps so I'll have to remove everything. Again... I'm not sure what you're thinking of when you mention sliding the tube over the pickup. What pickup? the brass tube that inserts into the bowl?

Thanks for the replies!

 

I assume #4 mixture screw tip isn't broken in its hole, is it?

 

See what's up.
Verify you have the correct Jets.

Close the Air Screw and see if the problem persists.

 

No but that would do it. I looked today to see for sure I had the washer & o-ring & they were in place with a nice tip on the mixture screw.

 

Hi Rick,

All the jets are the same on the carbs, I don't recall all the numbers now but I remember ascertaining that when they were apart. When I had them off yesterday or the day before (all running in together now) I only saw the pilot air jet as 140 on all & the main jets were all 105. Didn't look at the values of the others.

I'll close the air screw to see if it carbons on a run but that'll mess with my colortune & carbtune.

 

@KA1J - the tube that Mlew is referring to is the enrichment circuit siphon tube (the long brass tube that extends from the carb body into the bowl). That circuit should be sealed when the enrichment plunger is fully seated and therefore no air should pass through it. Open the enrichment plunger and you should be able to suck air through the circuit.

RE: diaphragm pin hole - I expect you found this wasn't the contributor as I would expect that to lead to a too lean condition rather than a too rich.

Another obscure thought - where are you picking up the vacuum for the petcock? It isn't #4 by chance, is it?

 

Aren't we talking about MIKUNIS here?

If so, did you replace the o-rings on the outsides of the float valve seats? One of those leaking (#4?) can cause a mysterious rich condition that will appear to be a bad float level.

 

Hi Fitz,

Yes, Mikuni BS33 carbs. I Believe the O ring was present. I bought a set of new float valve assemblies from Chacal and replaced the originals with the new ones. Probably could have left the original seats & filters in but wanted to replace the rubber at the tip & thought it best to get mated pieces.

When I checked the fuel level a couple of days ago it was a tad lower than the 3mm, all were 2mm low as I had used the wrong point to measure from. Now all are 3mm below the lateral part of the body and when I checked to see the levels, I held the sight tube in place for about a minute each to be sure there was no creeping up of the fuel level. It remained constant in all the carbs.

@ Lanker. yes, althoughit was the right thing to do, fixing the pinhole didn't help as I took the bike out last night and when I gassed up I was still getting 32 MPG and I checked the plug at the station & it was carboned again. The vacuum is coming from carb 2.

Sadly since everything I've done to restore this carb, I"ll have to remove the carb bank again and have another look at it. I remember all the jets were the same numbers so it must be something else and I'll have to pay close attention to everything on this particular carb. This'll be the third time I've had the bank out and it's a Royal PITA on the Maxim-X.

Ah well...

 

OK, since they're Mikunis there is one other thing to look at. There is a rubber seal INSIDE the tip (bottom) of the enrichment plungers. The one on the #4 plunger might be damaged so even if the plunger is "free" (not being lifted by the choke mech) it could still have a problem sealing off properly.

 

I checked it and there is no leak. When I open the enrichment plunger then I can suck. Releasing the plunger and it's closed again & no suck.

Well, this problem sucks... 8O

 

Boy, it does suck! But I'm highly intrigued to know the answer on this one. When a cylinder runs too lean there are many, many possibilities. However, too rich it usually only one of a handful of possibilities. You've already checked off (1) fuel levels, (2) Pilot circuit issues, (3) enrichment circuit issues, and (4) leaking petcock issues. The only possibility left that I can think of is that the slide isn't seating all the way and leaking fuel out of the main into the airstream. But, if that was the case it would only present when checking the plugs at idle. If you get some new plugs and do a WOT plug chop does the issue present then? If not, then I'd think the issue has do with the slide. If it does show up on the plug chop then there is excessive fuel being introduced into the cylinder from somewhere else (beyond the main).

How much do you trust the previous owner? Is there a chance he messed with the main needle seat(s) (are they adjustable on the BS33 - not sure).

It's gotta be SOMETHING. One thing that doesn't add up for me - you said you ColorTuned. If that cylinder is burning excessive fuel you should see evidence of it in the ColorTune. Did you do it recently?

 

Has you on the edge of your seat, doesn't it?

Sent him a PM to help him keep going through the checklist I sent the other day.

I think we are narrowing it down to a botched up pilot or main jet. And, from what I understand, the PO (or someone that worked on it prior) was the "Gorilla Type", and I wouldn't trust the size on the jets. Mainly because the cylinder in question probably has one enlarged from "Cleaning".

Waiting on an update.......

 

Just looked at the all the jets and emulsion tube, checked the O ring around the float valve & it's there & was new last year. visibly there is nothing amiss about anything regarding the carb. Maybe there's something else plugged in the carb but I can't find anything wrong with it.

Checked the ohmage from one end of the spark plug cable to the other and zero ohms, I have Iridium plugs with a built in 5K resistor. Regardless, I switched the plug wires on the Dynacoil to see if that switches the problem area & if so the problem would be with the dynacoil. If no problem, I'll try a new plug wire. They are new 8mm Accell solid wire so I'm sure they're fine though.

 

Have you done a compression check? Are you certain that's not oil getting burned up? Exhaust blockage of some sort in the #4 downtube? You don't have a family of mice living in the collector box, do ya? LOL. FFS - there is an explanation somewhere. Even though its not due I'd love to know that you value clearances are in spec if you can't find a red flag elsewhere.

I hope you have a cold beverage in hand to help you think during this process! I know how frustrating this is - I chased a too-rich issue for over a week until I finally discovered a broken pilot mixture screw. The good news is that my beer can returns paid for a new one by the time I found it!

 

I'm going to have to get a compression tester for 12mm. At less than 10K with the first shim check at 25K miles, there shouldn't be those kind of problems on only one cylinder.

Do need to get metric feeler gauges for this bike, the normal ones are too wide. Think these are like 6 mm wide.

LOL! I did have a wild thought maybe a mouse had built a nest in the air cleaner/velocity stack & when I checked the filter it was fine. No way one could have gotten in there but Something's affecting this cylinder.

I'll get it...

 

I once started up one of my parts bikes with just the collector box, and tons of debris shot out.....no mice though. But it sure was a hideout for some type of critter at one point in time.

I have the proper comp. tester and feeler gauge tools that you need.

I know this is a tough one to figure out. Maybe a road trip is in order for me to come see you?

 

Thanks!

That's always fine, it'd be great to see you again anyway. Lets see if all the picking away at the carbs that I've done worked. If I come to a dead end I'll very much appreciate the offer. I'd drive down your way but as you know, the engine needs to be cool before doing a shim check so my going there is out. I do have a head gasket set if the old one is not reusable.

 

The "High-hat" (Top) of the Enrichment Plunger isn't "C0ckeyed" ... is it?

 

Hi Rick,

I don't know but I don't believe so; I had the #4 carb apart as far as possible without breaking the rack. Tried to get the plunger out but only #1 will come out without breaking the rack. But... when I suck on the starter bleed pipe, there's a dead end & if I move the enrichment plunger then it freely sucks so I suspect the plunger is straight & seating well.

A friend suggested a possible broken piston ring. If that were the case wouldn't I have a lot of blow-by and oil that gets dirty really fast?

The amount I don't know is impressive...

 

I may be way off base here.... Are the air jets and passages clean and clear? You could have a clogged air jet or passage, causing an extremely rich condition.

 

Also... Do the slides pass the "clunk" test?

 

Broken Ring?
Possibility.
A Compression Test might help sniff that out.

The Hole would likely foul and miss after awhile.

If you have a Lean condition, ... AND a bad Valve Stem Seal ... the Oil would seep-in and get burned-off leaving build-up on the Plug.

Run it.
Have someone follow you.
Have them report on any Smoke they see.
Puffs. Color: White or Blue.

 

Air jets backwards? I don't know if Mikuni's are the same as Hitachi's tho.

 

Seeing as I hardly ever find the need to do a compression test I haven't bought a tester. The one from AutoZone doesn't have the 12mm insert that's needed with the Maxim X so I held off and decided I really should have this tool because it does answer questions... Bought one tonight from Advance Auto & it seems to be pretty good & will cover everything from lawn mowers & up.

This engine has a 11.20:1 compression and the numbers on a cold engine that hasn't been run in 20 hours are:

1 - 150
2 - 145
3 - 140
4 - 145

So the good news is #4 looks to have a good compression!

Maybe I should run the test on a warm engine at this point but I can't see that'll be of significance with these numbers.

Maybe I need a beer.

 

Looks like we can rule-out broken rings.

Exceptionally good numbers!

 

Yes, I'm happy with them. I'd like #3 to be higher but that's just splitting hairs.

Would there be any value in warming the engine & running them again? I can't see why but it's a variable. I'd probably get higher numbers yet but I wouldn't want it to be running temp hot, the pressure gauge's O rings might not like it much.

 

....or two.

You would have a slight change higher with a warm engine, however those numbers look great. In a way, it's reassuring that you don't have a broken ring or valve issues. Now you'll have to double check everything on the carbs.

 

Yes indeed. Rechecking yet again. And popping #2 beer BTW...

This'll be 4th time I've opened the carbs up and man what a bugger to figure this problem out. Knowing the rings are likely fine is very good to know right now, I'm not looking forward to reshimming another 15K down the road but I really didn't want to get into this engine right now.

OTOH, knowing a bike is in top mechanical condition is also a great feeling. When I rebuilt the XJ1100 I knew the top half of the engine was all in specs and I feel safe to take it on any long trip (well it does need the front fork seals replaced).

Back to head scratching on the carb issue on #4...

And beer #2

 

Make sure the slide passes the clunk test. Examine the condition of the tip of the slide needle too. Air jet clean and clear? Is the emulsion tube properly seated and the washer under main?

(Another beer)

 

Spent yesterday afternoon with Mr. KA1J, and after rechecking mostly everything that he had checked, we sincerely believe it was an overly worn emulsion tube. Not sure why that was the case on a bike with less than 10K?, but my guess is the PO (or someone that messed with it prior to him acquiring it) may have had the needle jet cockeyed and caused undue wear. I had a good spare to replace the worn one, and we made sure all the main jets were good (105's that weren't drilled out). We also swapped in another set of 35 pilot jets (with verified sizing as well) for good measure.

A short run, after a sync and color tune, showed all the plugs now had a good tan/grey color.

Waiting for an official follow up report after he puts some more miles on it.

 

Indeed! Xhondahack has it right. I just got back in from Rhode Island and a plug chop after 80 miles was ready to be had and it goes as this:



Again, sorry for the blurriness but shows the plugs are ALL looking good. My many thanks to all who replied trying to help me out. The problem was obviously present but it defied all my cleaning attempts. I Found the gas mileage improved from the 32 I was getting to 38 my initial fillup and at sustained 65-70 MPH speeds I got 40.6 MPG, a big difference.

Thanks to all but especially XHondahack who came so far to help me out & with a big box of tools/parts to help me out.

And here is my little Birthday Kid today on my way back from RI:



Time for another beer!

 

Nice, all looking even with no carbon buildup. During the summer months, you might even want to go a 1/4 to a 1/2 turn in on the idle mixture screws. Might improve the mileage a tiny bit, and give you a slightly lighter tan color on the plugs.

 

XHondahack; Thanks again for all the time you put into finding the problem, Your evaluation certainly was correct and your thinking was spot on. Thanks for putting other things aside yesterday to come so far and help me.

Cheers!

 

Not a problem. As I mentioned, by adding my "half a brain" to the effort, we'd figure out your troubles. Helps that I had some good parts leftover from other projects that we could swap over and prove out our theory.

I tried my best to work on the lighting, but here's a picture of the one you had in on the left, and a nice one similar to what I had put in on the right:


Now go get some new tires for that bike, and enjoy it.

Tony

 

Yeah! Excellent - sounds like you got it dialed in with some help from HondaHack and a beer or two - works every time (and if not, add another beer and repeat - eventually it works ;-)

 

xHondaHack

Picture of the jets is pretty good, but it is not that obvious to me what is wrong with the left one.

WOuld you please give me a hint?

 

Here's a much better picture showing the excessively worn area on the lower portion of what's supposed to be perfectly round:

That kind of wear will enable too much fuel to enter the air stream, and create an over-rich condition on that particular cylinder.

Tony

 

Hahhh! I see, I see now!

Thanks a lot!

 

@ Lanker; Yup. More than help, he's the one who figured it out, not me. He has a really great eye for detail. I'd gone over them till I was blue in the face and I missed that about the emulsion tunes. I never would have expected emulsion damage after so few miles. But now the bike is working beautifully so it was what it was..

I used to see splotches of carbon on the chromed part of the end of the muffler that would come out from the exhaust as the moisture from combustion would exit with soot & build up outside the exhaust. There were some splotches looking like dried india ink still showing up for 100 miles after this adventure yesterday but this evening I got home and found none of those splotches on the chrome.

Demon exorcised!

Niiiccceee