I can't stop fouling plugs...

Here's what I've done to try and fix this problem:

First I replaced the plugs and the engine ran sweet and fired on all 4, then after running it and letting it idle for a while it fouled these plugs to a pitch black thick enough that I could wipe the carbon/black off with a rag.

Also set the timing chain tension.

It also has the fuse box mod already done (new blade style) I have no idea now what each fuse controls on the bike except for two fuses, one shuts down all my accessories (turn signals, horn, neutral & oil lights, tail lights) the other fuse I take out shuts down the starter solinoid or kills the engine if I unplug it when its running. All the rest of the fuses I don't know, I'll try searching for the answer pretty soon here,

Then I took the carbs off to clean them and verify the jets (It was originally from Michigan and now its in Montana which is different elevation). They have the stock 110 main jet and 40 pilot jet in them... I stripped everything down and set all the rubber parts aside and chem tanked the metal parts. I took the carbs out of the tank and dried them off and blew out all the passages and reassembled everything. The bike started a little better but I still had the same fouling problem...

After that I synced all the carbs perfect and that helped starting a little bit more BUT same fouling problem...

By now I've gone through 3 sets of plugs (BP7ES) thats 12 plugs and I might need new ones pretty soon too...


Here's what I haven't done yet:

Rebuild the starter. right now it spins the engine pretty quick but I doubt its ever been looked at so it wouldn't hurt to get it some new brushes and a good cleaning. I have the bike on an battery maintainer so I know the battery is always fully charged.

Its not a YICS but a few people have told me that if I "T" the carbs together via the sync plugs the idle will come up a little and the idle will even a little and the notorious back fire when starting cold will subside a little. I'm gunna T them tomorrow because every little bit helps.

I hear there's a K&N or some company that sells a jet kit that really does things for its performance. Maybe this kit comes with a different pilot jet, leaner maybe?

I'm kinda at a loss for any more ideas. Any thoughts on this XJ guy's?

Oh and the compression on all cylinders is above 150 psi, sounds good to me...

 

pilot jets, how many turns are you out from bottom?

 

Don't "T" the Carbs.
Get it tuned right.

If you are in Sync ... Adjust the Pilot Mixtures
Start at the spot between 2-3/4 -to- 3 Turns Out from the bottom.
Closer to 3 Turns Out than 2-3/4.

See how the Plugs look after running it there for a bit.

 

The screw is out to 3 turns. I only have screws on two of the carbs though, the middle two. I have fooled with the screws before but they made no difference in the idle or fouling problem

 

Forgot to mention that if I leave the fuel petcock to Prime that the carbs begin to flood as in fuel litterly starts dripping out and into the air box. I don't know why I didn't think of this before but I probably have to re adjust the floats...

Oh and when I bought the bike there were the stock float needle and seats in a little bagy underneath the seat. this tells me someone has screwed with the carbs before and probably messed with the float height.

Should I adjust the float height like it says in the shop manual by unscrewing the bottom bowl screw and attaching a clear hose to the drain and watching how high the fuel comes up when I set the hose next to the bowl? Or hopefully there's a measurement the tang can be set at that will get the height correct?

Should I have a pilot adjustment screw on every carb or is it normal to have just the two middle carbs having a screw? the shop manual doesn't say much about them only that the stock setting is 2 1/2 turns out

 

my experience is that nothing is normal with the xj. if there is no screw, what is there?

 

Chacal has new pilot needles, and the little rubber "O" rings. I can't believe your bike even ran !

You "stripped everything down, set all rubber parts aside" then you tanked the main bodies. This means you removed the butterflies, shafts and 8 rubber shaft seals?

You dug the 4 little "O" rings out of the pilot jet wells? with something like a wire with a little hook on the end?

You ran a fine wire thru the brass tube that protrudes into the bowl, and thru the tiny hidden jet in the bowl?

You are correct about the float check- - fuel level if checked on the bike should be about at the gasket between the 2 screws ( and somebody jump in and correct me if that's wrong). Search topic: float level

Here's an idea- - your PO put the floats in upsidown! (maybe) Look for a picture.

And you are flooding. The pivot pin and the part of the float that it lives in are polished with 1,000 grit. Roll a bit of the paper up tight for that.
Might as well "clunk" them while they are apart.
Search topic : clunk test. . . carb cleaning old school. . . whole nine yards

Then you'll be ready to tweak 'em

 

Since most of the XJ-Bikes are wearing 20+-year old Hitachi Carbs; you have to be very thorough in servicing and cleaning them to have success tuning them.

All those years have added tarnish and oxidation to parts that need to be rid of it before any fine-tuning can begin.

Many need new gaskets and new complete Float Valve.
All need Emulsion Tubes cleaned and rendered free of foreign matter.
All need the Diaphragm Piston Bores de-oxidized and polished.

Those with Anti-tamper Plugs need them drilled-out for access to Pilot Mixture Screws for fine-tuning the Mixtures.

Once the Carbs are Bench Synced
Synced
Pilot Mixtures Set
Butterfly Shafts Lubed ...

The Carbs are ready for some serious fine-tuning!

Colortuning the Pilot Mixtures is a vitally important step.
Getting the Mixtures set to supply supplemental fuel beyond just Idle flow is required for a seamless transition from Idle to Off-idle and acceleration.

Taking your time to make sure each step in the process is done correctly sets-up the next phase until you have them dialed-in and are making adjustments to individual Carbs to match the ignition burn across the board.

Understanding how the Fuel and Air Jets are combined and what happens as the Pilot Mixtures are adjusted for the fine-tuning makes you ready to become a Tweaker and set-up your Carbs for the highest performance they will allow.

 

well good to see another member from the Big Sky. Where are you at, perhaps I could offer some meger assistance..............

my 750 has suddenly started running on 3 cylinders only, #4 is just always wet and black with soot, the pipe hardly gets warm unless it take it for 5+ mile ride.
I ran it down to reserve a couple days ago and I think I picked up a piece of crud from the boneyard tank I put on it.
I pulled the tank and did the batt charger/saltwater cleaning on it yesterday, llok good now.......time to attack the carbs once again.

 

I replaced the o rings on the two middle pilot needles. the outside carbs simply don't even have a hole for the pilot screw, they are sealed from factory so yeah it runs.

You dug the 4 little "O" rings out of the pilot jet wells? with something like a wire with a little hook on the end?

You ran a fine wire thru the brass tube that protrudes into the bowl, and thru the tiny hidden jet in the bowl?[/quote]

yes. This isn't the first 4 cylinder bike I've owned and had to clean the carbs on... But yeah they are all replaced.

I'm gunna recheck the float levels and take the carbs off again and double check everything. I'm pretty sure the previous owner didn't put the floats in upside down cause its been these same two carbs that flood if I leave the prime on. Even if they were on upside down they aren't now cause I know which is upside down and whats right as far as floats. I just need to readjust the tangs I bet to get the fuel to stop flooding out on the two carbs. And the PO did how ever replace the float needles so I have new needles in it

I'm gunna search the "clunk test" but I have a feeling I did that test but don't really have a name for it or really think about it when I did it.

I'm up in Bigfork/Kalispell area. I'll be moving to GreatFalls in Sept. though

Are you saying the two outside carbs actually do have mixture screws but are covered by the carb's aluminum and I could file down the aluminum cap and find a screw underneath it? I've been looking at other XJ's and they do have mixture screws on all the carbs but for some reason two of mine don't/are covered up...

 

"I'm up in Bigfork/Kalispell area. I'll be moving to GreatFalls in Sept. though "

Great, we can go for a ride then. What XJ do you have ? ? 550,650,750 ? ?

When I got my XJ the two inside carbs still had the anti-tamper plugs over the mixture screws. I guess the PO removed the plugs on the outside two carb so he could adjust them, but never pulled the carb to get at the two inside carbs. They were pretty easy to remove once I pulled the carbs the 1st time. Then I was able to get it dialed in pretty quick.

pic of the top of carbs, with anti tamper plugs installed

 

Rotaryboots- - The trick is to drill the plug without going thru and damaging the brass screw underneath. A small bit in a Dremel, drill towards the side, not the center, just "touch" it in, then pick the plug out with a small nail.

a "clunk" thread:
http://www.xjbikes.com/Forums/viewtopic ... +test.html

 

This shit is fascinating! I'm scared and inspired at the same time.

 

I'm taking the carbs back off tonight and getting everything double checked. While they're off I'm gunna take off those tamper plugs. And yeah the "clunk" test is very familiar to me and something I did when I rebuilt them the first time.

thanks for all your help guys, I'll keep you all posted on my progress with this gremlin.

osage, I PM'd you

 

back at ya.

sure you will get it, takes a little time like most stuff.
just lame to work on them rather than ride them on a nice summer day. oh well that's the price we pay for having old stuff.

 

Take EVERY precaution not to damage the slots of the Pilot Mixture Screws just below those Plugs.

If you are careful enough, the Plugs will be removed and you'll have access to undamaged Screws ... the Keys to ultra fine-tuning.

When you do have access to the Pilot Mixture Screws ... do yourself a HUGE favor and fabricate a screwdriver tip to fit the slot in those Mixture Screws perfectly.

The wings on the Pilot Mixture Screws are prone to movingn without the body of the Mixture screw if the screwdriver end leaves room to let them.

 

Well I got the caps off with out a scratch on the screws underneath. It was no problem at all actually.

the screws underneath the plugs were set at 4 1/2 turns out... thats not quite right... kinda explains a little though.

I have taken the carbs off again and will examine every part under a microscope. I'm gunna do the floats and everything in the morning and let you all know whats up with that.

Since the bike hasn't killed these plugs yet I'm gunna get some BP6ES plugs for it and see if that stops the fouling if I put the carbs back on and still have the same problem. Like I said , the engine clears up and runs pretty much fine after 3k rpm; but then again I don't really know what to expect from this engine being it hasn't ran 100% yet...

I'm betting right now on either the floats being off and flooding the bowls, or a clogged air passage, or something along the lines of the enrichment circuit... And I did the "clunk test" the first time and there wasn't one hesitation so I know thats all good.

I'll keep you guys posted

 

i'm also having major carb probs as well and after reading this page i kinda feel like hiding under the bed for awhile-and i do'nt generaly scare easly 8O

 

Though I don't have carb problems just yet- I've been getting ready to mod my exhaust, so- "What He said"

Yipe. 8O

 

Sorry its been a while getting back to you guys but here's that latest news.

I have finished completely rebuilding the carbs and have good news. The bike doesn't even need the Choke (enrichment circuit) to start when its cold, it literally fires right up within the first crank so I'm happy with that. The floats are all even and the carbs are all getting the right amount of fuel and not flooding. It accelerates great and quick through all the gears but who knows how fast I'm going past 80 on the odometer... i need a solution to that...
So all in all the second carb rebuild did wonders BUT...

It will still foul the plugs out if I let it sit long enough and just idle. Since this is a brand new set of plugs in it I'm taking them out and wiping them off if I've let it idle for a little bit. It doesn't foul the plugs nearly as fast as it used to but it still kinda does.

Right now I have all the pilot screws screwed all the way in to try and lean it out the best I can. I don't have that backwards do I? Clockwise (in) is lean and counter clockwise (out) is rich right?

I'm thinking of using a BP6ES plug in it to see if I can stop the fouling and get it to burn cleaner on the plug and get it to look brown and not pitch black.

 

you are correct.

 

I'm wondering if you're getting fuel leaking in from the enrichment circuit. Make sure you have a little slack in the rod that the choke cable hooks up to. If that checks out, you may need to remove the plungers and make sure everything down inside is in good working order.

 

Starting-up Immediately when cold without Enrichment indicates that the Mixture is too Rich.

Check to see that the Enrichment Valves are actually closing and getting seated.

Pilot Mixtures Screws "All the way in"
Not good.

You need to find-out what size Pilot Jets are installed in the Carbs.
If you (or somebody else) put New Jets in there ... they might not be the right sized Jets for that Bike and those Carbs.

You can very easily find-out how fast over 80 MPH you are going by continuing to speed.

Eventually, your exact speed will be written down for you by a State Trooper with State-of-the-Art Speed measuring devices!

 

It has #40 pilot jets on all the carbs. Tomorrow I'm going to just get new enrichment plungers and see if that helps to seat the valves.

Hmm a cop pulling over another cop? thats funny. Oh I'm a part time law enforcement officer. Was joking on the 80mph speedo though, just said that to indicate that it was running good...

My manual says it takes only 91 octane.. I'm putting 89 in her. that change anything?

 

The Gas they are serving-up in New England is a Summer Blend with a 10 to 12% Ethanol content.

If you are a "Tweaker" and set-up Lean using the Regular Gas with all that Ethanol ... you get some Knock.

I've been doing some at the pump "Blending" ... adding some Mid-Grade or splurging for the High-test on occasion.

My Engine just turned-over 20,000 Miles. It's running GREAT!
I'm not going to risk havaing detonation spoil an otherwise perfectly running Mill.

 

True. Yeah I'll start putting 91 in it instead of 89. its only a buck or two more in the end anyway. Hey my XJ is at 20,019 miles

 

Well I'm kinda at a loss here. I thought about maybe putting a leaner pilot jet in her but I guess they don't really make a leaner Hitachi pilot jet than #40 (looked up in Sudco). There is such a thing as a 35 small round main jet for the mikuni carbs and I think the thread is the same, but really I don't think 40 to a 35 is going to make all the difference on this. I was thinking, the timing can't be off on this bike because it is set at factory right?

It has the original exhaust on it, maybe its a little restrictive like something or some stuff could have gotten up in there and clogged it a little on one of the mufflers? One way to find out would be to take one of the mufflers off and see if there is a difference, thats pretty loud though and probably not worth it I bet.

Is there air jets I could change or inspect... again... that would give rich and fouling symptoms if they weren't functioning correctly? I don't think the main jet needle on the slider could be the problem but then again it might be because it will still run on all four and be rich on all four cylinders even with the pilot screws all the way screwed in. When I rebuilt the top part where you access the sliders I noticed the needles were flush with the top part of the plastic keeper, I could pull the keeper all the way down onto the needle but that would give it more fuel so I'm leaving that alone.

I'm pretty darn sure there are not vacuum leaks because that would make a cylinder lean and not rich.

A simple test I'm going to do is put BP6ES plugs in it and see what happens. I have a friend from here that has this same bike and he's running 6ES's and he says they don't foul and run fine. But I know this bike was tuned at/for sea level so at the least it should run a tad leaner at 3500' and above all run the 7ES' doing it too.

Any new Ideas guys?

 

I've got a few ideas for you to consider,
Your PO somehow ruined your carbs before you started working on them. He may have used some chemical that eroded the inside surface where the pilot needle seats. Both he and you cleaned 2 of the carbs without removing the pilot needles, which would hold the chemical, and erode the seat. For about $75, you could start over with a rack of E-Bay carbs.

It won't hurt anything to set the floats about 1/4 inch or 1/8 inch low, and see if you can get it to run lean. The pilots should be about 2 1/2 out, not all the way seated.

Ride the bike for 10 minutes without the air filter, just to see if it is too restrictive. You did say you had oil in the airbox, an oil wetted air filter doesn,t flow well, unless it's a K & N. I don't recommend running without a filter except this test.

You seem to know what you are doing, and are experienced enough to set these carbs up right. That's why I suggest that something was done to the carbs that you wouldn't easily catch. Did somebody drill out the jets? It would be nice if you could "borrow" a good rack of carbs.

 

The Aluminum Carb Bodies are hard to hurt. The Rubber parts? That's another story!

If the Problem is that you are Fouling Plugs; easiest solution would be to Set-up the Mixtures with a Colortune Plug.

If you don't have one or cannot borrow one; you're left to experiment with the Mixtures.
Since you are fouling the Plugs; we investigate sources of Fuel and reasons that the Plugs would Foul.

Too much Fuel?
Not enough AIR?

Have the Air Jets been removed and possibly switched?
The Haynes Manual has those values reversed. It's caught a bunch of us who have done complete strips.

Main Jets?
Are the Main Jets Stock or more than one bump-up Richer?

Main AIR Jet and Passage?
We addressed the possibility of the AIR Jets being Swapped.
Is the Main AIR Passage free and clear of foreign matter?
Are the Emulsion Tubes Air Metering Ports ALL cleaned and probed?
Did you hold the Tube to a light source and peer through the Meetering Ports on one side and out the other?

Diaphragm Piston Rise?
Are the Diaphragm Pistons drilled-out beyond OEM Specs as if the Carbs were altered for a Stage 1 & 3 Jet Kit?
Is there an extra hole in the bottom of the Diaphragm Piston where the Needle Valve is attached to cause the Piston to rise prematurely?
Are the Diaphragm Needles Stock?

Pilot Mixture Screws?
Originals or replacements?
Fine thread or Ultra-fine thread?
Removable or damaged?
If removed ... are you sure the parts were inserted in the correct order with the tiny O-ring at the Bottom and were the O-rings present?

Enrichment Valves?
Free movement?
Not getting stuck open?
Are the Forks that lift the Enrichment Valves allowing the Valve to close?
Look closely at the tops of the Enrichment Valves.
Are they "Square" of are the little "Top-Hats" leaning-over and bent?

 

Well it runs great and the plugs run fine and look like they should when you ride it normally like on the highway and will only foul if you let it idle for a while (about 2-5 minutes or so) then they will start to foul. So if I just ride it and treat it like a Stock GT500 mustang and don't let it idle for very long it runs like it should and pulls hard through all the RPM ranges.

The PO could have done some sort of mod or used a harsh chemical on it and killed some rubber pieces or enlarged the pilot jets from their stock levels. Otherwise everything looks and is stock on her like the pilot jets say they are 40 and the mains say 110 but who knows they could be 45-50 pilots after all these years and the main could be a little bigger. They look like they are the stock jets anyways. And taking them out was stockish too (kinda poped loose and then unscrewed) I could replace the pilots with new ones BUT I'm not interested in taking them out for the 4th time when she'll run fine when its not idleing and is cruiseing.

Chances are the air jets could be switched but I put everything back in the way they came out in the places they came out of, so if the PO put them in backwards then I probably put them back in backwards too. I'll do a bit of light reading tonight in the factory service manual and double check everything but as of right now I'm not entertaining the thought of taking them back out when I use this bike for highway use mainly and if I'm in town I'll just rev the engine a few times at stop lights to keep it clear.

By the way, Thanks a lot guys for all your help. I really appreciate it all

 

Relax.
The Air Jets must be in right.
It wouldn't run worth a damn if they weren't.

 

thats good to here. I'm thinking of getting new pilot needles for her and maybe enricher needles. I'm thinking there could be some weird chance that they aren't seating as good as they could be. They don't cost me much so I'll give them a try. Later on like on a rainy week or when it starts to get cold out I'll take the carbs off again and replace all the jets in it. They could be worn a little maybe.

All the carbs got synced correctly and perfectly and then someone suggested I make sort of an equalizer for all the carbs by T-ing them together via the sync pipes on the intake manifolds. Doing this evened out the idle slightly and raised the idle slightly. Now I've also heard that this is a bad idea but I did sync all the carbs before I did this so is there anything wrong with having them T'd? or?

 

It was my understanding that, that is basically what YICS does.

 

Did the new needles help? I'm in the same boat as where I'm fouling plugs even thought I'm fully closed on the pilot needles. I'm thinking I forgot to take the pilot screws and oring out when I carb dipped them (yeah yeah noob, I didn't know their was a teeny tiny oring down there!) but I did take/replace every other piece of rubber off and replaced it (except for the enrichment valve dust covers).

 

Check the condition of the Pilot Mix O-Rings.

Heat the tip of a Extra-Large Safety Pin
Make a tiny hook at the end while its heated
Stick-it in your Iced Tea and cool it down

Now, you have a O-Ring Tool.
Stick the Pin down the Hole and grab BOTH small Parts.
If the O-ring dissolved ... get new ones fm Chacal.