Cylinder #3, #4 lean at off idle

This has been causing me trouble from the time I first got the bike. With all of the wonderful help from the fine people on this forum I was able to do the following:
-check and replace valve shims as necessary, all are in spec
-clean carbs per rick's method, including polishing the innards so the carbs "clunk"
-synch the carbs
-colortune the carbs

Now, once warm, she idles wonderfully right at 1050, great throttle response throughout the entire RPM range. The only thing that bothered me was a popping sound at around 4-5k RPM. I cleaned the carbs again, same things happens. I checked for air leaks with a propane torch, none. I decided to shim the needles on carb 3 and 4. After putting in a .050" shims in both carbs, the popping went away and she seemed to ride smoother. After a tank of gas, and about 20 minutes of riding at 5k rpm, I plug chop. #4 has SOME tan around the insulator, and #3 is white, with some specks of black on the insulator.

I am at an absolute loss as to what to do. Despite being lean, I still average 36-39 MPG, which is quite acceptable gas mileage all things considered, which also causes me to think I'm not running lean?

More information: the bike starts right up, but requires a quick flick of the throttle to do so. After that it will idle at around 600-700 hundred RPM until warm (I typically just hold the throttle open a bit to keep it above 1050 so as to keep oil pressure at an acceptable level). She also dies when I give it choke, unless I find the "magic spot" where it will bump the idle to around 1100 and keep it there.

I have done all of the required maintenance to the bike (well, the new tires are still waiting to be put on) and this is the only thing that is bothering me.

Please, any and all suggestions are welcome and highly appreciated. I need this bike to be able to handle a fairly long trip at highway speeds.

 

Work on the Lean Holes INDEPENDENTLY.

Just keep adding some Richness at the Pilot Mixture Screw ... The Width of a DIME at a Time.
You should be able to Increase the Supplemental Richness and get some Coloration.
If the PLUG is CLEAN and WHITE ... Troubleshoot and find-out why you are running Lean.

The possibilities range from:
Manifold Air Leak at Head due to rotted O-rings
Cracks in Manifold
Loose Clamps
Carb Throttle Seals
Manifold Vacuum Test Rubber Hat leak
Wrong Pilot Fuel Jets
Wrong Pilot AIR Jet

 

Rick - I have the pilot mixtures set so that at idle, plugs #3 and #4 turn a nice tan color. At cruising RPM (5 - 6k) the plugs turn white.

As for your list of possibilities:
Manifold Air Leak at Head due to rotted O-rings - Do you mean that my intake boots are rotted? Please clarify.
Cracks in Manifold - Please clarify this. Do you mean the rubber boots have cracks in them?
Loose Clamps - checked all clamps, nice and tight.
Carb Throttle Seals - replaced when I was cleaning the carbs
Manifold Vacuum Test Rubber Hat leak - Put on brand new ones from Chacal
Wrong Pilot Fuel Jets - checked all, correct size
Wrong Pilot AIR Jet - I checked these when the carbs were apart, but will recheck. To make sure, the Pilot AIR Jet is located on the top portion of the carb, underneath the hat and diaphragm?

Thank you for taking the time to help me out.

 

I put in new intake boots from the airbox to carbs (using the 1.5" plumbing fittings) and this solved the issue of #3 being lean, however, #4 is still a bit off.

I put in a smaller shim on #4 (.020") as a test and pulled the plugs after 20 miles. It's now showing the insulator back to completely white.

I kept the shims on #3 on just in case.

What am I missing here? I'd like to run her without the shims. Is it possible the diaphragm needles on 3 and 4 are aftermarket and hence longer?

 

The Shim introduces Main Jet Fuel Supply a little bit earlier.

The Volume of the Fuel reacting to the Shim is regulated by the Main FUEL Jet.

You need ... Supplemental Richness.

Turn the PILOT MIXTURE SCREW ... Out ... about the with of a Nickel.
Check the Plugs after running with the Pilot Screw adjusted Out.
Watch the Color.
Continue to Tweak Out or In as needed.

 

Thanks for the quick reply Rick!

I'll try it out now and let you know how much it helps.

 

Checked all of my jets, again, and they are all stock.
Turned the pilot mixture screw out, used colortune to help, no change.

Just to make this clear, THE BIKE IDLES PERFECTLY and my plugs are all tan AT IDLE! It's once it gets into cruising RPM (4-6K) that the mixture leans out dangerously. I rode it around some more today and both plug #3 and #4 have WHITE insulators.

Also, what do you mean by this : "Manifold Air Leak at Head due to rotted O-rings" where are these o-rings? Is there a diagram I can reference?

AAAAAAGH! This is driving me crazy! Where could this air leak be coming from???

 

Tried to test the carb to engine intake boots for leaks with propane, and got nothing. Going to get some starter fluid and try again.

 

Ok, I am beyond frustrated now.

I checked off each item on your list, even replacing the gaskets between head and the intakes! Anything above 4,000 RPM and my plug insulators turn WHITE!

I tried adding "supplemental richness" and it has no effect!

What else can I check???

Is it possible this has something to do with the (stock) exhaust?

 

I have a similar prob with my Maxim. Riding around in town my plugs look fine until I get on the highway ride for a bit. I get home and wait for it to cool down. Put the plugs and #3 is white with black specks. The rest look fine. Adjusting the pilot screw on #3 only makes a difference at idle.

 

Could the passages of the YICS port be plugged up? Thought that it is supposed to help mix and even out the mixtures of the carbs at higher rpm's especially. I use a metal hanger, sharpened at one end and bent up to poke mine through every once in a while. Might not help or fix the problem, but couldn't hurt to try....

After all, they say that it runs different with the ports blocked off.

 

The o-rings you asked about are in the manifolds themselves; did you replace the o-rings when you replaced the gaskets?

White with specks is dangerously hot, not just "lean."

Throttle shaft seals?

 

I would look at the float levels here. Do the clear plastic tube method on the carb drains. Make sure the float level is right at the bowl screw washer.


MN

 

i'm having similar problem - i've been riding to work (6 miles one way) all week and my plugs were developing a nice tan color. #2 and #4 were a little on the light side so i turned the pilot screws out 1/2 turn and took a long ride yesterday. when i got home, they were all white.

i've checked for leaks with propane and found nothing.

is it possible to turn the screws out too far and miss the "sweet spot" and set yourself lean again?

also - i averaged about 41 MPG - i'm assuming MPG can be a rough indicator of how rich or lean you are running, no?

 

half turn is huge your plugs should have turned black or at least a lot darker. You sure you went out? Sure sounds like you went in...

 

righty tighty, lefty loosy - right? i was hoping i might've even fouled some plugs (carried a spare set) just to see if i was chasing the right rabbit.

edit: here's a possible eureka - the first time i cleaned the carbs, i installed a fuel filter - it's a cheaper one, maybe intended for lawn mowers? - beggars can't be choosers when you live in BFE. think that filter is restricting my fuel flow???

 

you got it right but very odd result...

 

any thoughts on the filter?

 

http://www.dansmc.com/spark_plugs/spark ... talog.html How accurate is this in regards to the XJ?

I'm going to post up a pics of my plugs for comparison.

rob_lit - hopefully we can both solve our problem with the tips in this thread.

jackncoke - I will try cleaning out the YICS port first as it's the simplest "fix." Thanks for the tip!

fitz - The o-rings are only used on the xj700x model, the air cooled model uses only the gaskets, AFAIK. Can someone verify this?
My carbs received a full rebuild, including new throttle shaft seals, right before summer.

MN-Maxims - my float level was set to 1mm below the lip on the bowl, as per the manual. When I check with my Clear Tubeâ„¢ when the carbs are on the bike, the level is about 4mm lower than the bowl screw washer. Keep in mind, this is the same on all 4 carbs and #1 and #2 function flawlessly. Should the float level be raised?

Skeeter - while it is possible that the filter is restricting flow, I would assume that if it was doing so it would restrict flow evenly to all 4 carbs.

I'm off to take pictures of my plugs and clean my YICS passage!

 

took it for a short ride to see if the color would come back (was looking good up until the long ride).

no luck - plugs still white.

got to thinking that since ALL my plugs turned white, it makes more sense that it's a fuel delivery issue.

tried idling with the gas cap open and saw little (if any difference) in the plugs.

then i started looking at my fuel filter - noticed a bubble in the top of it. when i revved the engine the bubble got bigger. significant? maybe - i also noticed that when the tank was down (i had it propped up when i was looking at it) the "intake" side of the filter was lower than the "out-take" side of the filter. so i shortened the fuel line to try to get the filter to sit better.

when i put the filter back in, i couldn't get it to fill up with much gas - just a little in the bottom (yes i put it on PRI). when i started the bike up - no matter where the petcock was at, it would just drip down into the filter. so, i'm thinking that's my problem.

i'll post when after i'm done with updates.

 

Skeeter,

If the bubble is getting bigger, it sounds to me like the engine is drawing fuel from the engine side of the filter faster than the tank can supply it to the fuel side of the filter. I have a bubble in mine as well, just from where it rests under the tank, but even at full throttle the bubble size remains constant.

Check with Chacal on-site here - he sells fuel filters for a really reasonable price, and ships fast, too!

 

i think i may be on to something here - after i "levelled" out the filter i limped it home (afraid i only had the trickle of gas and what was in the bowls to make it). i kept it under 3,000 rpms and parked it.

i disconnected the filter and verified i have fuel gushing out on all petcock settings.

before grabbing the nearest available item and throwing it as hard as i could, i decided to look at my plugs again. #1 looked pretty good, #2 was BLACK (this has been the leanest running plug i've had - she's turned way out), #4 was a light shade of tan. (i've been ignoring #3 cuz at my first check it looked perfect). i turned #1 and #4 out a little bit and #2 in.

then, i idled it a bit and the plugs look the same. i then revved it up and held it for awhile and they look the same. i'm off to take a highway test and see what happens. oh me oh my the ups and downs of motorcycle maintenance.

i double checked with my wife that the filter i had her pick up in town was not a lawnmower filter or something - she said she got it from the bike shop, but i think i will be replacing it with a 90 degree filter - i think it will fit better.

would i be right if i said pinholes in the diaphragms would cause the same symptoms? they looked good to me when i cleaned the carbs, but i don't have the best eyesight, either.

 

Can't speak to the diaphragm issue (I haven't taken the clean carbs plunge just yet), but the 90-degree filter is indeed the one I bought from Chacal. I've had it on the bike for...six weeks now? Haven't had any issues with it. Admittedly, my guy's just a little 550RJ Seca, but I like to think I put her through her paces at times...

 

Do you have a colortune plug? It really helps with getting the mixture in the ballpark range for fine tuning, talk to Chacal and he can hook you up.

It is my favorite carb tune tool, guess I am easily entertained.

 

Alright, I swapped in a new fuel filter as the one that was on there had accumulated some crud. I also swapped the plug caps between 1 and 3 and 4 and 2, to see if maybe it is an electrical issue. I also redid the float levels on carbs 4 and 3, cleaned the YICS passage and then took her out for a spin... and nothing! plugs #3 and #4 have seen the smallest amount of improvement and still show way too lean while plugs #1 and #2 are too rich.

The picture is of the plugs before I rode. Not much changed after.

I am waiting for my buddy to get over here with his multimeter so we can sort out the resistance across the plug caps and coils and eliminate that from the list of possible issues.

I am really at a loss here... I've invested over 3 months of work and hard earned cash to fix this bike up and this is my last hurdle.

 

fuel filter helped, but did not solve the problem. if i keep rpms down, the plugs look pretty good. when i rev up, she leans out. must be a main jet or diaphragm issue. i'm gonna give a can of sea foam a chance to prove it's worth to me once again, and if that don't do it, it's carbs off time again.

 

you will want to verify the jets are the correct size and check your air jets have not been swapped in addition to what you mentioned. Sounds like the right places to be looking though.

 

i know from the last time i cleaned the carbs that the jets are ok. here's a question though: i've heard some talk about shimming jets, and i noticed that all of my main fuel jets have a washer under them. are these the jet shims i've heard about? i assumed this was normal at the time, but i'm getting to the point of "leave no stone unturned"

also, are those washers supposed to be concave, cuz all of mine are.

i assume that removing those shims would make matters worse.

and, in case anyone wants to know, i have a stock airbox (no pods)

 

Alright, so, I believe I have solved my issue of leaning out the plugs.

I borrowed a multimeter and tested the entire electrical system. The results: everything was in spec EXCEPT the ignition pick-up coils which read 164 and 146 ohms. Swapped in a pair I picked up from Cycle Salvage, adjusted the pilot screw on carbs #3 and #4 and went for a ride...

plug #3 FINALLY has a nice black/brown coating and plug #4 is brown.

In my quest to find what was wrong I kept thinking that you need "air and fuel" but left out "spark."

Skeeter: do you perhaps mean shimming the needle? This is done to introduce main fuel supply earlier in the RPM range. As far as shimming jets, I am unsure and will leave that for someone else to answer. I would also advise against the SEAFOAM route and to clean your carbs properly. I learned that lesson the hard way (as I'm sure many others have, also).

 

as i've been also discussing in this thread i think the fuel filter might've been the culprit. today at work i replaced it with a clear "cone" type and see some improvement in 1,3 and 4. i'm not sure about 2 just yet. i don't have much parking lot here to do a real plug chop but will be doing one on the way home. tonight i will either be having some beers and patting myself on the back for a job well done, or i'll be taking a look at my emulsion tubes.

the plus side is i'm pretty sure i'm not burning any oil.

and i see what you're saying about shimming the needle. just wanted to double check that the washer on the main jet was supposed to be there.

but, since we're on the subject of main jet washers - are they supposed to be perfectly flat? cuz mine are all slightly concave (or convex, depending on how you look at it . . .)