What am I missing??

[XJ Rob]

Its been 4 years since I last posted about this problem. Life happens and things get put on the back burner I guess. I have been working on an 81 special on and off for the past 4 years. The problem I'm having is.... I cant get it to rev AT ALL, AFTER it warms up just a couple of minutes. Cold, it runs and revs great!! I've been through the carbs a dozen times I have went from 125 mains down to 110s across the board. I know it shouldn't have adjustable needles but it does ( PO put them in) The factory needles are NO longer available. Tried them in every slot possible. I have fixed a broken pick-up wire (the white one). Changed coils with another set of used ones. Cleaned all the electrical connections from the battery TO the headlight bucket (haven't opened it YET). This bike is STILL fouling the plugs black. Mixture screws are only turned out 1.5 turns. The battery is brand new this year. It has a full charge. After the bike stalls from trying to rev. It starts up after a few seconds of cranking and idles perfect. What am I missing. My original thread is posted if anyone wants to read it.

http://www.xs11.com/forum/showthread.php?t=28248

Thanks

[MPittma100]

Missing?

Black (rich) plugs means one of two things - too much fuel or not enough air.

Verify a few fuel related items: Check fuel cap vent to be sure it is not clogged. Make sure that the two vent lines for the carburetors are clear. Verify that you have proper fuel flow from the petcocks to the carbs. Carbs have to be super clean. If bike has been sitting a while with gas containing ethanol it, it is time to clean them. 1.5 turns out is normally not enough for the screws. Carbs need to be synced to get proper response. I would put the jets that are supposed to be in the carbs back in. Jet needles can probably be found on eBay or may find a member who has them here. Go to the "parts wanted" tab.

Check all spark plug cap to wire connections for corrosion. Pull apart wiring connectors, including the one in the headlight bucket and especially the one behind the fuse panel. Clean them if needed and put them back together using di-electric grease.

Verify that the charging system is working.

There are many threads on here for these procedures if you are not familiar with the how-to. You will get it running right.

Mike

[natemoen]

I agree that if the carbs have been sitting with gas in them then they need to be cleaned out again. I would also try removing the bottom of the airbox and running it and see of that helps. Or if you have pods, remove them and give it a try.

[Crusty Snippets]

Not running proppa

My 400 Seca is doing similar things, and I tried the same things you have. It is running way lean. The carbs also sat for a while. My latest bright idea is that the tube / air passage to the top of the diaphragms is partly blocked.
Will report back if that fixes it.

My XS11 runs real sweet but rich. And he runs better with new plug caps.
Got some good tips reading this thread.

These diaphragm carbs are new to me, so I am in study mode.

Unkle Crusty

[Dylano*]

Have you adjusted your pilot jets at all? Maybe the po put in incorrect pilots? I would think it would be more pilot jet related, rather than the mains, if it won't rev AT ALL ....now if in fact it revvs some, and cuts out only after about a quarter throttle and getting in slightly higher rpms, then I can understand looking at the mains, but otherwise I'd say pilots! And yeah like has been said, it could be lack of air rather too.. pods or stock airbox?

[motoman]

Have you adjusted your pilot jets at all? Maybe the po put in incorrect pilots? I would think it would be more pilot jet related, rather than the mains, if it won't rev AT ALL ....now if in fact it revvs some, and cuts out only after about a quarter throttle and getting in slightly higher rpms, then I can understand looking at the mains, but otherwise I'd say pilots! And yeah like has been said, it could be lack of air rather too.. pods or stock airbox?

Hi XJRob,
Definitely been awhile since being on here.
First off, the main jets are WAY to big! Stock mains on the XJ are 112.5's across all four.
Secondly, since you say the metering rods have suspiciously been changed, pull the vacuum caps and remove the slides. Pop the little clippy and remove the metering rods
Using a magnifying glass, look on side of metering rods near the top, and report back here the numbering/lettering on those rods. That will determine the main jetting needed.......ironically even if those later carbs have had the earlier carbs adjustable metering rods installed, (which i suspect), 120mains on center two cyls., and 117mains on outer two cyls.
This is from 3Phase's set-up on his 80Standard with the earlier metering rods. I would think 70+thousand on that set-up for the past 4yrs., with most of that duty done on LD rides............and I DO mean LD RIDING!
Back to your issue........need to know what metering rods are used before proceeding with correct jetting..........and of course, those mains HAVE to be Genuine Mikuni with the Mikuni logo stamped into them adjacent the numer size, no aftermarket junk like K&L.
Definitely curious as to what metering rods are in those carbies.

BTW, bikes running issues are, at this point metering rod and main jet related, not pilot jet related. Even though the later carbs circuits are more seperated as opposed to the earlier carbs, some fuel IS still drawn thru main circuit at lower rpms.......that IS a given!

[TopCatGr58]

I followed his link and viewed his old thread, he did post some photos of the carbs and they ARE the later model/style. I then followed the link to this photobucket account and grabbed these few images that shows the Jet Needle, the Slide Needle, and the main/pilot jet!

Jet Needle
Slide Needle
Jets

I can't see the Mikuni Logo on the top of the main jet! However, as has been said, sitting for 4 years, he needs to pull the main jet NEEDLE/emulsion tube and clean it again, as well as probably getting the real proper Mikuni jets and then he might be able to play with the adjustable slide needle??

T.C.

[XJ Rob]

I have pulled these carbs again THIS year. Cleaned them. Checked the float levels, Synced and even checked with a colortune. The jets and needles were in there when we bought the bike. The PO had installed a K&L kit and had installed 125 mains. He said because of the 4 into 1 pipe. There is a K&N filter in it with a stock airbox. My dad ordered 115s last year from MikesXS. I ordered 110s this year from
http://www.buyatvpartsonline.com/mik...c-699_707.html.

The emulsion tubes are the same ones pictured. I have cleaned those as well. This year I have repaired the pick up wire and cleaned all the electrical connections from the battery to headlight bucket. The fuse box has also been replaced.

One thing I can say I've noticed is, if I rotate the pickup coil CCW with my fingers, while its running the rpm's come up to above 1500. Could this whole problem be in timing??? My thought is .... It wouldn't rev cold either if it was timing. I also noticed that the plate that has the timing marks on it that is in front of the pickup coil has a slight wobble like it's bent. How important is it that it run "true"?? Also when trying to rev it very slowly, the vacuum advance causes the pickup to " Bounce" as if it doesn't have a smooth constant vacuum. Is this normal?? I am working on my dad's 81 Special. The XJ is mine and it runs fantastic.

[motoman]

Well, sounds like the vacuum advance hose is hooked incorrectly. Needs to be on #2 carb port NOT carb boot.
The K&L main jets that are obviously in it are NOT necessarily tottally wrong, since it DOES have some other mods. K&L sizing is done differently than Mikunis, and DO run substantually larger when compared to Mikunis the same numering size. If those are the later carbs with the recessed mixture screw adjustment, for whatever reason from T.C.'s posted pics, the metering rods are from the earlier 78-79 carbs. Those carbs originally had the 5GL16 metering rods that were in 80-81Specials and MidniteSpecials, non adjustable.
If you know for a fact it previously ran good, then a through cleaning, (removal of emulsion tubes IS mandatory, toothpicking all holes) of all the carbs is gonna be necessary for any kinda' baseline.

[natemoen]

I am still pointing at the needles. I fought running problems for about 2 years until o found out that I had the spacer on the wrong side of the clip on the needle. It was a night and day difference after I changed that spacer.

[XJ Rob]

This bike has never ran good since it's been bought. The vacuum advance is connected to the carb. I no longer have the 125 mains that were in the bike when we got it. For the couple mods that were done, the 125s seemed a bit much. It has always ran rich, and I have never been able to rev the motor. Jets were cheap. I'm afraid I'm working with a mixed batch of parts with the needles and mains. I am pretty sure that's all that was changed in the carbs before it was bought. The idle jets are still 42.5 stock.
If I'm correct on how the needles are stacked in the slide. It goes,

Plastic spacer at the bottom
C-clip in one of 5 groves
Small flat washer on top of the C-clip
Spring on top of the washer
Then the hold down with the screws.

[3Phase]

Wrong parts

Rob,

I noticed that you mentioned stock 42.5 pilot jets. That's not stock unless someone changed the carburetors and put on '80/'81 BS34-III carbs off of an XS1100.


The XJ1100 carburetors are supposed to have:

X2 needle jets / emulsion tubes (No Longer Available)
5GLZ34 jet needles / slide needles with non-adjustable clips (No Longer Available)
If the needles you have are stamped "Y80" they're most likely Keihin needles, not Mikuni.

112.5 main fuel jets
140 main air jet (press-fit, not easy to clean or replace)

47.5 pilot fuel jets (Mikuni N151.067 non-emulsion style, similar to the BS30/96 jets but without the air bleed holes)
170 pilot air jets.

If some or all of those have been replaced with after market parts and/or parts from the wrong manufacturer it may be difficult to adjust the carburetors.

.

[XJ Rob]

Rob,

I noticed that you mentioned stock 42.5 pilot jets. That's not stock unless someone changed the carburetors and put on '80/'81 BS34-III carbs off of an XS1100.


.

I am working on an 81 Special. My XJ runs great.
I pulled the lower part of the airbox off and no change. Fire right up cold and reved for about a minute. After a minute or so it was back to stalling when I tried. The plugs are black and sootie so I will get some new ones again.
I'm going to pull the carbs AGAIN and lower the needles all the way down. They are in the middle slot right now. Clean everything for the 4th time this season and put it back together.

[Crusty Snippets]

Pics

All the pics and info is helping me understand these carbs. For the 400 Seca, I have a photo of the carbs from the manual in my phone. Carbs look about the same.
My XS11 sounded like it was going to blow up at freeway speeds. But after I changed the pipes Yami runs real sweet. So the jetting was wrong for the old pipes.
Will continue to work on the Seca carbs and get it running right before I thouch the carbs on Yami.
I think you guys are calling the emulsion tube what the book calls the main nozzle. The part that the jet needle slides in to.
It is handy to have a blow up photo of the carb.

Unkle Crusty

[mack]

Carbs

with the plugs fouling like that it is likely a plugged pilot circuit. It's the only circuit that is functioning through all throttle settings. It's difficult to be too helpful because the carb set up is confusing me. The adjustable needles were on the 78 /79 carbs but the emulsion tubes look wrong. This is a mixed bag of parts.
Beg/ borrow a set of 80/81 carbs and try them before you pull all your hair out.
I think I have 5 sets here but 3 are for midnights and two I've torn down and cleaned, but haven't put them back together yet because I've been experimenting with ways to polish the bodies. If you can't find a set close to you, I can throw a set together and send them to you for diagnostic purposes.