Freshly rebuilt / cleaned carbs and issues

First off, thanks to everyone here for sharing their knowledge and love of these bikes. I've found a wealth of information here and it's readily accessible. Cheers!

Now, I've got a 1982 (1981 style non-YICS motor) XJ650. I just cleaned the carbs and installed fresh seals, gaskets, and float needles. I bought a set of new intake manifolds because mine were in bad shape. I adjusted the valves so they were in spec, installed the carbs, and synched them successfully with a 2-bottle sync tool. I tried to tune them using a colortune plug kit, but couldn't get normal combustion while I was using it. I tried it on cylinders 1 and 2, and 1 would occasionally flash blue (I could see spark far more often than I could see combustion?), while 2 was always yellow. I tried adjusting the idle mixture screws a little bit, but they didn't seem to do anything.

When riding the bike, it has almost no power. It'll rev freely up to about 5000 rpm then stutter in neutral. Since I can't seem to get the colortune to work, I'm not sure where to start.

Any suggestions would be very much appreciated.

Thanks,
Aaron

 

Stutter at 5k sounds like bowl fuel levels may be a bit low. Not sure why you are having colortune issues. You said #2 stayed yellow - did you try adjusting the screw in a good bit to see if you can get blue?

 

I hate to recoimmend this but.... Take another look inside your carbs. It is possible on the hitachi carbs to swap the pilot and main jet around. they look the same anf fit in eachothers places. You wouldn't be the first. You have to read the numbers and make sure they are where they need to be. ON the other side make sure you have the throttle and choke cables in the right place. What you describe with the 4-5k range and stumble is what the choke(enrichment circuit) does if I leave it on on my bike. You do have an airbox and filter installed correct? Yes it makes a huge difference.

 

I would have to agree with 85MaximXX... You wouldn't be the first and neither was I...
I don't remember the numbers on the jets, but the bigger jet feeds the smaller jet takes... I had 3 carbs out of 4 set up the wrong way due to a PO... I followed the odds and switched the remaining carb to the same direction, and made it worse... Next day I realized my problem, turned everything around the right way and could barely hold on when I gave it gas...
Mine revved up great in Neutral, but as soon as I tried to go in gear it ran terribly lean...

somewhere on here I saw a pic of what it should be. numbers and all... maybe in the service manual too...

Hope this helps.

Chris

 

Lets be PERFECTLY Clear on Jets and Placement.

Bottom / Fuel Bowl End.

Main FUEL Jet Large Metering Orifice >> Mounts to Emulsion Tube.
Pilot FUEL Jet Small Metering Orifice >> Mounts to Pilot Fuel Passage.

Top Side / Under Rubber Diaphragm / Under Baffle Shelf (If shelfs are present)

Air Jets:
Top Hole >> Pilot AIR Jet >> **LARGE** Metering Orifice

Ctr Hole >> Main AIR Jet >> **small** Metering Orifice

Bottom
Hole >> Blind >> Threaded for Shelf Special Fastener.

Pilot AIR Jet >> aka: Pilot Mixture Screw

Factory Preset: 2-1/2 Turns Out from Bottom.
Dealer Corrected: 2-3/4 >>>>>>0<< 3.00 Turns Out
(More than 2-3/4 Turns Out ... But, not quite 3.)

Member ColorTune Data:
Most Members report needing to adjust the Pilot Mixture Screw beyond 3.0 Turns Out for correct colorization and Richness.

 

Thanks for your responses!

I have already had the carbs back off three times! Turns out a did a piss poor job the first time of setting the float levels. Back off a few times to fix that. Was using tube held by the side, ended up doing the 17.5 +- .5mm off the base. That worked.

I checked all my airbox to carb boots and found some that were seated 'funny'. I won't say they weren't seated, but they just weren't quite right, so I fixed them, and so far so good. I'll be riding an hour each way to an engagement tomorrow so that will be a great test, but she feels great so far with more power than I've ever felt outta this little motor!

If I have more problems I'll take the carbs off. I'm almost a pro at it by now!

Cheers,
Aaron

 

Sure enough, my airbox to carb boot on cylinder three kept coming off at the carburetor. I think old age has warped and shrunk this rubber, so I can't stretch it far enough to get a good clamp on the carb throat.

Also, it seems that the rubber is thinner from old age as well so when the clamp is fully tightened on the boot/carb, it's still not all that tight.

To make matters worse, guess what happens to the airbox when lots of vacuum (load/throttle) is applied? It bows in toward itself, pulling any unsecured boots off the carbs! So, I can seat the boot on the carb, rev it up just fine, but as soon as the engine is loaded, it pops right off! The only real way to fix that is to order new boots that are the correct length and thickness. I went so far as to try adding electrical tape on the outside of the boot so that it would be thick enough for the clamp to get a solid hold on it... And that did nothing at all.

Anyway, just wanted to come back with my results so if others are having similar problems then can start here (it's a lot easier than pulling the carbs!)

Cheers,
Aaron

 

"The only real way to fix that is to order new boots that are the correct length and thickness. I went so far as to try adding electrical tape on the outside of the boot so that it would be thick enough for the clamp to get a solid hold on it... And that did nothing at all."

Some of us have used flexible tubing from Lowe's (1x1/2 by 1x1/2 flexible coupler) that fits perfectly. Plus, they cost about 3.80+ tax.

You might give that a try.. here's the link to the "how-to"

http://www.xjbikes.com/Forums/viewtopic/t=18757.html

 

Move the AirBox Closer to the Carbs.

Look at the Bolts securing the Box right under the seat.
If they aren't all the way forward ...
Loosen them and MOVE the Whole Airbox around.

 

That was the first thing I did! Thanks though, Rick, for the suggestion. I actually thought about filing down that groove so I could move the whole assembly even closer to the carbs with a small rat tail file.

I ordered the correct boots along with a new clamp to replace one of mine that is in sorry shape. I may run down to Lowe's on Monday to try the pipe coupler thing just to see how well it works. I'd rather have the correct boot on there long-term, though.

Thanks for the ideas and suggestions!

 

OK, well, it's partially fixed. Airbox to carb boots are seated correctly now, and it revs up to 7K+ in neutral, without issue.

I pulled the carbs again and set the float levels using my calipers to 17.5mm off the gasket mating surface, then verified with the clear tube. I also verified that the pilot fuel jet and main fuel jet were where they're supposed to be on all four carbs. Everything looked fine (except for a stuck float that flooded the carbs a bit... fixed with a tap tap tap) as I installed on the bike. Test ride showed that it delivered more power than before, with better acceleration, but still didn't want to get up over 5500-6000 RPMs in any gear at WOT.

Suggestions? Would the carbs not being synced properly do this? Or the idle not being set correctly? It sounds better at throttle too, but just doesn't want to get up in the revs...

Thanks,
Aaron

 

Check your plugs. Did you make sure you pilot and main jets are correct? I had almost the same issue with poor throttle response (wouldn't go over 60mph bc of the main and pilot jets were in the wrong spots. ) plugs fouled horribly.

Good luck!

 

I had a problem with my Seca 650 breaking up above 4 grand. After checking and rechecking everything over and over I stumbled upon a slide needle that had been pulled down in its plastic holder when a po forced open the slide stuck to the emulsion tube with varnish. This pulled down the needle effectively leaning out that cylinder. The needle has a shoulder machined into the top that if seated properly is not visible. If you can see the tapered are at the top of the needle then that is your problem.

 

My plugs are getting black FAST.

First off, I found out that the stealership sold me the incorrect resistor plugs - BPR7ES. I replaced them with the correct plugs BP7ES and surprisingly saw no major change in the way it runs. I ran it around the block a few times and they're already black on the cylinder I checked.

On top of that, it seems to be running funny all over now, and doesn't seem to want to rev high in neutral, after it warmed up. I think I'm gonna check out the ignition system next.

Next time I pull the carbs I'll inspect the needles. Thanks for the info.

 

The R stands for resistor, which shouldn't affect the running of the bike. The plugs getting black though, that is a telling sign that something is amiss in your carbs. As much as I hate to say it, it sounds like you may have to take your carbs off yet again and see if you can determine the problem. Did you clean the carbs (as chacal would put it) "zestfully clean"? Clunk test? Spray test? Jets all in order and the correct size? Your manual will tell you the jet sizes.

The main problem with these bikes always seems to come back to carbs.

 

I was thinking that I was having a weak spark, as a result of too much resistance in the primary ignition system! But, as it turns out, that's obviously not that case.

The carbs were pretty dang spotless when I put them back together. I will pull them off again and go through them again. I know the linkage and everything works fine, so there isn't any need to take them off the rack, right?

I just want to ride, and the summer's half over already!

Thanks for your help,
Aaron

 

An engine that is not synched will produce all sorts of funny, hard-to-diagnose problems. Assuming your valve clearances are within spec, a full and proper synch (and colortune procedure) that would be the next step to carb perfection......

 

Well, the way I look at it, we're all in this together.

You shouldn't have to break the carb rack down. In fact, at this point, I suggest you don't. Make sure you bench sync the set before you throw them back on.

Does the motor turn over easily? Or do you have to crank and crank? Is your battery completely charged? Original coils?

You can check resistance with a simple multimeter (both primary and secondary) to see what kind of juice is flowing. You can also check your plug caps, see if there is any resistance there. Post your findings.

As far as the carbs "looking" clean, there are a lot of small passages that, if blocked, can lead to the issues you're describing. I should know. I had this same exact problem, and removed my carbs several times before I got it right, and that was following Rick's excellent Carb Cleaning 101 guide.

Probably everyone on this board has pulled their carbs several times, for a variety of reasons. Don't sweat it.

 

Yeah, the motor turns over easily and fires right up. I know the pilot circuit is working well because the dang thing fires right up and idles rock solid. The battery is nice and juiced and the coils and wires are original.

I'm not too worried about pulling the carbs so many times, I'm a pro at it now! I remember looking at them the first time, thinking, "How am I supposed to get these stupid things outta here?" and now I just do my thing and they're off in ten minutes.

So I'll triple check the main and pilot fuel jets, and also check the air jets as well. I will bench sync again as you recommend, then sync using my baby bottle sync tool after it's all back together.

I'm pretty sure the float levels are A-OK now, as I just set them and when I rechecked them this morning on the bike, #1 and #4 were just right. I didn't do #2 and #3 cause they're harder to get to and they looked the same as #1 and #4 last night.

 

I know what you mean! I've helped a couple different people tearing their carbs apart, seems elementary. Let us know what size jets you have in there. Mine were all mixed up, even though I put them back where they were EXACTLY as they were taken out.

Doesn't hurt to be a little OCD when it comes to carbs.

 

OK, so I've got #40 in the pilot hole, and #110 in the emulsion tube (main fuel jet). I did notice the washer on one of the main jets was not the correct one, it was much thinner and also smaller OD. I swapped it with a good copper washer from my spare set of carbs. Not sure what, if anything that'll do... It means that the jet itself was a tiny bit closer to the needle.

I'll bench sync the carbs while I've got them off the bike. I checked the pistons and they are still in good working order, and respond to vacuum applied to the right place (not sure what the oblong port on the airbox side is called). Floats looked fine, needles looked fine. I blew air through literally EVERY orifice that I could, save for removing the idle mix screw and the enrichment circuit plunger, but I was able to put carb cleaner through them fine with the carbs apart, and their operation is normal.

Air goes thru:
main fuel jet + needle
pilot fuel jet
both air compensator jets
main and pilot air jets on the one carb I checked. I know I put those all in the same, and they're correct - #50 main and #195 pilot
enrichment pickup tube
enrichment well on carb bowl

OK, do I need to pull all the diaphrams out and check those air jets now? I only pulled one as I'm 99% sure I installed those jets correctly... and if one was right they all should be right. I was really meticulous about those jets.

What else, while the carbs are off the bike?

Thanks!
Aaron

 

Butterflies open and close easily? Clean? I washed the screws that adjust the butterflies down with carb cleaner, then applied some wd40 to them.

The ports on top of the carbs do have their respective covers, yes? I'd recommend throttle valve seal check, but you'd have to tear the carb rack apart to get to them all.

No pinholes in the diaphragms? The diaphragm tabs are lined up correctly in the slot? Needle/spring/cap all in place?

Do you have the springs in upside down? (just messing with you there...

Sounds like you've done everything humanly possible to those carbs... anyone else care to chime in?

 

Primary and secondary ignition coil resistances check out fine, they're within the 10% and 20% specified by the books.

Plug caps resistances, though, are not right. I got 7K ohms on caps for cylinders 1 & 4, and 5K ohms for cylinders 2 & 3.

In the service manual, it specifies 5K ohm caps for 1 & 4, and 10K ohm caps for 2 & 3.

Is this important?

EDIT: Total resistance of both coils (secondary resistance with caps) is about 27K ohms.

 

Only if you're OCD. Actually, it may just be some corrosion on the little screw on the inside of the cap. Or, it may be the beginning of the end for that particular cap.

Either way, replacing them is pretty easy (and cheap).

 

Len,

Would the carbs being mostly synced but maybe not 100% synced cause it to choke at 5-6K RPMs? That seems a little weird to me, but then again, my background is in fuel injection, not multiple carbs.

Reason why I ask is I used plastic bottles for my sync tools as I couldn't find glass ones. Last time I synced, once I got them close, everytime I'd start the motor the bottles would start to collapse, throwing the reading off. I think they're pretty close, but I dunno if that's good enough.

And for some reason, I had issues getting the colortune to work right, but that may have been due to the other problems I've been having that are now fixed.

 

Once you start getting into the upper part of the Power Band ... Your FUEL Supply is the Main FUEL Jet Output.

The factors for making more Power are pretty limited when you wrist-it Wide Open.

Fuel Supply from Tank to Combustion Chamber must be PROPERLY REGULATED and FREE FLOWING.
No Vacuum created within the Tank
Petcock Tower Screen Not Clogged
Petcock Metering Wafer Not Slipped
Passages within Petcock Not Clogged (Use Weed Wacker Line to Probe)
Petcock Vacuum Valve fully operational.
Hoses not clogged.
Inline Fuel Filter Not Air-Bound (( <<--- Impedes Flow))
Float Valve Beenie Screens Clogged
Float Heights Incorrect
Main FUEL Jet wrong size.
Emulsion Tube Air Metering Ports Clogged (( <<--- Common))
Pilot & Main AIR Jets Incorrectly Placed (( <<--- Haynes Error ))
Vacuum Diaphragm Pistons Sticking
Diaphragm Rubbers Cracked, Split or Pinholed
Diaphragm Rubber Not Installed in Locating Channel (( <--- Slip-out ))

 

Probably not, although some people might say that being "almost synched" is akin to being "almost pregnant"......there ain't no such thing! It sounds like you're covering all the basics with the carbs, make sure the air jets are in there correctly, big one up front, small one in the center hole, rear hole is for the cover plate screw (if used, not all of htem do), the needle should be a Y-10 and make sure the plastic head caps of the needles are pushed down onto the top edge of the needle shaft....and of course all of the other advice given in this thread........and then make sure you do a full and proper synch.

 

You guys rock! I've got a good list of things to doube, triple, or OCD check tomorrow, and the first thing is gonna be the gas tank/petcock since that's the only thing I haven't looked at at all yet. I was told that one way to clean that out is to blow compressed air through the petcock in reverse to help force crud outta it. Any thoughts before I fire up the air compressor?

I haven't thought about the fuel filter airlock thing, I'll look into that.

 

NO! You'll rupture the rubber diaphram inside the vaccum side of the unit!

 

OK, I'll take it apart and clean it that way then. Thanks for the warning Len!!!

 

Took apart the petcock, cleaned it well. Everything inside looked perfect. When you apply vacuum to the petcock, it very slowly releases it. Is that correct? It makes sense to me because you want CONSTANT vacuum in order to flow fuel, so if there's a slow release of vacuum it would ensure that as soon as the engine is turned off, fuel stops flowing.

The screen in the tank was a LITTLE dirty. The part about the air-locked inline filter though has me thinking a lot. I know mine has always had air in it. What is the best way to purge the air from the filter? It would make sense that if fuel isn't flowing fast enough to the carbs to replenish the fuel used at high RPMs it would bog down.

I just checked every main/pilot AIR jet and am certain the diaphrams are seated. The more I think about it the more I suspect that fuel filter...

I'll reinstall carbs, try to purge the air from the inline filter, and see where I'm at.

 

I'm an idiot. No, really.

It all comes down to faith. See, since I haven't had this bike too long, I wasn't sure about its reliability. I wasn't sure if I'd have some weird problem and get stranded somewhere. I wanted to be able to get myself out of a bind if necessary, so I have been carrying tools with me. These basic tools (socket set, pliers, screwdrivers, electrical crimpers + connectors) were stuffed under the seat.

Under the seat... What else is under the seat? THE AIRBOX INTAKE! Yeah, somehow I had blocked part of the airbox intake with the tools and their bag, not allowing enough air into the box, which made it run under too much vacuum, pulling too much fuel and running rich, not letting me get above 5000 RPMs. Hmm, that would explain why my fuel economy was about half what it should be.

I was so sure I had done something stupid with the carbs, or the fuel delivery system, or... that I blatantly forgot some very basic troubleshooting.

Thanks for the wonderful ideas, I do now know that my carbs are SPOTLESS and PERFECT in their operation, having gone through them so many times. Now, I can relax and ride my motorcycle with a huge grim on my face.

Cheers!
Aaron