Desperate - Can't get the idle down and the richness up

Ugh. Okay. It's desperation time. I've spent hours and hours and hundreds of dollars and nothing is really making a difference.

I just don't know what's the problem at this point.

I'm trying to tune the thing, and no matter what I do I can't get the bike to run "too lean." I turn the idle mixture screws all the way out and it's still acting too lean.

I've gone over every piece of the carbs. Had them completely disassembled and cleaned and soaked every piece. All four carbs pass the "thunk" test. All the jets are clear and clean. The needles are pristine.

I replaced the intake manifolds, the vacuum caps, and the airbox boots. I replaced the throttle shaft seals and the idle mixture screw o-rings.

I've both bench-synced the carbs and I've vacuum synced them.

I checked and adjusted all the valves and they are all as close to spec as they can get.

I've been following this procedure: http://xjbikes.com/Forums/viewtopic/t=3 ... rtune.html to try and set the mixtures, but my results are fundamentally wrong.

Here's what happens:
I set the screws to 3-turns out on all the carbs. Start the bike, it runs terribly. I set the idle screw in really far just to get it to run. Then I start turning out each idle screw and going through the process of listening for the idle to raise, turn it back down, turn out the screws, idle raises, turn it down, and so on.

At some point, however, I can no longer lower the idle, because the idle screw is all the way out. At this point the cycle is actually running okay. Throttle response is reasonable and it doesn't backfire (much). The problem is that it's still too lean - it doesn't come down off the revs fast enough, and the idle is too high. This makes it difficult to shift and it whines at 1500-2000 RPM at stop lights.

I have confirmed that the throttle return is working fine. When removing the carbs, the throttles were actually closing so that the butterflies were tight against the carbs. My guess is that it shouldn't be idling at 1500 RPMs when the butterflies are shut tight!

What the heck is the deal here. Either I'm not getting enough fuel or I'm getting way too much air, but I've replaced every darned part that draws air!

In checking my plugs, results are inconclusive, and this brings another question. Everyone talks about looking at the white bit to see what color it is to get a sense of mixture. On all my plugs, one side tends to be dark, and the other side is light or white. Is this normal? Does this mean my fuel isn't atomizing properly or something?

I know this is a long post but I'm extremely frustrated and quite desperate. Please, oh ye gods of XJs, heeelp!

(for reference, this is a 1982 XJ650RJ Seca, so it has hitachi carbs)

 

Another little detail, I did the (forbidden!) "ether" test looking for vacuums. I can spray staring fluid all over the manifolds and carbs and it never picks up a single rev. I'm pretty sure vacuum leaks are out of the picture.

 

Looks like you have done everything, but I did not see andy refernece to checking the float levels. Float level is critical and will cause some of your problems.
Did you do a compression test? What are the numbers?
Post your location, maybe a member is near and could also take a look.

 

I have checked the float levels, they are all correct. I did a compression test. numbers were decent. If I remember correctly 115 125 115 115

Location: Des Moines, Iowa

 

A couple other details:

I have stock 4-into-1-into-2 exhaust with stock mufflers and stock air filter. I just replaced the filter with a new OEM one from Chacal.

 

If I back all the mixtures well out and back the idle screw all the way out it runs decently. Throttle response is very good, with no hesitation on the blip, and no backfiring. It doesn't hover too much and drops back down to idle steadily, just slower than it should. The idle is high, but not ridiculous.

It's ridable like this, and I've been riding like this for a couple months. The biggest frustration is that it's hard to shift, as the revs come down slower than they should.

I feel like I'm SO CLOSE.

I got a bit more liberal with the starter fluid and set the thing back up to 3 turns on the mixtures and the idle screw turned WAY in to keep it running. I was able to get the revs to raise up a little bit by spraying a ton of the stuff around one of the throttle shaft seals, but repeated tests were inconclusive.

I'm still curious about the spark plug "brown on one side and white on the other" bit. I'm have no idea if that's normal or not.

 

Is this something you recently bought? Are the fuel and air jets the correct numbers?

 

This complaint has elements of "Wrong jets"

Main FUEL Jets = O
Pilot FUEL jets = o

Main AIR Jet = o
Pilot AIR Jet = O

AIR Jets are OPPOSITE From FUEL jets.

Look beneath the Diaphragm.
Remove the Restrictor Plate (If they're still there.)
Locate the AIR Jets.

They should be in this order:

 

What method did you use to check the floats? Wet (with fuel) or just dry?

They're either in spec or they're not. Specs are a range, if they're outside that range, then they're NOT in spec.

A shortcut has been taken somewhere, or as Rick suggested there may have been some misassembly. If the valves aren't truly within spec, and/or you only "dry" set the floats, you'll have no luck tuning the carbs.

 

I just went through a little tuning nightmare.
I think 3 turns out may be too much?
When the bike is warmed up, hook your vacuum gauge up and then close the 1, 2, and 3 sync screws in that order. Your idle should jump way up. Lower your idle screw so its about 3-4k RPM and work from there backing your sync screws out and your idle should fall as you back them out again, maybe try getting it synced up with less than 3 turns out.
Another thing are you doing this with the YICS tool in or out?

 

The SECA has no YICS.

Checked the floats wet, using the clear cup trick as two of my drain screws are stripped out. So, I replaced the float boal with a transparent plastic bowl and watched the level of fuel directly.

Okay yes, the valves have a range. By "as close as possible" I meant "As close to the center point of the range as I can get based on the precision of increments of the valve shims available for purchase." I.E. as in-spec as they can possibly be.

 

Regarding the jets, i checked the air jets (on the top) I had had them backwards when I first put the bike together and that caused a way way too RICH situation. I currently have them as you've pictured, and they have the stock values (195 idle, 50 main)

 

Regarding the jets: It's also possible to mix up the FUEL jets as well. Might want to double-check.

Re: Valve clearances: The Haynes manual has an incorrect spec listed for the 650R, as does one of the factory books; it incorrectly lists the same specs for intake and exhaust, .16~.20mm.

The correct spec for intakes is .11~.15mm, just like the rest of the aircooled XJs. You didn't by any chance use the .16~.20 spec for the intakes did you?

In regard to checking float levels on bowls with stuck screws, you can just move a "good" bowl to the carb you need to check, then put it back where it belongs. I know you're reasonably sure of the float levels, but a low float or two will cause lean running on those cylinders.

I realize that some of this seems redundant, but I'm just trying to go back over anything that might be causing the problem.

Pop the vacuum caps off the intake manifold spigots and see if they're still pliable, or hard as rocks and only LOOK fine. Might be as simple as a few dried out little rubber caps.

 

I'm pretty sure I did the "correct" valve clearance specs. I remember setting them differently than the exhaust. I asked around here a bit first before setting them.

I also just replaced all the vacuum caps with brand new units.

the interesting thing about the problem is that it seems to be affecting all 4 carbs equally. Also, regarding floats, I'm pretty sure I had too MUCH fuel in them, as I was getting a decent amount of overfill leaking into the cylinders. I've actually just adjusted them back a little bit to lower the levels and it's running the same (not sure if there's less overflow yet)

 

Not trying to offend you, but you've got too many "pretty sures" and "not sures" in your troubleshooting.

-Double check your valve clearances. Record and post.
-Run a compression test- post results.
-Double check ALL jet placements.
-Re-do your float levels using clear tubing, as per the factory-recommended procedure.

"Hanging idle" is usually a symptom of an out-of-sync condition, or wonky float levels, or both.

 

it's not so much a hanging idle as off-throttle it drops down to idle just fine. the idle is just too high. With carbs synced and the idle screw all the way out, all the butterflies close tightly to the carb bodies (I have observed this by removing the carbs), and it still idles at about 1,500RPM.

the odd thing is that it seems fairly consistent across all 4 carbs. I would believe some sort of assembly problem; I do need to check the fuel jets, but i can't imagine it would be running well at ALL if that were the problem. The air jets are definitely in the right place, I double checked them yesterday.

The compression numbers I posted are +/- about 2. They were all very consistent, all over 110.

I double checked valve clearances at the time and have them written down somewhere. I'll try and find the numbers but I rode out of town last night and won't be back for a couple days.

I can't do my float levels using the tube method, as two of my four drain screws are stripped. besides, I feel the clear bowl method to be more accurate. not only can I see the float level at the point the manual says to look, I can see the float level across the whole bowl. Carbs were leveled when I checked them. I can say with as much certainty as one can possibly say that float levels being low was NOT an issue.

It seems like a vacuum leak, but it's still odd to me that it's so consistent across all four cylinders. I do want to check the valve clearances again just to be sure; that's one area where I could see an issue, especially with the confusion about what they should be set at.

I'm getting pretty familiar with the inner workings of the bike (I actually tore this guy down to the frame and tore the engine down to the empty case to fix a transmission problem and reassembled the whole thing from scratch) but there's a few concepts about carbs that I'm not sure of:

question: Is there an air bypass built in to the carbs that allows air through regardless of the position of the butterfly valves? In other words, with the butterflies completely closed, should any air be able to flow into the engine? If no, then that leads me to the problem, as air is definitely getting in somewhere. If yes, them perhaps there is an issue with how I re-assembled the carbs regarding that bypass, and I did something that's causing too much air to flow through?

You do have me really curious about valve clearances though... if the intake valves are too open, it would certainly be drawing in more air... and thus running more lean.

Okay you've convinced me, I'll definitely re-check my valve clearances when I get home.

 

Compression figures are below Minimum Specs.

The Pilot Mixture Screws are AIR Jets.
The Pilot Screw essentially regulates AIR.
Because the AIR Passage is married to the Pilot Fuel Jets Supply, ... as the Pilot AIR Jet is turned to let more AIR into the Combustion Chamber ... FUEL is siphoned from the Pilot FUEL Supply and it MIXES with the AIR.

The AIR Supply is what you are adjusting.
The FUEL Supply is FIXED by the size of the Pilot FUEL Jet.

The FUEL Jet, ... the connecting PASSAGES, ... the Upper AIR Jet and PASSAGE, ... must be free and clean for the Pilot System to function correctly.

IF the Pilot FUEL Jet is clogged ...
ONLY --> AIR will be drawn-into the Combustion Chamber.

Limited by: The Pilot AIR Jet and the condition of the tiny O-ring.

 

That's below minimum specs? That's a bummer.

What would cause that? I just had the engine completely apart. Could bad valve adjustment cause low compression, too? The valves looked to be in decent shape, as well as the seats, the piston rings looked great, and I just put in a new head gasket; everything torqued to spec.

Regarding clogs, I thororoughly disassembeld all the carbs and soaked all the metal parts, and inspected every jet. They were actually really clean in the first place, no gunk, no residue, no clogs... but I cleaned them anyway. Blew them all out with an air compressor and soaked them in parts cleaner.

If there was just one carb misbehaving I could see something getting stuck in there but they're all four misbehaving equally.

I also just replaced the tiny o-rings in the idle air jets.

Good to know about the idle mixture screws in general. That makes a lot of sense. What you're saying is that the idle mixture screws THEMSELVES form a sort of air bypass to the butterfly valves. Bringing in air after the throttle to mix with the already-mixed fuel. This would explain why the bike idles with the throttles completely closed, because at this point air is being provided almost entirely by the mixture screws?

I'm gonna check and set those valves and subsequently check compression again as soon as I get home.