Ever feel like you met your match??

[DGXSER]

So, I went to XS East this week end. On the way to the rally I discover my rear tire is rubbing the swing arm. Let some air out, resolved enough to ride the weekend anyway.

Saturday, 70 miles into the run we stop for gas, shortly after I notice I have a low end miss. Brent was kind enough to put some Lucas in the tank, still no joy. So, I make the rest of the run limping on low end. Decide Sunday to head for home and not chance breaking down on the run. It runs fine at top end, I'm getting 38 MPG, can't tell anything is wrong above 3k. Made it home, 3-1/2 hours around 200 miles with no problems. All highway, running about 5k rpm at around 70-75 MPH.

So I narrow it down to no 1. Start to pull the carbs and see my mixture screw is gone. So I get one form my bag-o-carb-parts. Put it in, not much difference. Put the colortune in, sparks galore, bu mostly no combustion even with the mix screw almost all the way out, still looks lean, and only combust every so often.

So off with the carbs, cleaned them twice today. Still no joy. I am about out of clues on this one. I did synch and all four are about dead even on vacuum. I checked compression, dismaying but thats another story (around 100 PSI across the board. At least they are even.)

I did notice that when I first started the bike after removing the carbtune, but having missed the step of reinstalling the vacuum plugs, I got a backfire out of no 1 carb vacuum port a few times.

So, at this point, I am taking a break and open to thoughts. I'm leaving town for a few days so I will have time to regroup and renew my comittment to the Banshee.

[bikerphil]

Don, sometimes those colortune plugs don't fire all that well, try a fresh or known good plug in that hole and you can also try swapping wires, 1+4 and see if the problem moves. Could be a flaky spark plug cap.

[newc4]

I'd say its the pilot circuit still. Third time might be the charm, hence triple clean. On the later models I'm not sure if its a somewhat different mix screw. Might want to swap one with another carb that does work.

[DGXSER]

Thanks for the suggestions.

Phil, the colortune appears to have a good blue spark but does not fire the cylinder, which leads me to think fuel. I did swap plug wires with one and four and the problem did not move. I also put brand new NGK BP6ES plugs across the board, no change.

Darrell, ( I am still trying to put faces with names from the rally) I would tend to agree on the triple clean side if I had not gone through each and every orrifice as carefully as I did. It fires every so often, just not all the time. I just fired it up, rode it about 2 miles keeping it at or below 2k too keep it in the idle circuit. All four headers will sizzle water, but no 1 cools off and will let water drip off after several good sprays. That is with it still idleing

Something I have noted that may or may not help, it backfires out the left side pipe when you let off the throttle. I have had it pop a little on hard decel before, but this is a definite backfire, pop as soon as you let off the throttle and will continue as it idles every now and then.

[bikerphil]

Another thing that comes to mind is a loose pilot jet. I've taken carbs off a bike that had just been cleaned and found a pilot laying in the bowl, JAT. Maybe a vacuum leak from the intake boot gasket or the brass sync nipple came loose. Just throwin' ideas around.

[DGXSER]

Thanks Phil, I will check for vacuum leaks. The intake boot has some pretty good cracks on the outside, but looked good inside. Still worth a check.

I did think of the loose jet, however it was still in place both times I cleaned the carbs.

[GLoweVA]

I was thinking about a vac leak too, but wouldn't a leak make the problems worse at higher RPMs (more suction). (Unless the higher suction 'sucked' the leak shut)

Edit: You've got an SH, do you still have the Octy? Is it hooked to #1? The 'leak' could be from the vac line to the octy. Just a suggestion.

[DGXSER]

Thanks for the thoughts George, no octy, ditched that long ago.

[BA80]

Did you check to see if the tip of the missing idle mixture screw is broken off and stuck in the idle port? That would cut the fuel off at idle.

[DGXSER]

Thanks Greg, this is the newer style carbs, almost impossible to break the tips off, but here is the hole I found when I went to remove the carbs when I got home....



I always feel for the tip to come through when I bottom the screw out and then feel it disappear as I preset the mix screws.

[BA80]

I've never heard of a mix screw falling out of a late carb either.

If you have compression and spark the only thing it can be is fuel. Something is preventing the fuel from getting from the bowl, through the pilot circuit,and out that little hole.

[BA80]

I don't see any threads in there Don.

[DGXSER]

They are there, I think the spring in the kits I got was weak. This screw in there now is tight on it. I can feel the difference in turning the screw.

I checked for vacuum leaks by starting the bike and spraying the crap out of no 1 intake manifold, carb, and the vacuum cap with carb cleaner, no change.

[GLoweVA]

I'm racking my brain to try to think of anything.

Could the fuel level in #1 be too low?
Do the 81SH's have the same bowls as the 81H's? (ie the drain port to check the running level of the bowl)

Maybe there's something else going on here.
Why would #1's pilot screw come out and not the others?
Maybe there was a little backfire action going on in there that kinda forced that screw out in the first place. (it's not like gravity is going to help it out, so It had to get 'pushed' out)

Recap for my memory jog, New plugs, swapped #1 #4 and no change, no vac leaks, even compression across all 4 and an occasional pop from #1.
So, why is #1 not getting any fuel on idle, but seems to get it with more throttle (ie main jets)?

Question: Hypothetical, if the timing was off by one tooth, could the compression be a little lower and maybe the intake on #1 open just a little so that you get the pop?
Are the valve clearances okay on #1?

Sorry if this seems like a shotgun try, but I'm trying to think outside the box on this one.

Edit, just re-read the whole post and thought: what if you sucked some little debris into the idle screw hole (where the missing one was) and it's clogged the pilot circuit so bad that even though you were maticulous about cleaning them, you might not have cleared the pilot circuit all the way.

I know it sounds like I'm second guessing your cleaning ablility and I don't want to sound like that.

Hope my brain rant helps a little.

[bikerphil]

Maybe battery voltage is low at idle and causing a weak spark. You did just get back from a long trip and possibly the electrolyte boiled away from overcharging, JAT