another jetting question

[robywan_kenobi]

My bike is an '81 XS1100H. It seems to be running lean. A few things point to this conclusion; backfiring at decellaration, the pipes blued rather quickly after being installed (less than 500 miles), and I have noticed a few times in the last couple of weeks that when the bike is relatively cold (I always let it idle for a few minutes before leaving if it hasn't been started in the last hour or so) that if I nail the throttle, I get sporadic surges of power. Once the bike gets thoroughly warmed up those surges cease and the bike doesn't have near that power. It has been suggested to me that this could be due to the engine being cooler and therefore running a little richer. If all this sounds like a lean condition to you guys, what should be my next course of action? I have already run several cans of seafoam through the motor and I have synched the carbs twice within the last 4000 miles. I have also adjusted the cam chain tension once. Is jetting the answer? The bike is basically stock. The PO did install after market pipes, but I don't know which brand. They look pretty basic - 4 into 2 style. If jetting is the answer, how big a job is it? I am pretty mechanicall inclined, but am afraid of getting into a job that will take more than a Saturday to complete. I also don't have access to a large variety of tools. The bike is a daily rider, my only mode of transportation really - the wife drives our car and my son drives the pickup. Any help or info would be greatly appreciated.

[Ken Talbot]

Sounds to me like to need to go inside the carbs and clean them. Seafoam might help keep realtively clean passages workable, but it is not substiture for dealing directly (i.e. mechanically) with a plugged orifice or jet. There should be no reason to change jets as there's nothing there to wear out. Part of the lean condition might also be coming from out-of-adjustment floats. Either way, time for cleaning #1 of your triple-clean..

[strom]

Have a similar problem here... cleaned the carbs bout 5 times.

LP

[DiverRay]

After cleaning the carbs, DO adjust the floats!! They can make a big difference. You can pull the carbs and remove the float bowls without any major problem. Keep the carbs together, flip over and remove the bowls. check all the levels before you do anything, so you have a base line.
If the floats are at 25mm, drop them to 23mm. Make sure all 4 are at the same setting. The 2mm adjustment could make the difference. The actual value will be determined by the book, as my '79 standard may have different settings.

[skids]

Re: another jetting question

After market pipes/muffs can make a big difference! Read plugs with the throttle chop method.

Originally posted by robywan_kenobi
(snip)Is jetting the answer? The bike is basically stock. The PO did install after market pipes, but I don't know which brand. They look pretty basic - 4 into 2 style.

[robywan_kenobi]

OK, going on the assumption that the bike was getting a surge of power when it was cool, I thought maybe one of the carbs might have some gunk in it that was close to being washed away. As a side note, I had also, in addition to the description already posted before, noticed that the pipe on the number 2 cylinder never got as hot as the other three. So, with about 2 gal. or less gas in the tank I added 2 cans of B12 Chemtool to the tank and took the air box cover off and sprayed some carb cleaner into that end with the motor running. Started the bike and went for a ride. The surge of power is gone, its now constant. I have more power than ever. WOW its pretty awesome. Keep in mind that the PO had the bike for about 6 years and only put app. 500 miles on it, so that must be why the carbs gunked up. Now my problem is that the bike won't idle down. I have backed the idle screw all the way out, doesn't contact the cable stop at all at this point but the bike idles at about 2500 - 3000 RPMs depending on how warm it is. I was going to try re-syncing the carbs thinking that since one seemed to have opened up that might be the cause of the issue, but with the bike idleing so fast, it sucked all the mercury out of the carb sticks. Any suggestions? Anybody got a set of carbs cheap that might fit my bike that I could maybe rebuild and then just do a swap with the ones on the bike. Probably a good idea to have a spare set anyway.

[tab1324]

interesting

My bike won't idle down as far as I'd like unless adjusting the idle speed screw way down - and then it idles at 400 rpm. To get it around 1100 rpm I have to leave the idle speed screw setting a little higher and then after deceleration and stopping, I give the throttle a little blip and it comes down to around 1100... Probably doesn't make any sense but that's what it does.

Maybe yours is still lean if the idle won't come down. All the boots in good shape? I've heard lean conditions doing this. Try fattening it up a bit and see what happens. Heck, maybe it's too rich if it's doing this when warm. Sure your choke circuit is shutting off?

Tom B.

[robywan_kenobi]

tab1324, yeah I've tried the blipping the throttle thing with no luck. As far as I know the boots aren't leaking - I've sprayed WD-40 around the boots with the motor running and didn't notice a change in the RPMs. The rear boots look new, the front ones are pretty cracked, but I understand they have a metal liner and like I said, did the WD-40 thing so I don't think they're leaking. Really don't know how to "fatten it up" as you say. I'm really hoping not to have to pull the bike apart too much, it is my daily transportation to work and home, so I'm hoping to find a real simple cure. Not sure that's gonna happen, but I can still hope.

[TopCatGr58]

Hey Rob,

You say you had synched them 2 times before, but sounds like the pilot circuit was clogged, contributiing to your previous surge. Now that the surge is gone, the pilot circuit may have gotten more cleared. SO...your synch may have been WAY OFF? After pulling the carbs, inspect the butterflies and see if one is open much more than the others! If so, do a breadstick style bench synch. Then read below about an alternative synch tool!

Also, the 80-81 series carbs had the pilot screw chambers factory set and sealed with brass plugs! Have you removed these plugs to get to your pilot screws? If not, then you will want to drill thru them, put a sheet metal screw into them to use a lock plier on to pull/pry them out. Be careful and only drill enough to penetrate the brass caps so you won't damage the heads of the pilot screws beneath! Then you can check the pilot screws to see how many turns out they are from a gentle seat!?

There is a recent post about carb synchronizers on the other FORUM, very cheap to make a homemade one, the single 12 foot long tube will allow you to balance/synch 2 carbs without fear of sucking fluid into carbs since both ends of balance tube are both on carbs pulling against each other and not just against the fluid and open air/gravity! Keep at it.
T.C.

[tab1324]

fattening it up

To fatten carbs, take off the seat and unbolt the gas tank. Prop the tank up on the rear end with a block of wood. Start the bike and let it warm up and come off the choke circuit. Now, turn the idle mixture screws out slightly (small screw on top of each carb inlet side). when I say slightly I mean about 1/4 turn at a time. Adjust all equally.

Don't know if this is the cure but it's worth a try. Do the pipes seem yellowed or blue? That usually indicates lean. "fattening it up" should help if that's the problem.

Tom B.

[robywan_kenobi]

Yeah TopCat, I was thinking pretty much the same as you are. Since the carbs were synced before and now that it seems as though something (pilot circuit) has opened up, that sync is probably way off. I didn't want to have to pull the carbs off, but it seems as though I may have to. How hard is that really? I have read many threads in this forum how guys seem to pull their carbs off without a second thought. But it seems as though these guys have a lot more experience working on their bikes than I do. The brass plugs have already been drilled out. I believe I have read threads before that the pilot screws should be backed out about 2 1/4 turns from a gentle seat. Is that right?

Tab124, will adjusting the idle mixture screws affect anything other than the idle? The very name of the screw would say not, but I don't know. Yes, my pipes are blue. I had submitted an earlier thread concerning this and had pretty much surmised that;
1. it is an indication of a lean condition
2. that even with a perfectly tuned bike, I can expect the pipes to blue somewhat over time.
My pipes appear to be a relatively inexpensive, aftermarket, single wall pipes. I do not know the brand as they were replaced by the PO to the PO.

[TopCatGr58]

Hey Rob,

The trick to pulling the carbs is undoing the 10mm bolts on the side of the air box, and sliding it backwards towards the battery, this gets you more room to be able to pull the airbox rubber intakes off, then unscrew the 4 ring clamps that hold the carbs to the Engine Intakes, turn off your petcocks, pull the fuel hoses, gently rock the carbs up and down as you pull backwards to get them out of the intakes, there's a slight lip that you have to get it past, then slide them sideways, you'll then be able to get access to the throttle cable, the end will slide out once it's turned to allow the cable to slide out, you will need to rotate the butterflies ....you'll see how it fits. Then continue sliding them out, just be careful....the bowls will still have fuel, and will pour out when tilted a bit towards the rear or front!

Actually, the "pilot"=idle screws are 1-1/4 turns out from gentle seat....but that can change! The pilot circuit DOES contribute fuel in diminishing amounts as the the throttle is opened, but it does contribute more than just idle!

Back to the earlier question, you may want to go up about 2 main sizes with those 4-2 pipes, you probably won't need to go up in the pilots, just turn the screws out to about 2-1/2 to 3 turns, you'll probably find them at 1-1/4 or so....but maybe not since the brass caps were already removed....someone may have tweaked them?

The book says to set the floats with that stupid hose and the bowls full of fuel.....I just set mine to the same as the 80's which is at 23.00mm and they work fine(81SH). You should easily be able to pull them, adjust them and put them back on in an afternoon!!

[tab1324]

idle mixture screws

Yes, they only affect idle to my knowledge, but isn't the problem you're having based on the fact that you cant get your idle down? The blue pipes could potentially be from a lean idle mixture. I say this because even if you were a bit lean in midrange and topend, when you're riding the bike, the pipes are being cooled by the air. When you're idling, the pipes get very hot and don't have anything cooling them, resulting in blue pipes. I don't know that the blue isn't caused from aging but I do know a lean idle can make them blue as this affected my pipes.

Not sure of the year of your bike (you probably said it and I missed it) but pulling the carbs can be a chore. Although I recommend you do it yourself. You will learn so much about how motorcycles go together - I did. The airbox is usually the biggest trouble issue with removing them. What I've done is to take the rear airbox boots off by inserting a long flat screw driver between the airbox and the boot flange. You can tear up the boots if you're not careful but with a little patience they come right out. The rubber is soft enough that it flexes. Once they're out you may not have to pull the airbox. This is how it was on my XJ but not sure how yours is.

Good luck.

Tom B.

[pggg]

Right then, surging and backfiring equals a lean idle circuit. Screw the mixture screws out to the STRANGLED factory settings. Next, screw 'em out another 1/2 to 1 extra turn. A rich idle circuit is way preferable to a lean mix. Better response and smoother warm up.

[tab1324]

idle mixture screw # of turns

I would suggest if you havn't done it already...

Turn the idle mixture screws in all the way (with bike not running) to a gentle seat. Then turn them out 3 to 3 1/2 turns. This should get you close if not on the rich side. When you turn the screws in, count the turns - I'm guessing you're only gonna have to turn them 1 or 2 turns in until they seat.

Tom B.