'78 Standard......carb help?

[BikeWorx]

alrighty, just got this '78 standard last weekend.......runs good with the exception of rough idle (#1 & #2 cylinders kick in & out) and once you get her to idle she's choppy. Also, if you try to give her gas she falls flat out trying to die

I pulled the carb bank off, and am about to clean them and reset the floats......only 1 problem: i don't have a manual

Does anybody know what the float height is supposed to be?

Also, not sure if this matters much, but the previous owner took the stock '78 carbs and swapped them for a set off of an '80......does that make any differences?

Thanx for any and all advice.....would love to get this thing running good this weekend if possible

[TopCatGr58]

Hey Bikeworx,

The newer carbs are different internally, separate pilot and main jets paths, and the float bowls are vented thru the inlet bell, so that's why the plugs in the body a bit further up than the fuel inlets. However, they will perform equally well to the earlier models, you just don't have any adjustments in the Vacuum slide needle positions compared to the older carbs. Hopefully the PO has already drilled out the Pilot screw caps on the front top of the carb bodies, but if not, you'll need to to be able to access the pilot screws for both removing, cleaning, and then resetting for good idle. Also, learn about how to bench synch and then vacuum synch the carbs, again, from the tech tips!

PLEASE read and review the tech tips, from the MAIN FORUM page, not just the links on the left column of any page! You'll find pictures and such about how to clean them, what NOT to clean, how to replace the float needles and seats, how to remove the float pins WITHOUT breaking a post, etc.!!! READ THEM ALL!

[BikeWorx]

Thanx for the information, it is truely appreciated!

Hope you guys don't mind, but i went ahead and printed just about all the carb cleaning/rebuilding/synching articles i could find.....makes it alot easier to grab the printouts rather than run into the house and get online to check things while doing the cleaning!

With any luck, i'll have this thing running tomorrow! well, maybe.....still need to do the "pickup coil" wire repair as well.

Wish me luck!

[JWSanders]

Mind! Hell, they encourage it.

I've already made and ruined several printouts on the carbs

[Bud Manley]

You mena you don't have a computer out in your garage already?
I thought that was SOP.
Good luck with your carbs.
I've been running my bike for two years now and just discovered a broken idle/mixture screw been like that all along.
SHould be up and running just in time to put it away for the winter.

[BikeWorx]

nope, no PC in the shop just yet.....soon though.....VERY SOON

Got the carbs all apart and sprayed out......my gawd the gunk i found in some of them passages!!

Hopefully now it will at LEAST idle better than she did......still haven't found a "float height" setting as of yet, but still reading up on the subject

[randy]

Float Hieght = 25mm

[BikeWorx]

Thanx Randy, much appreciated!! Now all i need to do is yank the carbs off and reset the floats correctly......i "eyeballed" them and they seem to work ok, except for starving for gas after going WOT.......better luck tomorrow!

Here's a question: if the carbs are not set right (still need to synch them) will they cause backfiring through both the carbs and the exhaust under different throttle positions?

Changed a faulty vacuum advance today also.....pretty sure i need to re-adjust yet

[prometheus578]

Carbs can do that, but so can a lot of other things. First thing I always do with a newly aquired bike is run a compression check; get an idea of what the engine's doing. If they're all fine, no probs, but if they're not right, time to check the valve adjustment. (could be a burnt of bent valve, but we can deal with that later)
No amount of carb playing can compensate for loopy compression or tight valves.

[TopCatGr58]

Hey Randy and Bikeworx,

The 78-79 carbs do use the 25mm height, but he has a set of 80's on his early machine, IIRC, yes, just rechecked his post.!!

And the 80's use a lower 23mm setting, so that may be part of his starving at WOT, not enough fuel in the bowls!?

Also, did you take the tops off and inspect the vacuum slides, the diaphragms for pinholes, and ensure that the slides all slide easily without hanging up?!

Also, Bikworx, put the petcock on PRIME, and run it a while, and see if that fixes the starving at WOT. If so, then your octopus is probably clogged or not functioning properly and not letting enough fuel in to keep the floats full, whereas PRIME goes directly to the carbs, bypassing the Octy! Keep at it!
T.C.

[scoobes]

before you take the carbs off the bike mess round with the wires that come of the pick ups on the left hand side of the enginei had the same symptoms and i found a break in the wire from the pickups just a thought for you

[randy]

ooops!

Just read the title, you mean i'm gonna have to read the whole damn post from now on? Geez,, give a guy a break!

[BikeWorx]

keep the info comin guys!!

Replaced the vacuum advance/pickup coil assembly sunday.....the wires on the original were totally wiped out from way too many "repair" jobs, and i just happened to have a good donor to swap with

Was told today that the xs11 runs out of whack without the air cleaner/housing installed.......this true? I figured it would run a little lean, but enough to fubar things?

[TopCatGr58]

Hey Bikeworx,

From what I've seen, it seems the XJ's are more sensitive to the presence of the airbox than the XS, since the XJ's have the YICS system. The XS will be a bit lean without the airbox, but only 1 to 2 jet sizes, which can sometimes be compensated for by adjusting the float height without necessarily rejetting! But running for a little while during your tuning and fixing won't cause any damage, but if you are going to change the intakes or exhaust permanently, then you will want to look into possibly rejetting accordingly!
T.C.