Bike Idles at 1000, but blip throttle and rockets past 4k and stays or climbs

[skids]

PS, starter jets are operated with the "choke" lever.

[Snow]

Ok, I have decided to order a colortune to set the idle mixture correctly - I once removed the mixture screw caps from my GS750T and managed to bugger them up pretty badly, any advice on removing them cleanly on my XS?

[schpiff]

81 special carbs

I am/was goin thru the same thing friend, if you are runnin the 81 carbs, set the floats at 23mm and make double sure ya got the carbs synched pretty close to even ( i did it with a soft piece of wire then set idle at what worked for starters, then adjusted idle later) , made a world of difference for me
side note i got 110 mains and 42.5 pilots.

[Snow]

Ok, I got the colortune in the mail and decided to get the mixture screw plugs out of 4, then 1, then 2 and 3...
Well, it took me 20 minutes and I got #4 out just fine...then 10 minutes into #1, the drill made quick work out of the plug and I wasn't able to stop in time... I completely screwed my #1 mixture screw...

So, after many moments of anger and torment, I decided to pick up the 78E carbs I have, that I had tried out - Originally, my brother had these on his 78 XS standard but somewhere along the line, broke the mixture screws...go figure... so he had someone get the tips out and clean the area up a bit, but the carbs were never quite right after that.

So now, these 78 carbs have new float needles/seats, new main jets (140s) new pilot jets (42.5) and I have stolen the plastic floats from my 81 carbs, known good floats and replaced the old crusty looking brass ones. I have set the float height to both 23mm and 25.7 (well, close to 25.7 as I could get) several times and no matter which height, after running the bike (that's right, AFTER running it - if I just let it sit there on prime, she doesn't leak a drop), the #3 and #4 carbs leak like sives out the air intake side.

The #4 seems to leak a little worse than the #3. As I mentioned earlier, I got my colortune in - on #1 and #2, colortune now reports that all is well. On #3 and #4, after the bike starts leaking (float bowl overflow?), the mixture goes very rich (well duh, right?) and then I cut the petcock from prime over to on (vacuum lines for petcocks are plugged at this point, tank is on backwards) and the colortune reports a cobalt blue and then nothing but spark (again, well duh, right?)

My question is what the heck is making my #3 and #4 leak? I thought if the float height (now set at 25.7, I think I found out why 80/81 have different height - has nothing to do with the floats, the float needles are actually longer on 80/81) was correct and the valves/needles are good (and they are new, but from K&L rebuild kit) that there carbs wouldn't overflow?

Anyway, I spent from 11am until 9pm on these darned carbs and am out of ideas once again, BUT from as far as I got, Denny'z theory about the mixture being wrong and the idle set too high seems to be right on, even thought I am on different carbs, I started running into the same problem.

Should I plan on running up to napa for carb dip?

Help!!!

PS, I did sync the carbs tonight also

[schpiff]

Hi Snow,
I had a problem with my #3 carb getting the drips also..took out the needle and seat(which looked fine ) but when I went to clean everything up before reassembling I noticed some rubber off the o-ring around the seat was flaked off in the hole..I changed the o-ring and havent had a drip since. Hope this helps.

[Snow]

I've got the offending carbs sitting in carb cleaning buckets since last night, but you know, I did notice a little bit of flaking from the old o-rings under the valve seats, like maybe I didn't get the area very clean when I put the new seats and o-ring in a couple years ago...
Under the float valve (or above if right side up), there did seem to be a fairly good amount of gunk built up too, but I doubt that would make the carbs leak, but it prolly would cause performance issues.

[Snow]

DennyZ, you are the MAN! It was the idle mixture being off indeed making the idle seem to be correct when setting it too high, thus making it jump and stay around 4500 or more when going on a test ride

It took me a few tries, but I managed to get it pretty squared away, having to sync and colortune back and forth. I think what would have saved me some time was to presync with the bread wire trick, then sync, then colortune.

Thanks!

[Redbaron]

Engine rev

Had same problem, finally corrected this by pre-synching carbs. Pulled carbs to rebuild, when reinstalled this happened. Pulled carbs again and used a bread package tie as a gauge. Set the butterflies equally and try this again. Also check all slide diaphrams for proper operation, sounds like one or more may be sticking or hanging, blow into air horn at top of carb, slide should rise and drop quickly. push slide up, while holding finger over same hole, should drop slowly or not at all. As for idle mixture adjustment, lightly seat screws, turn in. back out one and one-quarter turns, per yamaha, and me, this is a good starting point. Warm bike up for at least five minutes,set idle in the 1000 rpm range, adjust idle mixture screws a quarter turn at a time out, until idle smooths or rises. My problem actually was, that i had idled the bike way up, without realizing but it would still barely idle, when i blipped it, it smoothed out and idled very high. had to reclean the idle circuits to repair. Final synch the carbs as a last step, not the first.
you'll only tend to make the bike run worse by trying to synch first. found out the hard way how important a proper pre-synch is. Take your time and be patient, triple check for proper adjustment on your pre-synch. "the pre-synch sets the starting point for the final synch, if butterflies are not set to a minimum opening, with all four the same, the resulting adjustments are much less accurate and harder or impossible to achieve."
there are some very good articles her regading carb adjustment and final synch, but i feel it would be a good idea to remind all to start at the beginning for better results. I use the vaccum synch apparatus shown in an article on this site to final synch, built one for 3 dollars and 30 minutes. after pre-synch gauges indicated the following:
Cyl:1-- 19 in. HG vac
Cyl:2-- 22 in. HG vac
Cyl:3-- 22 in. HG vac
Cyl:4-- 18 in. HG vac
As you can see, the pre-synch was very close and final synch took less than 5 minutes, achieved 25 in. hg on all. tweak idle mixture adjustment after these are completed. email me if this helps or if i can assist you further. hunterbilly@charter.net

[Jeff]

I just went thru my carbs for a 3rd time since some crud dislodged from the first two cleanings managed to lodge in #4's Pilot Jet. The Triple Clean everyone keeps touting makes more and more sense the longer I work on the bike.

Right now I seem to be experiencing similar problems to what is being described in this thread. When the bike is first started... even starting warm.... the idle sits nicely at 1k. Once I start riding or blip the throttle... it climbs to around 4k. The floats are all level and I did the benchtop presync. I don't have a tube rack yet to do a complete sync. The main adjustment for idle speed on carb 3 is all the way back and not even contacting the push arm so the idle is not turned up at all and it still idles initially at 1k. All of the needle diaphragms are in good shape with no leaks and the slides move freely like they should. The carb boots are all in good shape.

The few times I have been riding it... I've had to slip the clutch a bit to keep the idle down when I come to a stop. The only thing I can think of is that the complete lack of baffles in the exhaust is causing me severe grief.

[Jeff]

As an additional note.... other than the high idle after blipping the throttle.... the bike runs smooth. Before I blip the throttle... the bike purrs like a kitten at 1k. As long as I have a load on the engine..... everything runs great but the second I disengage the clutch.... away the rpms go. Could a problem with the vacuum advance or other timing problem be an issue?

[fusionking]

You don't say what your setting is on the mixture screws. Try at least 2 or more turns out. Mine did the same thing and 2 1/2 cured it! also REALLY watch fuel lines kinking, can't say enough about that kind of stuff. Garry

[stpbuzz]

same problem here on a 80G,
idles fine, rpm's wont come down for 30 seconds or so,
air box is off, if i cover the back of the carb (w/my hand) on #1 or #2 it may speed up, from idle, (not allways), and if i cover up #3 or #4, it will kill the engine (sometimes) ???
my son took the carbs of a couple of years ago, and its been sitting ever sence, i just got it running, but things aint right yet !
gona do the valve adjustment too, need that tool, and need the carb sync guages. etc.
colortune etc.?

if i figure out any new answers i'll post them,
time is a little here and there, at least my 80sg is running good.

later buzz

[Snow]

I wasn't able to continue on with these carbs as I managed to royally bugger up one of the idle mixture screw caps...and the screw beneath it, so I switched to my very poorly working 78 carbs, which I then starting brining back to life.

Up until yesterday, this problem was nonexistent for me...then when trying to get my midrange mixture correct, I lowered my needle one more notch and put the carbs back in. Cranked her up and instantly up to 5,000 rpm! Crap!

So, in sheer desperation, I decided to check the forums one more time and saw this from jkorn:

I have had my carbs apart a million times and could probably do it blind folded now, though not recommded. After trying many variations on my 79 equiped with a Kerker 4 to 1 and a Oil type air filter in the stock box I am using 140 mains with the needles up a notch (clip lowered raises the needles and more fuel). Tried up to 150's but the motor stubled too much and hated warm weather. I also have 180 air jets. Not sure what the ilde jets are but just a bit larger than stock. The bike runs GREAT. I have used the choke in the past to help determine if the bike could use a little more gas or less.

Well, I popped the 145 mains out and put the 140's back in and again adjusted the jet needle.

No more jumping...I am dumbfounded as I thought lean condition was causing the jumping. I still have a little more tweaking to do as I still have stutter between 5 and 6 grand, but that's nothing compared to the 4200-6 grand I started out with.

I am starting to believe that the formula for calculating the proper main jets only works for the carbs with unblocked off pilots and might be tooooo rich for plugged pilot carbs.

Tonight I reset my jet needle to factory default and hope I don't have to battle the little c-clip bastards again!

Btw, does anyone know of a tool that makes teh C-clips easy to remove? I have a c-clip tool but the arms are waaaayy too short to reach the clips and I now rely on a thin pain of needle nose pliers.

[stpbuzz]

i took the carbs apart, cleaned with carb spray,
it had 110's and 42.5's,
set the floats,
reinstalled;
same problem,
idle's ok at 1000,
bimp goes to 5000 ish,
------------------------------guess i'll check and re-check,
------------------------------maybe try a longer ride,
it aint been anywhere for a few years.

later
buzz

[cbird]

Get the $3 Chinese needlenose pliers then bend and file the tips to make a good C-clip squeezer.