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81 gs450l runs poorly on one cylinder

  • Thread starter Thread starter w/e_wrencher
  • Start date Start date
W

w/e_wrencher

Guest
alright, i'm done lurking, time to get into the war.
i've got a problem with a "doggish" bike.
have done:
electrex stator, r/r
carb dip (overnight +)
bench synch
manometer synch
complete electric sys. check up / maint.
[pods, 2-1 exhaust] out of neccessity, stock missing or in disrepair
120 mains, 17.5

at idle, it seems rough unless i raise the main adjuster to the 1800-2000 range, maybe a touch lower. drives out fine, seems to have no problem picking up speed, 70 mph in 5th easy:shock:. but, when i get back home, sit on the bike idling, it's fine. leave it idling, put it on the kick stand, get off the bike, idle goes to crap and eventually dies in 1-1 1/2 min. :confused:
i've pulled the carbs to check for clearance on the float, no problem.
did find that if i pull the plug boot on #2 cyl., minimal change, but noticeable.
pull plug boot on #1, it dies immediately. will start and idle on #2 only, with throttle help, but it doesn't like it.
this one's got me stumped, calling in the reinforcements!
thanks in advance.
 
Just taking a stab in the dark here. Pilot circuit in the one carb is likely still clogged. Also did you remove the seats for the float assembly? They have some tiny screens over them that may be clogged.
 
yep, there was nothing left to take apart. all the parts were dipped and soaked and brushed.
 
In your list of things done, I did not see what should be FIRST on the list...valve adjustment.

If they are not quite right and you adjust the carbs to try to compensate, things get interesting rather quickly. It is best to start with a good mechanical base, then adjust all the add-ons to that.

In order:
1) valve adjust
2) ignition timing adjust (usually not necessary with electronic ignition)
3) carburetor sync

As others have mentioned, there might be a circuit that did not get cleaned, even though it got soaked "overnight+".


.
 
Steve said:
In your list of things done, I did not see what should be FIRST on the list...valve adjustment.

If they are not quite right and you adjust the carbs to try to compensate, things get interesting rather quickly. It is best to start with a good mechanical base, then adjust all the add-ons to that.

In order:
1) valve adjust
2) ignition timing adjust (usually not necessary with electronic ignition)
3) carburetor sync

As others have mentioned, there might be a circuit that did not get cleaned, even though it got soaked "overnight+".


.
Click to expand...
A compression check might be in order as well.
 
thanks guys
i was headed there next Steve, only thing i haven't looked at.

i have the whole day slated for nothing but wrenching.
i'll keep checking in with updates
 
alright, been checking a whole bunch of things.
valves seem to be ok. checked carbs again, found that my float height was off a bit, alot actually, don't know what i was measuring before. adjusted it, now the thing back fires badly while riding, bad enough my 2-1 became duals. that, my friends, will get your attention! let it sit a few minutes, fires right up, idles great, go to ride, make it through a couple of gears, POW, and it dies. plugs look fine, tan centers, little black on outer ring.
i'm at a loss.
 
still backfiring, but not nearly as bad, adjusted floats lower for larger mains.
had them set at approx. 22mm, and thats when it was the worst. lowered them a couple of mm at a time, and it seemed to get better. at 22mm, it seemed like it was getting way too much fuel. just sounded like it was "slurpping" when i gave it throttle. checked intake for leaks and found none. i'm beginning to wonder if it's worth it to have the 120 mains, considering going back to the 115's.
 
You checked your valve clearances - good. But compression could be off because of other reasons (rings, valve stem, seals, etc.).
What were your actual compression numbers? (I'm assuming you checked). Are the two cylinders (compression) way off? If they are, you've got to get that resolved first.
You mentioned differences in single cylinder running - One of your coils could be on the verge of failure (see my other posts about this). Have you swapped coils - did performance follow the coil?
I think you get the idea.
If none of the above yields any answers - If I were you, I'd get a stock airbox from eBay. If the bike runs significantly better with that, you'll have most of your answer.
 
compression was:
#1 60-65
#2 45-50

did install new UNI pods, choked them down with an internal sleeve, as per my mechanic buddy suggested. also, set the air screws back to 1 1/2- 1 5/8 turns. starts right up with the choke, on it's own after a short minute. but power is still lacking on take off, and still cuts out and acts like it wants to die when up to speed,(1/4 - 3/8 throttle). got a few more things i'm gonna try, will check back with results.
 
w/e_wrencher said:
compression was:
#1 60-65
#2 45-50

did install new UNI pods, choked them down with an internal sleeve, as per my mechanic buddy suggested. also, set the air screws back to 1 1/2- 1 5/8 turns. starts right up with the choke, on it's own after a short minute. but power is still lacking on take off, and still cuts out and acts like it wants to die when up to speed,(1/4 - 3/8 throttle). got a few more things i'm gonna try, will check back with results.
Click to expand...
Did you have the throttle open and slides physically pushed up out of the way when you ran the compression check? Those numbers are awful low. If you get the same numbers again try putting about a teaspoon of oil down each cylinder and run the test again. If the numbers get better then it's rings for certain but doesn't rule out valves.
 
carbs were not on the bike for the test, had them on the bench.
haven't tried the oil yet, but i did leave the guage on each cylinder for a bit to see if it would drop, but it didn't.
 
got the mix

got the mix

put in 105 mains, and got the mixture spot on. sad thing is, it still cuts out at speeds above 35-40 mph when opening the throttle. i can ease it up to about 50, then it coughs no matter what until i back off completely.
 
w/e_wrencher said:
put in 105 mains, and got the mixture spot on. sad thing is, it still cuts out at speeds above 35-40 mph when opening the throttle. i can ease it up to about 50, then it coughs no matter what until i back off completely.
Click to expand...
Your compression numbers are really low. If you've run valve clearances then it's time for a topend job. Sorry to be the bearer of bad news. Just for grins, were the cams in the right position when you ran the valves?
 
i think so, not totally sure though. i've never really had the finesse it takes for valves.
starting to agree with the top end suggestion, unfotunately.
 
w/e_wrencher said:
i think so, not totally sure though. i've never really had the finesse it takes for valves.
starting to agree with the top end suggestion, unfotunately.
Click to expand...
There is a certain procedure for how the cams should be positioned. It would be hard to explain here. The easiest thing to do is just make sure that each valve you check is completely of its cam lobe. Fortunately you only have 4 valves so it isn't a big deal. Just rotate the crank until the lobe is facing away from the bucket on each valve.
 
alright, scored a clymers' manual this w/e at the shop i work for. got to nosing around, and there it was, tucked away in the back. anyway, it turned out to be the valve shims. remeasured tolerances, did some adjusting, runs alot better. now the next fix is 55 mph top speed. a little more tweaking on the carbs, and i should have it.
thanks Billy, for not letting me give up on the valves. i still hate dealing with them, though! :)
 
I know you have tried to get the carbs right. If it was me I would get a used stock air box and get rid of those pods. I have personally had alot of trouble with those things and when I re-installed the stock air box the bike ran like a different bike. Some people on the forum like the pods, I do not. With PODS on my 81 gs 850g, 55MPH was my high with 5000rpm's max. With the stock air box, red line and tons more power, no backfiring, and it will do 70 before you blink an eye. If you research this on the forum, many other people have also experienceed this. I would not have believed the difference until I saw it with my own eyes and felt it pulling on my arms!
I know you restricted the pods. Do you know (for sure) if you gave it too much air or not enough air (sounds like too much to me).

I am not trying to make more work for you but Suzuki spent alot of time engineering the air box and mixtures. It sounds like if I were you I would wonder if I am shooting in the dark with the mixture. You may get it with the trial and error method, I do not have the patience for this, some people say they spend years trying to get it right. Please do not take offence to this as I am not trying to be critical but trying to help you.

I'd watch ebay for one.

Good luck and have a great night.
 
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