i have not touched anything but the 4 vacuumposts on the bikes carb, the bike was running pretty well. i did a long testrun after long time out of use and it was driving like new, i almost run a complete fresh gastank empty, lots of power. but needet synchronisation also as a checkup after the longtime not in use . the day after the first testrun i wanted to sync the carbs, i used the carbtune like i did before on other bikes.
carb nr1 was completely down , i was able to get all 4 up and even. idle was smooth. it took me some time because the screws are not easy to touch, but i got it running perfect at idle .

after synchronisation it fires up nice but started to stumble ones on the road. i thougt it was low on fuel (reserve) so i went to the gasstation, it started up again with ease, but above 6000 rpm nothing happens, it just would not go higher , hesitates and stumbles like it is not getting fuel.ones above 6000 or around 7000
the problem gets worse as i reach home, it started running on 1 or 2 and almost died.
the bike has only 27.000 miles,
my thougt is that the carb needles are not lifting , like a vacuumleak
but all i touched was the litle plugs for the carbtune connection.
it is also difficult to test, in the garage , at idle it runs smooth , ones warm and under load its getting problems,
pulling the carbs is the last thing i want to do, i cat believe that it was running so perfect before the sync and now sudden something is so bad , only one day later. maby the little plus do not seal anymore?

 

Ik think it's thé plugs. Ik checked and all of them where black . Maby this happend when adjusting thé carbs they where running at Idle long time or maby they put wrong plugs in ngk dpr8ea . Of the carbs are to rich .

 

It sounds like it's running rich. If you were able to sync the carbs then you can rule out a vacuum leak. If it had a vacuum leak you wouldn't have been able to sync. Still, if the issue arises immediately after working on the bike, the first step is always to confirm your work

You didn't mention the model/year of the bike, but generally I'd be looking at the following:

Troubleshooting Possible Vacuum Leak:
-Check to make sure you put those rubber nipples back on the vacuum ports after syncing and that none of them are loose
-Plug the sync gauge back on and confirm vacuum as you blip the throttle. If any are non-responsive, that points to a vacuum leak

Troubleshooting Spark:
-Confirm spark plugs

Troubleshooting Fuel/Air:
-Check/replace fuel filter
-Check tank vent hose (if it's plugged then it'll stutter and stall after riding as the tank itself will go to vacuum, starving fuel)
-Petcock screen may be plugged
-Confirm fuel pump operation by unplugging the fuel hose downstream of the pump and holding it into a container. Then turn the key on and measure flow rate using a stopwatch. Check that it's in spec for your model
-Confirm valve adjustment (should really be done before sync)
-Check the air filter (may as well)

Carb Cleaning:
-If nothing else helps, you may have a gunk on main jet which is causing it to starve at higher rpms. The only way to check is to remove and clean the carbs. It may also be a piece of debris blocking something inside the carbs. Normally this issue would be accompanied by trouble idling, so I don't think it's the most likely cause of your issue, but if nothing else works, this is the only way to be sure that the carbs aren't gummed up

Hope that helps. Good luck

 

thanks for the reply , most of the causes i know, so, i changed the plugs witch datet from 1999 but where only driven for 1000 miles, they could have some oxidation on them and where giving a small fire, witch caused the rich mixture, they went more and more black every time i started it up to sync the carbs and caused the starvation
when i put them in, the bike's rpm imediatly went 4 to 500 rpm up without choke !!!,
i checked sync again after bringing the rpm down , wich was still ok, absolutely no vacuumleaks at all
i drove it , problem solved for 95%
on some occasions it hesitated @ 9000 rpm and does not go up further , on some it just pulled further like nothing is wrong. blipping the gas helped sometimes , but that is high rpms for blipping,, i am guessing its the slides that stick from long time not in use. i took one out and it wasnt easy to put back in, , and it felt a bit drity and not sliding like i wanted so i cleaned the slide and bore a bit, and sprayed some carbcleaner in.
i also had from now and then a slight hesitation @6000 or 7000 rpm , but also not always, maby that is the rpm when they start rising?? getting slow in rpm is no problem, faster like imediatly WOT and it hesitated just a little . while i was driving it i adjusted the mixture screws and that made a difference in the lower rpm's , i could get it real smooth from 0 to 3000
i will keep it driving like this, maby after a few fresh tanks it will clean itselve,
the po had it only driven 1000 miles in 12 years , and the back tire was only used in the middle, i gues he didnt went up in the high rpm's
the slides may need to move and clean a bit while driving , maby they stick a bit,
removing the carbs is the last thing, i know that i need fresh boots and rebuild kits or the problems can go worse.
for now ride it and see if any other problems stick there heads out. if the hesitation persists i remove the other 3 slides and get me some vaseline to keep them in place when reinstalling. (is vaseline a good idea?or something else, ? )
i have put new tires, new fork oil and its transformed from a dangerous tank into a bike that pretty easy corners. it is also easy to drive it fast and hard,

 

Your slides shouldn't need any lubrication. If they are sticking it's an indicator of another problem. You will just be masking the issue that will return.
The obvious statement is that they aren't lifting because of lack of suction.

To add to Tentacleslap's advice I would check for a vacuum leak. A couple easy things to start off with is to insure you got the caps back on properly where you had the sync gauge hoses. Also, spray some propellent down around the carb boots to insure they aren't leaking. While idling, spray something down there. If the bike revs, you have a leak. Some people use carb cleaner, or something like that that is highly flammable. I use propane or mapp gas. To me this is less messy.

 

problem solved for 95% it where the plugs, 20 year old plugs, last 12 years only 2000 miles, maby oxidated, the worked but weak spark, they went black pretty fast because of bad burning, , witch result in no power. changed plugs, checked syncro again witch was still ok baaam full power . now it just hesitates a tiny bit at 6000 rpm but not always , say 1 out of 8 runs at wot. but when this happens it picks up and above 7000 its smooth.
second hesitation happens also sometimes , say 1 out of 10, it suddenly wont go further than 9000 rpm. i took out the slides , cleaned them and the bores, grey sludge , feels a bit sticky, cant run the bike for now, waiting for parts to rebuild a leaking petcock.
because it runs some of the time smooth i do not want to take the carbs off, it might clean up itselve while driving a few tanks fresh fuel.

 

removing and cleaning the slides did it, today i went for a 100 miles trip and the bike was the first 50 miles just around 5000 a little rough but not hesitating anymore. just a little bit rough on the sound, after 60 miles the bike started to run smoother and smoother. problem solved .