My bike's engine won't rev up

Do you have spark on all four plugs?

 

Let me get this straight you changed something under the seat ? Did it work on all cylinders before the change ? Did it work after it was changed ? Is it just now your having this problem ? Changing the exhaust should not make a difference right away even with the wrong jets - the order things are happening is critical to figuring it out - the way I see it anyway

 

You said in the post above your engine gets too much petrol and the exhaust smells like petrol. Your carbs are letting too much fuel in and more than likely it's flooded very bad. Check your oil level and if it has gas in it change it right away. Also pull the carbs off and wet set the float levels. Make sure the o-rings around the seats are not leaking.
Troubleshoot the problem and narrow it down to an electrical problem or fuel problem or mechanical problem. Find a manual and read through so you can understand how to test everything properly.

 

I tried almost everything, you mentioned above. O rings, jets replaced, carbs cleaned, fuel level set... I have replaced the ignitor box, because some of the cylinders weren't working, but that was five years ago, i had no problems with it since then.

 

It is possible to accidentally put some of the jets in in the wrong spots. Check to make sure they are all at the correct locations.

It is possible to accidentally hook up the coils in reverse. Check to make sure they are hooked up correctly.

It is possible to accidentally reverse the order of the parts on the mixture screw. Make sure that the spring has the WASHER against it, and the little o-ring goes onto the screw last. If the o-ring is above the washer, it won't seat correctly and you can have issues.

Keep working at it with us, and don't give up. You WILL eventually get it going right!

Dave Fox

 

I started to experience troubles only at the test ride. Under 2000 rpm, the engine won't rev up, when i try to start and accelerate. This won't happen in neutral gear, when I play with the throttle, only just a bit. Carburettors were checked several times, we got their parts replaced, polished, but the problem still exists! Besides, when she leaves 2000 rpm, she runs like a dream. Her exhaust gases smell like she got too much petrol in the mixture, but whatever we do, it will not help, including changing the mixture. Sometimes, petrol floods some of the cylinders, so they stop. The engine drowns in petrol.

If you are truely getting spark and compression on all of your cylinders.
The statement above is a real good clue as to what is going on. The carbs have to be the issue here. They are the only point besides the vacuum port on the petcock on the gas tank. Pull the carbs off and rig a fuel tank above them with enough gas to duplicate the pressure on the needles and seats. Use the clear tube wet set method and with pressure on the fuel line you may see where your problem is. The design of the seats in those carbs have an o-ring around the outside of them. Those o-rings like to shrink and leak fuel by.