Hi All

My 98 ZX9R has a problem. The bike is a streetfighter and has had the ram air sytem removed.It has never run right since I got it. Basically its fine round town, but if you hit the highway and sit at 70-80mph for a couple of miles it looses power and runs on 3 or even 2 cylinders. Whack the throttle wideopen and it will splutter but eventually pull through and run on all 4 cylinders again. Pull off the highway and ride around town and it will eventually clear itself and run as normal again?

I read a lot about the problems caused by the removal of the ram air system and ended up on this and other websites and found a link showing how to run the fuel bowl vent tube into the air box. So I carried out this mod. The bike ran much better for it and gained some noticeable bottom end power, but sadly this fuel starvation after highway usestill exists?

Thecurrent set up is the first part of the ram air scoops exit the frame about two inches and at a diagonal angle to forward motion. Is it possible that air rushing past the scoops is drawing air out of the airbox rather than feeding it and creating a vacuum in the airbox and hence the fuel starvation? If that is the case why does it take so long to equalise?

I'd be grateful to hear any opinions, ideas, theories etc as I'd love to nail this problem.

Many thanks.

 

What do your plugs tell you? I would think if you lessen the amount of airflow into the airbox (due to absence of ram air ports) you might be running rich. At low end throttle, you're not using the main jets. When you "whack it open" you're dumping a bunch of fuel to the carbs without the benefit of pressurization behind it.(??)

 

It could also be your Motion tubes are worn out. This is where the jet needle sits, sometimes where they tapper they get worn out. On that bike Im pretty sure you cant replace the motion tube, but you can set the jets to run a little leaner. Most likely it is running to rich. Which is why after to ride it around town it starts to clear up after your flooding it with fuel. Other solution is to replace all the carbs. (: ... Hope this helps you.

 

I have not heard of that one. Did not see it in the fiche either. Please explain....I am interested on this. Thanks for bringing up a long ago question and possibly answering it.
Welcome to KF

 

Emulsion tubes are the tubes that run up the middle of the carb and feed the fuel into the intake, they are full of little holes and have the needle in em and the main jet at the bottom also known as the needle jet. When they get worn out it will run to rich... I spoke with a mechanic about these problems on my zx9r. If ya play with the needles and set it to run leaner it should clear up your problems. Emulsions tubes are a big problem on GSXR's also. Look em up on google you will find some pictures of them.

My carbs had to be reset numerous times and put the bike on and off a Dyno to get them right. The Dyno originally showed a bad fuel curve is how we came to the conclusion, bike is running good now ... Hopefully this helps your issue.

 

ok, yeah, the emulsion tubes are a big deal on these rides since they are so small and are prone to plugging up. I was not sure if you meant emulsion tube or not. Thanks for the clarification.