Thanks in advance for any ideas or help guys. I have a Vortex RVX that I am having issues with it missing at about 12,500 rpms. I use this engine for road racing. The problem seems to occur at about 12,500 or so. If I let my foot slightly of the gas it is almost like someone strapped a rocket on my back. The engine will gobs of power and I can then pull 14,000 rpms if I wanted.
I have had the engine rebuilt after having this issue last year but to no avail I am still having the issue. I have tried different carbs, pipes, jetting, everything I can think of.
Has anyone run into this type of problem before or does anyone have any ideas?????
If you can ease off the throttle and it pulls hard to 14k it’s jetting. Probably rich, but hard to say without knowing the details and looking at the piston.
Thanks Tim will look into that but I have tried jetting with two different carbs. Do you think it could be ignition possibly?
Ignition is rpm sensitive, not throttle position sensitive, so if you ease off the throttle and it revs to 14k it’s not ignition. Check the reeds, proper fuel supply and if those are good, work on the jetting. KZ’s can be picky about proper jetting and it is not unlikely that you could try two carbs and jetting that don’t work with your engine.
Sounds like it is too rich.
When you ease off the throttle, you are sticking the needle back into the nozzle and decreasing fuel flow.
Try a bigger needle, lower the needle, smaller main jet. You are close, not way off, just a little rich.
What needle, nozzle etc.. are you running?
I am going to pull the carb apart today and get that info. I will pst it as soon as I know. Thanks guys
I have been watching this thread because I thought it was lean.
Mr Pappas has forgot more about kart then I ever knew but this is why I was thinking that. By backing off the throttle a little arent you closing the slide? By closing the slide arent you reducing the air so in a sense “Fattening it up”? As for Bernie’s comment, isnt the needle only in the jet at the beginning of the throttle?
Sorry Glen I do not mean to confuse you and I am curious to hear what it was.
Well this is what I have in the carb.
Atomizer is a DQ266
main jet 172
Needle is a k98 with the clip on the top groove
Idle jet is a 60 and the other one in the bottom of carb is a 50.
The slide is a 50.D7
I was reading Tom Barth’s posting in another thread and he says that a K21 needle and a DQ264 atomizer with a 144 jet is good for a KZ engine? Any thoughts on jetting would be appreciated.
No problem Matt, I am confused myself this problem has been going on for over a year now. And I believe if I am correct that backing off the throttle you are putting the needle back into the atomizer or nozzle there fore reducing the amount of fuel and making it leaner.
Well from your set up info I believe you are lean. I am in the midwest and you could have a completely different weather set up. But the k98 needle is a very large needle limits fuel some use as a qualifying set up. Don`t know what you have to tune with but if you want to keep that needle you need to go to at least a dq268 tube or you could leave the tube and change the needle a k21 or k22 should put you close. Toms set up with a cq1 idle circuit 60 outer dq264 k93 needle works well am not always sold on the 130 main jet tho would start with a135 main this set up flows alot of fuel because of the small needle so to get peek power you got to be real close on the main jet. These are the set ups I use on a tm a pavesi seems to like less fuel so this should be a good starting point. Good luck
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