Hi all, I have this 90 viper that I can't seem to get running smooth. From idle thru full throttle it has a miss or sputter that I can't get rid of. It has been ported and polished and made into a true 90cc it has a 24mm keihin carb I've tried 148 thru 158 main and I'm running the stock piolet(sp) which I think is a 52? I think it has a koso intake also and I'm running 110oct race gas. It has a RC motersports pipe on it. One more thought the koso intake came with the OKO 21mm carb that I started with. Would that effect the way it runs, do I need a bigger intake with a bigger carb? If anyone can help me with this it will be grearly appreciated.
Thanks,
Lonnie

 

i have dinli 90 and it the same motor as a eton so i put a 54 mm big bore kit in mine and had to go down from a 140 jet to a 130 jet so u might need to go way down or get a 28 mm carb but mine is a power house now so it was worth everything i have done u should start at 120 and work your way up u will be suprise u can get the jet kits at hyper tune.com

 

Thanks scooter,I'll try that

 

You might want to check the wires on the coil...We had some problems with our Viper missing this summer after lots of riding on a washboard road. One of the wires was loose where it plugs onto the coil and not making a good connection.I just sqeezed the connector with some pliers to tighten it up and it was as good as new.

 

Thanks oldyeller, I did have one of the coil wires come off not to long ago. I'll check it out in the morning.
Thanks,
Lonnie

 

Tried a new spark plug? Check the gap too.

 

Thanks rapter, I'm running a NGK b7hs and when I pulled it it looked dry with ash/brown look to it. I don't know much about all of this so am I running the right plug,and what should the gap be?
Thanks,
Lonnie

 

Between .6 and .7mm according to my manual.

Usually when one of my quads starts missing it's the plug or I have had some trouble with the boot on my mini. When the jetting is off, it'll fall on it's face. When you're close and it's still off, it'll hesitate, then take off. I always work from fat back down. I can't imagine jetting causing the problem all the way across. Usually and idle is easy to obtain. You might also try looking for kinked fuel lines, check for a crack in the intake boot, clean the air filter, replace the fuel filter and make sure that pipe is sealed good at the port. Unfortunately, it's often trial and error when you chase a problem down.

Again, I can't imagine running straight 110 on one of these mini's. Do you know your compression? Have you run it before?

 

It didn't just start missing, it hasn't run right since I had it ported and polished. Right now I'm trying to work the kinks out, but this carb stuff is like rocket science. I don't know what the compression is I'm assuming its pretty good since I'm using a high comp. head and the jug was milled. I was told to run race fuel and mix it 50/50 with with pump gas but me being the average guy I figured that if some is good then more would be better. I have some 93 pump gas that I use for my other kids bikes so I'll just combine the two in the morning. I don't want to take it back to the guy that did the work because he lives 3hrs away and he seems pretty busy,plus I would kinda like to start learning how to figure this stuff out on my own so that I'm not bothering him all the time.
Thanks,
Lonnie

 

Carbs are easy, just time consuming. Always work from pilot to needle to main. Does it run better or worse? Only question you need to answer when jetting.

Turn the gas off. Does it run better as the carb runs out of fuel? Yes, then you are too rich. OR cover a portion of the air filter. Does performance improve? Yes, then you are lean.