Installed Top 70cc kit, RPM and run on issues.

[theo547]

I installed a 70cc top performance trophy kit with a dellorto 21mm clone carb w\ 86 main jet and leo zxr pipe. im running premix close to 20:1 (break in). stock air box with snorkel removed.

Im having two pretty nasty issues.

1. after getting up to 9000+rpms and letting off the throttle it will drop to about 7000 and stay there for a few seconds before dropping down to where it should be. cable is not sticking. ive swapped out the clutch and its doing it in the same spot. ive got dr. pulley's in the vari.

2. after I switch off the ignition it wants to run on for a second or two. it doesn't surge or anything it just seems like ive got some post ignition burn off.

things I havnt done that I plan on checking -
1. compression
2. more carb jetting.

any thoughts on what I should be looking for? a co worker of mine said he thought it could be related to the thick oil depositing on the piston and then burning off. ive looked at the dr. pullys and they don't look great, but ive seen a lot worse.

[2TDave]

Sounds like an air leak or lean. All my sliders wore fast on my 70.

[moofus02]

I would guess lean jetting with 20:1 mix ratio. I like being rich on my premix my sled I ran at 18:1 but I jetted accordingly. You get good ring seal with the extra oil. If you kill the ignition and it runs on you are hot enough to get pre ignition. Try pulling the choke on as you kill the ignition and see if it shuts down like it should.

Sent from my SPH-L720 using proboards

[theo547]

I didn't think of that. thanks for the input ill see what I can get done and report back!

[rpmcycleservice]

Jun 3, 2014 13:34:39 GMT -5 moofus02 said:

I would guess lean jetting with 20:1 mix ratio. I like being rich on my premix my sled I ran at 18:1 but I jetted accordingly. You get good ring seal with the extra oil. If you kill the ignition and it runs on you are hot enough to get pre ignition. Try pulling the choke on as you kill the ignition and see if it shuts down like it should.

Sent from my SPH-L720 using proboards

I agree.....that fat on oil is going to make the carb jetting significantly leaner......not to mention blowing oil out the exhaust like some of my nitro rc cars!!!.....if were doing a oval course on pavement...after 8 to 10 laps you can start to see a trail.....

[skuttadawg]

Extra oil sounds like a good idea to be safe but it runs hotter and leaner . I did use a 120 MJ with 70cc , pipe , Uni on a 19mm carb . With a 21mm you get more air so you need to upjet to get it right . I was using oil injection at the time and added some oil in the gas tank but it got the spark plug dirty .

I now run a 105 MJ with stock pipe since the other was too loud and premix 3.2 ozs per gallon .

[theo547]

I realize that this post is forever old, but I fixed the problem today.. only 6 years later!

My CDI was defective and not turning the engine off at times. It was also causing my engine to run like absolute shit at WOT. I'm not sure if I'm relieved or pissed. This project in conjunction with a few other issues basically made me put my scooters into cold storage.

[aeroxbud]

Better late than never. 👍

[Zino]

You have a ton of patience If i had the same issue for more than a couple years.
I would send My scooter off a cliff.
And Start over

[theo547]

Zino. It's been sitting in my garage collecting mothballs. With Covid shutting everything down... My other Hobby's have pretty much dried up. I figured I would get my wife's buddy back up and running (it had a bad master cylinder that failed after a caliper went bad) and I had also let that one sit for a few years also... When I got back to the buddy it's CDI had also failed, but that was a pretty straight forward no spark issue.

Idk. Pretty good week in the world of scoots for me. Lol. 2 back in action. I have a few more taking up space that I plan on moving on to next.

[Mech Warrior]

I can tell you most definitely that you need to upjet to atleast a 90 probally 95 main jet.