Jetting / plug question Cheetah Cub 421 4mil

[knoxvillebanshee]

I've got an 87 shee that I've been messing with. I bought it a few years ago pretty cheap and ran it until it blew up. The bike came with those OKO keihin knock off 30mm carbs by the way. When I had the motor torn apart we discovered that I was already .80 over so I had to decide whether to resleave, buy new jugs or do something else. I figured what the hell, so I bought a 421 68mm 4mil cub /hotrods crank setup and a NOSS coolhead with 20cc domes. My friend and I built the motor and put everything back together. I then added some CPI inframes, a +6 swingarm and new wheels and tires. To be safe, I ran 178 main jets and I have taken it pretty easy on the bike for the past few months (I've haven't run it for more than a few minutes at a time and I've always let it warm up good). It has been running ok, but I have some oil leaking from the tailpipes and the plugs are pretty wet and black all of the time. I just went from the 178 mains to 168's (I thought I had some 172's but I don't so I just ordered a set). I ran the bike with the new plugs down to my friends house to let it warm up and then ran it back wide open in third gear and shut it down while it was still gunned. I pulled the plugs and they are both a lighter tannish color and dry. (I'm running Motul 800 32 to 1 on 93 octane FYI). My elevation is about 650-700 ft above sealevel. I'm also running the stock airbox with no lid and a K&N filter kit.

 

I know I'm under carbed and that ideally I would have pod filters, but I ride alot of trails and dirt roads, so I want a good filter. Now I also understand that a cub setup is not for woods riding and all that, but I wanted one so I bought it - so be it. However, I would like some help in terms of jetting and what my plugs should look like.

 

Here are my questions:

 

1) Do 168 mains with 30mm carbs and an airbox sound way too rich for a 421 cub at 650ft elevations?

 

2) What should my plugs look like?

 

3) Will the stock radiator keep me cool enough?

 

Any other advice would be appreciated!

[locogato11283]

1. every motor is different and will need different jetting. if your plugs are tan then id leave it for now. what pilot? i run a 45..

 

2. if your jetting is right on your plugs will be tan or cardboard colored. if its lean it will be white. if its rich they will be darker or black.

 

3. as long as your moving. i wouldnt just let it sit and idle for a long time. remember cubs have way more coolant capacity that stock, so youll be fine.

[knoxvillebanshee]

1. every motor is different and will need different jetting. if your plugs are tan then id leave it for now. what pilot? i run a 45..

 

2. if your jetting is right on your plugs will be tan or cardboard colored. if its lean it will be white. if its rich they will be darker or black.

 

3. as long as your moving. i wouldnt just let it sit and idle for a long time. remember cubs have way more coolant capacity that stock, so youll be fine.

 

Thanks for the advice! My pilot is a 55 and I'm on the middle clip. It doesn't bog or anything. For what its worth, I can't be more happy with the way the cub runs. I got my setup from majicperformance by the way. Mike over there is super nice and very helpful.

[dajogejr]

I'm not sure how OKO carbs differ from keihin, but those main jets would be way fat for a normal keihin.

I know it may not be possible, but you really need to be in 5th gear at least to do your plug chop/check.

There is much less load on a motor in 3rd gear as in 4th or 5th.

 

With 20cc domes on a 4 mil stroker cub, you need to check compression to make sure 93 octane is enough.

You are probably fine...but you need to check to be sure. Hate to see you smoke a top end for not doing something as easy as a compression check...

[1bad4millbanshee]

i have same setup and i run 93 but i just smoke my top end should have did a compession check smh! whoops the guy i got it from said it would b fine on pump gas but when i get it back together looks like im doing one thanx! lol