421 Cubs

[06Shee]

Hey guys.. I just got cubs dune ported by Jeff@FAST. I had stock cylinders with some mild porting, and a 4mm stroker crank before I got the cubs. They pulled PERFECTLY on all gears. I had 330 mains and needle on 3rd clip ( I am at sea level ), on my 36mm mikuni flatside carbs.. Although, after I got the cubs with the same carb setup the bike no longer pulls at all. I mean it doesn't pull at all. For ex, I am on 4th gear going somewhat slow (not too slow at a point it will stall, but just cruising at 4th), then I pin the throttle at WOT, It would take like 4-5 actual seconds to actually start pulling and the hard pull to kick in, instead The bike just bog and slowly increases speed then suddenly pulls. My old cylinders used to pull everywhere, if I were to pin it from going slow it pulls. I have tried 330,340, and 350 mains and raised needle to 4th clip and still no pull on the cubs, I am running klotz supertechniplate oil at 32:1 ratio ( using premium pump gas) on 22cc domes. I would also like to mention that, for my air screw and pilots, well, I don

Edited March 13, 2009 by 06Shee

[shanYE west]

did it pass a leak down after you assembled the topend?

[tony cub]

leak down test???

[06Shee]

No I haven't, but I put brand new gaskets and o-rings and re opened the cylinders to check the gaskets and all is fine

[tony cub]

still need to test..that would be my fist thing to check..

[FireHead]

still need to test..that would be my fist thing to check..

Word. :geek:

[sleeper06]

Where is your compression at and timing,Jeff didnt tell you base jetting for the carbs,if he did he is most likely rite,I have doubted him before and allways ended damn close to where he wanted me,you will need to run bigger pilots with the cub,I also didnt know jeff dune ported cubs I thought it was drag or clean up,you will get peace of mind in a pressure test

[sheerider1026]

are you using t5 pipes with this motor??? if so.. that can be the problem... you need some cpi's or shearers.. i tried a set of t5's on my 392 cub.. it ran like shit.. what is your timing set at??? cubs love timing.. it really wakes them up.. i think i ended up at around +6 on my timing.. this bike likes to try and pull my arms outta socket!! lol

[06Shee]

Timing is set on +4. About the T5's yeah... some other ppl told me to get CPIs or some bigger pipes, could that be the prob?

[Darthwall]

I think if your jetting is ok and your leakdown test is ok I would definatly get a different set of pipes I went from a stock motor to a 4mm drag ported stock cylinder with 34PJ,s and had LRD adjustables on at first set for top end I had a small gain on power but after not riding it in 6 months didnt think much of it lol I got a set of CPI oof,s put them on and WOW its a hell of a difference front tires are off the ground through 4th now

[wesw]

cubs run leaner pilots and needles compared to stock jugs and usually bigger mains.

[okbeast]

I ran T5's on a 421 cub and it pulled plenty hard. Don't think that's the problem here, I'd look at jetting/airleak/etc.

[RadarRacing]

I think you are having probs in jetting. Boggy as crap under a load with mikunis would mean fat IMO.You dont say what your plugs look like. T 5's will run pretty well with a cub. I had T 5's on my old 392 cub and it pulled hard. I gained with cpis but I think you are fat on the main. I would have guessed like a 270-290 on the main. Those arent stock carbs, you wont need 390s. With a complete cylinder change your jetting can be up or down from what you had.