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421 4mill stroker jetting.


rascal

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just put together a 4mill stock rod 68mm big bore drag ported vitos motor. it has triple exhaust ports and was running on the stock carbs . the mains were at 390 and the vitos long needles were on the 4th down. yuk!! too rich.. dropped the needle to 3rd down and rejetted to a 370... too warm i think.

now im gonna change the whole carb set up to Keihin 34mm carbs with billet intakes. im gonna run the fatty pipes to help with the bottom and use the hemi head ll with 21cc domes on pump gas. it has the rickeys 200 watt stator and timing is set at 4 degree adv. ther is no air box . k n pods is it.....

WERE DO I START IN THE JETTING ... they came with 160 and 162 mains .. were should i put the needles!! my elevation is 1200 ft.

any suggestions are welcome

russ

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Dont have too much experiance with those cylinders though i jetted a pair once however they were not drag ported.I ended up at 158 main,50 pilot,cel needle 4th clip.This was with 35mm pwks.Start with the needle in the middle cel preferably ,55-52 pilot,175 main.This should be rich but safe to start foxin with

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thanks for the info guys.. got the mains at 165 and pilots at 57.needle are on 4th from the top. semms a bit snappy .who said fmf fattys wont rev!!. didnt get to rip it yet thow . waiting on the pods from my mail man !! i will post more in a few days !! :headbang:

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wow man ,, it wants more fuel with a 168 main . plugs both were a greyish light brown tint. i want it richer.... 170 or 172 should do ?

i do know one thing thow ......... very impressive from mid to top side with the drag ported jugs!! they have triple exhaust ports also.. too dam cool man .. :dance:

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162, 55, middle spot, and air screw out 1 turn. Just set one of these up at 1800 feet and it runs perfect.

mine was lean on a 165 main.. went to a 168 main and looked a bit better.. goin to a 172 or 175 and work from their. its too warm with a 168.

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I have the same 68mm bigbore cylinders and a 4mill long rod crank..except i have it setup for 30mm keihns and have a full airbox. Im right a t 158 on the mains and 55 on the pilots.

 

Im sure with just pods it would be around 165-168.

 

A Cpi or shearer pipe and big carbs really make a huge difference with these cylinders,but they lose a lot of the bottom in the process.The gains on the top a are great if all you do is drag or dune play,but the fatty pipe is great if you want to do it all with this particular setup.

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I OFTEN WONDER WHAT THE DIG BORE SHEARS WOULD DO FOR THE ENGINE,, it run great now thow with the fmf fattys. i had the raise the main jets to a 172 . plugs were to gray . it effn flies. my buddy took it for a rip and didnt wanna give it back!! he was amazed at the transformation. kuddos to vitos products and wisco . great people and the tech support is outstanding! :headbang:

thanks for the help guys !!

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I have the same 68mm bigbore cylinders and a 4mill long rod crank..except i have it setup for 30mm keihns and have a full airbox. Im right a t 158 on the mains and 55 on the pilots.

 

Im sure with just pods it would be around 165-168.

 

A Cpi or shearer pipe and big carbs really make a huge difference with these cylinders,but they lose a lot of the bottom in the process.The gains on the top a are great if all you do is drag or dune play,but the fatty pipe is great if you want to do it all with this particular setup.

you quad looks exactly like mine dude!!

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  • 4 months later...

I have the same 68mm bigbore cylinders and a 4mill long rod crank..except i have it setup for 30mm keihns and have a full airbox. Im right a t 158 on the mains and 55 on the pilots.

 

Im sure with just pods it would be around 165-168.

 

A Cpi or shearer pipe and big carbs really make a huge difference with these cylinders,but they lose a lot of the bottom in the process.The gains on the top a are great if all you do is drag or dune play,but the fatty pipe is great if you want to do it all with this particular setup.

 

What setting do you have your needles at??

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