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421 ported cheetah cub


pablopab50

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  • 3 weeks later...

Allright, I ran 160 mains, and the air screw is almost all turned out. Do I need a bigger or small pilot?

The idle is way too low. But giving just a bit of gas and it sounds good. The needle seemed ok (position) but how are you really sure if it's not too lean or too reach though... I got used to determinate whether it's too rich or too lean by the ear... Like I said at idle it's clearly too rich in my opinion cause it even stalls. And could it be the fuel screw?

 

( GROUND SEA LEVEL ) It was 50deg F

With Pods

Edited by pablopab50
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Allright, I ran 160 mains, and the air screw is almost all turned out. Do I need a bigger or small pilot?

The idle is way too low. But giving just a bit of gas and it sounds good. The needle seemed ok (position) but how are you really sure if it's not too lean or too reach though... I got used to determinate whether it's too rich or too lean by the ear... Like I said at idle it's clearly too rich in my opinion cause it even stalls. And could it be the fuel screw?

 

( GROUND SEA LEVEL ) It was 50deg F

With Pods

The 160 main is in the ball park but the spark plug will tell you if it's spot on or not.

 

As for the idle, on the Keihin's you typically don't want more then 2.5 turns out. And if you find the bike feels blubbery and opening the air screw past the 2.5 turns doesn't fix it, you would be correct that it's overly rich. Drop one size at a time though. What pilots are in there now?

 

Idle, just use the little black knobs on the slides to get it comfortably idling. Once it's close, use use the sync tool to get it perfect or feeler gauges to set the slides dead even if you don't have a sync tool.

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Well I blew one spark plug, it made a PAK pik and then the cylinder died. Changed both spark plugs for new ones and ran like new. But obviously I was running lot of oil at first 30:1 and then 32:1 Now I'm maybe around 34:1.

I used to run 36:1 in my stocker and it was perfect. But I'm still in the breaking in process as for the 421. I don't know my pilot size. I know for the main you can just unscrew the bowl and you will see the main but as for pilot and needle I guess you have to completely take it appart? As for the black knobs are you referring to the fuel screw?

 

Off-subject. Damn those shearers suck in trails. Powerband starts at 6700 or so. I knew I should have bought CPIs.

I have exhaust leak where the header mount on the silencer tube. I ordered cascades clamps. I'm using for now my old FMF rubber clamps but they do not completely seal. My head, cylinder, case, carb is all black from unburned fuel :(

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Well I blew one spark plug, it made a PAK pik and then the cylinder died. Changed both spark plugs for new ones and ran like new. But obviously I was running lot of oil at first 30:1 and then 32:1 Now I'm maybe around 34:1(These things tend to stay together when you know for sure what kind of oil ratio you have).

I used to run 36:1 in my stocker and it was perfect. But I'm still in the breaking in process as for the 421. I don't know my pilot size (Really, get that figured out). I know for the main you can just unscrew the bowl and you will see the main but as for pilot and needle I guess you have to completely take it appart? As for the black knobs are you referring to the fuel screw?

(The PWK's have a knob on each slide. The air/fuel screw is totally different)

 

Off-subject. Damn those shearers suck in trails. Powerband starts at 6700 or so. I knew I should have bought CPIs.

(Cubs aren't meant for trails)

I have exhaust leak where the header mount on the silencer tube. I ordered cascades clamps. I'm using for now my old FMF rubber clamps but they do not completely seal. My head, cylinder, case, carb is all black from unburned fuel :(

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  • 1 month later...

What do u mean u blew a plug, did u ever get the correct domes

By "blowing a plug" I meant burning. The plug either was badly fouled or it stopped working because I heard a bigger spark in the cylinder and in my opinion it's not from pre ignition. Right after 2 similar big sparks, the cylinder died.

Issue was fixed by changing the spark plugs. Now obviously the temperature is way colder but as mentioned in my last post I changed the pilot jet so I would safely guess that the engine should be less rich and thus burn the gas better.

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