built 6.5 clone running HORRIBLE after porting

[justinkk2005]

Hey guys, I recently asked about the 22mm mikuni.

Here is my carb setup.

needle jet set on 4th position (moved up and down, made no difference)
-had air screw all the way out, all the way in, no difference
12.5 pilot jet
120 main jet.

It runs amazing from 1/2 throttle up, but anything below its horrible.

I ported the hell out of the head and smoothed it out and polished both ports.

Would this have anything to do with the idling? I Mean its not rideable because of this.

Setup:
flat top piston
billet rod
18 lbs springs

 

[1992suburban]

bigger pilot

 

[Jdominique]

Yea, pilot is responsible for that rpm range. Order a 15 and 17.5 and try it out. It sounds like your main is right on.

 

[modelengineer]

You really shouldn't have polished the intake. The roughness helps the fuel mix properly with the air. You're only meant to polish the exhaust port.

 

[jr dragster T]

Can we see pictures of how extensively ported the head is?

 

[justinkk2005]

Can we see pictures of how extensively ported the head is?

I didnt take pictures of it because I didnt have a camera at the time, I pretty much made the ports bigger (obviously) and smoothed it out toward the valve where it kindra drops off a little. Thats the best way I can explain it

With a 17 pilot jet its to rich, with a 12.5 it runs horrible. Idk what to do

 

[Jdominique]

Did you try the 15 pilot?

 

[jr dragster T]

Something else isn't right, It should pretty well idle with just about any of those jets.

 

[Kenny_McCormic]

I think he opened it up to a point where it can't make enough intake velocity at low RPM. This is why porting is an art best left to people who truly know what they are doing.

 

[justinkk2005]

I think he opened it up to a point where it can't make enough intake velocity at low RPM. This is why porting is an art best left to people who truly know what they are doing.

it was just an experiment nontheless.

 

[jr dragster T]

You must have really opened up those ports! Slap a turbo on it, Velocity problem solved

 

[Rickracer]

Have you advanced the timing? Chances are you'll need to to get any power at lower rpms. I'd suggest a 4° to 6° advance key, might wanna grab two or three while you're at it, they aren't too expensive, maybe a 4°, 6° and an 8° so you can experiment.
Also, while you're at it, I would bump up the compression, shave the head, maybe run a thinner gasket, it kinda goes hand in hand with all the other mods you've done.
If you do take it apart, take some pics for us,

 

[justinkk2005]

Have you advanced the timing? Chances are you'll need to to get any power at lower rpms. I'd suggest a 4° to 6° advance key, might wanna grab two or three while you're at it, they aren't too expensive, maybe a 4°, 6° and an 8° so you can experiment.
Also, while you're at it, I would bump up the compression, shave the head, maybe run a thinner gasket, it kinda goes hand in hand with all the other mods you've done.
If you do take it apart, take some pics for us,

Here is a few pictures I made a video off in this build thread

http://www.diygokarts.com/vb/showthread.php?t=5879

I'm going to get a 14cc head and not touch the ports, but first i'm going to do a little more adjusting on it today!

 

[Rickracer]

You can touch up the ports a little bit and make A LOT of difference, work on the short turn radius and clean up around the valve guide, polish the exhaust, and rough up the intake with 80 grit tootsie rolls. You don't have to hog the ports out to increase flow, think quality rather than quantity, higher velocity quality flow will make more power than lower velocity higher quantity flow. I hope that made sense...:rolleyes3:

 

[justinkk2005]

You can touch up the ports a little bit and make A LOT of difference, work on the short turn radius and clean up around the valve guide, polish the exhaust, and rough up the intake with 80 grit tootsie rolls. You don't have to hog the ports out to increase flow, think quality rather than quantity, higher velocity quality flow will make more power than lower velocity higher quantity flow. I hope that made sense...:rolleyes3:

I messed with it today and it will idle PERFECT and if you just drive it easy it's okay but if you go do a hard run and stop it floods itself. I have to hold in the brake and the gas to start it and then when I try to get it to idle it POURS the black smoke, idles fine and will idle all day until you ride it then after that its horrible.

 

[Rickracer]

That definitely sounds like carb troubles, tell us more about it, what did you do when you "messed with it" to get it to idle, what size needle and seat, what are you using for a fuel pump, where is your float level, etc.???

 

[justinkk2005]

I'm not to sure on how to set a float level, it's just stock. Stock mikuni everything, except for my 120 main jet, 12.5 pilot, needle position is now the 3rd position (2nd pos made no difference, 4th almost fouled a plug), air screw 3 turns out (tried 2 and it was bad, best luck with 3rd) Gravity feed

 

[jr dragster T]

To adjust the float height you just bend the tab on the float where it contacts the needle. I usually set the float height where the middle of the float is inline with the gasket surface on the carb body.