Powerland 420cc GAB 2.0

[65ShelbyClone]

I assume it goes lean when I open the throttle too fast.

That is exactly what happens. A richer idle mix and pilot jet will help, but the problem will never go away without a pumper carb.

 

[bob58o]

That is exactly what happens. A richer idle mix and pilot jet will help, but the problem will never go away without a pumper carb.

I've also been told that I can try to restrict the main air bleed/jet with a long piece of thin wire inserted into the air jet all the way into the carb. - Thanks FHB!

If I understand correctly, a smaller main air jet would cause the main circuit to "come on" earlier and possibly help with the bog.

https://www.hotrod.com/articles/tuning-with-air-bleeds/

"Not only will larger air bleeds lean out the mixture, they’ll also delay the effect of that circuit by weakening its signal. Conversely, installing smaller air bleeds boosts the signal and speeds up the transition into that circuit. These factors have great influence over driveability. "

 

[bob58o]

So I have moved the buggy to a location with more real estate. More space to ride around and tune the carb. Unfortunately this means I get to mess around with it less often.

I started by checking the float height. It seemed as though the float level was too high according to what I've seen online. I adjusted it slightly.

I put a fresh plug in and increased the pilot from 30 to 35. I decreased the main jet from 155 to 145.

I drove around for a while trying to get a feel for where the tune needed work. It seems as though with the larger pilot, the off-idle WOT bog improved. It didn't go away, but no longer killed the engine. It would hesitate, but then accelerate.

The 1/2 throttle stumble seemed to come back.

After about 10 minutes of riding with some three or four 15 second stretches of WOT I went back and adjusted the air screw. I think I turned it in to richen the mix to see if I couldn't work on the bog. I slammed on the pedal and it died. Couldn't get it started back up. I waited like an hour and tried again. Still wouldn't start. Compression felt normal. I didn't check for spark, but it seemed like I was getting spark. It almost wanted to run sometimes. I pulled the plug and it was pretty sooty, very black. I put a new plug in and it still wouldn't start. I didn't have any carb cleaner / starting fluid or I would have tried to start it like that. Next time, I guess I start with a carb breakdown and cleaning. I've taken this carb apart at least a dozen times, so it is very likely that it is dirty.

First world problems.

 

[rk970]

Have you ever thought of using a CV carb. Something like in the 32~34mm range?

 

[bob58o]

Have you ever thought of using a CV carb. Something like in the 32~34mm range?

I know nothing about them. Like a Harley carb right? Does it include an accelerator pump?

Got a link for something like that?

 

[65ShelbyClone]

Constant velocity (CV) carburetors are a lot like vacuum secondary automotive carbs except there is no secondary. There is a throttle blade that you control, but the actual throttle is a slide controlled by vacuum signal. I don't know of any that have accelerator pumps. They sort of get away without them because the slide doesn't open fast enough to really need one. Fuel economy and smooth response are more the goal with CVs. They were/are popular on street motorcycles without EFI.

For all-out performance a pumper carb is still king.

 

[rk970]

Well I got my 2004 FZ1 to make 142hp to the rear wheel. 66 cubic inches with CV carbs. Pretty low performance I would say..

 

[65ShelbyClone]

Ok.