Pred 212 with gx390 carb

M

magna_503

Member
I'm tuning the pred 212 with a gx390 carb. Currently it has a .043 #109 jet on there. It idles fine at 2000rpm, but has a slight hesistation at first throttle. But if it's idle at 3000rpm, the hesitation is reduced a lot.

I tried .039 about two weeks ago but it would only run half choke.

Picts of sparkplug below, it looks slightly rich. I think I'm close, I'll see if I have a .041 to tried



What do you guys think I should do?
 
I'm gonna try a different spark plugs, and an idle jet of .026 -.028 and see if that fixed it. It's only $3.00 for the idle jet for now.
 
Did a little idle tuning today. Got it to idle smoothly at stock 1800rpm, but it still is still hesitating when take off. I ended up increasing idle speed to 2600rpm for now so it'll take off smoothly without the hesitation. It'll cruise around 15mph at 2600rpm. Which is great when i'm riding in the street and not have to worry about being pulled over.

Once .026 idle jet is here, i'll probably set the idle back down to 1800rpm, but I might just keep it at 2600rpm and not use the throttle when cruising.

I did have a few hickups, broke a chain from the motor to the jackshaft. I swapped out from a 40t to a 36t. The 36t sprocket (ratio of 8.71)was thinner than the 40t sprocket, I did not check this when installing the 36t. It was 1/8" thinner and was enough to cause the chain bind and broke.

I still need one more tensioner to prevent the second chain from popping off. Otherwise, it feels good riding for a few short rides today.
 
After a hard ride (20mins) today. Spark plugs actually looks leaner in picture due to lighting, it looks more like a brand new spark plug color before installation. I don't remember if I have the stock etube or the 140etube, but I swap it in and up the jets by 2 sizes and see what happen. Maybe this is why I can't rev passed 6200rpm no load, and didn't see passed 4800rpm while riding. I want it closer to 7000rpm. Any hints on how to make that happen, beside swapping out plugs and upping the jets?

Motor has a billet flywheel with 18lbs springs, and 2 mufflers in series, and a gx390 carb.


 
Last edited:
magna_503 said:
After a hard ride (20mins) today. Spark plugs actually looks leaner in picture due to lighting, it looks more like a brand new spark plug color before installation. I don't remember if I have the stock etube or the 140etube, but I swap it in and up the jets by 2 sizes and see what happen. Maybe this is why I can't rev passed 6200rpm no load, and didn't see passed 4800rpm while riding. I want it closer to 7000rpm. Any hints on how to make that happen, beside swapping out plugs and upping the jets?

Motor has a billet flywheel with 18lbs springs, and 2 mufflers in series, and a gx390 carb.
Click to expand...

Maybe let the exhaust flow better by ditching one of the two mufflers.

7,000rpm is quite a lot out of a rather stock 212cc engine....you need to consider a better cam than stock IMHO.
 
The connecting rod will be the first item to break in that engine at high rpm. Agk sells billet con rods and many other upgrades. What kind of transmission are you using?
 
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