Hunting Predator 420

C

chaznaster

New member
Messages
23
Reaction score
22
Location
Concord, MA
My son and I are working on an Arachnid go kart build. A few years ago we got most of the parts, including the engine. It ran well then.

As often happens, life got busy and have picked the project up again this summer. We have made good progress so decided to take out the motor to run it for some motivation.

Our issue is that the engine started "hunting" with the governor moving in and out, across the throttle range. We cleaned out the idle and main jets (101 = 0.040) and blew out the carb, which helped but did not eliminate the problem. We then upped the main by one size to 104 = 0.041 having read that these motors are jetted small at the factory for emissions reasons. Now we run well at idle as well as WOT but it still swings at mid throttle.

Does anyone have and advice on best next steps?

Many thanks!
 
C

chaznaster

New member
Messages
23
Reaction score
22
Location
Concord, MA
Thanks for the info - good to know it will not do this under load!

Regarding removing the governor, I was under the impression that that would allow higher RPMs and require a billet flywheel so the stock one does not explode. Would it be enough to limit the throttle travel with the stop screw?

Also, I am unclear, is it wabbit or duck season?
 
B

BrownStainRacing

Well-known member
Messages
1,360
Reaction score
1,346
chaznaster said:
Thanks for the info - good to know it will not do this under load!

Regarding removing the governor, I was under the impression that that would allow higher RPMs and require a billet flywheel so the stock one does not explode. Would it be enough to limit the throttle travel with the stop screw?

Also, I am unclear, is it wabbit or duck season?
Click to expand...
Tune it to max rpm with the governor installed. It might jus surprise you how much power it has at 4200 rpm max,.......when it's tuned right.

Big blocks make power down low, it does not need screaming rpm like a small block does.
 
C

chaznaster

New member
Messages
23
Reaction score
22
Location
Concord, MA
BrownStainRacing said:
Tune it to max rpm with the governor installed. It might jus surprise you how much power it has at 4200 rpm max,.......when it's tuned right.

Big blocks make power down low, it does not need screaming rpm like a small block does.
Click to expand...
Sounds interesting ... but for now we need to stay focused on the build or we will never get it done. I am easily distracted by bright, shiny objects ...
 
R

redflash

Well-known member
Messages
650
Reaction score
619
okay Chaz...heres the deal. When you remove the governor it will allow you to reach high RPMs if....if you have added a cam, ratio rockers, added thinner head gasket, Larger Mikuni Carb and other power items. If you keep (as I have on my arachnid.) the original Carb ( even over jetted)
You will never reach the rpm range of Danger. As your motor sits, now, you do not need a flywheel and billett rod. Those two items are a safety necessity if you expect to reach rpm's over 5000 on a regular (racing) basis. With the stock 420 carb you will NEVER reach much over 4000 rpms, even with a aftermarket cam, and other speed items.........so the reality is......that you have no need for the billett flywheel and rod. So bottom line............................................Pull out the governor, and low oil sensor, and you'll be just bueno....mi amigo

Da redflash
 
C

chaznaster

New member
Messages
23
Reaction score
22
Location
Concord, MA
redflash said:
okay Chaz...heres the deal. When you remove the governor it will allow you to reach high RPMs if....if you have added a cam, ratio rockers, added thinner head gasket, Larger Mikuni Carb and other power items. If you keep (as I have on my arachnid.) the original Carb ( even over jetted)
You will never reach the rpm range of Danger. As your motor sits, now, you do not need a flywheel and billett rod. Those two items are a safety necessity if you expect to reach rpm's over 5000 on a regular (racing) basis. With the stock 420 carb you will NEVER reach much over 4000 rpms, even with a aftermarket cam, and other speed items.........so the reality is......that you have no need for the billett flywheel and rod. So bottom line............................................Pull out the governor, and low oil sensor, and you'll be just bueno....mi amigo

Da redflash
Click to expand...
Cool. Thanks for the tip! I had no plan at this point to go for more RPMs but if I can get to 4000 that easily, it seems like a no brainer.
 
You must log in or register to reply here.
Top