Edelbrock Carb Fix- Stiff Thumb Throttle

Contributed by: Tom Hartley -Bare Performance Sponsored Rider

When I first installed my Edelbrock carb onto my Suzuki Z-400, the spring pressure of the carb had my hand cramping within a few laps. I got tired of that really fast, and decided to do something about it. Here’s the report – It makes a tremendous difference.

Previously, in an effort to reduce the pressure required to push the thumb throttle, I unwrapped the throttle spring 1 1/4 turns, and that made a big difference in the tension. I also cut one full loop out of it.

Now, here’s what I did to the accelerator pump spring(s). There are two. This first pic shows them both. One is on the accelerator pump (you can see it on the bottom of it), and the other, sitting to the right, goes in under the pump.

 
First thing I did was cut out the top and bottom loops from the spring on the pump itself. If you look closely, you can see the difference in the spring. This spring only comes into play at full throttle. You Edelbrock users know that tension you get from about ¾ throttle all the way to full? This spring controls it. Cutting the two loops makes it easier (lightens the spring tension).

Now, for the spring under the accelerator pump - I got another spring from Ace, and no, I don’t know what the part# is. It’s a lighter spring - much lighter! It was a little longer that the stocker, but I cut it to length, and re-wrapped the end. Yeah, I know the pic isn’t good, but you can get the idea of how much lighter it is - Stocker on the left, new one on the right:

Put it all back together, fired the bike, and checked it. It is an incredible improvement, and it’s not hard to do. It probably took an hour total, and that includes running to Ace to find a spring. I’d say my carb now throttles as good or better than the stock carb did.

RIDE REPORT:

I put some EXTENSIVE testing on this mod at the track. We had a scheduled practice, so most of the usual racers were there. I put in four 15-minute motos on the new track layout. I didn’t have any cramping in my thumb, and surprisingly, had very little arm pump at the end of the motos. I doubt the lack of arm pump was due to the throttle, but more in the line of conditioning.

Before, my thumb and right hand would cramp so damn bad that I’d lose grip with the hand. I’d have issues where I couldn’t throttle in the air, just because my hand was relieved to not have to “hang on.” The results were bad on landings… Nose-low mainly, from not being able to push the throttle. At any rate, if you’re an Edelbrock user, you’ve GOT to do this - I felt better on the track today than I have in a very long time…

QUESTION -
"I have my pump tore apart right now.how do you get the spring off of the pump itself to cut the ends?"

You don’t take it off - you need to clip it while it’s still on the accel pump. You have to have some very strong wire clippers to do it, or use a Dremel to start the cut, then weaker wire clippers to cut it. If you use the Dremel route, be VERY careful to isolate the spring (compress it) from the plastic collars the spring sits in. If you melt those due to heat build-up of a cut off wheel on the spring, you’re going to be buying a new accelerator pump from Edelbrock Motorcycle Division. Take your time, and make deliberate moves. It’s easy, though it may sound difficult.

QUESTION -
What spring size did you use?

It was 3/8″ x 1 1/4″ x 0.25. That’s (spring diameter) x (length) x (wire diameter), and the spring is available from any local Ace Hardware store.

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