"Recently, all the major modern karting organizations have adopted a new rule that mandates all carbs (except slide valve type) employ an auxiliary throttle return spring. This was done in response to several incidents and injuries. This extra spring is designed to return the shutter to the closed position in the event the primary carb spring fails.
At this stage, the VKA has not taken any official action on this situation, but I thought it would be appropriate to show a few of the available solutions in the interest of safety. Other solutions should be acceptable as long as the solution will close the throttle in the event the primary throttle return spring fails." LYNN HADDOCK
Rolh, one of the biggest problems is many people have the throttle setup to pull at the throttle rod but don't have the cable setup to push all the cable back when they let off the throttle. They expect the tiny carb return spring to do all the work. In most cases it can't. Most throttle cables feed the end into a washer or disc or something simular at the throttle rod. That washer or disc needs to not only pull but needs to have a wire stop (cable stop) on the return side to be sure the cable gets pushed back up the housing. Some people also use 2 washers when they have the ball end on the end of the cable so the ball is captured to pull and push. This is an often overlooked area on a kart.
07-21-2017, 09:59 PM (This post was last modified: 08-07-2017, 10:51 AM by Jim Waltz.)
A couple of thoughts.........
I got a bit of a surprise this year at Blue Max Kart club in Davis California when going into the right/left "S" turn (really almost like a chicane) at the bottom of the hill during qualifying as I found myself at full throttle going into this tight section.
I was lucky that I had some years ago experienced a runaway engine when the cylinder base gaskets blew out on my KT 100, and I very rapidly got on the brakes and throttled the intake by putting my hand on top of the air box, thereby covering the intake holes in the air box.
Why? The throttle return spring on the carb had failed and the return spring up at the throttle pedal definitely did not close the carb.
Got it fixed before the first heat by swapping a carb from a spare engine in my trailer, and went on to take first place amongst club members in the F-100 class that day.
Those little wound springs on the carbs are not as reliable as one might imagine.
Now, as regards vintage karts, I have been finding that the cables from the aluminum block on the side of the frame seem to want to bind a bit on the 820's that I typically run, and I have taken to adding an auxiliary spring at the engine. A little bent steel bar bolted to the intake manifold, and a tension spring from there to the swivel on the carb shaft seems to work really well. I'll need to take a photo and post here when I get a moment.
In other news, faithful readers might enjoy seeing the way I handled the throttle business on my First Edition of the Kalifornia Nykes. Lots of details on this build are posted here on the Forum, but here's a photo of the assembly I mounted on the bottom of the frame at the seat.
What you might find interesting is that this assembly provides for a positive forward stop and a positive return stop. I really don't like the idea of using a fully-compressed compression spring as a positive forward stop, as the springs tend to kind of miss-align as they are fully compressed, and potentially end up allowing a lot of force to be exerted on the throttle shaft at the engine - when your (my) energetic foot is pressing hard on the throttle pedal, and really trying to push the throttle at the carb past wide open.
I've also attached an illustration of the assembly which provides details.......
I totally agree with the need for a spring to return the PEDAL in addition to the weak carb spring.
Here is different one that got me a while back:
I pulled the air cleaner to squirt fuel down the carb.
When I put the filter back on, I did NOT tighten the clamp.
After a lap or so, the clamp slipped down over the carb linkage and it stuck on full throttle.
With no kill switch (yeah, I'm a fool) it was all I could do to reach back and stop a strong MC-6.
Solution:
My filters have a rubber casing at the top. I drilled a .500 hole in the rubber, so I can squirt into it without pulling it off.
Then I use a rubber stopper to plug the hole. Occasionally, I forget to plug the hole, but that is a minor problem compared to stopping a high revving Mac.
i already use return springs on some of my engines.
over time , as i reset up carb combos i've been adding them but i think a better idea will be just to backfit them all.
as simple as a pull back spring from the throttle lever to a good holding point can make or break your day.
years ago i took a turn around the pits with a stuck throttle and failed brakes.
the carb already had a spring looped and clipped into the carb cup but it got knocked off by someone helping start the engine.
that was a little to exciting for me!!
i drilled a more permanent hole into the cup and bent the spring in the hole so it's non removable.
zero problems since.
I'm a huge advocate for extra return springs and kill switches. Not a real big advocate of the clothes pin style spring, as I've seen them slip and cause more problems.
Don't know how many times the kill switch has saved me, the engine or another competitor. And knock on wood, contrary to what people say the kill switch has never killed an ignition or tci box. And it's really nice to pull in the pits and push the button and that's that.
Thanks for posting this Rolf. I've been thinking about it ever since I read it the first time. So today I went out and bought a couple of springs and a kill switch. Both will be installed for Oreville.
