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Maverick Spark
I saw recently on Facebook Group pages from the Vintage Karting Assocsiation (VKA) and Vintage Kart Club of America (VKCA) posted (threads) questions about Maverick Spark. There have been articles from the various Karting Magazines (the magazines have been scanned and posted at the FB Groups' Files tab (Library). Starting this post with the idea to assemble these articles. No guarantee on how successful I will be in completing the task. Some past updates on other topics taken years. LOL.

This is from Karting Digest, 1977 July:
.jpg   PW KD 197707 11 Maverick Spark.jpg (Size: 3.16 MB / Downloads: 92)
.jpg   PW KD 197707 12 Maverick Spark.jpg (Size: 1.6 MB / Downloads: 74)
.jpg   PW KD 197707 15 Maverick Spark.jpg (Size: 1.49 MB / Downloads: 61)
very good article,,,no one believes me when I say we had a button on the steering wheel.....and yes it worked....but sometimes costly...

I think it was banned in 62-63????

We ran maverick for years. It worked fine. For some reason it was never happy on the open 101's, but worked well on all the early engines, and on the '91. My Pop decided the wires from the steering wheel to the engine were too long, so he developed a cam-operated microswitch and worked it off the carb throttle arm. It had a detent on the throttle pedal to let him know when he was at full throttle but not in maverick. I was gonna attach a pic of Charlie Craibe's Scorpion/Mc30 showing the switch, but I guess I've exceeded my allotment of space. Ted
Beware the articles only take you so far. With the shortage of pistons and parts, trying to do this today if you are not 110% sure of how everything works is flirting with a ride on the pick up wagon and back to the pits.
Amen, Steve. We're not racing for REAL championships today, so it's wise not to jeopardize these scarce and valuable engines for an extra boost of power. Ted
maverick spark is neat a real thing and does give you extra power.
do we need this on the old engines?
probably not .
but it is fun when that little extra kick goes in near the end of the straight. Big Grin

d Cool
Dave L.
Properly timed maverick spark is essential to the long term survival of the Mac engines if they are going to be run at rpm above 12,000 for the 100 cc motors and 11,500rpm for the 101s. The most common failure of the Mac engines when used for racing and revved up high is rod failure due to tension loads. The failure will occur in the form of a broken rod bolt or structural failure of the rod at the narrowest point of the beam right below the wrist pin boss. The failures are the result of inadequate combustion chamber pressure when the piston reaches TDC. In order to achieve enough combustion chamber pressure to help offset the inertia of the piston the ignition timing needs to be 30 degrees BTDC plus or minus 1 degree at high rpm. The problem is that it is very difficult to control detonation down at the bottom end of the rpm range with 30 degrees of advance so the magic of maverick is that the engines can be set up with static timing controlled by the points and condenser at 24/25 degrees BTDC and then the engine will transition to 30 degrees when the engine speed reaches the point where the points can no longer follow the cam.... or as it is often referred to as "float". When the points float the timing is determined by the relative position of the coil legs to the magnets in the flywheel. The 91 series combination of crank key location, five degree flywheel and coil location happens to work out just right and the only thing needed is careful attention to the point tension so make sure the float does not happen too low in the rpm scale. The 101 engines came with the standard flywheel so the timing is approximately 25 degrees when the points float and that is simply not enough advance to keep the engine from self destructing. The first thing anyone running a 101 engine should do if you plan to race it hard is to replace the original flywheel with a 5 degree version. It is also important to note that the static timing setting plays an equally important role as point tension in determining if and when the maverick transition occurs. Many racers struggle with carburation problems with the 101 series engines and they "solve" their heating issues by setting the timing way down at 21/22 degrees BTDC. When the points are set for that level of static timing they open less in terms of gap and for a lesser portion of the rotation of the crank. Accordingly, if set up with plenty of point tension the low lift/short duration setting results in the points being able to follow the crank up to a much higher rpm so they never float and maverick spark is not achieved. To "save" your 101 engine from near certain rod failure the engine needs to me timed at 24/25 degrees static and have a five degree flywheel.
Steve O'Hara
What was the recommended point spring tension for the 100cc Macs? I've forgotten.

Snap-On Tension gauge...

.jpg   Tension gage full.jpg (Size: 600.38 KB / Downloads: 38)
(09-12-2019, 10:05 AM)Scott Elkes Wrote: What was the recommended point spring tension for the 100cc Macs? I've forgotten.

Snap-On Tension gauge...

It was hard to get over 20oz at the contacts with OEM points but the REBCO points had a thicker spring and you could get up to 24oz easily. I ran REBCO and had a special tool for tweaking the spring to increase the tension. You have to be careful with how you bend the spring. If you just increase the existing bends by squeezing them tight they will fail. The trick is to make a forming tool that allows tightening the bend but spreading out the deformation over a wider section of the spring.
Steve O'Hara
Uh-oh, I feel a brain cramp coming on.  I thought the objective was to use a tension low enough to let the points float.  What did I miss?

Also, referring back to the external  switch that Gary and Teddy mentioned: does it  work the same if the switch grounds the points, or does it need to open the circuit upstream of the points?

My kill swich is wired to ground the points, but the motor keeps running until the RPM falls below maybe 1500 RPM.

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