Exceeding 6100rpm with the Briggs 206?


(Alan Domme) #1

How could a 206 exceed the 6100 rpm limit provided by the factory limiter? My son received a mild warning in tech for his Mychron reporting a 6133 (6150 being a DQ) on a lap. maybe on a long downhill straight the engine could mechanically over rev due to clutch lock up?

(Bryan Williams ) #2

I think I’ve seen this before. From what I remember a mychron shouldn’t be used as a tool to determine the revs. I think they should be using an approved tech tool that can verify the limiter. Not sure if it would clip onto the plug wire like the mychron but would definitely be more accurate.

(Tony Zambos) #3

Think that there are couple of scenarios in which the Mychron could incorrectly show that you exceeded the rev limiter. First would a bump or curb that would get both rear wheels off the track. The second way would be just reading the max rpm off the gauge and not downloading the data to Race Studio. The reading of an over rev could be a signal that has a lot of noise on it. Seeing it in Race Studio would show the bad signal. You might have a bad rpm sensor wire, or it is not sufficiently tie-wrapped to the chassis.

(Alan Domme) #4

Thanks guys- Looking back at previous data it looks that this was just an erroneous reading.
I was told our club uses 6150 as the cutoff to allow some leeway for small error in measurement.

(Jack Mazury) #5

As the others said those Mychron Rpm cables aren’t 100% accurate especially with all the vibration on a 206. I don’t think I have ever seen one read a perfect 6100.

(John Leah) #6

Over the years I have run 2 different Alfanos on my karts mainly with Honda GX 160, Briggs V twin, and 390 clone.

I use the max rpm setting and 2/ ignition setting as normal.

I gear for 5,500 - 6000 rpm.

Just occasionally the Alfano has recorded way out max.
readings. ie. 7000 plus.

Last time this happened I was running the 390 clone. I thought I was geared for 5,500 max. Alfano was recording 7000 plus max consistently.

Changed the whole Alfano system for my spare, same result.

To shorten the story I found the engine was running way too rich.Plug was black sooted up. Cleaned plug and rejetted and got expected readings.

Seems as though Alfano was counting clean sparks at the plug rather than impulses in the lead?

Anyone else experienced similar or have an explanation?

(Scott Sawyer) #7

Could also happen if he was at the front of a train of karts. The rev limiter can’t stop you from physically over revving the motor. If he was geared shorter than the karts behind him and they were pushing it is possible to turn it faster. It’s the same as when a driver in a car goes for third gear and gets first. There is a rev limiter but physics wins.

(Bryan Williams ) #8

My thought on that would be yes maybe physically the crank is rotating faster than 6150 but the ignition module, being a digital piece would still only fire so fast. Just a thought.

(Matt Abel) #9

I went through a tech class with Dave Klaus and this topic was brought up. There are some engine builders that use 6150 or above to show that their engines are so much better. When actually it’s more than likely their own tach that’s showing that.
He told us that the way the limiter works it makes the signal fuzzy when it hits the limiter. The mychron and any tach is generally taking an estimation of what the RPM is so when you get close to that limiter the mychron is trying to take that signal and estimate what the RPM is actually reading.

The way we check at our track is use the exact same tach on everyone’s kart that is only used for tech. It is a little easier to see if one kart is off compared to another. A competitor can reprogram their own tach but if we have one independent tach that everyone gets measured by then it takes one more variable out of the equation.

(James McMahon) #10

Exactly, the ignition pulses get cut and become erratic at (and beyond) the 6100 limit… and dataloggers rely on that pulse signal.