Comer k-80 engine tuning

[David Tenney]

Is there anyone out there that can share the secrets of tuning the Comer K-80 carburator? I understand the major difference in performance of these engines is in the carb and the tuning. While this is a great motor for Rookie sportsman, the engine seems much more sensitive to the needle valve settings than a restricted KT-100. Anyone have thoughts on the variabilty of power from engine to engine for thr Comer? Again, from what I have seen so far, the performance seems broader than what I have observed in a restricted KT-100.

[Jean Stafford]

Right on all counts.

This little engine is a bear to tune, and is very sensitive to adjustment of the needles.

There seems to be no real tech on the carb, as long as it still has the dump tube ball in place, and measures correctly at either end, and overall length, pretty much anything goes. BUT, it sdoesn't take much to screw one up, so proceed cautiously.

During the tuning phase of dyno testing the K80 I've found moving the outer diameter of the needles 1/32" can mean the difference between running strong, and just running. Worse yet, temperature and humidity conditions change the requirements, so you have to chase it.

Data acquisition and mapping seem to provide a good alternative to listening to the driver, or measuring acceleration on the track, and eliminate one thing the driver has to do beside drive. You can then map the EGT with the CHT and tune fron this frame of reference. A little expensive though.

Good luck

[David Tenney]

Jean, thanks for the reply. I have a mychron Pro that I can use for Data logging. What EGT temp do I look for and where do I insert the probe? Seems like a little overkill to me. I guess I will have to continue on the trial and error technique. How much difference is there between engines? Is the difference mostly in the carb. I would guess on a flow bench they all flow about the same. Also, I hear there are different ignitions available....are these worth the dollars and where can I purchase one?
Thanks from a Comer newbie..

[Jean Stafford]

quote:

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Originally posted by D Tenney:
..What EGT temp do I look for and where do I insert the probe? Seems like a little overkill to me. .

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I think around 1125F would be about appropriate. HOWEVER, location of the probe is critical to the numbers you are going to see. I recently placed a probe in an SSX can so that the probe was in the center of the flow from the engine, then had an opportunity to use a can whose probe wasn't located there. There was a 200 degree F difference.

I would like to see the probe tip in the center of the flow, and within 1" of the piston face. This would mean that you'd have to secure a probe mount to the muffler on the top and outside of the engine, then drill a hole for the probe thru the muffler that just clears the probe. Install the probe so that the tip is now in the center of the opening of the muffler. This should be about right.

Now the question of legality arises. since it's acceptable to mount EGT probes in other engines and pipe assemblys, I ASSUME, it's acceptable in this instance as well.

I recommend data acquisition for all new karters, and especially those with young drivers who concentrate on driving while on the track. Some of the units out there can be "played back" and at least you can see the maximums. EGT and CHT should be compared together though, and you should run 50-100 degrees rich of peak EGT while maintaining CHT's. If the CHT drops and the EGT is rising, you're lean.

The graphing packages are great for allowing you to see what trends are taking place, and worth the money in the long run.

As far as costs go, and for my part I follow the KISS principal. I don't personally run any data acquisition, but have a Pi Research system for my grandson. That'll change this winter, as I find I don't have time to look at the gauges either...

If you have any other questions, or just want to talk racing, check out our website at, Staffords Racing or e-mail me at .

Jean Stafford
Jean@staffordsracing.com

[ August 08, 2002: Message edited by: Jean Stafford ]

[JAARON]

My K-80 runs about 750 egt 415 cht ngk b10hvx plug

[Joe Rosse]

I mounted an EGT sensor (Digatron) by getting a brass compression fitting with a pipe thread on the other end, plus a nut with pipe thread (a bit hard to find). Then attached it with the compression fitting that is part of the original Digatron probe. Drilled a hole directly in-line with the exhaust port--fortunately there's an "open" spot on the can at the very point.

However, I've been having a hard time getting stable temp or tach readings. Can anyone tell me what the correct tach code is for the Comer engine and Digatron KT32 tach?

[Jean Stafford]

Joe,

Contact Digatron and explain your problem to them. I suspect you are having the same problems we were having with our Tach unit on the dyno when we tested the Comer K-80.

We took a short piece of wire, stiff covered, wire and wound it around the plug lead, and grounded it to the motor.

These little things make a lot of "noise" sheet metal rattling, loose screws, etc, and grounding the loop of wire seemed to eliminate the problem.

AIM made a special lead for the My-Chron system that incorporates the loop in the Tach lead that eliminates the problem.

Good luck.


Oh Yeah, It's my understanding that the EGT probe should be mounted directly in the exhaust stream, as near to the center of the flow. I've found that as you approach the edge of the header, or side of the muffler, the temps go down dramaticly. For instance, in a SSX-V can muffler, the temperature drops about 150 degrees F when the probe tip is 1/4" out of the center of flow.

I've just installed an EGT probe in a muffler for a K-80 for dyno work purposes, and placed the tip in the center of the exhaust port, and one inch inside the muffler. I'm seeing readings as high as 1200 F, and a strange EGT curve as the engine gains RPM.

AND I too am getting a potful of "noise"

Just my bit of data....

[ August 13, 2002: Message edited by: Jean Stafford ]

[ August 13, 2002: Message edited by: Jean Stafford ]