Author Topic: The 2 minute mod jet kit...How it works  (Read 324 times)

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Offline Steve in Sunny Fla

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The 2 minute mod jet kit...How it works
« on: February 12, 2020, 02:19:27 pm »
       From time to time I see comments from folks about just sticking some foam in the airbox with stock carbs, and thinking they have the 2 minute mod jet kit.  Ahhhh NO.

       When I built the jet kit some 13 years ago, I was looking for a way to make the carbs run better without the major hassle of removing and reinstalling the carbs as you work through getting the jetting correct.  That's how all other jet kits are built... install jets, install carbs, run bike, remove carbs change jets reinstall carbs, run bike... And then of course there's the needle changes. Most guys never actually get it right.

      Now consider this... jetting is optimizing the air / fuel RATIO . So we can add fuel to richen... or reduce the air volume. The idea is to get the RATIO correct.  As long as enough air volume remains to not starve the cylinders during maximum filling, we're golden.

      When I built the 2 minute mod jet kit, I bought a stock bike And fitted it with a datalogger and wideband o2 sensor. (I already had built the 1109 engine in shoodaben, so that's not a good test mule).  My efforts were to find the right combination of jetting to work with the stock needle and trim airflow by partially restricting the intake to correct WOT . 

     there's lot's of stuff going on inside a carburetor. Needle tapers, interface to needle jet diameters, emulsion tube air bleed locations, pilot and main jet air correction jets, main jets, pilot jets ... lots to consider.  Most companies that build jet kits replace the slide needles. These new needles are adjustable, but generally have a root diameter giving way to a single taper to the tip. Never the best if fuel economy is to be considered.  The stock Keihin needles are superior in construction, and have multiple tapers depending on the slide height and airflow needs. This is how the stock needles in the zg1000 can provide great economy and power with the 2 minute mod jetting. It was the best option, I just needed to get the main jet, fuel level and airflow correct.

       During this process, which was done openly on the COG forum at that time,  Jim Snyder offered a mechanical sliding airbox restrictor. I played around with a fixed restrictor that could be attached to the airbox. In the end I opted for the foam blocks because they fit exactly what was needed. The foam block restricts airflow; is adjustable by cutting; is easily installed; Is easily removed to trim for optimum airflow; and is frugal.

     When installing the 2 minute mod jet kit, attention must be paid to proper fuel level. The kit includes clear tubing and explicit instructions on getting the fuel level correct, along with the proper main jets.

     Bottom line, the 2 minute mod jet kit works. It's the easiest and most intelligent way to get the jetting right that I could come up with. It takes about 2 minutes to pull the foam, trim it, and change the jetting. Compare that to the conventional method, and pulling Concours carbs.

    I don't know that I've ever actually explained this before, but now you know.  ;)

  Steve

     
« Last Edit: February 13, 2020, 01:05:43 am by Steve in Sunny Fla »
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Offline ONO Bob

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Re: The 2 minute mod jet kit...How it works
« Reply #1 on: February 12, 2020, 02:35:14 pm »
Thanks Steve,
This helps a lot.
Best Regards
Bob
2006 Concours, 1978 KZ650
2002 Low Rider
1987 750 Ninja, 1987 VF700 Magna
1981 CSR 650
1977 KZ 6750

Offline DC Concours

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Re: The 2 minute mod jet kit...How it works
« Reply #2 on: February 12, 2020, 03:08:26 pm »
Thanks Steve. I like these refresher courses on the old carbs. Can you remind us what the best foam setting is that works for most people?

1.5" inch wide?

Offline Steve in Sunny Fla

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Re: The 2 minute mod jet kit...How it works
« Reply #3 on: February 12, 2020, 03:42:13 pm »
Thanks Steve. I like these refresher courses on the old carbs. Can you remind us what the best foam setting is that works for most people?

1.5" inch wide?

No, that's to small. About 1.75 is right, within 1/8" certainly. And yes, if you really want to dial it in, 1/8" makes a difference. Some guys like to cut the block smaller thinking it will help economy. It doesn't, it just makes the acceleration flat. Steve
C-14 ECU flashing for performance and rideability enhancement
C-10 Carb work , cams, & performance enhancements
 " Modifications for sport-tourers, BY a sport-tourer"
https://sites.google.com/site/shoodabenengineering/home

Offline Jim Snyder

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Re: The 2 minute mod jet kit...How it works
« Reply #4 on: February 14, 2020, 12:07:50 am »
When I got the 2mm tuned out I was consistently getting 46 to 50mpg, if I could keep my hand from twisting the glass thingy. It is a must have modification for the C-10 engine. Of course my Silverbullet did have a few other "slightly" modified parts. But the 2mm mod was probably the second best mod ever invented right behind the 7 gear unit.
"Some days you're the windshield, and some days you're the bug" Get used to it cause thats life !!!

Offline DC Concours

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Re: The 2 minute mod jet kit...How it works
« Reply #5 on: February 14, 2020, 01:26:14 am »
How did you manage to get those great mpg?? Are those hwy miles?



When I got the 2mm tuned out I was consistently getting 46 to 50mpg, if I could keep my hand from twisting the glass thingy. It is a must have modification for the C-10 engine. Of course my Silverbullet did have a few other "slightly" modified parts. But the 2mm mod was probably the second best mod ever invented right behind the 7 gear unit.

Offline Jim Snyder

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Re: The 2 minute mod jet kit...How it works
« Reply #6 on: February 14, 2020, 02:33:46 pm »
How did you manage to get those great mpg?? Are those hwy

Yes sir those were highway miles on the slabs at 70 mph. A huge part of those numbers also had to be attributed to Steve's 7th gear unit. Twisties mileage varied greatly due to excessive throttle usage.
"Some days you're the windshield, and some days you're the bug" Get used to it cause thats life !!!