ZRX1200 Carb Conversion

[Bonz]

Modified airbox that breathes much more with an automotive frame filter. I also have the Chinese 1179 kit.

The carbs had the original Keihin jets in it. Just the needles were the dynojets.

Gotcha. Factory pro has a kit for the ZRX that uses the air box with a big ring K&N Filter inside. It jets the same more or less as pods. 130-132 mains, 35 pilots 3-ish turns out as baseline fwiw. ZRX 1200 big bores are 1224 (1164 stock), 1100's are 1109 (1052 stock). Jetting doesn't change for either of the big bores. At least with the ZRX.

My thought is 140s and 38's are going to be on the large side. But that's the half the fun of being a guinea pig in the newer era of working on older bikes.

Will be interested to see how she runs.

[Bonz]

Once the bike will start and idle, sync the carbs. Mid-range and top end don't matter at that point, gives a consistent baseline to start.

Then find the main that pulls best at high rpm, once the needle has cleared the main jet.

Then work with the needle position clip, then back down to the pilot and adjust anything with that.

[IanDMacDonald]

Once the bike will start and idle, sync the carbs. Mid-range and top end don't matter at that point, gives a consistent baseline to start.

Then find the main that pulls best at high rpm, once the needle has cleared the main jet.

Then work with the needle position clip, then back down to the pilot and adjust anything with that.

How do I tune the needle? How will I know to drop the clip or raise it?

Then, the pilot? I presume too many turns out on the A/F screw equals pilot too small, and vice versa?

[Bonz]

You got it on the pilot, if you go past 3.5 or 4 turns for sure, it needs to be larger. 1.5 or less and go smaller.

Even if the main jet isn't perfect, the needle clip is what you're tuning for mid-range response, roll on, fuel mileage at cruise.

It's definitely subjective based on the seat of the pants. If it feels rich, raise the clip to put the needle further into the main jet to lean it out in the mid-range roll on, and cruise conditions. If it feels lean lower the clip on the needle to get more of the needle out of the hole.

With the AFR gauge on my ZRX and the ZZR 1200 carburetors, a half clip position was worth .5 air fuel ratio either way all else equal, making one change at a time and comparing.

Fuel mileage can be a great help as well with respect to needle position. If gas mileage is in the high 30s or low 40s, you're probably pretty close. I would expect the more modern ZRX carburetors would get you into the lower 40's on the whole.

From what I've read in the old thread when this was first done, the performance increase should be noticeable regardless.

Did you drill the vacuum port? I always understood the vacuum advance on the XS1100 helped with fuel mileage when it pulled in the advance at high vacuum cruise.