ZRX1200 Carb Conversion

[IanDMacDonald]

Welp, the time has come. Performance-wise: The bike runs phenomenally. However, I presume that the throttle shaft seals are shot (increasing the idle with the idle screw, I have a hanging idle. So, I have it all the way down where I have a crisp idle, and maintain the throttle to prevent it from dying.) I don't want to bugger up the butterfly screws, attempting to remove them. So, I decided to invest in the ZRX1200 carb swap.

I've read enough threads on the topic to make it a side project. I ordered a Chinese jet kit to try various size mains (aiming for 135/140), and pilots. I'll leave everything else alone. I bought a universal choke kit, and I'll try to mount it into the airbox (I understand the box needs to slide forward, so prepared for that). From there, I'll follow Tad's thread on the vacuum advance mod, and take it slow so I drill it out correctly.

I hope to have this completed over the next month. The Mikuni's will get put on the shelf.

[Desert Dave]

Good luck! I'm in no way an expert, but from everything that I have read those Chinese jets have been known to cause a lot of issues.

[IanDMacDonald]

Good luck! I'm in no way an expert, but from everything that I have read those Chinese jets have been known to cause a lot of issues.

Once I have an understanding of jet size, I can always swap the jets to Keihin.

[DiverRay]

The problem is the Chinese and OEM do NOT correlate size to size. A 140 main OEM may run well, but the Chinese 140 may be lean or rich.

[IanDMacDonald]

The problem is the Chinese and OEM do NOT correlate size to size. A 140 main OEM may run well, but the Chinese 140 may be lean or rich.

Fair point.

[cajun31]

Those butterfly screws are not that hard to deal with if you use the right tools. I have done many. The key is to use a JIS screwdriver and I have found that if you slightly tighten the screw down just a bit then back them out it makes it easier. The screws as you are probably aware are peened on the other side and when you reinstall them just use a small dab of blue loctite on them. When rebuilding carbs I just go ahead and tear them all the way down and work on one carb body at a time going through everything. I always replace the shaft seals. Just eliminates problems. Much better to do that versus those zrx carbs if the only problem is the shaft seals.

[bikerphil]

The key is to use a JIS screwdriver and I have found that if you slightly tighten the screw down just a bit then back them out it makes it easier

Yes! A serrated grip tip JIS will take those screws right out. Good advice.

[DEEBS11]

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[DEEBS11]

Note: Chinese jets are drilled cheaply without much quality control. You can have two jets with the same number with different orifices due to burrs. In the end you are not saving any money. They are almost impossible to work with. The bike will run but it won't run right.

[LAB3]

Yes! A serrated grip tip JIS will take those screws right out. Good advice.

Anyone running Japanese machines of any type are just asking for headaches by not using JIS screwdrivers! Well worth the $15-20 to get a set on eBay, I've never stripped out a screw head since finding out the difference and ditching the Phillips head screwdrivers.

https://bike.bikegremlin.com/10583/phillips-vs-jis-vs-pozidriv/

[IanDMacDonald]

Anyone running Japanese machines of any type are just asking for headaches by not using JIS screwdrivers! Well worth the $15-20 to get a set on eBay, I've never stripped out a screw head since finding out the difference and ditching the Phillips head screwdrivers.

https://bike.bikegremlin.com/10583/p...s-vs-pozidriv/

I havd a whole slew of JIS screwdrivers. I had the carbs superheated to hopefully make them easier to remove. They did not budge.

[LAB3]

As mentioned those screws holding the butterfly to the shaft are peened so they don't work their way out and into the engine, using a die grinder or Dremel tool to reduce the splaying is necessary.