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Setting up CV34s on an 82 KZ750 LTD 16 Oct 2018 09:05 #792371

  • LRSimons
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Hello all. Finally have ran out of solutions from reading and need some specific advice.


82 KZ750 4 cylinder with Keihin CV34 carbs- single main jet variety. Got it in a trade a while back and now it's become a personal challenge to make it run like new!

Got it kinda-sorta running. Would only run on choke and ran very unevenly. Fixed a few things, took me a couple tries to get the idle passages clear. Still wouldn't run right after some work. I initially though it was some large issue (cam chain jump, compression, etc) but now I'm thinking it's more of a death of a thousand cuts type deal. Here's where I'm at currently.

Discovered that some genius had been inside the carbs before me. The plugs were missing (made some from old rivets) and the #3 needle is the wrong part. Looks like the n10a needle as opposed to the n01a. The #3 cylinder was running hotter than the others and I couldn't figure out why previously.

I am NOT running the stock airbox. It's old, leaking, huge, and ugly. I have a set of pods and will be running them. I will not be running the stock exhaust. Not sure what I'm doing with that right now but I don't think it will be too complicated to fab a basic 4-1 collector going to a small simple muffler.

Need advice regarding the jetting I need to run. Mains are easy to find and cheap. I'm planning on #140s based on what I've read. The pilots are a bit more tricky. It seems the part I have stock are n424-03 #35 jets. They are 23mm long and have 3 holes placed 180 apart. This pilot jet seems somewhat difficult to find affordably. They are $13-$20 each (OUCH). It seems that the other pilot jet used is the n424-25 (used on the 2 main jet cv34?) It is shorter and has a different hole pattern, but is far cheaper. Is this jet compatible with my carbs?

I'm thinking small washers may be needed to shim the needles if the midrange is too lean. Doesn't seem like a big deal.


Thanks!

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Setting up CV34s on an 82 KZ750 LTD 17 Oct 2018 04:47 #792424

  • Nessism
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You might want to consider a jet kit like those sold by Dynojet. Pretty sure they don't mess with the pilot, just the main and needle.

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Setting up CV34s on an 82 KZ750 LTD 17 Oct 2018 10:16 #792438

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I have the same bike, jetted with pods and 4 into 1 Vance and Hines.I agree with Nessism- I bought the dynojet kit and it had everything I needed. It comes with different needles adjustable with a clip so you can get them dialed in without using washers or some other method. . Of course it also comes with an assortment of jets. I have not had problems running the pods. All my problems have been dirty carb related. It took me a long time of trial and error to get them set up properly, but I think you will have that with any carb when you remove airbox and put 4-1. Once they were set up properly they were all good. The other thing to think about is I bought the 4 into 1 brand new. In the process of getting the carbs set up properly and jetted correctly I really blued the brand new chrome pipe. After the fact I found out people used blue away or other methods to keep from discoloring brand new pipes.
1980 KZ750 LTDx2
1978 KZ1000 LTD
1976 KZ900 A

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Setting up CV34s on an 82 KZ750 LTD 17 Oct 2018 19:31 #792460

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Thanks for the replies. I am aware of the dynojet kit, was hoping not to go down that path as I'm trying to keep this project as cheap as possible. It looks like the main components are the main jets and adjustable needles.

I'm not sure why the stock needles weren't made adjustable- never seen one like this before. Are the dynojet needles a different profile than stock? What position ended up running the best?

Think I may go ahead and order the main jets and see if the pilots can be left alone. I have no problem playing with shimming the needles to save 80 bucks. Worst case scenario I end up ordering the kit and have some spare parts to collect dust.

Anyone know the purpose of drilling out the slide hole like the dynojet instructions say to do? I would imagine faster opening of the slide for more of an accelerator pump effect and better throttle response.



I'm still not convinced on the whole cv carb design to begin with. A cable slide design seems to be much simpler and more effective. Perhaps a cable actuated slide would be too touchy on a bike of this power level. My experience mostly lies with small bikes and sleds- more forgiving for sure.

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Setting up CV34s on an 82 KZ750 LTD 29 Oct 2018 17:02 #793052

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Got my new needle and jets in the mail, needle is fine but turned out the jets were a different style. Got mad and drilled out the stockers. Took a 1/16 bit and tried to reduce it a little running against sandpaper, don't think that did anything. Found online that a 1/16 bit is roughly equal to a 159 keihin jet by diameter, so figure about a 155 accounting for a rougher surface from a drilled vs reamed hole. I don't know if any of that is accurate but it seems about right.

Fired it up, no change. Made some needle spacers today running the smallest washers I had on the drill against the grinder. (ghetto lathe)

IT RUNS! Idle is richened up enough to let it run somewhat normally. It does fall off somewhat around 5k, but it is at least ridable. Decent power down low, can't even imagine what revving all the way out would feel like.



Anyone know why the "off" position on the petcock is labeled "on"? On mine it leaks out enough to let it idle fine, but starves it while riding. Couldn't figure that one out at first.

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Setting up CV34s on an 82 KZ750 LTD 29 Oct 2018 19:15 #793062

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Unless the petcock is in the prime position, off is any time where is no vacuum to pull the petcock diaphragm open.

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Setting up CV34s on an 82 KZ750 LTD 29 Oct 2018 19:55 #793067

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Oooooh "pri" means prime not primary. So just lets gas go past the vacuum flapper thing. In that case mine is probably messed up as it's not delivering fuel as it should. I know it worked at one time when it sprayed gas everywhere while cranking.

Maybe the tube fell off. If not and the flapper is no longer functioning, I'll run it on prime I guess. The float needles seal fine so it shouldn't leak and make a mess if (when) I forget to shut it off.

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Setting up CV34s on an 82 KZ750 LTD 30 Oct 2018 04:27 #793078

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I'd either rebuild or buy a new petcock. If rebuilding, use OEM parts. If you leave the bike on prime it puts too much pressure on your float needles and you could fill the crankcase up with fuel while the bike is parked.

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