'80 KZ750 in Missouri

Hey yo. Just picked up this non-runner today. Everything is wrong with it. Figured it would be fun to mess with this winter and step through all the systems.

First step, obviously, is to just make sure I can get the engine to run. Was told there might be a bad coil. Gas tank is gummy and rusty as all hell, carbs need a go-through, etc... You know the drill!

Anyway, here's a pic. These forums seem to be a wealth of information, glad it's here.

That looks like a good winter project, not to bad looking either. Just noticed the CV carbs and what looks like Uni-Filters. I wonder if the PO has re-jetted? Might be why it sat and became yours.
Good luck getting it up and running, and you will find a lot of helpful info in the Filebase section, right corner of KZR tool bar.

Yes, I'm excited. Only 5000 miles on her, too.

CV carbs, you mean constant velocity...

Are these carbs not stock? Will definitely find out if they're jetted when I get into them. I know I can just do some reading on this but how lean will the engine run on foam filters like those pictured and non-jetted carbs?

This is the most Posted topic on this forum, Pod Air Filters and re-jetting. If you do a search, you will find a lot of info, some completely worthless and some spot on.
First those will have a Jet Needle that has only one groove, so washers are needed to lift the needle up, then the main jet size needs to go up a couple. Maybe larger Pilots, 1 size. but with the CV carb, it needs a good signal through the air system for proper operation. Places like Dyno-Jet sell kits that are set up to re-jet your carb for the application. Some here like their Pod's on CV carbs, but most wouldn't. Much easier to tune a set of manual slide carbs.

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martin_csr wrote: The 80-83 KZ750-Ltds & 81-83 KZ650-CSR share a lot of parts. If you'd prefer a 1-piece seat, I'm pretty a seat from one of the models mentioned is a direct bolt-on.

Good to know! I was thinking of going with a custom seat pan down the road, towards the end of the winter, but if the look grows on me (which it kind of is doing), I will definitely consider!

Thanks.

Hey guys!

So I got it started. Dismantled the carbs and cleaned all jets and passage ways. The tank was awfully rusted so I cleaned it out with a couple different methods and got it shiny enough for right now. I'll probably coat it in the future once the bike proves to be worth it! Cleared the petcock and ensured that it was functioning correctly. Turned the pilot screws out to 2-1/2 turns just as a starting point.

So it idles well. The plugs look okay, too. So this makes me believe that the pilot circuit is working correctly. The problem I'm having though, is that under any throttle the bike wants to die. If I let it warm for a while, I can get one good rev out of it and it falls back to idle, but the throttle isn't sustainable. If I hold the throttle open at 25% or so, it immediately starts to die. If I give it a good throttle twist, it will jump up in revs but if I give it another immediately after, it dies also. It doesn't want to run at any RPM above idle.

I'm doing some digging around the forums and searching as much as I can, but I figured I'd just drop this here really quick to see if this is easily diagnosed. I've never had this exact problem on a bike before so I don't know where to look first.

Yes, I bought the bike with uni-filters on it. Yes I know this can cause problems but the bike should at least rev up under a bit of neutral throttle, even if the filters will cause problems. Right?

I know this isn't the tech forums but I don't want to start another thread just yet. Thanks in advance and I'll be sure to keep searching.

Edit: Planning on checking the timing advancer for proper rotation. Will take off carbs again, double check proper slide actuation. Let me know of any other ideas.

I don't suppose while you were working on the carbs that you noted the jet sizes? This may help, as long as they are that size and not drilled out.
Also did you check the fuel level, using a clear piece of tubing up the side of the carb, attached to the drain? it should be just below the gasket surface of the Bowl to body surface, within 3mm.
Vacuum leaks between engine and carb are more likely to show up at Idle. 2 1/2 turns out on the Idle mix screws is a tad lean but might be OK. Did you look at the slide diaphragms real close to make sure they are not torn or have pin holes? Also just at the throttle Blade, there are very small holes in the Carb bore, these are for The transition circuit. If plugged you won't get any fuel through them = bad.

Secondaries were the stock 125. Couldn't find numbers on primaries maybe I'm blind. I'll double check.

Float levels will be double checked on next carb disassembly. This could definitely be the case. Mechanically, they lined up but I know that isn't thorough enough. I'll run through the other things you mentioned as well.

Also, this may be a dumb question but what is the purpose of the plastic stops that sit next to the jets in the carb body? I'll upload a picture if you're not sure what I'm speaking of.

Thanks for the reply.

See if there are any shims under the needle, on the slide. If those have only 1 groove, then they would most likely need shimming to raise/ Richen them. Get the Pilot or Slow Jet # as well.
I think you will find the guys here will do their best to help, but like I said earlier CV carbs and Pods, = the most posts.

Yes I know. Maybe I should just try to hunt down a stock airbox before anything else but I didn't think that pods would have enough of an effect to completely disable the engine at any throttle.

Well check the Carbs really well, fuel level #1, jet sises #1.1, got to know both basically.
The CV style Carb relies on the signal going through the Airhorn and Venturi, to raise the slide and needle.
So if you are good at carbs, then you could get it to work, just how well. If the rest of it is stock, and the jetting is stock, then an Airbox would be much better.