1977 KZ400-A1 (DELUXE A)

So I'm fairly new to working on any dual carb setup, but not new to carbs. I'm working on this bike that belongs to a buddy of mine, had been sitting for years, but ran when parked. Wanted me to clean carbs / do a tune up.

Got carbs apart and they were awful. Tank had rusted pretty bad, and all that rust went down in he carbs. I was able to get them cleaned though, and did not use a rebuilt kit at that time.

Got her fired up, and runs fine, until it drops down around 3000-3500 rpms or so, then falls on its face and dies, unless the choke is on. If I hold the choke lever down, I can set the idle down to around 1200-1500 with no problem, and will idle great.

I've set the valve clearance, cleaned and set the points, new spark plugs, and with every thing I did, it did run better at the higher rpms but had the same issue on the bottom end. I then found that one of the carb holder boots was sucking air, and temporarily sealed the outside with some silicone until my new ones come in. I'm no longer sucking in air, but still has the same issue. I also notice a lag when trying to rev the bike up without the choke on.

So I pulled the carbs apart again last night, and blew through everything with air, and ensured that no rust had gotten back into the carbs, which it hadn't. I'm looking for a good carb rebuild kit to hopefully resolve this issue, but not having much luck, so I'm needing 2 things.

1: some good links to some carb rebuild kits for this bike.

2: Maybe some other ideas on what may be causing this if not the carbs.

Thanks for any help, and sorry for the long ass post, but wanted to be as specific as possible. lol

Too early to say if you need a rebuild kit. In my experience you don't have the idle (slow speed) jets and/or passages clean yet. Motorcycle idle jets are tiny. I mean tiny! They are not easy to clean but what I often do is boil them in distilled water for 15 to 20 minutes. Check them to make sure you can see a hole all the way through the jets. It's a tiny hole. Did I mention it was tiny? If not open boil, them for another 20 minutes. Some jets even have holes drilled in from the side. Everything has to be open and clean. I've used a #10 Guitar string to force the hole open only after trying everything else.

Wrap some electrical tape around the straw on a carb or brake cleaner aerosol can and force the spray into where the jets screw in. The spray has to come out near the butterfly holes in the carb throat.

Screw the mixture screws in until they just bottom counting turns and 1/2 turns. Be gentile! Only have to seat them not tighten them. Then remove the screws, There is often a washer and spring on the mixture screws, and squirt carb/brake cleaner into those holes until you see it come out somewhere else. Carb throat and where the idle jets mounted. Then put the screws back in til they bottom and screw them out your previous number of turns.

Don't feel bad about not getting them clean on first attempt. These carbs are not like those on a car. They have tiny tiny holes and plug easily when they sit with fuel in them for a year or more. Did I mention the idle jets have tiny holes? Most of us have to pull the rack two or three or more times before we get them really clean. No shortcuts to cleaning carbs. They have little bitty tiny holes and all must be clean for them to idle correctly.

I didn't want to get into a full blown "how to rebuild carbs" there are plenty of those on the web and youtube.

Some folks remove all the jets, screws everything that can be removed from a carb and soak it in Berrymans Chem Dip overnight or use an Ultrasonic cleaner for several cycles. Often those methods will clean the idle jets ... somewhat... idle jets are not for the faint of heart. If you think you got them clean, clean them again. Make sure you can squirt cleaner through the jets from both directions. And you get a nice strong stream in both directions.

The carbs that I'm familiar with are motorcycle / atv carbs. So I'm familiar with withe tiny jet openings. I can see through all my jets, and can blow through them. I may try to boil them like you suggested. What I'm thinking is that they are open, but not open enough. I also do not know how far the the air / fuel mixture screws are supposed to be opened up on this bike. It does not state it in my Clymer manual and the carbs had been dicked with previously before I got the bike in my garage. One carb was set almost 3 turns out, and the other was only 3/4. lol. I still think it would be worth the time / money if cheap enough to just get the kits, as some of them were pretty boogered up when I pulled them out, like someone had used pliers on them at one point in time.

Check if the needles on the screws are broken off and if the seat inside is munged. 1 1/4 is a good starting point.
Steve

The needles weren't broken, and looked fine as the seat also. I think I just found a kit on ebay that services both carbs for a good price also, might just go that route.

Very good. Be sure that you can squirt carb cleaner all the way through the idle passages and it comes out back by the butterfly (CV carbs). Often that passage will be clogged as well as the jets. The mixture screws that far apart means someone tried to tune it and probably didn't have that one, with the 3 turns out, clean enough. Remove that mixture screw and make sure that passage is open as I indicated earlier.

What you describe are classic symptoms of a terribly lean low speed mixture. Typically, it is the result of clogged low speed jets or passageways, or leaking intake manifolds, or both.

Speaking of broken needles, I bought a set of 26mm carbs off eBay a couple- three years ago ...unbeknownst to me... with two of the mixture screw's, sharp needle points snapped off inside the bodies.
Anybody have a remedy for getting them out withou wrecking the body!??
F'n eBay crooks.

When cleaning jets you need to draw a strand of copper wire through the openings and run it back and forward a few times. They may be physically open and you can spray carb cleaner through, but usually there is a surface layer which doesn't come off without the wire. As area is proportional to the square of the radius a very thin layer making the orifice slightly smaller can easily make 10+ % difference to the surface area of the opening and the fuel flow. I usually strip some electrical wire to find something the right diameter to go through the hole and then having got it through run it back and fore to clean the whole thing, being soft copper it won't damage the brass of the jet and wear the opening at all. I've often been surprised how supposedly clean jets have opened up to the point where I can physically see the opening is bigger, particularly on the very small idle jet openings in some carbs..

Guitar string or strand from a wire brush.
Steve