1975 kz400 needs some tuning

[jordevo42]

traded some garden that I built and a couple bunk beds for this on craigslist. Couldn't be happier with that trade as most of the tough/expensive stuff is already done. Not a huge fan of the paint job but that's not my main concern right now. I have intentions to do something with the back end and maybe polish everything up (although I kind of like the contrast between the shiny parts and the dull aged look that the motor has acquired over the years.) Maybe fashion some knee dents into the tank after I give it a much needed clean out.
The guy I got it from was only able to get it to run with the choke on. This is the first carb I've ever torn into and I'm glad that its a mikuni cause its super easy to take apart and make changes. He had this motor set up with a single vm32. I've done some tinkering and I now have it idleing alright with the choke off.
It is my understanding that:
1. This carb (vm32) is generally said to be way too big for this motor, I don't know if this engine has any major work done to it but I seriously doubt it.
2. The pod filter is complete shit. I would get a k&n but I want to make sure that this carb will even work for me before I buy one on this size.

I really don't want to send it to a shop and pay them to do the same troubleshooting that I can do, and I like to learn so any suggestions are appreciated.

I assume that he picked the vm32 to compensate for the carb lost in the 2 into 1 conversion. I've read that a lot of people suggest 28 or 30 for this motor but that is for the dual set up? I believe my current settings are a 180 main, a 50 pilot, 2.5 slide, needle on the lowest setting and A\F screw 3 turns out. I was able to take it around the block 0.3 miles and had to pop start it twice cause it bogged out and had very inconsistent rpms.

I really look forward to sharing the transformation (no pun intended) of this bike with you all. I am thinking a real deep burgundy or blue with some aztec like teal accents for a paint scheme. A chopped down and low profile kz750 tail is on my mind as well. Any help that you can provide with adjustment is greatly appreciated. I'll include some pics of the bike now.

 

[Beaner242]

Nice bike. First thing I would do is get rid of that filter. They are crap, I know from experience. Not sure about the carb being the right size, but someone on here will be able to help you with that. Good luck.

 

[firebane]

Without being a dyno I couldn't tell you. But I have a vm32 with my bike and it runs fine. Regarding the choke .. well looking at the exhaust on that bike and running a single carb well your going to have to do some jetting on it most likely.

I'd ask the PO if they had done any jetting to it and if not well thats going to be where you need to start. That pod is going to give you grief and another possible reason why its not running well.

Your going to have the naysayers on here about the 2-1 setup running a single carb but don't listen to them.

Take some better pictures of that 2-1 setup and the design of that can be a possible issue as well.. ie .. air leaks at the engine mount or even at the rubber coupling. That rubbing coupling doesn't look to great either.

Oh and last thing are you 100% sure you have that inline filter on right it looks like it could possibly be on backwards and I would personally look for a better one that too.

 

[jordevo42]

Ya. I've tried several different jetting combos but this is the closest so far. I only have certain jets right now so I hope I'm in the ballpark. I feel like a 50 pilot is sorta strange though for some reason. Ill start by ordering a k&n for it. I did do a wd40 test on the 2 to 1 manifold and the rubber leading up to the carb. No response too that so I guess its tight. Here's some better pics. Thanks for your help.

 

[Nebr_Rex]

1) I'm not a fan of 2/1 manifolds, but what do I know.
If people are happy with them, then so be it.
2) The fuel filter should have an arrow for direction of flow.
3). Does that pipe have a baffel or is it open. That will affect
your jetting.
4) A 32mm carb might be a little small for a single carb setup.
Dual carb 28mm/30mm is about right for an unmodified bike.
5). Your jets are large for a 32mm carb.
6) Rear sprocket looks worn out. Chain and sprockets get replaced
together because they wear as a unit.

.

 

[jordevo42]

Well thats how I got the bike so im not going to change it up now. I do have the stock carbs but one is in real bad shape and I dont want to deal with them. The fuel filter is heading in the right direction, but nevertheless Im buyng a new one. The pipe does have a baffel, if you look close you can see one main center hole and then some holes drilled around it. dunno much about the exhaust system on this bike but i like it. if my jets are too large then which one should I go down on, pilot or main or both? Ill wait for the K&N to arrive before I do any tuning again. The chain is brand new and new spockets are on my shopping list. was thinking maybe a 41 or 43 tooth instead of stock 45 as I would like to go interstate speed without over working the motor. But ill wait till I can really ride it around to determine whether all that is necessary.