1982 KZ750 Spectre vacuum reading

Thank you for the input everyone,

I suppose the real question I was asking is: is 4k RPMs with choke fully engaged normal? I am wondering what your idle RPMs are upon cold start with full choke personally.

Thank you TexasKZ for finding a specification for vacuum level. I am from the automotive technician world and 19in HG is normal for me, so that clears that up.
I have seen the method of adjusting the fuel level in my KZ750 factory manual. However, does this mean you must check it with the carburetors on the bike, and fill it with gas each time just to make sure? I know it is 4.0mm. I just set them to as straight and level as they could be by eye.

It seems to be firing on all cylinders as well. I'm scratching my head on where to exactly go from here. I could check for vacuum leaks at the intake manifold boots.
I could also check float level precisely. Other than that I feel it is down to the jets themselves and if the carburetor has any internal leaks, Pilot jets may need adjustment seeing they are 2.5 turns out.

If anyone else could provide me some insight it would be greatly appreciated. I'm trying to get this bike going as well as I can. I'm trying to make sure it runs well enough and there are no major problems before purchasing it. He wants 300 bucks for it. It's been sitting around for about 10 years and this is the first time it's been running since.

Thanks all

-KzJM

If it has been sitting unused for ten years, and it runs well enough to even take vacuum measurements, I’d call that a win. Already worth $300 easy.

It is very likely that all he rubber bits are hard, cracked and leaking. The carb holders, the vacuum hose to the petcock, the boots to the air box, the rubber diaphragm in the fuel valve(petcock) on the fuel tank.

It is quite possible that the valve lash has never been checked since it left the factory.

Four thousand rpm seems pretty high to me. I vote for air leaks.

Keep in mind that you will need to do ALL of the routine maintenance items listed in the manual. Assume that none of them have ever been done. Do all of them, including a full overhaul of both braking systems. 

The bike will also need new tires.

Still, unless the bike is seriously rusted or has a broken frame, $300 is cheap.
 

The owner claims to have replaced the brake caliper piston seals, both reservoirs are dry so I'll have to see about that. I take it compression is good. Rubber parts actually look decent, all of the hoses seem to be intact. I bet it's leaking from the carb boots. The interesting thing is that the CV34 has a fast idle link, I can see it opening the throttle. When I get it off the fast idle link it seems to idle correctly. I think it might just be out of adjustment but I am unsure

No disrespect, but we get hundreds of threads here like this one where the bike won't run properly, and I'd throw down a sawbuck the problem is the carbs.  

You might want to check my signature for info for new riders, and go through the list to see what applies.

www.kzrider.com/forum/forum-index/faq-wi...owner-things-to-know

How is it that your working on the bike but have not bought it yet?? You must know the owner somehow.

One thing I will say is that the 750 Spectre motors when running correctly are very strong, just one notch down from the GPZ. I put one in a 650 I built and after riding it did not regret all the work it took (converting it to chain drive)

For what it's worth, the Keihin CV34's have a feature which allows adjustment of "on choke" idle speed.  I hesitate to even mention this because this feature is not responsible for the problems this bike is having, plus, performing this adjustment shouldn't be necessary.  Anyway, by opening or closing the slots shown, the choke function and choke idle speed feature is affected.



 

I see where you are coming from, however the bike only idles high when the choke is fully engaged. When the choke is opened even a hair (just to get it off the fast idle link) it idles normally. By the way yes I know the owner so I've had a little time to screw with it. I can hear slight primary chain rattle at idle but I've been told this is normal. I have been through the carbs already and they looked almost brand new inside, however I cleaned each passage and made sure everything was proper. My question to you guys is what you believe it could be, I know there's a lot of variables going on here so it can't be as simple as that. I'm just trying to make sure its a good motor and bike before buying so I'm just trying to get it going as well as I can. So far I'm thinking either vacuum leak from the intake hoses or that tiny plastic knub over the pilot jets aren't sealing properly. 

I've got to be honest, for $300 if it's got compression and oil pressure it's worth every cent   

Thats what I'm thinking, I'm just looking for a good summer ride so I'm not trying to make it perfect. I'm thinking about just doing a budget build and seeing where it goes from there. I'm happy to be a part of the community here and I'm grateful for the knowledge others share.

KzJM

Nessism wrote:

For what it's worth, the Keihin CV34's have a feature which allows adjustment of "on choke" idle speed.  I hesitate to even mention this because this feature is not responsible for the problems this bike is having, plus, performing this adjustment shouldn't be necessary.  Anyway, by opening or closing the slots shown, the choke function and choke idle speed feature is affected.



 

When I got my KZ750 it would not fast idle at all even at full choke.   I did that adjustment and now it works pretty well.  Full choke to start and start lowering the lever as low as the bike will idle smoothly.  When the engine is hot the idle will be pretty high if full choke is applied.