TOPIC:

Hello to all!

My first post here. I'm a second-time KZ650B owner, having sold the first years ago and having kept my eyes open since then for a nicer example. I found a pretty good one a couple of weeks ago and it promises to be a fine bike after I get it sorted out a little.

First up is an exasperating fuel/air problem. In original form it was barely running at all at lower rpms and would not idle. If you were careful you could sneak it up the tach at which point it would run great.

So I pulled the carbs, which are the original slide-throttle carbs and cleaned them thoroughly. No improvement. My assumption was that low-speed jetting was way lean and I worked my way up from the 15 pilot to a 45 pilot with pilot caps (the funny #50 jet) removed. It now runs really well at low-mid rpm but won't pull higher.

After learning that the #15 pilot was in fact stock, I'm taking the tack that the problem is not with the jetting itself but with something else, and the most likely thing I can think of would be a relatively large air leak. I plan to return to original jetting (or close, see questions below) and look for other problems).

So, after all that windup, here are my questions:

- Why is that funny #50 jet/plug thing there over the pilot jet? What does it do, and why don't other carbs have it?

- Everybody seems to agree these bikes are tuned EPA-lean from the factory. What is the conventional wisdom on fixing this without paying $100+ for a jet kit? Is a 17.5 pilot a good move or am I better off starting off with the original #15?

- All the usual air leak sites look pretty good on this bike, and by that I mainly mean the carb holders, clamps and that I've verified the sync-hole caps are there and in good shape. Any wisdom on where I might be getting a big air leak, without there being any significant visible problems in the sealing parts?

- Is there any benefit to low-to-midrange power, or to efficiency, to be had by substituting non-original carbs? I was thinking about CV carbs, or even CV-pumper carbs off a KZ750 or later model KZ650. I don't want to get big carbs for top-end and sacrifice low- and mid-range power. I like the response of smaller carbs for most of my riding.

- If there is a more ideal setup, then perhaps I should just start looking for a set of carbs on Ebay, and not bother spending money on the current setup, particularly the holder rubbers. What other part would I need to go with whatever carbs I would want to use? In particular which carb holders should I use, and would I need to change the intake rubbers or even the airbox?

Sorry for such a long first post, but hoping some of the more knowledgeable folks here will have a few pearls of wisdom on these issues. I appreciate all responses.

Thanks!

- Glenn Carpenter; Golden, CO

Hi Glenn, Welcome to the forum.

Have you checked all the basic tuneup specs first, points, timing, (both ignition and valves), valve clearances, compression?

I've checked some of that stuff but not all yet. However I'm quite convinced the problem is carb related, because I can get the bike to run well at any rpm range with one carb setting or another, just not good in all ranges with the same setup.

So far today I've returned to original jetting and pulled and plugged the vacuum line to the petcock to eliminate that as a source of an air leak. About to go for a ride, but it seems to be working a little better but still a far cry from perfect at low rpm.

Are you using the stock airbox and stock exhaust systems?

Yes, all stock and original except drop-in K&N filter.

Update - I had a good deal of success with this tonight. I raised the needles to the highest position, set the air screws at three turns out and replaced the vacuum line to the petcock. With the original jets back in the carbs the bike now idles reasonably well at 1300rpm when warm and runs nicely throughout the powerband up through at least 7krpm or so.

It is still lean at low revs, so I'll try to get my hands on some #17.5 pilots sometime soon. It drops a cylinder when you reduce the idle, so my bench sync will need to be improved on with the real thing. And it does have some amount of air still leaking in, through the manifolds I think, so I'll order up a new set of those.

I'm happy, though - the bike is fundamentally rideable, for the first time since I brought it home a couple weeks ago.

Where's the best place to get carb rubbers?

glenncarpenter wrote:

Where's the best place to get carb rubbers?

Your local pharmacy.

No, really, ebay or www.z1enterprises.com/

Welcome. Good to hear you've got some progress in getting her to run better. How about some pics of your rides?

I suggest you heed the advice to tune the bike up before adjusting the carburetors further. You are moving the wrong direction as far as tuning goes. Get a Clymer or Kaw Service Manual for your bike and perform the tune up procedures. Put the carburetors back to their stock configuration and the combo will probably give you the results you are looking for.

Thanks for the reply WG. I've read a lot of your posts here and I respect your experience with these bikes.

Despite that I have to say in this case, I disagree. It's just not always realistic to cross all the t's and dot all the i's and take the 100% by-the-book approach when trying to get an old bike like this back on the road. Sometimes you have to cut to the chase and take care of the most obvious problems first, in my case the carb issue. Not to mention that after you've worked on enough bikes you start to have a pretty good idea about what is and is not going on with any particular issue. I'm confident the ignition and other tuning factors aren't having any significant major detrimental effect on the way this bike is running.

Did you actually read all my posts in this thread? If so you'd see I may have fumbled around a little but obviously I'm getting things straightened out.

It would be helpful, since you obviously have more experience with these bikes than me, if you would actually answer the questions I asked.

glenncarpenter wrote:

Yes, all stock and original except drop-in K&N filter.

The K&N could be why you are running lean. I understand they flow so MUCH more air than stock.

You raised your needle to accomodate the extra air, and now you want to add a bigger pilot jet. You may really just need a bigger main jet and then that could mean lowering the needle and going back to the stock 15's pilots and turning those airscrews back to 1-1/2 out instead of 3.

Sooner or later you'll get around to checking all the tuneup specs anyways. If those specs are off now, adjusting carbs at this point will just be wasted, as you would need to adjust carbs again when you tune it up, right? You did say it was an exasperating air/fuel problem...we're just trying to help.

Post edited by: OKC_Kent, at: 2006/10/20 17:25

Kent, that pretty well summed up my thinking in the advice I gave Glenn. No point in getting into disagreements regarding the way to approach working on a bike. Lots of ways to approach getting an older bike running right I guess.