Fine Tuning Kz650

I am looking for ideas and help with getting my carbs set just right. As they are now, I've got a decent bottom end, flat from about 2500 to 4500, alive from 4500 to 7500, and gutless from 7500 on. I may be going to a 4-1 exhaust until I can modify the stock ones to where I want, but for now I am trying to figure out why the power is coming in only at one place.

As for mechanical, I've checked compression and I have 140-150 dry in all cylinders with choke off and throttle wide open. My valves are all within spec and my timing is functioning correctly. I still have the points and condensers, but I have set them, gaped them and the advancer moves fine. I have not synced my carbs other than the bench top sync I did using a drill rod.

When warm my bike will generally hold a 900-1200 idle, though it has died a time or two while idling.

Any thoughts are appreciated on what I can change to get the power throughout the RPM's to be more consistent.

Thanks,
KC

Check the voltage at the coils - low voltage here can cause problems - if it is low check all the connections in the circuit - if cleaning tightening doesent improve - you could try the coil wiring mod that wiredgeorge recommends - it worked for me - there are plenty of people here that will both agree and disagree on this one -

before i get jumped on for suggesting this - it may not be the problem - it is however a common cause of poor running - or so i've been told - no sense in running around changing wiring if not needed - its worth checking out - as is any other advise you get here - with so many differing opinions someone will be right!!!!

good luck

Checking the coil voltage is a great idea, probably not your entire issue, but definitely worth checking out. Good work checking compression, valves and timing before digging into carbs. You didn't mention what kind of intake you're running, or what size jets/needle clip positions. Based on your strong bottom end, lagging in the middle and then falling off up top I'd wager your needles need to be reclipped and need larger main jets. Just a guess since I don't know what's in there now though...

Put the stock airbox back on, set the carbs back to stock specs, and see if the problem goes away. That should at least give you a baseline from which to work if you still feel compeled to change the exhaust and go back to pods (which, of course, I do not recommend - though others might.) Ed

Ok, coil voltage is fine, I checked it a while back and it hasn't been an issue. Also, as the power/performance is very repeatable and RPM specific I ruled out most electrical/mechanical issues not connected to the carbs. I checked compression and valves and timing to ensure I wasn't missing anything.

She runs with no backfiring, popping, or other odd noises. If I go WOT just after take off the engine starts to choke out and almost die, not sure if that is common for non-accelerator pump carbs.

As for intake, I don't have access to a stock airbox so I cannot switch back even if I wanted to. I have considered going to either the VM26 or BS324 carbs, but I do not know if this would help or if there is something I can do to my VM24's to make the motor run a little hotter. Also, including the carb switch I've looked at K&N pods to replace my emgo style filters.

Eventually I want to switch out for a 750, but if that never happens then I want to get as much power out of the stock engine as I can. Right now I only get about 35 mpg and stock Chevy pickups have more top end and almost as much acceleration.

What do your plugs look like?

N0NB wrote:

What do your plugs look like?

When I did the compression test, two were light tan, two were a dark brown. This was after riding 12 miles home and idling for about a minute.

The darker ones may be a bit rich. Sonds like you may have to lay in a supply of plugs and do a bunch of throttle chops to figure out your jetting.

If you think you'd need an airbox, I think I have an extra but probably don't have the filter cap as I sent one to OKC_Kent a couple of years ago.

N0NB wrote:

The darker ones may be a bit rich. Sonds like you may have to lay in a supply of plugs and do a bunch of throttle chops to figure out your jetting.

If you think you'd need an airbox, I think I have an extra but probably don't have the filter cap as I sent one to OKC_Kent a couple of years ago.

I appreciate the offer, but I think it is very close right now. Mainly I am looking for a way to enrich the mixture from off idle to 4500 RPM's and from 7500 up. I am looking at KN filters, but I don't want to go that route till I decide on carbs and an engine swap. For now I think it needs to be enriched because I have some improvement in that range if I pull the choke lever up about 1/3 of the way, even when the bike is warm.

KawiConvert wrote:

I am looking for ideas and help with getting my carbs set just right. As they are now, I've got a decent bottom end, flat from about 2500 to 4500, alive from 4500 to 7500, and gutless from 7500 on. I may be going to a 4-1 exhaust until I can modify the stock ones to where I want, but for now I am trying to figure out why the power is coming in only at one place.

As for mechanical, I've checked compression and I have 140-150 dry in all cylinders with choke off and throttle wide open. My valves are all within spec and my timing is functioning correctly. I still have the points and condensers, but I have set them, gaped them and the advancer moves fine. I have not synced my carbs other than the bench top sync I did using a drill rod.

When warm my bike will generally hold a 900-1200 idle, though it has died a time or two while idling.

Any thoughts are appreciated on what I can change to get the power throughout the RPM's to be more consistent.

Thanks,
KC

I notice in your tag line it says:

"with pods "

The symptoms are:

"As they are now, I've got a decent bottom end, flat from about 2500 to 4500, alive from 4500 to 7500, and gutless from 7500 on."

This part sounds like the main jets are off:

"gutless from 7500 on."


This part:

"flat from about 2500 to 4500, alive from 4500 to 7500,"

Sounds like the needle taper is wrong or the needles are in the wrong place.

With pods, you can make engine tuning your life's work. The jet sizes and needle taper sre dialed in by the maker to match the flow characteristics across the RPM band. Changing to pods changes the flow characteristics.

KawiConvert wrote:

She runs with no backfiring, popping, or other odd noises. If I go WOT just after take off the engine starts to choke out and almost die, not sure if that is common for non-accelerator pump carbs.

NO, it's not. Mine has no ac pump and it hits hike a freight train if I slam the throttle open.

Here is one thing nobody thinks about and I learned the hard way:

Check the rubber diaphragms on the vacuum pistons for tiny slits around the edges. If they leak just a little, they run lean at light throttle hit but run sort of OK at larger throttle. I screwed with jets a long time before I found out the rubbers were leaking just a little.

Also: check the fuel levels in the bowls with clear tube. Poor throttle hit is a classic symptom of low fuel level.

The other way to improve throttle response is to raise the needles.