Carb issues again

Hey everyone,

So here's the deal. My 76 Kz900 was running awesome, I was at a shop the other day and the tech was checking it out. He mentioned my pods were looking done, which were true they were on there last legs but the bike ran great. No flat spots, started on the first kick fast as hell. So I ordered in some new pods, XS pods to be exact and put them on. So now the motor was getting more air and the bike ran worse than it ever did. So I adjusted the air screws and it ran ok but had a couple of flat spots. So I synced the carbs adjusted float heights and now it bogs and runs like ass!! It's been rejetted for the pods and has a 4 into 2 exhaust with after market mufflers on them. Like I said before I changed the pods and synced the carb she ran great. The carbs are synced as specified in the shop manual 23 cmmh and the bikes runs like shit. Valves are in spec, carbs are in spec, they were out significantly and I know pods will make the bike run like shit, but ran great with the old ones. Anyone got any ideas why just because I installed new pods and synced the carb it is now running like shit?
Thanks in advance
BD

"carbs are synced as specified in the shop manual 23"....

It won't necessarily be the same pod vs pod due to different air flows to the carb intakes... Remember, your sync/jetting was set for toasted pods (strong or poor air flow)...

As I have been learning in my case, Keihin CR Specials especially during my final jetting...

Example: The motor has been running strong, no hesitations, blurps, popping sounds etc... got through emissions at half the regulation CO% but my plugs are still on the carbon size..

I just installed my 112 main jets and went to dial in my carb sync, slightly out of 2cmHg spec... Well wouldn't you know it, I screwed the sync up so bad I had to start all over and bench sync the damn things....

It doesn't take a hole hell of a lot to throw these out of spec to run as you stated, like "shit"... I had exhaust & carb popping, hard starting, erratic idle you name it....

NOTE: Carbs aren't my gig so I'm still learning! :laugh:

What I've learned is this (Larry C & Plummen plus experience going through the process)... Carb syncing is a bitch, end of story but I want to/must learn this process for myself...

With any modifications accomplished on the motor, example my case 903cc now to 1015cc, performance camshafts, different carbs, the important part is get the 4 carbs synced to the same value, don't get all weird on trying to obtain the spec of 20cmHg for example. The important part is that they are the same vacuum readings at idle and in response....

Place a cooling fan on your motor while adjusting/syncing your carbs... There's a lot of tweaking so any air flow aimed at the motor is better than none... Preferably two fans on each side....

Slow jet/pilot screw... 1-1.5 turns out for start per manual...

Set your idle at ~ 1500 rpm while adjusting for sync.
Get all 4 measurements within 2cm, preferably 1 cm between the 4. It's a back and forth process, trust me...

Once established, then adjust your idle down to 1000rpm...

Vacuum readings still good?
If not re-adjust slightly again... remember, a slight change such as 1mm will cause your vacuum heights to change a couple centimeters and one adjustment will also slightly or largely change another carb reading....

As in my situation, once I got it to at least idle at 1500rpm, then out with the Gunson Color tune to adjust the slow jets (pilots) in between syncing for anything under 1500rpm and the motor would stall....

Once the slow jets (pilots) where on the mark, idle down to 1000rpm, slight tweak here and there and now she once again purrs to life with a flick of the start switch to spec....

The final vacuum readings all came up to 20cmHg, 1-2cm between the 4.... A twist of the throttle and all 4 readings raise and fall in unison...

In your case, you may even have to re-jet, who knows...

Now I take her for a ride... Any hesitations or falls on her face (too lean mid range), may have to adjust/change the needle jet clip position.

Then with WOT and mid range jets/adjustments on the mark and only then, go after my slow jets (pilots) which I already know are too large. I have the next size smaller jets for this...

Install my smaller jets, Gunson color tune, check the idle for 1000-1200rpm (I know, spec is 800-1000) and take her for a ride....

Install new plugs and keep an eye for not too lean of operations... All is good!

Isn't carb syncing/jetting fun........ Hell no it ain't but it is what we do and you as well must learn this grasshopper... :laugh:

OMR

Oh carb syncing sucks!! Thanks for the input tho', I'll be at this again today hopefully not until 4am like last evening. I'll let you know how I make out.

"Oh carb syncing sucks!! "... Yes indeed! :laugh:

BTW, do your self a HUGE favor and get yourself a Morgan vacuum set... The Gunson Color Tune is a plus as well

www.carbtune.com/

Got the morgan carb tune. Works great, just wish I could get the bike to work as good.....Gotta look into the colortune.

Gunson:

If you listen closely, you can hear the idle change and this is just from one carb... Think what happens once all carbs are dialed in... Yeah baby!



BTW: Condition of your intake manifolds?
Hard, cracked, not sealing etc....

Intake manifolds are brand new. Did everything before I synced them.

Make sure the pods aren't covering up anything important:

KZRIDER PIC

Ok, so here is the update. So I synced the carbs again. Everything was balanced Idle was spot on. Turned off the bike buttoned everything back up and tried to start it. Now it will only start with the choke half on. Idles good but when I went for a ride no power at all. Bogging and running like shit. So tore the carb off again bench sync and another sync. Bike wouldn't start and just backfired out the carb. I'm losing it!!! So this is my question to those who are running pods. So the bike ran great when I had toasted pods on it. So once I put new pods on it and synced them no power, nothing runs correctly. What is usually the jetting for pods and after marker mufflers on a 4-2 exhaust.
Thanks
BD

For, headers, and pods on a 76 I would go 122.5 on mains. I would raise the needle one notch (fourth groove from the top) and one turn open on the air screw. Also make sure that the "inrichening plungers" (what you call the choke) close all the way. These are the cause of most problems on these carburetors. These can stick partly open on one or more of the carbs and will start flooding the respective cylinder once the engine starts getting hot. You can test this in many situations by opening and closing the "Choke" rapidly in succession a few times ending on the closed position. This will ensure that the plungers are all closed.

Do you still have the old pods? If so, I'd put them back on just to see if everything returns to normal. If it does, then I'd just say it's jetting or pilot screw adjustment. If it still runs poorly, then something else may be the issue (i.e. fuel blockage, etc.).

HerrDeacon wrote:

Do you still have the old pods? If so, I'd put them back on just to see if everything returns to normal. If it does, then I'd just say it's jetting or pilot screw adjustment. If it still runs poorly, then something else may be the issue (i.e. fuel blockage, etc.).

No, threw them out. I already thought of that, but they're gone. Gonna tear these carbs down again and put bigger mains in.