Happy Carb Story....so far

Often a lot of the carb stories here are complicated and problematic, so I thought I would post a happy story about finding my way through my carbs.

I purchased an old 75 900 as wreck from a couple of guys in Squamish, BC last year. I had heard the engine run once but it was in a bad way. During this start I noted a LOT of compression (thanks to the vicious kick back of the kick starter and the subsequent bruises) but nobody knew what had been done to the engine. It was fitted with 4 into 1 exhaust and pod filters. I crated the bike and shipped it to NZ last year and this month decided to remove the engine and drop it into my current (legal) frame. I reset the valve clearances, repaired a bad helicoil repair, changed the oil and filter, cleaned it and muscled it into the frame. These old engines are bloody heavy!

Hooked it up, supplied fuel and gas and fired her up. I had taken the fitted carbs, cleaned and reset them to 'standard' spec's. The needles were at the 3rd clip and the mains fitted with 130 jets. Idled great but was all over the show during a ride and full throttle runs.

I double checked the ignition timing and lifted the needles a notch to richen it through the range thinking that since it was fitted with pods that it was maybe more lean than rich. Really, during the ride it was so busy surging and 'random' that analysing it was difficult. Another ride confirmed no real improvement, so I lowered the needles down to lean it and this made a noticeable change but the torque curve was still not consistent. Opening the throttle fully and then during the surging incrementally rolling off throttle improved the engine, so I double checked this with bleeding in choke to see if that had any effect and it didn't really improve or disprove my thoughts that the bike was running too rich.

Thinking that dropping the needle any further would be pointless, I scavenged out a set of old carbs and changed the 130 jets down to 120's. I also synched the carbs (with a single vac gauge  )to improve the bench setting with the intention to improve the performance and eliminate a vibration that their 'out of balance' was causing. Ensured the idle screw was 1.25 turns out, I returned the clips to the 3rd position on the needles and upon riding the bike noticed a major improvement. There seems to be a slight probable leanness right at full throttle but I was unable to get the time to trouble shoot that yesterday.

The bike is pulling really really well through the rev range and possibly I might've reached the zenith of the tune for the pods, considering I have dropped the jets down from 130 – 120. Are 125's available?

I have had the same experience on both my Zed's. Having bought them without knowing a lot about their history, I have found both of them to be modified (or fucked with) and both running too rich. It goes to how that you should never assume you have to richen up a system because you have pods or exhaust mods. Well, at least not to the extent I have found other people have. Like Wired George and Jay say – make sure your compressions are good, ignition timing set, plugs and the rest of the system running well before you start goofing with the carbs and confusing the issue.

More later.

Post edited by: WTF!, at: 2006/12/05 21:24

Post edited by: WTF!, at: 2006/12/05 21:33

Post edited by: WTF!, at: 2006/12/08 18:36

Well a ride today seems to confirm under full throttle more requirement to lean the mixture out.
Backing off the throttle from full open causes the hesitation to clear.
Does anyone know if with stock carbs, yoshi 4 into 1 and pods - changing from a 120 main jet down is normal? What size would be best?

I understand its all relevant to the engine mods but I just don't know what has been done to this engine and I cannot find my compression guage to get a better idea
It has plenty of compression and I am surprised at my analysis of being too rich at full throttle.

Thanks for the ideas.

The huge image file makes the post very hard to read... Not sure where you got your carb specs from. Standard main jet is #112.5, jet needle clipped to 2nd slot and #17.5 pilot jets for 75 Z1B carbs... if you have earlier carbs, #112.5, #20 pilot and 3rd slot. If you run pods/pipes, you shouldn't need to reclip the jet needle but could go to a #117.5 main jet.

Thanks WG, I have removed the image file. I believe them to be the early model carbs. The synch mechanism is a screw and locknut for the 1 - 3 carbs and a 7mm (?) bolt on the 4th. The idle adjusment is on the RH side of the carbs and the Choke lever is cased in the black plastic unlike the carbs on the 76 Z900 I have. Not very accurate description...

Anyhow - I will look for some 117.5 jets and reclip as suggested. When you say the 2nd clip, do you mean from the bottom or the top? IE: lean it out.

Great advice, thankyou.

The Z1 carbs all look fairly similar but the 73 and EARLY 74 versions have slotted screw adjusters w/locknuts on 1, 2 and 3 as you noted and that barrel thing stuck on #4. They also have large hex drain screws to allow quick access to the main jet. In late 74 (Z1A) assemblies, they got away from the #4 hex fitting and stuck another adjuster on that carb. In 75, they changed the type of pilot jet to the current style and used small 6mm drain screws which are common on many of the other VM type carbs. The early Z1 carbs were definitely performance oriented and if you can keep them sync'd, they deliver great performance. If you have the one with the hex fitting, you can remove the hex fitting and sync the #4 carb by turning the barrel with some pliers. Make sure when you bench sync, to do this... then try and figure out how to get the barrel back on without messing up the adjustment bwhahaha! Honestly, one of the secrets of working with the Z1 carbs is to totally disassemble the entire sync mechanism. Stretch the compression springs that are internal (don't lose the small fittings that are also in there) and clean everything good and then lube the thread on the barrel and clean the thread where the locknut goes so that it will turn on easily after you get it sync'd as they want to become "unadjusted" when you try to tighten the locknut otherwise.

HI WG,

Yeah I noted the tendency for change when snugging the locknut up and will definately take your advice on cleaning those. You hit the nail on the head with your description of the carbs, so I guess I have the 73 models.
Now yesterday, someone else looked at the engine and said "that looks like a 1000 head"

I wouldn't have a clue, like I mentioned I never found my compression guage and have no clue as to the mods on the engine - which of course, effects the tuning requirement. I removed the picture but will try to post another to see if anyone can identify any other changes to the old donk. Again; thanks for your time in reply.
Steve

i7.photobucket.com/albums/y299/Steve76/100_1021.jpg

Here is a link to a photo of the Zed. Anyone able to identify if the engine might have a 1000cc head on it?

Cheers

From memory... there are a number of different heads used on Z1/KZ bikes from 73-80. Earliest Z1s had the vacuum ports cast onto the cylinder rather than be found on the carb holders. Then the next head is similar to all the other 900 heads except for cosmetics. I am sure the Z1 restoration nuts could point out a few differences. These heads went from black with bare fin edges to regular unfinished in 76 I think. They made KZ900s out of leftover parts in 77 but also came out with the KZ1000 that year. The 1000 head is similar except for the notches in the valves where the split keepers retain the retainer and springs. The notch shape changed AND they went to 8mm exhaust studs. The 8mm studs give the head away as a 1000 head. In 79, in the US, they put passages down to near the exhaust port on the head and fixed reed valves into the valve cover. They stayed with 8mm studs and the heads were pretty much the same except for the passageways and different valve cover. They also shaped the cam idler differently to take advantage of the larger center area in the new valve cover. This idler won't fit inside an older style valve cover. From the pic, your cylinder head, based on color and style, appears to be either a 76/77 KZ900 with 6mm studs or a 77/78 KZ1000 with 8mm heads. It doesn't look like the smog head. Note in the pic I posted that the valve cover has a different look and notice that the area towards the front of the bike on the valve cover is raised... this is the reed valve area. These were connected to a vacuum switch operated by vacuum from the carbs that opened the reed valves to dump crud into the exhaust ports to be burned for emissions purposes.

Excellent WG, thanks for the info. Today the helicoil repair the last owner did shit itself with quite the bang and I limped home on 3 with a sparkplug in the Left pocket. I think its time to swap the engines back...