'74 Z1 jet question

I got a carb kit from Z1Ent, but it has two differences from what's installed now, so I'm wondering about the diffs.

Pilot jet in both is 17.5, main is 2.0. (BTW, what do those numbers represent? Millimeters?)

The installed needle is 5J9; replacement is Y45. To my eye and micrometer, they're the same. Are they?

The other jet (needle jet?) installed is 115. Replacement is 113. What would happpen going from 115 to 113.

74 903cc, 4 to 1 Kerker, 2800 ft altitude, no other engine mods. Stock VM 28 carbs.

Thanks

You need to get a manual to get the names of the various components down some... this would confuse most folks I guess, but I will give it a try...

You bought either Keyster kits via Z1E. The kits contain the parts to do the Z1, Z1A and Z1B carbs. Essentially, the Z1B is different than the Z1 or Z1A in that it uses a #17.5 pilot jet which is actually not going to fit your carburetors and a #20 pilot jet. Use the #20 pilot jet clipped on the 3rd slot. The main jet is a #113... the factory was a #112.5 but that is how they come in the carb kits. The Y45 jet needle is the same as your jet needle. Y45 is the Keyster badge number. 5J9 is the Mikuni number.

Thanks for the info, and sorry for the bonehead errors on my part. My bike is a '75 Z1B, so the 17.5 pilot jet works in it.

I've been running the 115 main jet, needle clipped on the top slot because it's been running rich and we tried to lean it out a bit. If I switch to the 113, does that lean it out? If so, then I guess moving the needle back to the middle slot would work with the smaller main.

I appreciate the help. BTW, the 2.0 I referred to is the needle and seat valve size.

Here's a picture of the plugs. 2 and 4 look pretty good, 1 okay, but 3 is really fouled. Plugs are in order 1 2 3 4.

I was confused about the 74 label in the original post... The #113 main jet vs the #115 main jet? I am surprised they give you a #115 main jet. You didn't mention what type airbox you have nor the pipes. Are these stock?

OK... the sooty #3 plug. Soot may not be the carburetors' fault. First, have you checked valve clearances? Second, have you checked coil voltages? I have tech articles written on both subjects on our website... see "wg's Tech Stuff Index" link. First is called "Valve Clearances" and second is called "Coil Repowering". Don't bother muck with the carbs till you have looked at these articles and gone through the trouble of making sure these issues are correct because no matter how much carb adjustment you do, the soot will remain unless these areas are corrected. This stuff is so common that I put this stuff on a CARBURETOR website.

OK... you have the correct valve clearance and coils are firing as they should... now check compression. If you have low compression on cylinder #3, you can adjust the carburetor till the cows come home and not fix the soot. If compression is OK, try swapping #2 and #3 plug wires... its OK, they come off the same coil and fire at the same time. Swap or clean the plugs, swap the wires and see if the problem stays at home on #3 or moves to #2... you could have ignition related issues. Specifically, bad wire, cap or bad spark plug.

LAST, if you have done ALL this stuff, and you still have soot on #3, adjust the float level using the service fuel method (plastic tube held next to carb body). Sync the carbs and adjust the pilot fuel mixture and idle. Then recheck your plugs and if #3 is STILL sooty, turn the pilot air screw out a turn.

If you don't do the stuff suggested in the order suggested, it is counterproductive. Good luck. BTW: If you have the stock airbox, leave the carb settings in OEM setting positions: #112.5 main jets (113), #17.5 pilots and 5J9-2 jet needle setting (2nd clip slot with slots counted top to bottom) and air screws out 1 1/4 turns from lightly seat to start out with.

Post edited by: wiredgeorge, at: 2007/07/18 07:44

Compression was all around 130-140, valves all within clearance (if I recall, .05 - .1) except the #4 exhaust, which was .15.

Did your coil mod and checked the voltage and it was good going into the coil. (Couldn't get a reading coming off the plug wire). Batt voltage good, 12 at adke, 14 at 4K rpm. Tried switching the 2&3 plug wires; no change. Have gone through 4 sets of new plugs, no change. Checked the float level with the clear tubes, dead on.

Last night I was working on carb #3, and found that the little o-ring around top of the choke plunger had broken. About 1/4 of it was missing. I'm trying to locate a replacement, and expect that might make a difference.

I'm going with the settings in your last post. Stock airbox, Kerker 4 to 1 exhaust is the only change.

wiredgeorge, I really appreciate the help and expertise. You're a great guy to spend so much time helping us out here.

Just another bike nut... since I do this stuff for a living and the Lord has been good to me and met my needs, I don't feel I need to be tight with helping others, I guess... Looks like you have worked through all the non-carb related stuff that could cause this issue.

OK... FIRST try turning out your air screw another turn... The stock carb settings I noted are a baseline. The choke plunger has a small 9mm oring underneath and the rubber cap on top. If the cap is the problem, fixing it will make no difference. If the 9mm oring beneath is gone, this would cause an air leak... whitish plug and erratic idle.

The soot you see is likely the air/fuel mix. Not enough air. Since you have stock airbox, no problems with the air filter since the other plugs look OK. If turning out the airscrew doesn't fix the problem, then you will have to remove your carbs and clear the airjet. This is located on the venturi edge on the side of the venturi that the pilot jet is located on. The other airjet is for the main jet. Remove the air screw/spring and pilot jet. Hold your finger over both holes and squirt carb cleaner (WEAR SAFETY GLASSES!!!!!!!) into the pilot airjet and see that it comes out the hole in the engine side venturi in a FINE spray. Then, squirt carb cleaner through the pilot jet... into the end that goes DOWN into the bowl. It should come out a fairly TIGHT spray pattern... If it splatters at all coming out, the jet wasn't drilled right and should be replaced. This can be a problem with aftermarket pilot jets. Spray carb cleaner into the pilot well and make sure it comes out the air jet (wear eye protection) and last into the air screw well and see if it comes out the pilot well... If any of those things are a problem, send me a note offline and I will explain what to do.

I went through the carbs and installed the carb kits from Z1Ent. Followed wiredgeorge's cleaning instructions, and ensured that carb 3 was clean.

I've concluded that in fact, carb 3 had a plugged or partially plugged pilot circuit. After the cleaning I went for a ride and the low rpm and fouled plugs problems were gone. Wohoo!

Now it's a matter of fine tuning the setting and re-syncing the carbs. It has just a slight stumble when pulling away from a stop, and the exhaust tends to pop when I back off the throttle.

It pulls hard all the way to redline. Does seem to actually pull a bit harder when I back off from full throttle to just slightly less than full. It will take some riding to get a better feel for that. Might try the 115 mains instead of the 113s.

BTW, safety glasses are a must, or I'd have had carb cleaner in my eyes. Also, keep your mouth shut. And, I got some NAPA spray carb/choke cleaner, and that stuff works really well. Very high pressure in the can, and really cleans off the grime and sediments. I got some on my skin and could feel it sort of sizzle.

Glad you got things substantially worked out... try richening the pilot mixture to help get the bike rolling... it is lean; the backfire on decel is the tip-off. Start turning out the mix screws 1/4 turn in and see how that works... it is unusual for a Z1 to run lean off idle.

Anyway, PLEASE, ALWAYS wear eye protection when using carb cleaner. I wear safety glasses that are snug on my face and wrap around even when doing routine mechanical work. Can't tell when something will pop loose and hit you in the face.

Well, my problem returned. I just declared victory too soon, after a short ride. After a few more miles, soot city.

To recap, my 1975 Z1B 900 sat for several years, and I have been trying to get it running well for months. I have been fighting a really sooty plug in cylinder 3 since getting it running, and recently the #4 cyl is also running rich. Not oily, just lots of black soot. Cyls 1&2 run clean.

Pulls hard to redline. Good in mid-range. After putting in new plugs, it runs great throughout the range, but after a while (10 miles or so) old man soot creeps back in. Seems to be a problem with the pilot jet circuit, at small throttle openings, around 1-2k rpm.

Bike was running fine when parked years ago. I’m out of ideas. Any suggestions?

So far: Compression OK. Valve clearance OK. Changed oil and filter. Changed plugs (4 times). Put in carb kits from Z1Ent, using standard jets and needle clip settings as per WiredGeorge. Cleaned carbs, 4 times. Last cleaning followed instructions from WG re ensuring the pilot circuit is clean and carb cleaner sprays out when, where and as it should through the pilot circuit. Synched carbs. New petcock. New fuel line with in-line filters. New Air filter (airbox, not pods). New crush gaskets on exhaust. Carb holders are flexible, not cracked, checked for leaks, nada. New rubber covers for vacuum lines. Put in WG coil power supply mod. Switched plug wires for cyls 2 & 3. Have fiddled with pilot air jet screw about a zillion times, and can get it lean enough to backfire on decel, but even so, still have 1 or 2 rich cylinders. Hard to tell which cylinders are backfiring. Checked dwell and timing, twice. Points look good. Checked in the dark for spark leaking from the plug wires. Even after all that, #3 runs rich.

Pretty stock, except for kerker 4-1 pipe. 2800 feet altitude.

I’m willing to spring for Dyna coils and ignition, but since changing the wires on cyls 2 & 3 made no difference, I’m thinking it’s not a spark issue. I want to put on pods, but again, until I get the oddball cylinder cleared up I don’t want to make changes.