New Guy Signing In

Hello everyone - I just joined KZR and want to say hi to everybody. I have a 1978 KZ650B I am close to getting back on the road, and think this forum will be a big help in doing so.

Right now I'm trying to get to the bottom of a no-start situation with the carbs - It will start with starting fluid, but not gasoline so I'm thinking clogged carbs, but I'm also checking the timing/points. I do have a manual, but is there a step-by-step in here somewhere that can explain it too? The bike is totally stock, with no pods or mods. Here's pic of it fresh out of the barn - it looks a lot nicer now...

Actually, my first question: what purpose does the big vertical spring between the carbs serve? My bank of carburetors doesn't have one (yet), and I'm wondering if that might be contributing to my no-start problem..

Welcome aboard. That spring (called "throttle cable pulley spring") pulls the carbs shut as you release the throttle. I wouldn't bother starting the bike without it because the engine may rev uncontrollably high without the spring in place. Ed

Wow - you totally blew my mind - that is Exactly what it did when it started on fluid, and then very briefly on gasoline...the #4 and 3 pipes got really hot from the exhaust, #2 was hot but not as hot as #4, and #1 was pretty cold.

A little backstory here - I got the bike from an estate sale, it had been stored inside for over two decades. There was an obvious electrical short from the Run switch that melted some of the wires, and I couldn't find a side cover, but other than that it was in great shape. I repaired the wiring, I'm getting 155-165 lbs compression out of each cylinder cold, new coils, wires, plugs etc - but THAT is exactly my problem! Well, that and it won't draw gas through the carbs.

I went through the carbs again yesterday using a pilot fuel-flow chart I found in here, and everything checks out fuel-flow wise; the manifold boots are still soft and without cracks, I have good spark at the points but I had to replace the original screws which stripped out when I tried to make sure the points were adjusted right, and the carbs were absolutely pristine inside when I opened them up for the first time when I got the bike. Seriously, I have Never seen carbs as clean as they were - they were shiny and everything, even the jets, looked new - but I went through them anyway.

The bike has 11 thousand miles on it and appears to have been put in the shop for the electrical short, but then somehow got left behind over 20 years ago in the mechanics shop where I found it, and so now I'm trying to solve my 'won't-run-or-idle' problem.

The tank is off the bike, and is also in almost-new condition inside. I've been adding gas to the carbs through the fuel line with a little squeeze bottle just to see if it will run, and it Did very briefly, but won't stay running; and when it Did run, it did race way up...so when that spring gets replaced, is there a very good chance it will run and idle?

Does the tank need to be on the bike to run? And do all the carbs need to be full before it will run?

I think you will find that the 1978 KZ650 has a vacuum operated petcock. If it does, and you run the bike with the tank off the bike you will need to run a long vacuum line from the carbs to the tank or else the petcock won't operate. If you use a different tank without the vacuum operated petcock you should temporarily plug the vacuum line to the carbs. The carbs should be full or nearly full to run the bike.

Also, are you familiar with the fact that the KZ bikes use JIS screws NOT Phillips? They look the same, but using Phillips screwdriver on the JIS screws will ruin the screws because the Phillips drivers do not fit the screw heads properly. If you need info on the JIS drivers let me know. You can easily make them yourself using Phillips as the starting point or you can buy them. Ed

The tank does not need to be on for the engine to run, but the carbs do need to be full. Most folks use an auxiliary tank, but if you can put the main tank on a table close to the bike, you can run a longer fuel line from it to the carbs. If you have a vacuum petcock, plug the vacuum line and set the valve to PRI. If it has a manual valve, set it on RES or ON, depending on how much fuel is in the tank.
This is also the setup for checking the fuel level in the carbs.

If you are getting a big spark at the points, it is likely time to replace them and the condenser. Be very careful when reconnecting the wires. There are both metal and fiber washers. The order of them is very important, else the points may be constantly shorted.

650Ed - Yes, I have a set of Vessel JIS screwdrivers I use exclusively on Japanese bikes, and a tutorial on making them would be great! But when I started on the points and plate, I noticed somebody had been in there before me because the original screws were all chewed up. It looked like they got stalled by how tight the screws were, because they didn't want to budge. I had to use some PB Blaster and needle-nose vise-grips to get them to turn, so I replaced them all with same-size screws once I got them out. It was a PITA, though...those things did not want to give it up! I got them all out safely though.

Good to know about the vacuum lines - I have a Virago that does the same thing. Likewise with that bike, it seems vacuum plays a big part in petcock feed.

TexasKZ, I'm getting a decent spark at the points, but it's not excessive. It look regularly sparky. The points are still pretty meaty and don't appear pitted or anything. I've cleaned them up and sanded them a bit, but I suppose it wouldn't hurt to just replace them. There's still about 2mm on each arm/set. I'll have to take some pics and post them, the condition of this bike is just amazing, and in a Good way. Everything looks new on it.

Once I get a new spring and the little circlip that keeps it on it's post I think I'll put the tank back on and hook it up and see what happens. The mount for that looks pretty static, though...how does it work?

Phillips tips have a bit of a point at the end that JIS tips do not have. That point prevents the Phillips tips from fully seating in a JIS screw. I have ground down the tips of DeWalt #2 and DeWalt #3 Phillips to make them fit JIS screws. The large crosshead screws on the cases take modified #3 bits (or genuine #3 JIS bits). To modify the DeWalt bits you need to grind the very tip a little, then test fit, then grind a little more and test fit, etc. until the bit no longer "rocks" back and forth in the screwhead. Picture 1 below shows how a DeWalt #3 bit fits the case screws of my KZ650 after being ground properly. The #2 DeWalt bits can be modified the same way to fit smaller JIS screws. Pictures 2 and 3 below shows DeWalt #2 and #3 modified bits. Pictures 4 & 5 below show a comparison between my homemade modified bits with the authentic JIS bits. Ed

Here's a pic comparing dimensions of JIS bits to Phillips bits. Ed

Thanks for the info!

I've been doing some digging around and can't find that spring - part no. 920811028 - you don't know anybody who would have a spare they'd be willing to part with, do you? Or is there a suitable aftermarket substitute? Doesn't have to be OEM...

The distance between the two shafts is 4 1/2 inches - I was thinking Lowes might have one!

I found a couple new old stock ones, but they're not located in the US and the sellers are asking about $50 + shipping. You may want to start a new thread on this site under the Classified - Wanted category to see if someone has a used one. There are quite a few folks here with used parts, so someone might have an old set of carbs that they are breaking apart.

Also, you might want to start a thread on kz650.info . That site deals primarily with KZ650 bikes and it has many members, so someone there might also be able to help. Ed

There's one on Picclick/Ebay for $20 plus shipping, but it's for a 1980 KZ650 CSR; (Part no. 928011394); would they be the same, or are the carbs that different?

Different. Ed

REVISION:

I don't know if the spring is exactly the same or not. I originally thought it was much different, but that is because I thought the KZ650-CSR came with CV (constant velocity) rather than VM carbs. I have since found that it was the later (1982 and up) KZ650-CSR bikes that came with the CV type carbs, so the spring on the earlier VM carbs may be the same. Ed