Hey all... I'm 18, from PA, long time listener, first time caller kinda deal.
I recently bought a '78 kz750b non-runner for next to nothing... Figured I needed something to keep my busy through the rest of COVID-2020.
This is actually my second time writing this... First one deleted for some reason. Doh. But the bike has compression, but no spark. Point resistance testing checks out, and I have voltage going to the coil. Primary winding resistance seems fine, but I just realized that my clamp meter only reads up to 2,000 ohms. Time to make a Harbor Freight trip! For some reason the PO used two different plug caps, one with a 1k resistor and one with a 5k. I'm pretty sure they're "burnt out." I hope that's the issue at least. Also, has anyone ever replaced glass tube fuses with the bladed style? My box is cracked, and I'm having continuity issues, so I figure I might. Only three fuses in the box anyway.
The rest of the bike seems fine, aside from the starter. It spins, spins, spins, cranks once, then spins some more. Starter clutch maybe? That'll be fun to replace.
I plan on going for a scrambler style, complete with the heavily controversial pod filters. I've read that foamies are better than the pleated style? Any input? But thanks for reading! I guess we'll see where this goes!
Howdy fellow 750 twin owner.
Definitely clean and gap your points. believe it or not, check your kill switch. (no shame, it bites almost everybody at least once) For that matter, since it may have been sitting for quite a while, work the key and the kill switch through their range a few times to rub off any light corrosion that may have formed.
Don't know if you've already seen it, but if not, check out Classic Octane's KZ750 twin scrambler build. www.youtube.com/c/ClassicOctane/playlists I know some people won't like that he cut the frame, but I think the end result is pretty nice. I've been contemplating a scrambler build myself.
Thanks for the advice! I checked resistance across the points, but I have yet to clean them. Most likely a task for tomorrow. I also tore apart the kill switch and cleaned all the contacts. It was pretty grungy. And thanks for the resource! I've happened across that build before, but never really looked into it. I'll have to watch the series!
So I've been slowly plugging away at the bike recently., and got a few things done. I ultrasonically cleaned and rebuilt the carbs, and unfortunately while doing so noticed that the left carb's idle adjust screw (NOT the mixture screw) is stripped at the carb body. I plan on drilling out the hole, filling it with JB weld, and tapping new threads into it. We'll see how that holds up. I might need to remove the return spring though, because I have a feeling that it's what stripped the housing (it's SUUUUPER stiff). I also bought a new coil, plug wires, and plug caps, and after installing them I got spark! Once I reinstalled the (slightly broken, not synchronized) carburetors, I kicked it over about 1,000,000 times, then took a break to order a new starter clutch... But on the millionth-and-first kick it started!! I only ran it for a few seconds, as it doesn't currently have an air filter on it, but I'll still count it. That's where I'm at now, though. I have pod filters and a starter clutch coming tomorrow, and a spare set of jets that came with the rebuild kit to try drilling larger. We'll see where that goes!
Cool project. What carb kit are you using? beware that all carb kits for these bikes I have seen do not come with the correct needles. they come with a generic needle that works but it is not as good as the factory needle profile. Also a word of caution on the pods, they can work fine but make sure you have high quality pod filters, any filter that partially obstructs the diaphragm port will make the bike run like crap. the cheapy emgo filters WILL cause headaches. I Also if you are having issues with weak spark check voltage to the coils. Very common for the switch gear to degrade and not pass full voltage. this will make starting harder and running rougher. I convert all my vintage bikes to spade style fuses. Most auto parts stores will have something like this www.dx.com/p/8-way-boat-car-blade-fuse-b...circuit-2015416.html
Thanks for the words of advice! I used a carb kit purchased on ebay from a reputable seller. I also didn't trust all of the parts, so for now I only replaced the seals and gaskets. Now, at the very least, I have a spare set of somewhat sketchy jets. I bought a pair of pods branded as "2fastmoto," if I recall correctly. They're oiled foamies, with metal grate surrounding them. Probably (almost definitely) not as good as K&Ns, but I don't have that kind of cash to spend... I'll add a picture once I test them out. Also, I think I'm still getting slightly low voltage to the coils. Better than none at all though! I plan on eventually redoing most, if not all, of the wiring harness, complete with new, bladed fuses. I glanced at the run/kill switch, and the contacts are pretty corroded. I cleaned them with a fingernail, but I definitely need to really shine them up soon.
I would suggest doing the “ coil mod’ which is adding a relay and power the coils directly from the battery. I’ve never used the foam filters so I can’t comment on the efficacy, but I would inspect the inside flange and make sure it is not obstructing the ports on the intake.
I worked on the bike for a few hours over the weekend, and a good bit got done. I replaced the starter clutch, which took WAYYY longer than it should have. The old springs were absolutely trashed... I'll include a pic of old vs. new. So I smeared some loctite on the flywheel bolt, buttoned everything up, and tried turning it over. It still didn't work. Doh. On the plus side, I now know that my starter clutch is in good shape! Also, if the plugs are out it does turn over. After a second teardown, I figured out that the planetary gear system in the starter motor is screwed up. I'll add a picture if I have one on hand, but what's happening is that the ring gear is slipping, allowing the whole system to move relative to the output shaft if met with enough resistance. I assume it is free so that if the engine kicks back it doesn't fry the starter motor. I think that the ring gear is shimmed from the factory, and it's just worn down over time. Hopefully I can fix it, because a new (used) starter motor runs about $200. I'd probably just buy a spare engine if it came to that.
Also, the pod filters came, and they sent me the wrong ones. At least there are more things than just that preventing me from starting it, so I can't be too mad. I hope to receive replacements within a week or so. I plan on drilling the carb jets today or tomorrow, and tomorrow I'm getting the title transferred to my name! I don't know if I mentioned it, but I took a bit of a gamble and bought a "non-titled" bike. It turns out that I know the guy who has the title. Lucky me!
Edit: Has anyone seen a flywheel like this? All the vids that I've seen use a different style, with weird cutouts along the sides.
There are two flywheel styles. early 76-77, and late 78-83. the late model is a better design.
Those are the type of pod filters that will give you problems. They have a deep internal flange that will block the diaphragm port (and other ports) These ports need to be completely unobstructed for good signal across the carb. You can see on the K&N how there is very little flange on the boot so not to block the ports. This is critical.
timmdur wrote: ! Once I reinstalled the (slightly broken, not synchronized) carburetors, I kicked it over about 1,000,000 times, then took a break to order a new starter clutch... But on the millionth-and-first kick it started!!
Getting mine going after 30 years, I kept the truck on the bike battery while using the electronic starter and throwing starting fluid at the carbs. Still took probably at least 20 minutes for it to run. Starts beautifully now.