1980 kz750 ltd jetting/power issues are sapping my will to live

The engine was definitely getting hot before I rejetted it. I didn’t notice any excessive heat after I rejetted it, just the increased power loss. I was planning on refreshing the top end next summer anyways if I decide to keep the bike, so as long as I’m not noticing any huge issues should it be fine until then? It also seeped oil from the half moon plugs on the valve cover but since I rejetted that has also gone away. I ordered an exhaust that should fit in the meantime so I’m hoping that I’ll actually have a bike to ride for the rest of the year instead of the barrage of problems that I’ve been dealing with until now 🙃

Contact these folks. They list a slip on for the KZ750, I recently bought a full system from them and they are good folks to deal with.

www.ripplerockracers.com/product/kawasak...tems-to-fit-1980-85/

I would be careful riding the bike without the muffler on as there are a lot of things we dont know. Have you been checking the spark plugs frequently? That would tell you pretty quickly if its running lean or rich.

No, I don’t have a 5/16” spark plug socket. I could probably buy one but that means I’d have to ride my bike to get it… and I definitely don’t want to put the old muffler back on since I’ll bet that would be even worse. 
Worst comes to worst I think the exhaust will come in 2-3 weeks so I could just wait it out until then, although that’s kinda painful since I only have another 8 weeks max of riding left before it gets cold

think it’d be okay to just ride 10-20 minutes just to run to the store and get a socket to then check my plug conditions? Just in terms of sound when I was testing with the muffler off earlier, it sounded pretty healthy if not a bit rich so I’m hoping if my fuel mixture is off it’s at least on the side of rich which should be safer for the engine

I dont want to tell you if its safe or not in case it isnt. The best thing to do right now is test your bike at idle and when riding for smooth operation. Warm up the engine and see how the rpms return to idle. If they return very slowly, your pilot circuit is too lean. If it returns quickly and dips below idle, its too rich. Testing for highest idle using the fuel mixture screws...Yada yada.. there is lots of information on the world wide web for this and I cant remember it off the top of my head so you could probably do some research for testing your carburetor jetting on the bike. Maybe look into it tonight and mull over it while you sleep then with a fresh mind go and start tinkering!!!

 

Sweet, I will! Thank you. Assuming I get the fuel mixture sorted, does the straight pipe cause any damage risk because of the lack of back pressure, etc.? Or is the main hurdle with straight pipes the fuel mixture and running lean/rich as a result? 

As Wookie58 mentioned, running without any exhaust system at all (exhaust shooting straight ahead out of the ports) is a bad idea, but running it with with all the pipes and the muffler in place and the baffle assembly removed should be no problem, other than the noise.

Changes in the muffler make relatively small differences in the mixture. Maybe none. 

Changing what goes on before the carburetors (air filters and such) can have a major impact on the mixture.

In your case, I suspect something like this......

The po forced you to install individual filters. Normally, this requires a small change in jetting. Up one or two sizes on the mains, backing out the low speed fuel screw a little and maybe raising the needles a notch (or with a thin washer). It would be a good idea to consult the factory service manual to see what the factory jets were so you can determine how far away you are from that. It is possible that the po had some creative ideas about that, too, so you may have started pretty far from the mark.

Packing the baffle in the muffler created its own set of problems. At very low rpm, some of the exhaust gas was able to escape, but as rpm goes up, the volume (amount, not noise) also goes up, but the blockage would not let it pass. This likely led to a buildup of pressure in the system and during that moment near the end of the exhaust cycle when both valves in the cylinder are open (that is called overlap) the pressure in the exhaust system pushed back into the cylinder, shoving some or all of the fresh mixture back through the carburetors, causing low power, or no fire at all, thereby creating a sort of home made rev limiter.

Personally, I think it would be a good idea to attack one problem at a time. I would put the exhaust system back the way it was and concentrate on getting the bike to run properly. If you want to start with the new muffler, that is fine. Pick one and stick with it until the rest is sorted out.

Ignition system- coils getting full power? All wires in good shape? Good spark plugs? Secondary wires connected to the correct plugs? Timing correct?

Camshafts properly timed? Valve lash correct on each valve?

Carburetors. I know. Jetting close? Fuel levels correct? Diaphragms perfect? Signs of physical damage? Properly synchronized?

The factory service manual covers all this and can be a great help in slogging through the process.
 

If you think that its running rich right now without a muffler attached, putting any muffler back on could make it run even more rich which would not solve your issue. I agree with TexasKZ and I would try to look through what he has explained. At this point its probably best to take a step back and look at everything again. Checking valve clearance at school might not be possible. There is also an advancer behind the right engine cover. Make sure that it rotates  freely. Mine was completely stuck on my 1000 and it couldn't rev past 3k.

So the issue with my home packed muffler is that the end cap is very tightly wedged in the muffler and I don’t really have the means to get it out without damaging it while I’m at school. Even straight piped, I still have headers and everything—it’s just the section of muffler in the back that’s removed. 
when I tested it without the muffler for a short time yesterday it ran pretty much as it should and solved all the issues I was having. Before, aside from the power and revving issues, I had an idle that was clunky and inconsistent (lots of fiddling with the idle screw as I rode), and also it wouldn’t idle below 1500 without stalling. While the muffler was off, it pulled to redline without any big flat spots and the idle was able to run at 1000-1100 smoothly. It also dropped right back down when I revved in neutral, didn’t hang or drop below idle or anything like that. 
As for the exhaust, since I can’t deal with it at school, I just ordered a new muffler that should be more free flowing. I already have everything upstream of that so I’m just going to keep the current headers installed. It’s just the back 18 inches of pipe that I’m changing basically—and without the muffler installed the header is still there so at least I’m not just shooting exhaust directly out of the ports. Super loud though

Here are my jetting increases:

pilot: #35 -> #38
main: #65 -> #70
secondary main: #125 -> #140
I have not tried to shim the needle yet either. 

as far as the other things you suggested to check out: 
diaphragms are perfect and ignition is strong. Also the fuel levels were low in two float bowls but I adjusted that when I rejetted everything and now all fuel levels are in spec (4+/-1mm is was my target).
Spark plugs I replaced about 400 miles ago and I’m having a friend drop a socket off today so I can check how they’re looking. I have not vetted my valves yet which I know is not great but I also don’t think that’s feasible to do in my apartment parking lot… 
basically though I’m pretty sure almost every symptom I was running into was resolved by dropping that muffler though. I’ll try to confirm it with some more testing later today though. 

Oh and you were talking about the advancer—I tried checking that the other day and stripped out  even though I was using JIS. I think they’re seized and I’ll have to drill them out to get that cover off, which is not possible until I’m back home as well. 
however, given that I was able to pull straight to redline I’m pretty sure that would rule out a stuck advancer, no?

ihatecarbz wrote:

Oh and you were talking about the advancer—I tried checking that the other day and stripped out  even though I was using JIS. I think they’re seized and I’ll have to drill them out to get that cover off, which is not possible until I’m back home as well. 
however, given that I was able to pull straight to redline I’m pretty sure that would rule out a stuck advancer, no?

You need an impact driver, the type you hit with a hammer, to remove the cross-point screws.  It's not a JIS issue.  

Ah gotcha. Well, I guess I’ll have to keep that in mind moving forward if I ever need to unscrew anything else 👍