TOPIC:

Today, I replaced the friction plates (and springs) in my clutch and fitted a new clutch cable to my KZ750 LTD.

While I was taking the bike for a spin to check that everything was working fine, I decided to take the bike on the highway to see how 4th and 5th gear worked. Previously, I had been having trouble with 4th gear in that it would not accelerate at all. I figured this might be caused by something with the clutch (possibly slip) which is one of the reasons I replaced the friction plates.

On the highway, the bike pulled through 3rd gear just beautifully, but once I got to 4th gear, it would only accelerate ever so slightly. I could tell that I was pulling away from the car in the right lane, but I was holding it at wide open throttle and not getting much acceleration. Eventually I shifted up to 5th. Then suddenly, the bike jolted like the clutch slipped and I lost a lot of speed. It kind of felt like the bike was low on gas and that's why it lost so much speed. It stuttered (like it was low on fuel) a few more times at low RPM so I downshifted back to 4th and the same thing happened. Once I got off the highway (after cruising slowly in 3rd gear) there were no problems except for the occasional backfire.

Since i have recently checked the cylinder pressure (perfect), cleaned & balanced the carbs, replaced the clutch cable and friction plates, I'm thinking that this might a timing chain problem. I'm wondering if what happened was the chain jumped due to the torque and chain wear elongation over time (it is inverted tooth chain if I'm not mistaken). I think that would explain the backfire and loss of power (due to the engine being mis-timed now).

Has any one experienced this before?

The more I think about this, the more I believe that it is a timing chain problem since when the bike lost power, it did not shoot up in RPM - it dropped.

I’m not a expert, but should the whole rpm range be fine for gear 1-3, but not 4 and 5 if it was a timing issue?

If it was the clutch you should be able to provoke it in 3 also?

When you give full throotle in 4-5 can you ferl / hear the engine give full power but you only missing the rpm increase?

Can it be something with the gear box? I don’t have any idea...

Are you sure the float level height is dead nuts on? I recently had a similar issue with a GPz750 I was bringing back to life. Turns out it was going lean and higher RPMs. The issue was much more prominent in higher gears where the engine had less mechanical advantage. I upsized the jets two sizes and it ran beautifully. The point being a lean condition can create the situation you describe. One of my best diagnostic tools is "What did I touch last?" I'm just wondering if the tab on one or more float levels was changed during the cleaning. Fuel line kinked, some piece of schmootz, whatever, but I'd make sure you verify the fuel is right. Did it run well before you blew the carbs apart?

I bet it's either carb/fuel related or the ignition, possibly a weak battery or bad ignition coils. The motorcycle needs a good, fully charged battery to run right. I would charge it with a good motorcycle charger & do a high beam load test. After charging it should be at least 12.6 VDC, but a good battery will be higher. With the headlight high beam on (engine off), the voltage should drop to about 12.2 VDC. If it drops below 12 volts, then the battery may need replacing. I use a Ctek US 0.8 smart charger & VC97 digital multimeter.


...

What type of carbs are on it?
Steve

I'll respond in the order that comments were posted:

-Can't recreate the issue in 3rd gear. In 4th & 5th gear, I give it full throttle but the engine doesn't rev very high, it doesn't get loud, and it doesn't pull.

- I'm sure the floats are dead on, I spent a lot of time making sure they were, haha! But that is interesting you mention the jets, someone has mentioned that to me in the past. When I first brought the bike to a mechanic after I bought it, I asked him if the jets were changed (I bought it with Vance and Hines exhaust on it) and he said they looked to be. Maybe he was wrong... I have put pod filters on it since. Maybe I should consider a stage 3 jet kit? I wrapped the headers and the pipes coming off of cylinders 2 and 3 have turned white (the wrap is black) so maybe I am running too lean. Also the fuel like is a kinked at the inline filter and I thought to myself that it might be a problem... the cross-section of the fuel line does shrink at the kink. I've been fine tuning the carbs for a while and it run much better than it used to, but I've always had this 4th & 5th gear problem.

-I'll double check the battery, but I had new coils and spark plugs put on in April.

-It has the keihin carbs on it.

First thing I'd Work on getting that fuel line routed nice that was what I pictured when I first read this. The V&H wouldn't have needed much in the way of jetting but with the pods you should check around to see what others are running.

I guess you have CV carbs, if so get rid of the pods and go back to stock air box, you have a V&H exhaust so possibly the idle and main jets need going up in size by one or two, as for the wrap it slows the pipes from cooling down, i woild not use it on mine.

A kink in the fuel line will cause exactly what you described. Happened to me.

I had primary main jets at 70 and secondary mains at 140 when i had k&N pods on my Keihin CV34 carbs 1980 kz750E1 . It ran well.
Stock jets are 60 and 125?
What make pods? Remove a pod and look inside. Some cheapo ones have a lip on the inside which blocks an air jet intake side of these carbs.


Getcridcof the wrap as kevski advised.

I will fix the kink in the fuel line, just gotta figure out a good solution because there isn't much space with the inline fuel filter and the petcock being so close to the top of the carbs.

I'll check the jets, but I ordered a jet kit just in case. I have genuine K&N pods

After reading some online, I wish I still had my stock airbox because people are saying that CV carbs don't like to work with CV carbs!

I'll save the header wrap discussion for another post...

You are right. There's not a lot of space under the tank for fuel line and filter.
The photos below are taken from the right side of my bike and you can see the fuel line goes down between carbs 3 and 4. This gives me no sharp bends (kinks).
The second photo shows the line from below. All curves are gentle.



Is your fuel filter designed for a motorcycle ? Some non motorcycle ones need a fuel pump to work properly

When I had the pods and a Mac 4 into 1 exhaust the bike ran well with the jetting described in my earlier post. A jet kit should work also.

The main reason I got an airbox is because I was going for a more stock look. Best thing I did with the carbs was getting the service fuel level inthe float bowls in spec