Sputters at about 1/4 throttle

Is it suggested that I remove the timing advancer completely from the bike and dissemble and clean the arms, or can I lube it in situ by simply spraying some lube on the arm pivots?

Thanks.

Assuming the advancer is similar to mine, I would remove it to clean and lube it. On mine the cam rides on a shaft. If I open the two weights so the little arms are not engaging the cam I can slip the cam off the shaft. This then allows me to clean and lube the shaft and the inside diameter of the cam, so the cam will operate smoothly on the shaft. Take note (take a picture if possible) of the orientation of the cam before you remove it from the shaft, because it is possible to install it 180 degrees out of position. On mine there is a mark on the cam and a hole in the backplate. The marked side of the cam goes toward the hole. Here are a couple pics that may help. Again, yours may be different, mine is a 1977 KZ650-C1. Ed

Thanks for that. I will take a picture and keep close eye on the way it is on there.

Well, I took off the advancer and it was hanging up a bit. I cleaned and lubed it up and it operates very smoothly now.

It did make a difference with the sputter, but not completely. It still struggles at about 2500 rpm up.

I checked to see if my petcock is operating properly, and all seems well there. I guess the next step is to clean up all the electrical connections and make sure the coils are getting what they need. I have the green Dyna coils (they are relatively new), so I think I am OK there.

I am so close to getting this bike on the road! It shifts nicely and idles like a champ. I just need to get this sputter sorted.

Thanks again for all the help. I will most likely be picking your brains again soon. :blush:

If you still have points, the Dyna electronic ignition would be money well spent. Also, make sure you're getting 14.4V to the battery at 4000 rpm.

Alan

Haybus wrote: If you still have points, the Dyna electronic ignition would be money well spent. Also, make sure you're getting 14.4V to the battery at 4000 rpm.

Alan

The 1981 KZ750-E2 doesn't use points; it already has electronic ignition. Ed

The issues continues.

I cleaned and lubed the advancer, and it moves nicely. I checked the voltage at the coils, and there is less than a 0.5 V difference as compared to the battery. Is that close enough? I looked through the connectors, and all but one where nice and shiny. I cleaned that up and made sure the ground on the engine was sound.

After all that, it is still sputtering at about 3000 rpm and up. I took the rest of the day to service all three calipers, switched the forks from my parts bike to my project (the seals were leaking on my project bike), and then lubed and set the steering head bearings.

So, I have all the peripheral jobs complete. Now all I need is to get the engine running properly!

Is it time to maybe change the needle clip position? The idle is nice and smooth, so I am happy with the pilot circuit.

I wish I had a magic wand to get it going properly!

Well ts o me it sounds like you have done a lot of checking. Before trying to re-jet at all. Make double sure that your float/ wet fuel level IS correct. This has a huge effect on the fuel available to each jet/ circuit. Make double sure it is within spec.
Then if it is right, then make jetting changes. The easiest is the Needle which can be raised with either a clip position if so fitted, or shims. This would be for 1/4 throttle to 3/4 throttle approximately. There is of course some overlap between carb circuits. Yours would also have a slow main and a high speed main. The slow main may need increasing. Hard to say from not riding the bike.

I just re-checked the float level this week using the clear tube method. Each one was within 3 mm of the top of the float bowl. Maybe it need to be closer to the top of the float bowl?

My problem is that I don't know that much about carbs, so even after riding it, I am unsure of the cause of the symptoms.

I will try to lift the needles to see if that maybe makes a difference.

Thanks for the help.

I'm sure you've checked, but make sure the diaphragms don't leak on the slides. No pin holes,or leak at the lids. Slides also must be orientated correctly. Besides the hole where the needle drops into, there will be a vacuum hole in the slide. It must face the engine/ intake side of the carb.

I have a trick for checking float heights, if/when you remove them from the bike. Draining each bowl to thread in a drain plug adapter, filling the bowl, then removing the bowl to adjust, filling, draining, repeating seems like a lot of unnecessary steps. Unless you have a drain port, then maybe this isn't that useful. I procured 4 8 ounce paint cups from the hardware store, the opaque ones with the measurements on the side, for $1 each. Mark 3mm from the top with a fine tip sharpie on each cup. Set the cups in a row, in a plastic tub to catch any possible spills. Remove all 4 bowls, or 2 if you only have 2 carbs . Set the carbs on the cups, they're just about the same size as the bowls. Set your tank, or an aux tank above the carbs and connect the fuel line. Turn on the petcock and fill the cups, partially close the petcock when the fuel gets near the top to prevent rapid overflow if the float(s) is/are way off. Shine a flashlight from the back side of the cup and you'll clearly see the level in the cups. Adjust float tang(s) as necessary and repeat.

Alan

Motor Head wrote: I'm sure you've checked, but make sure the diaphragms don't leak on the slides. No pin holes,or leak at the lids. Slides also must be orientated correctly. Besides the hole where the needle drops into, there will be a vacuum hole in the slide. It must face the engine/ intake side of the carb.

I have checked the diaphragms for any tears, and they look good. Is there a specific way to check them, or is it just a visual inspection?

I was under the impression that the slides only went in one way, as the top of the diaphragm isn't round, but comes to a point on one side instead. I will certainly check to make sure I have them in the correct position.

Haybus: I do have a drain port on my carbs, so it isn't that bad at all. It is taking the carbs off the bike that sucks! Your cup idea seems to be a good one. Anything that saves time is worth it.

I wonder if it is worth changing the fuel level to the high end of the specifications. If I remember correctly, the spec is 3 mm +/- 1 mm. Maybe making them all 2 mm below the top of the float bowl would be a good thing (unless 1 mm wouldn't make a big difference).

Now, to be sure, it is the point at which the float bolt meets the carb body that I am to be measuring from, correct?