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yup...small stumble.
- CDNTX650
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So far, The bike runs like a champ from idle to red line, But if i cruise at about 3000 to 3500 rpm it has a small stumble when cruising and when i accelerate out of it. The bike will pull cleanly through it if i am ripping from a stand still or below that or if i dont go to hard on the gas.
I have the what i assume are VM24ss carbs with only the airscrews on the side. I set them at 2.5 out as any less and the idle slows down, and up to 3 seems to slow a bit too.
on my to do list, Valve lash next summer (bike has 135psi across the board so i left it for this summer) and i just ordered condensers to make sure as i dont know when they were changed. I have cleaned these carbies myself and prior to this with air and carb cleaner and i always run sea foam and non ethanol fuel.
So, i have tried to rule out alot and right now...i am not sure what else to check. Any ideas??? I cant tell if its rich, lean or points related. It does seem worse at richer pilot screw settings...but i cant see needing one size down on the pilots..
It isnt really that bad, so at this point it can wait till next winter when i have 6 months of crap to check the lash etc...but with stock stuff on the bike its really driving me nuts.
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- CDNTX650
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- 650ed
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1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)
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- CDNTX650
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Thats all we have here is those damn resistor plugs. Ill have to order a set then and try.
Timing has been set with a timing gun. Never set the dwell as i have no meter. Just made the gaps set at a spec i found. (cant remember what that is) but i dont think it is to large from what i remember. I did clean and lube the advancer already prior to setting the timing and verified it works with the timing light.
Parts n more was out of points, so ill try again. Condensers are on the way.
Stock jetting last time i had the carbs apart, i verfied it with a search on here.
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Would guess imperfectly clean carb pilot circuits.CDNTX650 wrote: ...if i cruise at about 3000 to 3500 rpm it has a small stumble when cruising and when i accelerate out of it. The bike will pull cleanly through it if i am ripping from a stand still or below that or if i dont go to hard on the gas....
Good Fortune!
1973 Z1
KZ900 LTD
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- 650ed
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Remove the points cover on the right side of engine. Under it you will see 2 sets of points. The set on the left fires cylinders 1 & 4; the set on the right fires 2 & 3. When replacing points observe carefully how the little bits and pieces are arranged where the wires attach. Some of those pieces are actually insulators and if you leave any of them out or put them back in the wrong place the points will be grounded and won’t work. Take a very close look at the contact surfaces of the points. If they are pitted you really should replace them. You can sand down pitted points, but they will quickly pit again. Replace one set of points at a time so you can look at the other set in case you get the little bits confused.
Use a 17 mm wrench to turn the nut NEAR the end of the crankshaft clockwise while looking in the hole above that nut. (Do NOT use a wrench on the smaller bolt on the very end of the crankshaft to turn the engine.) Inside that hole you will see a vertical pointer cast into the casing. As you turn the 17 mm nut you will see a 1 & 4 and F and T roll by and then you’ll see a 2 & 3 and F and T roll by. Each F and T has a line next to it.
Here’s the method I use for static timing. I turn OFF the ignition. I disconnect the green wire near one coil and the black wire near the other coil. (This is not in the book, but it makes checking continuity much easier for me.) After installing the new points or cleaning up the old ones, turn the 17 mm nut while watching the points. When points set 1&4 are at their widest gap adjust them (by loosening the 2 screws that hold the points to the backplate) so the gap equals 0.35 mm. Turn the 17 mm nut clockwise through a full revolution again and double check this gap. Then repeat this for points set 3&4. Now set your meter to test continuity and clip one wire to the leaf spring on points set 1&4 and clip the other wire to ground. Turn the 17 mm nut clockwise until the 1&4 “F” mark aligns with the pointer mentioned above. You want the continuity across point set 1&4 to just break when the F mark aligns with the pointer. The idea is that when the continuity just fails is when the points will fire their respective coil and cylinders. In order to adjust the point at which continuity fails you loosen the 3 screws that hold the backplate to the engine and slightly turn the backplate until the meter shows a break in continuity. Once you have the 1&4 set timed properly you can check the 2&3 set to make sure they break when the 2&3 F mark aligns with the pointer (they should or something is not right). Don’t forget to plug in the green and black coil wires when you are done, and put a little grease on the rubbing block felt. Assuming you are using new points of the correct type this should enable you to get the timing very close. Trying this with old points may give poor results, especially if the points are pitted and/or the rubbing blocks are worn.
After you have set the gap (which in effect sets the dwell) and the timing using the method above you can use a dwell meter and timing light to fine tune dwell and timing. If you have followed the above procedure carefully, very little if any fine tuning will be needed.
Sorry this is so long. It’s not as difficult as it sounds. Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)
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- CDNTX650
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And that the choke plungers are fully closing when the choke is supposed to be OFF. And that the choke mechanism is functioning correctly.
Another possibility could be worn pads on the choke plungers.
In this diagram, the choke is ON (plunger in raised position).
Would also visually inspect for fat blue spark on brand new spark plugs, install the new plugs, test-run for several miles in the stumble throttle range, followed by throttle chop and plug reading.
Carry along a short length of hose that fits snugly onto a spark plug, which enables removal at roadside without burning fingers.
Good Fortune!
1973 Z1
KZ900 LTD
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- CDNTX650
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