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1980 750 LTD 4 cylinder odd choke issue
- apbling
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Bike has been running great! I have 1000 miles on already in about 2.5 weeks. I've been experiencing an odd issue though when I choke the bike. It's done this since I've had it. When I start it with the choke it fires up and idles fine. The INSTANT I take the choke off, #1 cylinder sputters and fires. EVERYTIME this happens (when cold). The bike runs perfectly fine and #1 fires just fine when off choke. My plugs all look pretty decent. Things I have done:
1. Cleaned carbs. Verfified all passages and holes are good.
2. float heights are perfect
3. idle screw is adjusted properly and oring in good shape(i've tried tinkering with it too, no change)
4. polyester plug is very snug fitting.
5. Good spark, good compression
6. timing is correct, valves adjusted to spec.
Seriously guys, the bike runs like a champ, but it bothers me it doesn't fire on #1 when choked. I'm not sure if it's too much gas or too little... any suggestions? As for now I'll keep riding it!
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- Patton
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1980 750 LTD 4 cylinder w/ CV34's... bothers me it doesn't fire on #1 when choked. I'm not sure if it's too much gas or too little... any suggestions?...
If #1 resumes combustion upon being un-choked, it's likely being over-choked (receiving too much gas -- meaning overly rich fuel mixture) while choke is applied.
As choke flaps are presumably functioning okay, would suspect a pilot circuit issue.
Good Fortune!
1973 Z1
KZ900 LTD
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- apbling
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- Patton
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Good Fortune!
1973 Z1
KZ900 LTD
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- apbling
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- Motor Head
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- FIX UP YOUR BIKE RIGHT AND CHEAP
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Well if so I would pull the float bowl on the offending Carb, this can be done with the rack still installed. Then on the bowl there should be a brass tube with a small hole in it, this sticks up when the bowl is off but right side up, so you look into the bowl. This where the choke circuit gets its feed of fuel, make sure its clear of being plugged. Other wise from the top of the carb you can take off the lid for the diaphragm and pull out on the choke knob, you should see the plunger open up a passage in the top inside of the chamber. If you got a 90 degree air fitting you can blow out the passage here while the knob is pulled out.
Edit: The more I look at the diagram the more I think you have Kehins?
1982 KZ1000LTD K2 Vance & Hines 4-1 ACCEL COILS Added Vetter fairing & Bags. FOX Racing rear Shocks, Braced Swing-arm, Fork Brace, Progressive Fork Springs RT Gold Emulators, APE Valve Springs, 1166 Big Bore kit, RS34's, GPZ cams.
1980 KZ550LTD C1 Stock SOLD Miss it
1979 MAZDA RX7 in the works, 13B...
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- Patton
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Nothing else is coming to mind besides an already over-rich carb pilot circuit.
Perhaps the pilot jet is too large, or might be reamed out from overly aggressive cleaning, whereby the pilot circuit is too rich regardless of the air adjustment. And application of choke is overwhelming the engine's ability to combust the already over-rich pilot circuit mixture. Or perhaps the pilot air jet (if applicable) is partially clogged.
Just guessing here.
Good Fortune!
1973 Z1
KZ900 LTD
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- Patton
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...Good spark, good compression...valves adjusted to spec...runs like a champ...doesn't fire on #1 when choked....
If not already done, would verify correct gap on #1 spark plug.
And also test with a brand new spark plug in #1 cylinder.
Thinking NGKB8ES. But should follow plug recommendation per FSM.
Good Fortune!
1973 Z1
KZ900 LTD
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- apbling
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I agree Patton, it does sound like a pilot issue. The jet is actually a new to me/used one. The original was plugged tight, so I thought I struck gold when I found this. Only thing it didn't change my choke issue, but made my overall idle and off of idle performance much better. Verified pilot passages are clear.... This is really a stumper. I'll check with the spark plug. They are new wires, but old caps...could this old cap be an issue? I was assuming it was a carb issue since it seem to be 100% related to the choke.
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- Patton
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Swap #1 and #4 spark plug wires to see whether the problem moves to #4.
Swap the #1 carb pilot jet with one of the other carb's pilot jet to see whether the problem follows the pilot jet.
Results may be helpful to further diagnosis.
If not already done, would remove #1 spark plug, hold its base against the engine head (to ground the plug), and visually observe spark quality while spinning over the engine. Look for fat blue sparks -- not wimpy thin orange sparks.
Am presupposing that compression and valve clearances on #1 cylinder are within specs.
Good Fortune!
1973 Z1
KZ900 LTD
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- Patton
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...I'll check with the spark plug. They are new wires, but old caps...could this old cap be an issue? ....
Weak spark could be caused by an imperfect cap, or poor connection between cap and plug wire.
Sometimes helps to trim back the plug wire, which allows a fresh bite by the cap.
I prefer solid core plug wires and non-resistor caps and non-resistor spark plugs. Just a straight shot high intensity loop without any resistance other than jumping across the plug tip.
But this does cause radio interference, if that matters.
In any event, would assure against having more than one resistor in the high intensity loop. Meaning, only the wire, or only the cap or only the plug.
Good Fortune!
1973 Z1
KZ900 LTD
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- apbling
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That wouldn't cause the plug to run hotter, causing long term issues with my combustion components, would it?
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