Does it behave any differently, with the air filter removed?
CA160 Won't Idle
Hello everyone,
Long time lurker/first time poster.
Working on a CA160 (single carb) for a customer. Bike came in with many engine issues due to PO trying to rebuild the top end. Worked through all of that and now have an engine with strong compression, cam correctly timed, valves set to 0.002" intake and 0.003" exhaust. Points gapped at 0.014" and timing set both static and dynamic (timing light) dead on the F mark. Advancer free and working fine. New plugs, condenser and points. Strong spark (for a 160, anyway!).
Carb has been ultrasonically cleaned (three 30 minute cycles) and all jets and passageways checked, double checked and triple checked with compressed air and spray cleaner. Floats set at 20.5mm (spec 19.5 + 1.0mm for ethanol fuel). Floats (brass) are symmetrical and free of holes. Air screw initially set at 1.5 turns out. Reused stock brass (scrupulously clean and in good shape), even though my rebuild kit was Keyster and very high quality. Jet needle is in middle position. Main jet is #95 and pilot jet is #40 (also tried a #38). Carb vent is clear. Carb is correctly assembled with no missing parts per the fiche. O-ring on air screw is new and sealing well. Confirmed no vacuum leaks by spraying brake cleaner on all intake joints while engine was running.
Symptoms are like this: Engine starts immediately. Once warmed up, it revs just fine, but the idle is uneven and misses. Exhaust smells rich to me. Adding choke only makes the problem worse, indicating that mixture is too rich. Tried backing out the air screw to lean out the mixture, but no effect, even if air screw is completely removed. I have to keep blipping (or slightly lifting off idle) to keep engine running. Anything above idle the engine sounds great. No smoke, and immediate, strong revs.
Yes, I double/triple checked the pilot jet air passageways in the carb body (actually, both pilot and main jet passageways).
- Blew air through hole in intake horn to air screw hole, clear
- Blew air into air screw hole and got strong air flow through hole in intake horn, through where pilot jet screws in as well as through the small hole in the base of the carb throat.
I thought the float level might be too high, so I shut off the gas with the engine running and waited. Sure enough, once the fuel got low enough, the engine settled into a nice, smooth idle with no missing. Of course, once the fuel go too low, it'd quit, but I thought this gave me the answer. So, I raised the floats (dropped the fuel level) a few mm. No difference. Tried raising floats some more; still no difference. Finally got to the point that I had the floats so high that when I put the bowl back on, it pushed the floats up, closing the needle valve so no fuel would flow at all.
So I went back to square one and reset the floats to 20.5mm. I then placed a clear battery drain tube into the drain hole in the bottom of the bowl and used it as a sight gauge to see where the fuel level actually was. It came right up to the top of the bowl, just a hair below the body of the carb. That's what I'd expect for proper float height. I shut off the fuel and started the engine. Same symptoms as before. But I watched the fuel level in the bowl and it slowly came down as the engine consumed fuel. When the bowl got to about half-full, the engine suddenly began to idle perfectly. I could rev it up just fine and had good throttle response, at least until the fuel dropped so low the engine wouldn't run anymore. Turning fuel back on got the engine running again, and if I played with the fuel shutoff to keep the fuel level in the middle of the bowl (which seems WAY too low to me) the engine ran great.
So, why would I need an abnormally low fuel level to get the engine to run correctly? What say ye, gurus? I'm not often stumped by carb problems - I do a lot of rebuilds here on way more complex carbs than this and usually have great results. But this one is whipping my butt.
Thanks,
Jim
Long time lurker/first time poster.
Working on a CA160 (single carb) for a customer. Bike came in with many engine issues due to PO trying to rebuild the top end. Worked through all of that and now have an engine with strong compression, cam correctly timed, valves set to 0.002" intake and 0.003" exhaust. Points gapped at 0.014" and timing set both static and dynamic (timing light) dead on the F mark. Advancer free and working fine. New plugs, condenser and points. Strong spark (for a 160, anyway!).
Carb has been ultrasonically cleaned (three 30 minute cycles) and all jets and passageways checked, double checked and triple checked with compressed air and spray cleaner. Floats set at 20.5mm (spec 19.5 + 1.0mm for ethanol fuel). Floats (brass) are symmetrical and free of holes. Air screw initially set at 1.5 turns out. Reused stock brass (scrupulously clean and in good shape), even though my rebuild kit was Keyster and very high quality. Jet needle is in middle position. Main jet is #95 and pilot jet is #40 (also tried a #38). Carb vent is clear. Carb is correctly assembled with no missing parts per the fiche. O-ring on air screw is new and sealing well. Confirmed no vacuum leaks by spraying brake cleaner on all intake joints while engine was running.
Symptoms are like this: Engine starts immediately. Once warmed up, it revs just fine, but the idle is uneven and misses. Exhaust smells rich to me. Adding choke only makes the problem worse, indicating that mixture is too rich. Tried backing out the air screw to lean out the mixture, but no effect, even if air screw is completely removed. I have to keep blipping (or slightly lifting off idle) to keep engine running. Anything above idle the engine sounds great. No smoke, and immediate, strong revs.
Yes, I double/triple checked the pilot jet air passageways in the carb body (actually, both pilot and main jet passageways).
- Blew air through hole in intake horn to air screw hole, clear
- Blew air into air screw hole and got strong air flow through hole in intake horn, through where pilot jet screws in as well as through the small hole in the base of the carb throat.
I thought the float level might be too high, so I shut off the gas with the engine running and waited. Sure enough, once the fuel got low enough, the engine settled into a nice, smooth idle with no missing. Of course, once the fuel go too low, it'd quit, but I thought this gave me the answer. So, I raised the floats (dropped the fuel level) a few mm. No difference. Tried raising floats some more; still no difference. Finally got to the point that I had the floats so high that when I put the bowl back on, it pushed the floats up, closing the needle valve so no fuel would flow at all.
So I went back to square one and reset the floats to 20.5mm. I then placed a clear battery drain tube into the drain hole in the bottom of the bowl and used it as a sight gauge to see where the fuel level actually was. It came right up to the top of the bowl, just a hair below the body of the carb. That's what I'd expect for proper float height. I shut off the fuel and started the engine. Same symptoms as before. But I watched the fuel level in the bowl and it slowly came down as the engine consumed fuel. When the bowl got to about half-full, the engine suddenly began to idle perfectly. I could rev it up just fine and had good throttle response, at least until the fuel dropped so low the engine wouldn't run anymore. Turning fuel back on got the engine running again, and if I played with the fuel shutoff to keep the fuel level in the middle of the bowl (which seems WAY too low to me) the engine ran great.
So, why would I need an abnormally low fuel level to get the engine to run correctly? What say ye, gurus? I'm not often stumped by carb problems - I do a lot of rebuilds here on way more complex carbs than this and usually have great results. But this one is whipping my butt.
Thanks,
Jim
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I’ve been running without the filter. Given the symptoms, I’d think adding the filter would only make it worse (less air), but I’ve not tried that yet.
Confirmed just now that it's the same with or without air filter. I'm using a stock air cleaner element and connector tube.I’ve been running without the filter. Given the symptoms, I’d think adding the filter would only make it worse (less air), but I’ve not tried that yet.
May want to double check air screw needing, or not needing oring, my cb350 was very hard to get idle set until i found out my carb air screw did not use oring,
Also 1-1/2 seems far out to me but i dont know your specs.
id check float valves and needles, you can blow into a peice of gas line pressed against valve seal with needle in to make sure its sealing.
float level set to bowl gasket surface right?
Original spec carbs/ floats for bike?
Both cyl run the same?
Gas cap seal check? Reserve/ reg / petcock compare? Although i doubt that, unless its got a weird petcock on it
Also 1-1/2 seems far out to me but i dont know your specs.
id check float valves and needles, you can blow into a peice of gas line pressed against valve seal with needle in to make sure its sealing.
float level set to bowl gasket surface right?
Original spec carbs/ floats for bike?
Both cyl run the same?
Gas cap seal check? Reserve/ reg / petcock compare? Although i doubt that, unless its got a weird petcock on it
Thanks for the reply, Maxparker!
Fiche shows an O-ring. Tried screw at all settings from all the way in to all the way (falling) out. With screw all the way in, engine dies. Starts to run well at about 1 to 1.5 turns out. But only runs well if fuel in bowl is at the halfway mark.
Float valve definitely seals well - bowl does not overfill or overflow. I was able to confirm this by using a piece of clear hose inserted into the carb drain hole as a sight gauge.
Float levels set by measuring to the gasket surface (NOT the gasket). Correct setting confirmed by sight gauge technique (see original post). Fuel rises to essentially even with the top of the bowl, or slightly below with float height set at 20.5mm from gasket surface. Seems correct to me.
I'm 99.9% certain the carb and floats are the OEM stock items - matches the fiche perfectly.
Both cylinders run the same.
Gas cap seal eliminated because I'm running with an external fuel source.
Fiche shows an O-ring. Tried screw at all settings from all the way in to all the way (falling) out. With screw all the way in, engine dies. Starts to run well at about 1 to 1.5 turns out. But only runs well if fuel in bowl is at the halfway mark.
Float valve definitely seals well - bowl does not overfill or overflow. I was able to confirm this by using a piece of clear hose inserted into the carb drain hole as a sight gauge.
Float levels set by measuring to the gasket surface (NOT the gasket). Correct setting confirmed by sight gauge technique (see original post). Fuel rises to essentially even with the top of the bowl, or slightly below with float height set at 20.5mm from gasket surface. Seems correct to me.
I'm 99.9% certain the carb and floats are the OEM stock items - matches the fiche perfectly.
Both cylinders run the same.
Gas cap seal eliminated because I'm running with an external fuel source.
Hmm.. this is probably beyond me then. only other things id think to check would be throttle plates, felt seals if they have, Jet orings ok and seated well? Mine are super hard to seat. Main needle could maybe drop down a notch, Float pins move really smooth? Slides smooth, diaphrams no have no rips? Thats about all i got. Good luck!
Thanks, Max. This carb is super simple - no diaphragms, no felt seals, no O-rings on the jets, no butterflies. Just a slide for the choke, and a round throttle slide. That's why I'm so stumped - there's just not that much to go wrong here. I just can't imagine a reason the low speed circuit would "want" the fuel level in the bowl to be that low to run correctly.Hmm.. this is probably beyond me then. only other things id think to check would be throttle plates, felt seals if they have, Jet orings ok and seated well? Mine are super hard to seat. Main needle could maybe drop down a notch, Float pins move really smooth? Slides smooth, diaphrams no have no rips? Thats about all i got. Good luck!
I thought of dropping the jet needle down a notch or two, but that should have zero effect at idle. I may still experiment with it though...
I did have some trouble at first with the float interfering a bit with the bowl gasket and hanging up, but a quick trim to cut off a small bit of the gasket solved that.
And even if I could somehow set the float to maintain it that low, I'm afraid it'd be too lean at WOT. I'm out of ideas here...
Is the float bowl vent open?
Yes, vent is clear.
Make sure slide cutaways are facing air cleaner side. Make sure needle isn't loose and dangling off of throttle cable.
Both good, thanks.Make sure slide cutaways are facing air cleaner side. Make sure needle isn't loose and dangling off of throttle cable.
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