Evo CV Starts on Starting Fluid
HDF Community Team
Joined: Dec 2005
Posts: 5,427
Likes: 2,623
From: NC USA
I forgot to mention - the check valve (needle) is bad to gum up when one sits long enough to gum the jets.
With the bowl off, you should be able to shake it and hear a distinct rattle. If you can't, the needle is stuck and/or the fuel port is blocked. That will not let the accelerator pump or get fuel to pump. Very common issue with these carbs if they're gummed up.
With the bowl off, you should be able to shake it and hear a distinct rattle. If you can't, the needle is stuck and/or the fuel port is blocked. That will not let the accelerator pump or get fuel to pump. Very common issue with these carbs if they're gummed up.
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4th Gear
Joined: Jul 2022
Posts: 8
Likes: 2
From: CO
I forgot to mention - the check valve (needle) is bad to gum up when one sits long enough to gum the jets.
With the bowl off, you should be able to shake it and hear a distinct rattle. If you can't, the needle is stuck and/or the fuel port is blocked. That will not let the accelerator pump or get fuel to pump. Very common issue with these carbs if they're gummed up.
With the bowl off, you should be able to shake it and hear a distinct rattle. If you can't, the needle is stuck and/or the fuel port is blocked. That will not let the accelerator pump or get fuel to pump. Very common issue with these carbs if they're gummed up.
When riding at half throttle it will backfire and cut out and die. New fuel, new petcock, new carb.
HDF Community Team
Joined: Dec 2005
Posts: 5,427
Likes: 2,623
From: NC USA
Did you buy an actual "brand new" carb?
HDF Community Team
Joined: Dec 2005
Posts: 5,427
Likes: 2,623
From: NC USA
There's a guy in the Shovel section who has used 3 of the $50. Chiwanese CV40 copies with good luck. That's the only way to buy a new CV40 carb far, as I know. Not judging, just curious.
Easiest thing to check, take the timing cover off and see if the cam sensor is melting. If it's bad, that will cause your symptom of backfire/die.
Easiest thing to check, take the timing cover off and see if the cam sensor is melting. If it's bad, that will cause your symptom of backfire/die.
Intermediate
Joined: Sep 2022
Posts: 42
Likes: 16
From: Delano, MN
Sounds lean? Does it clear up and take off at full throttle? What do the spark plugs look like? If the plugs or pipes are showing lean and it pulls hard at full throttle, try shimming the needle. 5 or so #3(?) stainless washers from the local hardware store under the needle should do it. Keep an eye on the plugs so you don't burn a hole in the pistons.
I picked up one of the import carbs from DK this spring. Spent a couple weeks messing with jets trying to fix the mid-range stumble. Shims fixed it. Got pretty good pulling the carb off the bike...
I picked up one of the import carbs from DK this spring. Spent a couple weeks messing with jets trying to fix the mid-range stumble. Shims fixed it. Got pretty good pulling the carb off the bike...
Tourer
Joined: May 2011
Posts: 469
Likes: 158
From: Alberta
Something doesn't add up. If you are at 1/2 throttle going down the highway you are running entirely on the needle and partway into the main. So fuel flow ( amount in the bowl ) could be causing your problem, so you need to check the floats to see if the carb is getting enough fuel. Even with low fuel level in the bowl it is unusual for the engine to quit, as if you roll back off the throttle it will pick itself back up and keep running, just won't want to accelerate.
With carb issues, you really want to take everything back to stock and go from there. Then just change one thing at a time. In most cases with these carbs, a sportster needle, adjusting the mixture screw and leaving the stock slide alone is the trick to getting these to run right. Even with aftermarket pipes and intakes. Leave the jetting stock and adjusting your mixture screw will tell you if you need to change a pilot jet. Too often these bikes are jetted too rich and with jetting always consider the altitude where you ride. That has a big affect on jetting. As you go up form sea level, every 1000 feet your stock carb gets about 1 % richer.
Also don't rule out an electrical/ignition problem as they can sometime mask themselves as a carb issue.
With carb issues, you really want to take everything back to stock and go from there. Then just change one thing at a time. In most cases with these carbs, a sportster needle, adjusting the mixture screw and leaving the stock slide alone is the trick to getting these to run right. Even with aftermarket pipes and intakes. Leave the jetting stock and adjusting your mixture screw will tell you if you need to change a pilot jet. Too often these bikes are jetted too rich and with jetting always consider the altitude where you ride. That has a big affect on jetting. As you go up form sea level, every 1000 feet your stock carb gets about 1 % richer.
Also don't rule out an electrical/ignition problem as they can sometime mask themselves as a carb issue.
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