Carb cough

[CarlBrain]

Getting some bad carb cough. Have a 80" shovel with I think an Andrews AB cam. Tossed a CV carb on it and ran great. Started easy and the choke worked.

Now the choke doesnt really idle up when used. The bike idles very low when cold. If I let it sit for an hour and go to start it, it's a bitch. Have to give it gas to keep it running and coughs/ dies out. Runs fine down the road though, it's just the idle and low rpm.

Carb has an adjustable needle in it, moved it up one notch to try and richen the low end, see if that would help. Has 48/180 jets. Any idea wtf is wrong?

I checked for intake leaks.
Plugs look good.
Rebuilt and cleaned carb also.

[TriNortchopz]

Maybe an answer in here:

Harley CV Carburetor Tuning Issues & Troubleshooting

Troubleshooting the Harley CV carburetor

Hesitation or stalling can sometimes occur after tuning or rebuilding your Harley CV carburetor or if your Harley carb has not been maintained.

The following are common issues sometimes encountered after tuning or rebuilding a Harley CV carburetor. Please refer to your installation instructions included with all CVP Tuners Kits. When installing a rebuild kit (OEM, no instructions) consult your factory service manual for instructions...

1) The #1 cause of hesitation and performance issues following a carburetor rebuild or install is VACUUM LEAKS...

2) Check that the Needle Jet (nozzle) is installed correctly. Installing the jet upside down will adversely impact the fuel spray and needle metering.

3) Clogged idle mixture circuit. Inside the CV carburetor there are a series of tiny passages connecting the mixture screw, pilot jet, and air intake jet located on the front face of the carburetor (pictured below). Dirt or old fuel that has become lacquer will clog these passages causing hesitation or lean popping...

4) Accelerator pump weak or not spraying. Check that fuel sprays from the accelerator pump nozzle when rolling on the throttle (test with engine off). The accelerator pump diaphragm will wear or crack over time or if left to sit in a fuel filled CV carburetor for extended periods and will eventually deteriorate.

5) Pinched or cracked slide diaphragm. If the slide diaphragm becomes pinched or is unable to seal, the slide will not function correctly. Slide diaphragms for the Harley CV carb slide are not sold separately, so the only fix is to replace the Harley vacuum slide.

6) Over-drilled slide port. On the underside of the slide there is an offset hole used to displace vacuum/air as the slide moves up and down. The size of this hole can adversely effect the position and rate of travel of the slide. For several years many articles and companies promoted the practice of drilling the slide using a 1/8" drill bit. This was later found to harm performance and cause erratic behavior as the slide attempted to bounce and search for correct positioning...

7) Exhaust leaks. While not often associated with a carburetor problem, an exhaust leak is often overlooked and can lead to off-idle hesitation and deceleration pops. The gaskets between the head pipes and the exhaust ports of the heads is a crush fit that will leak if the pipes are removed, reinstalled, or over/under torqued. Cool air drawn into the exhaust at these seals will result in hesitation or popping commonly misdiagnosed as a carburetor problem. Modified pipes and removing the baffles will also impact performance regardless of how a carburetor is tuned.

8) Gas cap venting. Another problem that will cause intermittent issues with fuel delivery is a gas cap with a malfunctioning vent. The built in vent inside the gas cap allows air to be drawn into the tank to displace the fuel as it is used. If the vent sticks closed a vacuum will build inside the tank thus slowing fuel delivery and sometimes starving the carburetor. Replace the gas cap as needed.

9) Worn float fuel valve. The float valve constantly meters the fuel level in the float bowl. If the rubber valve tip becomes worn the carburetor is prone to flooding. Also if the valve sticks due to a build up of lacquered fuel you may experience erratic fuel delivery.

10) Finally do not underestimate the importance of fresh clean fuel and a fresh set of spark plugs. Gasoline that is old or left to sit in the tank or fuel system will change over time, often becoming lacquer and clogging small passages...


Harley CV Carburetor reference diagram

Click on image below to view diagram with H-D part numbers.


Read more here:

https://cv-performance.com/harley-cv-carburetor-tuning-issues

[Tattooo]

Idle circuit is blocked a little,,,

[CarlBrain]

Already read through that. I'll try cleaning out the idle circuit again, see what that does. Might get lucky.

[Tattooo]

Already read through that. I'll try cleaning out the idle circuit again, see what that does. Might get lucky.

It's tough to get it clean... You really need to soak it, spraying carb cleaner through it usually won't get it clean....

[CarlBrain]

Cleaned it out again. Never did get to give it a good dip though. Runs a little better. Idle still low when cold. Still starts first kick so whatever.


It's only an issue when the engine isn't up to operating temp.

[Tattooo]

Cleaned it out again. Never did get to give it a good dip though. Runs a little better. Idle still low when cold. Still starts first kick so whatever.


It's only an issue when the engine isn't up to operating temp.

Glad it's a little better.... Now go buy some Sea foam at the auto parts store... Put some in your gas tank and go for a long ride....

[CarlBrain]

Glad it's a little better.... Now go buy some Sea foam at the auto parts store... Put some in your gas tank and go for a long ride....

Will do. Thanks for the help.

[pan620]

I have soaked carb parts in Se Foam and say no difference in appearance of the piece let alone clean it out, my opinion!

[farmall]

Fine cleaning of carb passages normally requires strip and soak. If problem persists it's painless to do it right the next time.

Those curious can read the MSDS for any "cleaner" they dump in the tank so they can buy stronger/cheaper/more chems at a hardware store.

[Tattooo]

I have soaked carb parts in Se Foam and say no difference in appearance of the piece let alone clean it out, my opinion!

LOL That's your problem, your supposed to put it in the gas tank... LOL

Be leave me it works.... all of the 70s 80s Hondas are know for clogging up the carbs if they sit for any amount of time... You can put Sea Foam in the tank and it will clear the carbs in a tankful....

[pan620]

"It's tough to get it clean... You really need to soak it, spraying carb cleaner through it usually won't get it clean"....
But now you say sea foam will do it, if it worked like you say why would you go to the trouble to soak it or even take them off? That stuff will not clean your carb...My experience!

[pan620]

Not trying be rude, just what i have experienced

[Tattooo]

"It's tough to get it clean... You really need to soak it, spraying carb cleaner through it usually won't get it clean"....
But now you say sea foam will do it, if it worked like you say why would you go to the trouble to soak it or even take them off? That stuff will not clean your carb...My experience!

I said since it's close and running much better... Try Sea Foam... Yes if it's really clogged up you need to soak in it a good carb cleaner....

[Tattooo]

Not trying be rude, just what i have experienced

Not at all I know where your coming from...