CV Carb Runs Lean / Plugs Look Rich - Harley Davidson Forums

Carburetor Related Find discussions on carburetor related goodies here. Swap and trades? Rebuild information and tuning for the pre EFI systems.

CV Carb Runs Lean / Plugs Look Rich

Thread Tools Search this Thread
Old 06-28-2005, 01:37 PM
HDF Tech HDF Tech is offline
Thread Starter
Join Date: May 2005
Posts: 14,506
Thanks: 0
Thanked 53 Times in 14 Posts
Default CV Carb Runs Lean / Plugs Look Rich

Harley Davidson Motorcycle Runs Lean / Plugs Look Rich

Sounds familiar? You have a Harley Davidson motorcycle with plugs that look rich, but it runs like it's lean and wants more gas!

First, if you have any air leaking in at the manifold seals, or the throttle shaft (common on S&S Super B's), you wind up having to jet the low speed rich or run the idle mixture screw way out. Manifold vacuum is high at idle, so any air leak is much worse at low speeds and you get lean pop, as soon as you get 1/4 throttle, the jet is way too rich and foul plugs. Spray something like starter fluid on the manifold seals and on the throttle shaft and see if the engine speeds up. If so, make necessary repairs and go back to original jetting.

Next, float level can cause the same problems, but in addition if the carb is more than a few years old, the float can absorb gas and get "heavy" causing the fuel level in the bowl to be too high even though it's mechanicaly set right. If the fuel level is even 1/8" over where it should be the emulsion tube doesn't mix the air/gas in the correct ratio and you can't jet it out. Replace the float with a new one and try again.

Last, and easiest to try is this. Unless you live in the desert it should be getting nice and chilly in the winter, and the good high test you run in the summer to keep the engine from hot detonation will now be keeping the engine from reaching operating temp. Switch to regular gas in the winter and check the plugs. Regular gas burns hotter than high test and will cause the combustion chamber to run cleaner. Many folks waste high test in cold weather and on lower compression bikes that don't burn it cleanly. This trick also helps when emmissions time comes around as it can reduce unburned hydrocarbons. Hope this helps!


Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
READ this for CV carbs and stock carb fixes on your evolution motors OneHarleyAtATime Evo Classic Models 33 01-02-2018 06:38 PM
READ this for CV carbs and stock carb fixes and tuning on your evolution motors OneHarleyAtATime Carburetor Related 4 06-11-2017 06:09 PM
CV Carb Running Rich ellisem Exhaust System Topics 4 04-19-2017 07:14 AM
Help - Stumped - 1995 Softail Carb Issues Gnap123 General Topics/Tech Tips 2 08-31-2015 02:32 PM
CV Carb with new jets - Nice! virtualmike13 Exhaust System Topics 4 10-26-2007 11:45 AM

carb, cv, float, harley, lean, level, motorcycle, pop, pops, rich, run, running, runs, shovelhead, winter

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump

Featured Sponsors
Vendor Directory

All times are GMT -5. The time now is 01:13 AM.

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites.
  • Ask a Question
    Get answers from community experts
Question Title:
Your question will be posted in: