Hello, I have a weird issue I'm trying to figure out. The bike is a 1998 883 that has been sitting up for a while. It fires right up and idles but when you give it a lot of throttle it start to blow black smoke out the exhaust. At half throttle the rpm's will drop and black smoke will start chugging out of the exhaust. It reminds me of a diesel engine.

I cleaned the carb, checked the jetting 160 main and 42 idle, checked for any bad intake hoses and changed the plugs. I have the adjustment screw on the carb 1 1/2 turns from bottoming out. I appreciate any help.

Here are the plugs out of the bike. These are the old plugs. I put a new set in.

 

Is the needle jet, needle assembly, emulsion tube all in proper position. The needle jet can get put in upside down and cause problems you describe. I believe the long side of it goe up into the venturi chamber. I could be mistaken, someone else will correct me if I am.

Might want to change the intake seals, they could be 19 years old. It's real easy with the carb off. Use some red grease on the seals.

John

 

Here is a site with information on your CV Carb. It may help with your diagnosis of your problem. http://sportsterpedia.com/doku.php/techtalk:evo:carb02

http://sportsterpedia.com/doku.php/t..._on_sportsters

 

Thanks for the info guys!! I'm going to work on it this evening after work.

 

 

Bike does not leak any gas and ignition is good. I have not checked compression yet. I fires up quick even cold and idles fine. It's just when you give it throttle it starts acting up.

I'll post an update.

 

 

Check your slide diaphragm for pinholes or a tear while you're in there.

John

 

As was stated previously, if it is idling okay and the issue presents itself when the throttle plate is half open the issue is with the vacuum slide, needle, or needle jet. Make sure the vacuum slide is operating correctly, if it is not opening correctly or the needle jet is in upside down (long side should be up), it will cause these type issues.

 

Wanted to give an update on this issue. I disassembled the carb (again) and doubled checked everything. Well, the needle jet was missing. I replaced it and the bike ran like new. Thanks for all the help and info!!