Honda Twins banner

1 - 13 of 13 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
Hello all I'm new to this bike and new to riding in general. I have a 1984 CB450SC and I'm trying to figure out why my right carb is popping into the air filter box and the plug on that side is running a dry, sooty black. I've read it could be because it's running rich on that side, but I'm not sure how to actually adjust the carb to run leaner. There is a single brass looking screw that hangs down from the front of the carb, but other than that there are no visible adjusting screws on the carb. I'm guessing they're all inside? How do I adjust to make it run leaner?

This "pops" only on idle and runs just fine at higher speeds. When I pull up to a light or stop sign the "pop" threatens to stall the engine (and has).

I've changed to hotter plugs (DPR7EA-9) from the ones that came with it (DPR8EA-9) but I don't think it changed anything. Any help would be appreciated. Pictures with arrows a definite plus. Thanks!
 

·
Registered
Joined
·
500 Posts
Black spark plugs could be cause by dirty air filter, weak spark or too rich fuel/air mixture. Check in you FSM your pilot screw set up, could be that simple.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #5
Thanks for your help, including the FSM. Is this the pilot screw you're referring to? (circled in red below). Thanks. 20190520_141944.jpg
 

·
Super Moderator
Joined
·
10,201 Posts
The mixture screw adjusts the mixture at idle. It has little impact on mixture at higher throttle settings. I don't think your floats are adjustable but one could have a leak causing a high fuel level in the carb. Crud in the float valve/seat area could prevent the float valve from sealing, also leading to high fuel level in the carb. Decel valve stuck open would cause a rich condition. Missing plug under the slow jet would cause it to run rich but then it should have been doing it since the last time the carbs were off.

You might want to review the carb rebuilding tutorial just in case you end up taking that route:

https://www.hondatwins.net/forums/63-fuel-supply-carburation/24191-rebuilding-vbulletin-carbs.html
 

·
Registered
Joined
·
7 Posts
Discussion Starter #9
Thanks I'll update this as I go. I tried adjusting the screw above but it had little effect on the problem. I'll move on to the other possibilities you mention.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #10
So I took the carb apart and cleaned it. I think it might have helped the issue somewhat but not sure. I'm beginning to think it's related to the coil, but again not sure. I ordered a new coil from RMSTATOR but it died within a km. Yeah that was pretty annoying. Put the old coil back on and got myself home. I saw a discussion on here related to replacing the old coil with a GM one so I might try that, unless anyone has any recommendations for coils that are easier to come by than the original one. Thanks again.
 

·
Sensei
Joined
·
27,018 Posts
Why are you running resistor plugs?... Did you change to non-resistor plug boots?
 
1 - 13 of 13 Posts
Top