[caferacer3]

I purchased a CB400 that had been sitting for two years untouched. It was previously rebuilt and sold to the guy I bought it from who didn't use it for a few years before I got my hands on it. I cleaned up the carbs (mikuni brand - from the previous rebuild) with an ultrasonic bath and changed the oil. There didn't seem to be much wrong with it other than build up from old gas, which was fixed by cleaning up the carbs. It's running pretty well, but the engine will choke out if it's throttled up too quickly. A quick 1/4 turn of the throttle will kill the engine. It's not really a problem when riding because I just take it slow in the lower gears. Past second gear it shifts smoothly no matter how quickly I go through the gears.

One theory I have is that the pilot jet is too gummed up from sitting that it's causing issues idling and in the lower gears. I am trying to avoid having to rejet or replace the carbs if possible. Another theory I have is that the new air filters I put on are causing too much airflow. I put mesh metal cone air filters on and, from what I'm seeing, that could be causing the issues.

Any thoughts or comments on the issues I'm experiencing and any suggestions for fixes are welcomed. I am a noob to motorcycle maintenance... this cb is my first motorcycle and I am trying to learn how to fix it up myself.

Also, any recommendations for air filters and fixes are greatly appreciated!

Thanks!

 

[Donthav1]

Do you still have the old filter or filters? If so, put those back on & see if that fixes it, then we can go from there.

There are endless threads across the internet from people trying to figure out how to tune out drivability issues with pod/cone filters. If you want to keep the cone filters, you will probably have to rejet. But don't worry, it's pretty easy to do.

 

[mike in idaho]

Check out the accelerator pump parts in the carb.

 

[caferacer3]

Do you still have the old filter or filters? If so, put those back on & see if that fixes it, then we can go from there.

There are endless threads across the internet from people trying to figure out how to tune out drivability issues with pod/cone filters. If you want to keep the cone filters, you will probably have to rejet. But don't worry, it's pretty easy to do.

No, I don't have the old filters. They were dried out and the foam was breaking. I saw a discussion about putting distance between the filter and the carb would I need to do that if I rejet or would rejetting fix the issue with the cone filters? Do you have any thread suggestions I should check out for tuning with the cone filters?

I don't feel connected emotionally to the cone filters, so I will probably try different filters before rejetting. If I still have issues, I'll move forward with rejetting.

 

[Donthav1]

What other drivability issues does it have? Does it bog only at start up & go away after the bike warms up or does it do it no matter how long the bike has been running? Does it do it with the choke activated? Does it idle ok? Mike's suggestion of accelerator pumps sounds most likely but i just want to get more info so we can be sure.

 

[DD23]

Mikuni carbs ?

What carb numbers ?

 

[caferacer3]

What other drivability issues does it have? Does it bog only at start up & go away after the bike warms up or does it do it no matter how long the bike has been running? Does it do it with the choke activated? Does it idle ok? Mike's suggestion of accelerator pumps sounds most likely but i just want to get more info so we can be sure.

It's mostly on start up. It does happen when the choke is on. It idles fine once it's warm, but if you rev in idle it might kill it. There aren't any other drivability issues. It mostly does it on start up and gets better when the bike is warm.

 

[Montanabill]

for a quick diagnostic test wrap your pods with duct tape. cover about 2/3ds of the filter and see if it runs better. I have worked on so many different bikes with pods on them I finally got an assortment of washers and such that I could insert between the filter and the carb to get them to run right.....not all bikes can be jetted around missing stock air box and air filter being missing;