Topic: Jetting

[Fred T]

I just put a Kerker exhaust with a shorty reverse cone style muffler (no baffle).  Since it sounded too loud, I inserted  baffle inside the pipe, between the collector and the muffler.  The bike stars and idle fine, but when I open the throttle quickly, it hesitates to rev, and then picks up.
Settings are as follows: Stock pilot, and main jets, stock air box, air mixture screw 1 1/2 open.  I tried different air mixture settings, and the closer the air screw, the better the engine revs, but idle gets worse.
At this point, I believe the problem could be baffle restriction or I will need to re-jet.  So I will appreciate some advice in order to be sure if I need to change pilot size jet, main size jet, needle, or all of them, and what sizes to pick

[CycleRanger]

What bike??

[Fred T]

What bike??

Oooops , sorry, is a 1975 CB400F

[dave500]

you cant snap these throttles open from idle,how does it go doing it a little slower?riding the bike above say 5 grand you should be able to snap it open.

[Fred T]

you cant snap these throttles open from idle,how does it go doing it a little slower?riding the bike above say 5 grand you should be able to snap it open.

Dave, going slower on the throttle, the engine behaves much better. I will try to ride it tomorrow if weather improves, but in neutral, at 5000 rpm, if I snap the throttle it still lags.

[dave500]

yeah sounds a bit sluggish,did it run better before the kerker?

[HondaMan]

This sounds suspiciously like one or two low float bowl levels...

[classic bike tuner]

try lowering the needle one position  normally this wil solve the pickup problem

[cgswss]

Did you mean lowering the needle or lowering the clip.  Its sounds like a lean surge to me which should be helped by lowering the clip (raising the needle) to give it more gas.

[dave500]

remove the airscrews and drain the carbs leaving the drain screws out,then blast compressed air into the airscrew holes,refit the screws and see how it goes.

[Fred T]

I will go ahead and blow carb cleaner and compressed air without the drain screws.  I suspect the engine is running lean, as it gets better if I close the air screws. The bike had an MC Again 4 into 1 header, and was running okay, unfortunately it rooted and I had to replace it.  This new pipe is less restrictive, that's why I think maybe up sizing the jets could be the solution.
Last, I will try what Hondaman says,  and check float levels, but as getting out and in the carbs is pain in the ###  I'd like to be 100% sure if I need to change jets.

[Fred T]

Yesterday, I blew carb cleaner, and compressed air into the air screw passage,  and  had no improvement at all with my engine response.
Any recomendation about changing jets?  sorry to ask, but my knowledge about jetting is very limited 

[Fred T]

I decided to take the carbs off, and check float levels, raise the needle a notch, and try with bigger mains.  Hope this solves the problem.

[iron_worker]

Check to see if the idle jets are clear while you're in there.

IW