Exhaust stutter at 1/4 throttle in all gears

Hey everyone, apologies up front if this is not posted in the proper area. I'm having an exhaust stutter at cruising speed around 1/4 throttle in all gears. As soon as I roll past this a little ways it goes away, but returns when you come off the throttle. Basically you can't hold a cruising speed without the muffler making this stuttering sound. Performance rolling through this area is fine, bike doesn't surge or hesitate that I can feel and pulls nicely out of this position all the way to WOT.

The bike a 1974 CB550 with 19,000 miles on it. It has 022a keihin carbs currently running stock pilot jets #38 and up sized main jet #115's with the needle clip moved down one notch. I'm running pod filters and a 4 into 1 mac exhaust with DCC short reverse cone muffler. Compression is good in all cylinders, valves and cam chain adjusted last week. Carbs were synced a while ago, but not recently. Plugs are good and it has new points and condensers. As I mentioned bike starts up no problem, idles properly and throttle response is nice and even throughout the ranges. The problem appears to maybe manifest just after the bike is fully warmed up, 5-10min of riding.

I have an audio file I recorded with my phone so perhaps I'll try to figure out how to get that uploaded.

Thanks for the help. If I should direct this question to another area, please let me know.

Why are the needles dropped a notch, combined with pods? Did you do the jetting?

What exhaust system?

The needle position is going to be very important at 1/4 throttle. At idle / WOT it doesn't matter a bit, but at the bottom end of opening the throttle. needle position is critical.

Pods typically mean more air flow (unless they're shit EMGO pods which actually means totally random airflow depending on the phase of the moon). More air means you need more fuel, which means you raise the needle and/or increase main jets. Not lower the needle which reduces fuel.

Thanks for your reply. It's a Mac 4 into 1 with a shorty reverse cone muffler. The Pods aren't EMGO, but could be pretty similar in terms of crap quality. When I ordered them they were a fairly expensive pod and I thought they were K&N, but after they arrived they said Taiwan on them. I later went back and reviewed the add and sure enough, they said, "K&N style". Having said that though, I don't think they are as bad as one would assume. The bike appeared to be running rich according to my plugs which were black on cylinder 2, 3 and 4, so that's why I moved the needle down a notch to lean things out a bit. I also want to go from 115 main to 110 to see if that helps, but haven't done that yet. The bike is already running rich so raising the needle isn't going to help that situation. I see what your saying, that it may help with the stutter off idle, so maybe it's just my main jet that needs to be decreased and the needle clip moved up to the top.

Thanks again for your reply, any more thoughts?

If you're sure it's running rich then drop the mains. I never jetted my CB500 or 550 back when I had them. Just ran stock carbs and air box.

Is it just a sound, or do you 'feel' the engine stuttering? It might just be your bikes personality shining through. They're all special in one way or another.

Def running rich! I'll drop the mains to 110's and see what happens but you'd recommend putting the needle clip back up would you even though its rich? It was at second notch from the top and was still making the sound so there's only one more notch to move before it's at the top.

Doesn't feel like anything really maybe a slight hesitation as it moves from 1/4 throttle at cruise to acceleration but nothing serious. More annoying to hear it reverberating like it does while your cruising.


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You need to re-set float levels +1mm
Dropping needles is also needed.
Do you have oval or round filters? You 'need' the oval ones as round restricts airflow
The MAC has a highly restrictive baffle, you need to 'obtain' a better one from a different system (or their 'race' version?)