Posted this over in the touring section, but mkguitar suggested I repost this over here so I'll copy my post from that thread.


I tore the 91 ultra apart looking for the cause behind an excessive sucking sound through the intake digging in deeper I found this.

Intake lobe on the front cylinder has the finish wore off. Could this be the cause behind the noise.. not letting the valve open far enough? Factory 80" with approx 35k on rebuild and its an andrews ev27 and new hd lifters with right at 10k miles on everything.

At first I thought it was an intake gasket leak had then intake off probably 6-7 times. Swapped carb off of my sportster (both s&s) compression test but no leak down test and never put air in the cylinders.

Thanks for any insight you guys might have.

 

It would have to have worn down a considerable amount for the valve not to open far enough...sucking sound is affecting the performance at all??

 

Not that I have noticed. Still seems to run as strong as it ever has and no other noises or changes in exhaust note.

 

I had this happen , last year. Thought it was intake leak. Replaced seals & didn't fix sucking sound. Finally figured out rear rocker box cover gasket was blown. Right in the center, blew out a piece of gasket. Replaced & hasn't "sucked" yet. Something to look at.
Ride Safe,
Harold

 

Oh really? Well that may be the best news I've heard in a long time. I noticed a few days ago that my rear rocker box had an oil line around it. Never would have thought that could cause any noise.

 

Doesn't look odd from here?
Scott

 

Its gone matt on one of the lobes....this is usually a sign that the hardening has gone south.

 

And we have a winner!

Resealed the rocker box put the lifter block back in, adjusted pushrods and wa-la no noise. Still should look into the cam but it wasn't the cause for any noise.

Thanks for all the help

 

I have a sucking noise too... sounds like it's at the intake, but only on acceleration. No intake leaks... I'm assuming it's just the sound of the motor sucking in air through the free flowing A/C.

 

I was always under the impression that, if your bike is making a sucking sound, it's because your bike sucks........ BWAAAAAAAAAAA!