Low rpm flutter when not loading the engine.

[John Schmidt]

Not loading...meaning not accelerating regardless of how slight. The sound is a bit of a flutter in the exhaust sound under about 2500rpm+/- a bit. Give it a little gas and it goes away, once at highway speeds where the rpm is at or above the rpm mentioned it goes away and runs fine. Acceleration is as strong as ever so has me a bit flummoxed as to the cause. It had started doing this on my old bike(2 wheeler) which is the reason I overhauled the carbs last summer. When I bought the trike last fall I transferred the rebuilt carbs over and now have the same sound. Strangely enough, it didn't start again until a few days into the trip to Athens. It doesn't seem to affect how the trike runs, just not the smooth idle we're all used to or when cruising down the street at reduced speed/rpm.

I've been tossing around various ideas/thoughts about possible causes. One thought was possibly a slight hole in one of the diaphragms that developed over time...these aren't new bikes after all. Also, years ago I installed I/S springs so could possibly one or more be weakened with time and not reacting as designed. When doing the rebuild I found a couple of the cutoff valves not working so rather than buying new, I merely stopped them all up using some pellets from my son-in-law's air rifle stash. It hasn't affected how it runs and only get a minimal amount of burbling upon decel which is hardly noticeable. My mileage overall during the trip was in the low 30's so really not displeased with performance. So...any thoughts on this or have any of you had the same experience?

[pancho]

Probably need to sync the carbs and tune the pilot screws John.

May need to clean the carbs, sounds like they are not flowing evenly.

[John Schmidt]

From the original post: "It had started doing this on my old bike(2 wheeler) which is the reason I overhauled the carbs last summer."
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They got a hot bubble bath in an ultrasonic cleaner & some good cleaning solution. That was followed by a good blowout using my air compressor. They were first bench synced followed by a running sync using one of the digisyncs. All the pilots were set the same...forget how many turns out but most likely at or just under 2 full turns out. What I found strange is after moving the carb bank over to the trike from the old bike it didn't so this for the first few hundred miles. It's quite possible I need to sync them again since they're now on a different motor.

[JimC]

John,
We have a digisync if you are in the neighborhood.

Jim

[Jims99]

The cheap vacuum caps don’t last long on these hot engines. Red eyes are made much better. I put a set on in a pinch, didn’t last me 6 months. Started the invisible cracking.
John,I would try opening the two front carbs mixture screws an extra 1/4 turn. The front runs a bit cooler and may need the extra fuel. I know on some bikes I’ve had in the past, (till I found my last bike) the front carbs have had one jet size up on the fronts. I e heard of it being done on the valks, so may be worth a try.

[Bret SD]

Hey John, have you checked the exhaust studs? Mine like to loosen up here and there.. I also tighten down tube bolts and clamps.. those I check first when the bike is running 'off' a bit. It usually fixes the niggles I'm detecting.

[pancho]

From the original post: "It had started doing this on my old bike(2 wheeler) which is the reason I overhauled the carbs last summer."
================================================================
They got a hot bubble bath in an ultrasonic cleaner & some good cleaning solution. That was followed by a good blowout using my air compressor. They were first bench synced followed by a running sync using one of the digisyncs. All the pilots were set the same...forget how many turns out but most likely at or just under 2 full turns out. What I found strange is after moving the carb bank over to the trike from the old bike it didn't so this for the first few hundred miles. It's quite possible I need to sync them again since they're now on a different motor.

It certainly wouldn't hurt to take a look at the sync again John, set them up on this bike, also I agree as others have mentioned, a small vacuum leak could give the same symptoms. Being that it only seemed to show up after a few hundred miles might me look at the vacuum caps, hoses and O-rings first.

[TTG53#1717]

I had something akin to this going on for a while in my ‘97 Std. and no amount of spraying, hose checks, Sea Foam etc. had any effect.

I decided at one point to swap out to Interstate slide return springs and, low and behold, one of my stock springs had a pretty significant kink in it that didn’t allow the slide in that carb to fully return.

I straightened out that spring and it immediately solved the problem. Satisfied with that, I did the swap.

[sixkiller]

This issue began for me my first ride after rebuilding the OEM petcock. Rode fine for the first 50 miles or so, then the "flutter" began. Could it possibly be related to the diaphragms? I'm a novice and did the rebuild using a youtube video. 1998 Standard with 54000 miles.