Stutter on throttle input...

I sync'd my carbs this weekend, while putting the front end of the bike back together. The carbs started out looking like a staircase, with #1 WAY above #4. After syncing, the bike does run much smoother, and gives a nice even idle sound now.

And the bike certainly pulls harder than it did before as well. However, I notice that on occasion, I get a stutter(like a fuel starve) when I roll into the throttle. Its not a hesitation, but a stutter. I can hear what sounds like a lack of fuel (a few pops), then the bike takes off.

So the question is, how to proceed to finish tuning the bike properly?

I will add, the bike seemed to run lean in Chicago with the stock exhaust that was rusting apart. Replaced with a MAC 4-1, and the bike starting running better with this exhaust. I've now moved up to Denver, an elevation gain of 5k feet. The bike will most likely be taking trips to 10K feet this summer as well, and I've been thinking of going to the pod air filters for it too.

 

Anyone?

 

You need to get yourself a colourtune now to really dial in the fuel air mixture. You'll be glad you did.

 

A local motorcycle guru told me that a stutter on throttle means a miss... So if the bike hesitates, one of the cylinders didn't fire correctly.

With my bike it was a combination of syncing the carbs and ditching the metal plug caps (which over time were arc'ing on the motor) for some decent rubber ones... nothing fancy or high performance, just not metal.

 

You shouldn't have to do much other than adjust your PMS for the elevation change. The elevation in Denver doesn't really have much affect on CV carbs and since the manufacturers set their bikes up to run lean at sea level, they run fine up here.

I regularly ride between 5000 and 12000 feet above sea level. I've never had to rejet any bike I've owned for the higher elevation.

If you lived in Leadville (10,000 feet) you'd probably want to rejet for the elevation, but at 5000 feet there is no need.

 

I would "Read" the Plugs. The "Stutter" could indicate a Lean condition in one or more of the Holes.

When you roll-on some throttle; the Mixture is critical. Too much Fuel for the Air and the Bike fails to Burn the too-Rich Mixture and Boggs-down untilthe Main Jet supply -- supplies the corrected Mixture for Ignition.

Too Lean and there isn't enough Fuel for the Ignition Stroke and the Spark ignites a far too lean Mixture that goes-off like a flash-bulb causing a backfire.

The optimum Pilot Mixture is one that will support Ignition and allow the Bike to Idle with a supplemental Richness that will support Ignition by supplying just enough Fuel to Mix with the Influx of fresh air as the Throttles are opened until the Main Jet Supplied Mixture arrives at the Combustion Chamber.

 

After rereading, I forgot to mention, this isn't at idle. I'll be cruising down the road, and give it more throttle to speed up. This is typically when I notice the stutter, going from part throttle to wide(r) open.

 

Well. ... if that's the case ... then, I'd look hard at the Emulsion Tubes and Main AIR Jet Passage.
If the Carbs haven't been Cleaned anytime lately, the Emulsion Tubebs should be popped-out, examined and each of 16 to 20 Air Bleed Ports cleared of any material that might have accumulated in them.

If they are OK ...

You need to be sure that your Carbs can pass the "Clunk Test" and that the Diaphragms are pliable and free from any defects.

If the Diaphragms Pistons are slow to rise under Open Throttle ... There isn't enough Fuel going in to make Power ... and a Lean Condition will result.

You should be able to look at your Spark Plugs and get a "Read" on that!

 

Well they definetaly pass the clunk test. Those things slam down nicely, and I get good engine braking too.

I'll probably pull the bank this weekend, after the truck is back together and check the tubes, as well as the plugs.