Ok...been scratching my head for quite some time now on this and seem to have baffled my mechanic. Here's my issue. I have a 2001 Heritage Softail TC88 with Mikuni 42 carb, K&N 3910 air cleaner, and V&H Big Shot Long exhaust that misses/stutters between 1/8 and 1/4 throttle. It accelerates fine, but when trying to maintain speed, say 25 mph in 2nd gear, 35 mph in 3rd gear, or 45 mph in 4th gear, it misses to the point where I can feel the bike jerking and can hear the thumping in the exhaust. Here are the specifics on the Mikuni: Pilot Jet = 25, Needle Jet - 97, Main Jet = 160, Accelerator Pump needle = 50. I have tried a 20 Pilot Jet and same issue occurs. What's even more perplexing is I get the same issue with the original CV carb. I've troubleshot the fuel system i.e., vacuum petcock, changed fuel filter, checked tank vent, main fuel line...all good. Checked for intake leaks (WD-40 spray around intake manifold)...no leaks. I changed spark plug wires, swapped ignition module with a known good one, checked battery connections...still have same problem. Mechanic thought exhaust valve on front head was sticking...pulled both heads (just to be sure) and had them checked out/new seals installed...reinstalled and encountered the same problem. Not sure if this is an electrical, fuel, or mechanical problem, but any insight would be greatly appreciated.

 

Classic jetting symptoms, but you did replace the carb. Hmmmmm.

 

Start by going up a size on the pilot jet. Sounds lean just off idle.

 

That is a lean condition, yes.
Move the pilot up to a 27.5 and see what the response is.
I will say that most Mic's run ok with a 25.
Scott

 

Thanks for the input. I'll try the 27.5 pilot jet...although my mechanic will probably tell me not to. I know he's going to tell me it's way to rich of a jet for a TC88. I'll try nonetheless. In the unfortunate event that this remedy doesn't fix the problem, any other suggestions?

 

The smaller the engine, the lesser signal at the carb, the larger jet orifice needed to wick the fuel into the venturi.
Scott

 

I have this same problem on my 03 road king. and it isn't consistent sometimes it happens sometimes i will go several days without it happening. the hard part is i just bought the bike and know nothing about it other than it has v&h exhaust as well.

 

Lean probably.
Scott

 

mine is the police edition and is fuel injected.

 

I would think it's from the reversion pulses. Can a thunder jet help with tuning?