Shovelhead sputtering at full throttle

[HarmBMW]

Hello,

I got a 1973 Shovelhead which has issues when go full throttle, in every gear.
When I give it a quarter to half throttle it runs fine and can ride it to around 50mph.
Can't go faster, because than the engine sputters/ is stumbling.

1200cc, S&S Super E with 0.295 intermediate jet and 72 main jet. Upsweep fishtails exhaust (with custom mufflers made in, does that care?).
I rode with an 76 main jet and switched today to 72, it gave the engine more power and it goes a little bit faster (55 mph), but still issues at full speed/throttle.

Engine starts great, 1/2 kicks, cold and warm. What should I check now to give full throttle?

[JBinNC]

Assuming the ignition is good (coil, wires, plugs, points if any) and the timing is correct, keep jetting down until it cleans up. Here in the humid South, I find a 68 main jet is the right answer more times than not.

Jim

[HarmBMW]

Thank you. Yes, ignition and timing are correct. I will order a smaller main jet, will buy a 70 and 68 and give it a try. Should the intermediate jet keeping at 0.295?

Referring to https://www.sscycle.com/docs/default...g.pdf?sfvrsn=0

[JBinNC]

You are right in the middle of the intermediate jet choices that work. You might try a 28 intermediate, and if the motor is smooth at 50 mph cruise, that would be OK. Bike might not accelerate as hard with the 28. Just a matter of experimentation and choosing what you like.

Jim

[DoomBuggy]

Let me guess, runs great until you hold it on full throttle where it accelerates for a second or two and then starts sputtering like crazy? If so, read on...

That is what my panhead with a Super E did until Jim gave me the solution. My carb is an old one with a fixed air bleed that controls when the main jet kicks in. Jim had me slowly open that air bleed up a little at a time until the sputter cleared up.

Now if you have a newer Super E with the adjustable bleeder then you could just change it. I'm on the road today otherwise I would post up pictures, but Jim can explain it better then I can anyhow.

[HarmBMW]

@DoomBuggy, yes that’s my experience since changing the main jet from 76 to 72. It has a little bit power for 1-2 seconds and than it sputters. With the 76 jet it didn’t have even that power, so getting closer.

I have the old version S&S Super E. Plugs are black when I checked them.

[DoomBuggy]

Here is a link to my thread on the issue, follow at your own risk, lol.

https://www.chopcult.com/forum/showthread.php?t=56262

[docmel]

Check easy things first:

1. Running an inline gas filter? Most off the shelfs can constrict fuel flow
2. Filthy petcock screen filter or filthy pet cock? Un beleivable how gummed up a pet cock or its in tank screen filter can be
3. Adjust the accel pump as per SS intructions?