Stutter attempting go over 3k rpm and tachometer all over the place (may be related?)

[No H2O]

Those pipes shouldn't be causing the problem. It may be something you will have to live with, unless you want spend more money on a thunderjet. The s&s carbs are good carbs, but they do have their shortcomings.

It looks like those thunderjets are like $70 with free shipping.
Can't be that hard to put in, or can they?

One other thing I noticed is this breather dohickey emanating from the rear cyclinder. It wasn't on the 107 and the mechanic said the 117 needed it, forgot the rationale. Could that be contributing to this issue?

 

[mleach72]

That is the rear cylinder breather. It is different on the 117's. That line used to go to the air cleaner. Someone put a small filter on it, which is fine, but they got rid of the one way check valve. The front cylinder line is a high vacuum line to the manifold. This brings up an interesting question. Without that check valve, is the manifold sucking air through the engine through the rear cylinder breather? If so, that would create a major intake leak, which would create carb problems. Anyone know?

 

[mleach72]

 

[Sven]

Air intake leak is lean so it will stall. Bike stall at idle? No. Then no air leaks.

 

[mleach72]

Air intake leak is lean so it will stall. Bike stall at idle? No. Then no air leaks.

Not necessarily. I had a manifold leak, and I (unknowingly) adjusted the carb to compensate for the leak. The problem showed it's face elsewhere, but it idled just fine. Once I got the leak fixed, I had to readjust my carb.

 

[mleach72]

It looks like those thunderjets are like $70 with free shipping.
Can't be that hard to put in, or can they?

One other thing I noticed is this breather dohickey emanating from the rear cyclinder. It wasn't on the 107 and the mechanic said the 117 needed it, forgot the rationale. Could that be contributing to this issue?View attachment 69693

You may have fixed your own problem. Hopefully, someone chimes in and gives their opinion. If it is a leak, that would explain the excessive decel pop.

 

[No H2O]

Air intake leak is lean so it will stall. Bike stall at idle? No. Then no air leaks.

No stalling at idle, ever.


mleach72 is your's a 117 and if so, what hose do you have connected to your rear cylinder breather?

 

[mleach72]

No stalling at idle, ever.


mleach72 is your's a 117 and if so, what hose do you have connected to your rear cylinder breather?

Yes, I have a 117. I have a forcewinder ac, but the breather goes to the ac like the stock set up.

 

[No H2O]

S&S says I need to upgrade my 40,000 main-jet-air-bleed to a 60,000 main-jet-air-bleed

 

[mleach72]

That's a possibility, but an air bleed change normally isn't necessary unless you are running crappy pipes. I still think the missing check valve is causing a vacuum leak. A vacuum leak would produce symptoms like you are experiencing. The valve was put in there for a reason. Try this: Take that filter off of the breather hose and start the bike. Check the hose to see if there is a vacuum. Rev the engine a little when you check it. If there is a vacuum in the breather hose, I am pretty sure this is the source of your problems.

 

[No H2O]

That's a possibility, but an air bleed change normally isn't necessary unless you are running crappy pipes. I still think the missing check valve is causing a vacuum leak. A vacuum leak would produce symptoms like you are experiencing. The valve was put in there for a reason. Try this: Take that filter off of the breather hose and start the bike. Check the hose to see if there is a vacuum. Rev the engine a little when you check it. If there is a vacuum in the breather hose, I am pretty sure this is the source of your problems.

ok so if I take off the mini breather filter dohickey and rev the bike with my finger at the tip of the open hose and if it tries to suck my finger in then I have a vacuum leak?

the question remains though wouldn't that cause a more random sputtering rather than a reproducible sputter at 3k RPMs?

 

[mleach72]

ok so if I take off the mini breather filter dohickey and rev the bike with my finger at the tip of the open hose and if it tries to suck my finger in then I have a vacuum leak?

Yep. You would with no check valve.

 

[mleach72]

ok so if I take off the mini breather filter dohickey and rev the bike with my finger at the tip of the open hose and if it tries to suck my finger in then I have a vacuum leak?

the question remains though wouldn't that cause a more random sputtering rather than a reproducible sputter at 3k RPMs?

Vacuum leaks are funny. They will cause lean spots in the rpm range. Usually reproducible.

 

[Sven]

Crankcase vs. Atmosphere: Think of the piston being at top dead center, Under that piston is air about to be transferred over to the other cylinder that is at bottom dead center. That is the sucking pulse, then stops, then pushes it in a newton kind of effect. A crank could care less about air having an effect on driveability. Crankcase is in a constant battle of maintaining 14.7 psi. Air passes the rings and down the cylinder, adds more air to the crankcase, so it pushes out the breather, then newton matching the suck back in.

Carb vs. Vacuum: The battle with 14.7 on the outside of the engine is; whoever enters the chamber sooner to neutralize that vacuum pull of the piston going down on the intake stroke. Air leak is after the carb, meaning, think of E finding the shortest path. So as the vac is being neutralized, the carb's heat block spacer has two sides for a leak. The intake manifold has two leaks past the carb jet at their mounting points. Where that vac would pull fuel out, the leak is throwing off the fuel to air ratio and cause a stall, a sputter, or hard starting exposes those variables to check off the list.

Tail vs. Chasing one:
Every time I got burnt rolling a bike up on the rack was to never check compression first. Threw all those parts at it and have to tell the owner it's low on compression. And I would check compression on all those bikes before this one. The one bike I didn't check first. What are the odds.

 

[Brent Herridge]

Mark,

I had similar problems that started after I messed with the air cleaner. I had minimal other symptoms before that, but after I cleaned it I must've had an air leak, 'cuz it was doing exactly what you describe.

Kinda long, but the whole saga is here - https://www.bigdogbiker.com/threads/carb-adjustment-still-not-right.84974/

Bottom line - I had to re-jet it to fix what the last shop did to it. Runs like a champ now. And popping on decel was MUCH worse when it was too lean, before the re-jet.

 

[No H2O]

Drove it to the mechanics shop, he detached the breather hose emanating from the front cylinder from the carb port and wrapped it around and told me to ride and see if things improve.
The theory being that the air being output from the front cylinder is going into the carb and adding more air into the air/fuel mix thereby creating a leaner mixture.
As I rode away on the highway it sputtered just as before but then it was fine for the rest of the 15 minute ride.
Next day it had one initial sputter but then was fine for the rest of the 30 minute ride.
Since then the sputters have been much smaller and less frequent than before the hose detachment.
So overall I'd say it's better but not 100% solved

 

[mleach72]

Drove it to the mechanics shop, he detached the breather hose emanating from the front cylinder from the carb port and wrapped it around and told me to ride and see if things improve.
The theory being that the air being output from the front cylinder is going into the carb and adding more air into the air/fuel mix thereby creating a leaner mixture.
As I rode away on the highway it sputtered just as before but then it was fine for the rest of the 15 minute ride.
Next day it had one initial sputter but then was fine for the rest of the 30 minute ride.
Since then the sputters have been much smaller and less frequent than before the hose detachment.
So overall I'd say it's better but not 100% solved
View attachment 70430

Capping off the vacuum port on the carb does the same thing as replacing the check valve in the rear breather. In the service manual, they claim running a vacuum in the engine is beneficial because it cuts down on oil mist in the crankcase and provides a better piston ring to cylinder seal. It should run ok either way though. Did you adjust your carb? At a minimum, you should have adjusted the idle mixture.

 

[No H2O]

Capping off the vacuum port on the carb does the same thing as replacing the check valve in the rear breather. In the service manual, they claim running a vacuum in the engine is beneficial because it cuts down on oil mist in the crankcase and provides a better piston ring to cylinder seal. It should run ok either way though. Did you adjust your carb? At a minimum, you should have adjusted the idle mixture.

I only adjusted the idle speed since, after the hose removal, the low idle was making the tachometer flash red and yellow until i opened the throttle a tad.

How should I adjust the gold "+" idle mixture?

 

[Jersey Big Mike]

If you haven't previously, since this made a difference, I would replace that hose with a new one and see if it stays as it is now or gets better or worse.

 

[LHS]

I might as well throw my two cents in there .LOL
Get rid of that wonky little air breather - put the one-way check valve back in and get another piece of hose and run it over to the air cleaner were belongs - put the other hose from the front cylinder back on the carburetor plate where it belongs.
Re-jet the carburetor and adjust it and your problem will more than likely be solved.

117 & super G carb