Bike stalls in High Elevation? Advice?

jasnusc · #1 (**permalink**) 02-16-2009, 08:10 PM

31 / 74 Jets
S&S Super E Carb
S&S 100" Engine

Took a ride up to the local mountains ( 6500 ft ) and my bike ran like shit! It died twice and I had to keep the rpms up to keep it running at signals.

My buddies who also have choppers didnt have as much of a problem. They complained their bikes were running shitty but they werent dying on them.

Whats my problem?

I dont know that my jetting is perfect but it runs really good at 1000 ft where I live.

jasnusc · #2 (**permalink**) 02-16-2009, 08:12 PM

I know its going to run allot different at 6500 ft but Im trying to figure out why mine wont run at all and all my buddies just complain about horse power loss.

Based on that info does that mean i have the wrong jets in my carb now and just dont realize it?

tfstrum · #3 (**permalink**) 02-16-2009, 08:58 PM

Were you the only guy with a 100", the E carb, the type of pipes you're running? There's probably a couple of things that made your bike die.
http://books.google.com/books?id=aSK...esult#PPA45,M1

Merlin Hawaii · #4 (**permalink**) 02-16-2009, 09:20 PM

As you go up in elevation, the air becomes less dense

And your A/F mixture becomes richer,

So you have to lean it out,

By turning the A/F screw IN (You shouldn't need to rejet unless you're going to STAY at the higher elevation)

It could be that you were already running a bit rich to begin with, and the rise in elevation compounded that

Now that you're back home - you can go through the tuning sequence to find out where you are

.

golfish · #5 (**permalink**) 02-17-2009, 02:54 PM

Quote:

Originally Posted by jasnusc

31 / 74 Jets
S&S Super E Carb
S&S 100" Engine

jasnusc,
That seems rich to me. I think I'm running 29.5/70 (I think its a 70)...but I'm running a G carb body. On the E I ran 29.5\69 with open pipes.

jasnusc · #6 (**permalink**) 02-17-2009, 03:02 PM

Quote:

Originally Posted by golfish

jasnusc,
That seems rich to me. I think I'm running 29.5/70 (I think its a 70)...but I'm running a G carb body. On the E I ran 29.5\69 with open pipes.

I suck at this jetting stuff!... I changed them several times, went through the S&S setup instructions and it seems like it runs fine.

But I want it to be as good as it can be!

Looks like its time to mess with them again.

Merlin Hawaii · #7 (**permalink**) 02-17-2009, 03:16 PM

Quote:

Originally Posted by jasnusc

I suck at this jetting stuff!... I changed them several times, went through the S&S setup instructions and it seems like it runs fine.

But I want it to be as good as it can be!

Looks like its time to mess with them again.

You just have to get in the right mindset

It's not rocket science

But pure mechanics

Action = reaction. A specific action will have a predictable outcome

But you need to take a systematic, methodical approach - and not make random changes, hoping they'll work

The carb (or EFI) will tell you what it wants

.

jasnusc · #8 (**permalink**) 02-17-2009, 03:51 PM

Quote:

Originally Posted by Merlin Hawaii

You just have to get in the right mindset

It's not rocket science

But pure mechanics

Action = reaction. A specific action will have a predictable outcome

But you need to take a systematic, methodical approach - and not make random changes, hoping they'll work

The carb (or EFI) will tell you what it wants

.

Yeah..

Its just a matter of lack of experience.

S&S recomended .295 or 31 with 72 or 74 when I told them what I was running.

Dont notice any difference between .295 and 31 or between 72 and 74.

So I just stuck with 31-74 not knowing the difference.

Follwed all the Setup Instructions and have been riding ever since assuming its fine.

jasnusc · #9 (**permalink**) 02-17-2009, 03:57 PM

Actually with the .295 I was having a problem where my bike would Cough through the Carb and stall when i would start to take off from a signal.

In an old post I was asking for advice and Scary mentioned I should try .31 even though he thought it sounded a little big and since I switched to that it doesnt to it anymore.

Merlin Hawaii · #10 (**permalink**) 02-17-2009, 04:23 PM

Quote:

Originally Posted by jasnusc

Actually with the .295 I was having a problem where my bike would Cough through the Carb and stall when i would start to take off from a signal.

In an old post I was asking for advice and Scary mentioned I should try .31 even though he thought it sounded a little big and since I switched to that it doesnt to it anymore.

Scary is the man for Super E and G

golfish · #11 (**permalink**) 02-17-2009, 05:09 PM

Quote:

Originally Posted by jasnusc

Actually with the .295 I was having a problem where my bike would Cough through the Carb and stall when i would start to take off from a signal.

Mine will do that when I hit a lot of traffic or lights...basically when it gets hot.

Merlin Hawaii · #12 (**permalink**) 02-17-2009, 06:25 PM

Quote:

Originally Posted by jasnusc

Actually with the .295 I was having a problem where my bike would Cough through the Carb and stall when i would start to take off from a signal.

To me, that indicates an accelerator pump adjustment

.

MechWerks · #13 (**permalink**) 02-17-2009, 06:37 PM

Also go over the float level setting carefully. Too many people ignore the float level like it is some simply on/off valve for gas from the tank. The gas level in the carb is set by the float height and how high the fuel sets in various circuits. As normal air flow through the carb pulls at various circuits and ports, it is apparent how a change in height determines how it can be either easier or more difficult to meter off fuel.

One of the more lost engine tuning arts is vacuum readings in the manifold. If you have ever played with adjustments while watching manifold vacuum, you get a feel for how one thing affects another. Mechanical timing, valve timing, spark curves and carb settings all change manifold vacuum. Since it is outside air pressure that pushes air through an engine the various effects on that pressure have significant impact on engine performance.

Similar engines are not the same and changes to outside parts further separate differences.

A hot engine can cause the intake air to expand, basically similar to going to altitude and reducing air mass, causing the A/F mix to go rich. Plugs foul at idle causing a stall. On the other end of th spectrum, opening the throttle from idle causes an air increase and a lean condition, the accelerator pump throw raw gas on the problem and usually prevents the lean condition. So a high rich or lean from incorrect accel pump setup can cause a bog or stall.

As Merlin Hawaii pointed out, this stuff isn't difficult, just attention to detail, and methodical changes and noted results. Random changes without assessment only leads to confusion and upsets the synergy needed in an engine assembly.

One passing thought....engine manufacturers will always recommend rich jet setups as a start...reduces the liabilty going rich instead of lean and burning an engine. And rich IS the correct starting point.

MechWerks · #14 (**permalink**) 02-17-2009, 06:38 PM

I gotta type faster...beat me to the accel pump.

MAKO6 · #15 (**permalink**) 02-18-2009, 01:50 AM

I read you are using a G body with undersized jets. On a 100" motor I would think that Bernouli Law comes into effect here (do a web search for a full description) , with the oversize bore of the G series. Resonance and inertia in the carb bore are reduced resulting in decreased flow (vacum).. Fuel is metered through the main jet based on HG (inches) of vacume present in the flow chamber. When an oversized carb body is used, the vacum is reduced given that the displacement of the cylinders is fixed (in your case) at 100".

Typically this can be resolved with a modified cam allowing a larger volume of intake per stroke. Rejetting to the "best" size will help, but either sizing the carb to the motor or modifying a plenum restricter to the G series carb I believe would give better results.