fine tuning advice

I cleaned up my carbs and its running beautifully, but i need to fine tune it. It runs strong up to about 6K and when it gets there it slightly flutters, just as if its not tuned exactly right, it sort of cuts in and out like my carbs are slightly off. Carbs are synched, but I think it may be an air/fuel adjustment. I have a 4-1 V&H with full baffle and stock air box. When at idle, when i blip the throttle, the bike hesitates, then revs up. Thats if you blip it fast. Does that indicate rich? Just need some advice! Thanks!

Did you rejet when you changed the pipe? How do your plugs look? White, black, brown? Your plug color will tell you it it's rich or lean. Black is rich, white is lean. YOu want them to be pretty nice even light brown in color.

I'll give the plugs a check. I shoulda just done that first. My minds all over the place.

I did not rejet. I had seen on here that with the V&H and a baffle with stock airbox that I may be able to get away with it

Also I set the air/fuel screws initially to 1.5 turns out

All the plugs appeared really clean except for one. The cylinder furthest left if sitting on the bike. It was extremely carbon fouled and somehow had a smaller gap on it then when i installed! So I took that plug out, and switched it with a clean one from the cylinder next to it. I also turned out the air screw another 1/2 turn or so and it made no difference. Plug came back coated in carbon after a 2 minute ride, still breaking up around 6K and higher. Any ideas?

freebyrd24 wrote:

All the plugs appeared really clean except for one. The cylinder furthest left if sitting on the bike. It was extremely carbon fouled and somehow had a smaller gap on it then when i installed! So I took that plug out, and switched it with a clean one from the cylinder next to it. I also turned out the air screw another 1/2 turn or so and it made no difference. Plug came back coated in carbon after a 2 minute ride, still breaking up around 6K and higher. Any ideas?

Would check service fuel level in #1 carb, using the clear plastic tube test. The level may be too high and causing excessively rich mixture.

Are the pilot adjustment screws located on the side or on the bottom?

Good Luck!

Hey Patton! How do you perform that test? And how would it be corrected? I'm not sure I understand that. The air screws are located on the bottom side of my carbs

freebyrd24 wrote:

...All the plugs appeared really clean except for one. The cylinder furthest left if sitting on the bike. It was extremely carbon fouled and somehow had a smaller gap on it then when i installed! So I took that plug out, and switched it with a clean one from the cylinder next to it. I also turned out the air screw another 1/2 turn or so and it made no difference. Plug came back coated in carbon after a 2 minute ride, still breaking up around 6K and higher. Any ideas?

Patton wrote:

...Would check service fuel level in #1 carb, using the clear plastic tube test. The level may be too high and causing excessively rich mixture....

freebyrd24 wrote:

...How do you perform that test? And how would it be corrected?...

It may take longer to read this post than to actually do the test. :lol:

IMO, this test is superior to the upside-down while disassembled-on-the-bench by-guess and by-golly dry measurement method which may get in the ball park but often misses the mark. (But admittedly, some folks do in fact report achieving consistent and accurate results from using the upside down dry measurement method.)

Here's how to do the "clear plastic tube test" which checks the real-world float bowl service fuel level as will exist under actual operating conditions.

The test may be done while the carbs are on the bike and with no disassembly required (other than removing the float bowl drain screw).
And may also be done with carbs on the bench (holding them level of course).

Do each carb separately, one at the time.

Carbs must remain still and level during the test.

Turn petcock off.
Fuel line remains attached to carbs.
Remove side-located drain-screw from float bowl,
which drains and empties the float bowl.
(May use a shop rag to catch and soak up outcoming fuel.)
Must begin the test with an empty float bowl.

Use short length of clear plastic tube.
Size of clear tube should match drain-screw hole.
Twist-thread clear plastic tube into drain-screw hole.
Some folks prefer using a small plastic barb-style connector fitted into the drain-screw hole with the clear tube attached to the connector, but it's really not necessary, because a little leakage doesn't invalidate the measurement.

Allow tube to loop naturally without kinking, and hold clear tube against top edge of float bowl.
Keep it steady - don't let it move.
Turn petcock on.
Watch level fill and rise up in clear tube as fuel fills float bowl.
Fuel level visible in tube matches fuel level inside float bowl.
Slight fuel leakage from the drain-screw hole is immaterial and won't invalidate the test.
Repeat test to double-check result.

Smoothbore carb has larger bottom-located drain-screw hole. So I use a tapered rubber grommet pressed or twist-threaded inside the drain-screw hole with the clear plastic tube fitted snugly inside the grommet.
Test procedure is otherwise the same.

There is a special tool available for fitment into side-located drain-screw holes. It is a relatively expensive thumb-screw affair with clear tube attached that threads
into the drain-screw hole.

With CV style carbs having a combined function bottom-located nipple for both over-flow and drain, just attach the clear plastic tube to the bottom located nipple.
This does not apply to carbs having separate independent
drain-screws and overflow nipples.
(Use the drain screws. Not the overflow nipples)

Refer to manual for specs as to ideal height of service fuel level.
A typical "correct" fuel level is slightly below the float bowl gasket,
say 1/8 inch or 2-4 mm.

Float height is a critical factor for proper carb function, and once set, should last a very long time without needing any re-adjustment.
Actually, the "testing" is usually much easier and quicker than the "adjustment" of the float tangs which requires removal of the float, bending the tang, replacing the float, and again testing the level.

During the float tang adjustment process, it's okay and faster to use only one float bowl screw when checking the level between adjustments.
(This time and effort saving tip is courtesy of wg).

As known, small adjustments to the tang make large
differences in the fuel level, so go with tiny increments.

Hopefully, all the fuel levels will be just fine, and without needing any adjustment, which eliminates from the list of suspects a too high (rich) or too low (lean) fuel level as the cause of an apparent fuel mixture issue.

Anyone thirsting for additional reading about this is encouraged to type clear plastic tube test into the above Search Forum box, and click on Go, which should result in a list of several threads where the topic is discussed, and with more detail about the tang adjustments.

Good Luck!

Ahh very nice! I'll try that tonight hopefully! I have the overflow nipple on the bottom, and a drain screw for the float bowl on vacuum operated carbs. There is no "off" for my carbs, so do I just drain while not running and then to refill do i just start it up to get fuel flowing in?

freebyrd24 wrote:

Ahh very nice! I'll try that tonight hopefully! I have the overflow nipple on the bottom, and a drain screw for the float bowl on vacuum operated carbs. There is no "off" for my carbs, so do I just drain while not running and then to refill do i just start it up to get fuel flowing in?

Use the drain screw hole.

Engine must be OFF for the test.

With engine off, vacuum style (diaphram) petcock is supposedly unable to pass any fuel except when in PRI (prime) position. So just assure it's not in PRI position.

When all setup with the clear tube being held firmly in place alongside the floatbowl, and ready to refill the empty floatbowl, turn petcock to PRI position, and watch as fuel level rises inside the clear tube.

Good Luck!

Excellent! Shall try that! But won't the carbs almost need to come off to adjust the tang? Or you think it could be done on the bike? I'm almost thinking to just go ahead and take them off and set up a system on a bench

freebyrd24 wrote:

...won't the carbs almost need to come off to adjust the tang?...

Yes. Carbs on the bench.
Remove float bowl, float pivot pin, and float.
Carefully holding float in hand, ever so gently bend the tang very slightly in the desired direction.
Then reassemble and re-test fuel level while carbs are still on the bench.
Repeat tang adjustment as required to attain correct fuel level.

Because only #1 plug was sooty, could opt to check fuel level in #1 carb before removing carbs from the bike. Fuel levels in #2/3/4 may be okay, but would check them also just to be sure. Actually, the test is easy with carbs still mounted as usual on the bike, so long as they are level (which is easier when using a centerstand).

If the fuel levels are within specs, should first assure all non-carb components are up to snuff (compression, valve clearances, battery, ignition, good quality properly timed spark, ample clean fuel supply, clean air filter, etc., etc.) before blaming the carbs.

Remember -- even perfect as-new carbs can't compensate and should not be expected to compensate for deficiencies in other areas.

Good Luck!