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4 Posts
Discussion Starter #1
The engine of my custom bike (Screaming Eagle 103) stalls every time I fully open the throttle, regardless of the selected gear and the speed at which the bike is going. Meaning the engine starts spluttering and stops delivering power and acceleration. By just slightly releasing the throttle the engine goes back to normal operating mode. Except when at full throttle, the engine otherwise runs smoothly.
I have checked the spark plugs, coil (ACCEL Twin Cam Super Coil with 0.5 Ohm primary resistance) and wires.
The carburetor (Mikuni HSR 45) has been recently replaced hence should not cause the problem.
Any suggestion would be greatly appreciated.

Premium Member
1947 FL 1972 XLCH 1989 FLST
20 Posts
Is it immediate or does it take a few seconds 10-15 enough to empty float bowl. Clogged fuel filter, fuel line separating internally (de-laminating), easy to eliminate these. Valve float from broken spring, not so easy. Just guessing though!

Super Moderator
20,413 Posts
You need to figure out if its fuel or spark. Take it out an let it bog down, then pull the clutch and hit the kill switch before it catch up and runs again. Then see if the plug reads wet or dry.

By description, it sounds like its not getting enough fuel.

44 Posts
Roll-off Method:
This method is a good way to get
the main jet either correct or within
one size of correct. It is based on the
fact that that as the throttle is closed,
the air/fuel mixture richens momentarily.
This normal enrichening can
be used as a diagnostic tool.
The test is started with the engine
running at an rpm high enough to
ensure that it is “on the cam.”
Open the throttle fully and let the
engine pull for several seconds.
Then, quickly close the throttle to
about the 7/8ths position.
If the engine seems to gain power,
the main jet is too small (lean). Fit a
larger jet.
If the engine hesitates as the
throttle is rolled off, the main jet is
too large. Fit a smaller one.
When the main jet is correct, the
engine will continue to run smoothly
and evenly as the throttle is closed.
Note that a main jet that is far too
rich or lean may cause the engine to
misfire at full throttle.
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