Sumping issue theory
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Road Warrior
Joined: Jul 2007
Posts: 1,362
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From: georgetown ky
Sumping issue theory
could it be possible that running them at to low a rpm could cause it?
i.e. 60 in 6th gear.
if Im cruising along I run 60 in 5th bout 2500 instead of closer to 2000 in 6th
fot 60 mph?
just s thought
i see the guys with a 117 are having a lot of trouble
maybe if a 117 was running 60 mph the rpm should be up closer to 2750 or 3000 rpms?
i couldnt give a accurate rpm as I havent ridden on.
is this possible?
i.e. 60 in 6th gear.
if Im cruising along I run 60 in 5th bout 2500 instead of closer to 2000 in 6th
fot 60 mph?
just s thought
i see the guys with a 117 are having a lot of trouble
maybe if a 117 was running 60 mph the rpm should be up closer to 2750 or 3000 rpms?
i couldnt give a accurate rpm as I havent ridden on.
is this possible?
Banned
Joined: Jan 2017
Posts: 17,008
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From: in a cave at the foothills
What little I know on sumping I have read here. Dealers, I mean honest ones that I know have dealt with next to none of it. I have only read about it here. And the ones that have experienced it, from what I understand at least, have heavily modified engines. That being said I doubt lugging has anything to do with it. Just my observation.
Grand HDF Member
Joined: Nov 2017
Posts: 4,251
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From: Texas
Harley's service bulletin identified high-RPM operation as a condition that could lead to sumping; they didn't say anything about low-RPM operation. That said, lugging is bad for many reasons, but sumping is probably not one of them.
The Stage 4 sumping issues may be directly related to high-RPM operation; a Stage 4 build doesn't really show it's improvements until about 4500 RPM and higher; accordingly, I suspect Stage 4 owners spend more time in that upper RPM band than most other M8 riders do, and since high RPM has been said to be a precondition for when a bike does sump, that may explain why the Stage 4 bikes seem to experience the situation more frequently than other engine configurations. Stage 3's power curve is also biased towards higher RPMs, and the original TSB specifically called out Stage 3 and 4 builds as being susceptible, although that was later revised to include all M8 engines.
The Stage 4 sumping issues may be directly related to high-RPM operation; a Stage 4 build doesn't really show it's improvements until about 4500 RPM and higher; accordingly, I suspect Stage 4 owners spend more time in that upper RPM band than most other M8 riders do, and since high RPM has been said to be a precondition for when a bike does sump, that may explain why the Stage 4 bikes seem to experience the situation more frequently than other engine configurations. Stage 3's power curve is also biased towards higher RPMs, and the original TSB specifically called out Stage 3 and 4 builds as being susceptible, although that was later revised to include all M8 engines.
Outstanding HDF Member
Joined: Oct 2009
Posts: 2,791
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From: Smalltown,USA
Like I posted we have several other threads on sumping.
Last edited by tbob; Jul 15, 2018 at 07:19 AM.
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