Magnum XK Clutch Slip (?) Question

Hey all,

Did a lot of research on this and tried some things out but I'm still having an issue.

Here is my current setup:

78 Magnum XK

E50 2HP

15mm Bing (needle on lowest (richest) clip with a 2.17 atomizer and 78 jet)

MLM intake

Metal mesh "Ken Roff" Filter

MLM People's Pipe (larger header)

E50 Jammer v6.4 with weakest springs (soaked in Royal Purple Max ATF)

Royal Purple Max ATF (stock fill level)

16x40 gears

No air leaks or related issues.

My problem is that - from a stop - when I twist the throttle the RPMs rise quickly but the ped doesn't accelerate at a comparable speed. I think the clutch is slipping too much. If I pedal as I roll on the throttle it "catches" and accelerates better. Without peddling the moped struggles / slowly gets to 10mph or so, RPMs then drop and I'm assuming the clutch engages and accelerates as anticipated all the way through the rest of the range up to about 40mph.

Anyone have any ideas? I'm thinking its ATF related but haven't tried any other fluids yet.

Thanks everyone!

Andrew (edited)

Re: Magnum XK Clutch Slip (?) Question

Probably Fred /

With your set up a stock clutch with the kickstart springs and maybe a few holes in the shoes to lighten them would be about perfect,

The jammer clutch is more suitable to put high output kits

Re: Magnum XK Clutch Slip (?) Question

Hey Ken,

I had similar issues like I'm having now with the stock 2 shoe clutch and stiffer springs. I assumed that having the jammer clutch would alleviate it with the increased friction material and it having 3 pads. Do you think there is anything I can do to the jammer to help with the low-end issue? I'd like to use what I currently have if possible.

Thanks as always!


Re: Magnum XK Clutch Slip (?) Question

Probably Fred /

Change springs to lighter to tune your clutch to your liking

Re: Magnum XK Clutch Slip (?) Question

According to treats the weakest springs come pre-installed on the Jammer. Any other suggestions? Anyone?

Re: Magnum XK Clutch Slip (?) Question

Little update on this.

Drained the Royal Purple Max ATF and put regular Type F in to see if that would help the clutch engage earlier. No real noticeable improvements from a stop.

When on the stand the clutch wont start to engage until at least 2600 RPM. When I'm on the ped and I give it 1/4 throttle or so it slips until around 4500-5000 RPM, starts to catch, and then the RPMs drop off as the clutch engages.

Anyone have any thoughts ?

Had a similar issue on my stock 2 shoe clutch but another member suggested I get an OEM 3 shoe with some blue springs.

Thanks all!


Re: Magnum XK Clutch Slip (?) Question

Probably Fred /

With a performance pipe 5k+ rpm is what you want because that’s pretty much where most mild pipes starts to hit the powerband, some pipes don’t hit the power band until 8,000 RPM

I don’t think you really understand what clutch tuning is about, basically your bike doesn’t move until it engages which you want when the pipe hits! You can’t have it both ways on a one speed,

It’s just like a high stall torque converter on a auto tranny drag car,

you basically don’t move or have any power until you’re at your stall speed so if you have a 5000 RPM stall speed on the torque converter your car is going to scream at the 5,000 rpm the entire time which you want to keep into into the power,

You may not be tuned perfect with your carburetor either but having Low RPM tuned clutch you’re going to stall on a hill and you will have to pedal up it and your takeoff will be boggy until you get enough speed for the pipe to hit

Re: Magnum XK Clutch Slip (?) Question

Hey Ken,

I understand what you are getting at with the stall speeds. My only concern is that I feel like my low-end is crap due to the excessive slipping, and could be better. I also get what you're saying about not having it all with a single speed clutch / motor. I'm just concerned about revving so high off the line and if its in fact a problem. If all is normal and its just the way it is I guess i'll just apply more throttle from a stop.

But for comparison, I have an E50 Maxi with the same carb, intake, filter, similar gearing, Estoril pipe and a stock 3 shoe clutch with kickstart springs and it grabs around 2,800 RPM off the line and runs strong up to about 40mph as well. I just don't know if my issue with my Magnum is clutch related or because the pipe I have has a longer header and hits later in the RPM range or what.

Another update:

Took the OEM 3 shoe clutch with kickstart springs out of my Maxi and put it in the Magnum and gave it a try. Bogs off the line.. Might try putting the blue springs in there tomorrow to see if it will catch / run better off the line without needing to pedal.

Re: Magnum XK Clutch Slip (?) Question

Probably Fred /

Pipes matter, Estoril pipe has way more low end and is my favorite pipe (derestricted version)

I run 4 of them

You have to bend the header to fit a angle magnum cylinder

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