MkIII High Compression, Will It Start?

phil yates · May 26, 2014

baz said:
if your going to fit a mikuni i would go for a TM40 pumper its one of the best mods i have done on my commando you have to cut some of the gusset away on the frame but will give you one sweet running bike ,i have tried a brand new pair of mk1 amal 32s a 32mm CV mikuni a 34mm VM mikuni and a 36mm VM mikuni but the TM40 flatslide pumper gets my commando moving the way i like it between 3000rpm and 7000rpm but it will rev past 7500revs if i let it and with a solid tickover ,,,,,,,,,,,baz

Thanks baz
That sounds very impressive performance wise. I've been very happy with the two 34mm round slide Mikunis I've used. The pumper sounds real good. I'll discuss that with Don Hoff, the builder in Iowa. Thanks for the info.

Phil

phil yates · May 26, 2014

phil yates said:
baz said:

if your going to fit a mikuni i would go for a TM40 pumper its one of the best mods i have done on my commando you have to cut some of the gusset away on the frame but will give you one sweet running bike ,i have tried a brand new pair of mk1 amal 32s a 32mm CV mikuni a 34mm VM mikuni and a 36mm VM mikuni but the TM40 flatslide pumper gets my commando moving the way i like it between 3000rpm and 7000rpm but it will rev past 7500revs if i let it and with a solid tickover ,,,,,,,,,,,baz

Click to expand...

Thanks baz
That sounds very impressive performance wise. I've been very happy with the two 34mm round slide Mikunis I've used. The pumper sounds real good. I'll discuss that with Don Hoff, the builder in Iowa. Thanks for the info.

Phil

Just a foot note.
The only trouble I've experienced with BOTH Mikunis (which is odd because no one else has, that I know of) is sticking slides due modern "dry" fuels. At first I didn't know what was causing the issue. But finally, adding a slosh of upper cylinder lubricant to the fuel tank before refuelling completely solved the problem. Bit of a hassle I guess, carrying such on long trips, but these days I'm a one day trip man only. I keep the UCL at home, and slosh up (like at the pub) before heading for the refuelling port (gas station).

pete.v · May 26, 2014

phil yates said:
[Just a foot note.
The only trouble I've experienced with BOTH Mikunis (which is odd because no one else has, that I know of) is sticking slides due modern "dry" fuels. At first I didn't know what was causing the issue. But finally, adding a slosh of upper cylinder lubricant to the fuel tank before refuelling completely solved the problem. Bit of a hassle I guess, carrying such on long trips, but these days I'm a one day trip man only. I keep the UCL at home, and slosh up (like at the pub) before heading for the refuelling port (gas station).

The slide springs are also a bit weak, along with the draw of the Norton causing them to stick open. Sort of a catch22 if you will.
Take the springs and give them a bit of a stretch, or I should say, have Jenny take the spring out and give them a bit of a stretch.

phil yates · May 26, 2014

pete.v said:
phil yates said:

[Just a foot note.
The only trouble I've experienced with BOTH Mikunis (which is odd because no one else has, that I know of) is sticking slides due modern "dry" fuels. At first I didn't know what was causing the issue. But finally, adding a slosh of upper cylinder lubricant to the fuel tank before refuelling completely solved the problem. Bit of a hassle I guess, carrying such on long trips, but these days I'm a one day trip man only. I keep the UCL at home, and slosh up (like at the pub) before heading for the refuelling port (gas station).

Click to expand...

The slide springs are also a bit weak, along with the draw of the Norton causing them to stick open. Sort of a catch22 if you will.
Take the springs and give them a bit of a stretch, or I should say, have Jenny take the spring out and give them a bit of a stretch.

Yes Pete
A fair bit of suck on one carburettor. If I recall, originally with the problem (back about 93) I tried all sorts of things including a heavier return spring. I didn't like making the twist throttle heavier but regardless it didn't resolve the problem. I had that carburettor in pieces so many times it drove me crazy (and I never recovered) until like a light bulb going off, I slopped in the UCL. Have had 20 plus years of no problems since. Sadly though, never recovered mentally.

Ron L · May 26, 2014

Phil wrote: Is your 4 pole starter the original one upgraded? What exactly are 6 AWG cables? And what compression are you running?

My starter is a used HD field coil with a Norton drive end that has been modified to take a ball bearing. I have done a dozen or so 4 pole conversions over the last few years and find that good HD starter housings are getting hard to find, so I have been using new aftermarket Harley starters to build good Norton starters. 6 AWG (American Wire Gauge) is fine stranded welding cable. I use it to make my own starter cables. It is quite flexible and will carry plenty of current.

I don't know what my compression ratio is. I obtained the head after the work was done on it. It is milled until it just touches the valve seat of the oversize intake valves! :shock: I have cut valve reliefs in the piston tops, so that will lower it a touch, but it still takes a healthy kick.

The starter will turn it easily, but I have to be very careful about kickback and check the torque for the kickback mechanism every time I'm into the primary. The engine has been together for about 15 years and I have to admit I've destroyed 3 sprag clutches due to kickback. All were my own fault. Low battery, too tight on the kickback device, etc.

phil yates · May 26, 2014

Ron L said:
Phil wrote: Is your 4 pole starter the original one upgraded? What exactly are 6 AWG cables? And what compression are you running?

Click to expand...

My starter is a used HD field coil with a Norton drive end that has been modified to take a ball bearing. I have done a dozen or so 4 pole conversions over the last few years and find that good HD starter housings are getting hard to find, so I have been using new aftermarket Harley starters to build good Norton starters. 6 AWG (American Wire Gauge) is fine stranded welding cable. I use it to make my own starter cables. It is quite flexible and will carry plenty of current.

I don't know what my compression ratio is. I obtained the head after the work was done on it. It is milled until it just touches the valve seat of the oversize intake valves! :shock: I have cut valve reliefs in the piston tops, so that will lower it a touch, but it still takes a healthy kick.

The starter will turn it easily, but I have to be very careful about kickback and check the torque for the kickback mechanism every time I'm into the primary. The engine has been together for about 15 years and I have to admit I've destroyed 3 sprag clutches due to kickback. All were my own fault. Low battery, too tight on the kickback device, etc.

Thanks Ron
I never did know much about the upgrade of the starter. I'm told Tri Spark digital ignition does not kick back so I plan that path.
I won't wait for an Alton starter, best to upgrade what is already there. I'm pretty sure it will handle 9.5:1 compression.

Phil

phil yates · May 27, 2014

For any MkIII owners interested, Alton got back to me this evening with the information below. It will be too late coming for me but for others it might not be too far off next year.

Hello Phil,

Yes we are working on an MK3 upgrade in kit form.

It was to be released last year but we finally didn’t go into production for various reasons such as time and resources. We are currently looking again at our prototype to see how we can transform a successful prototype into a production model in order to be able to supply it at a good price without losing quality.

We hope to have a clear idea by the end of the year of a real and final release date.

Thanks for your interest.

Kind regards,

Beverley

MkIII High Compression, Will It Start?

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phil yates

pete.v

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Ron L

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