Fullauto, JS short stroke build pics

gripper said:

I was wondering what the red coating is inside the crankcases?

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Glyptal paint, maybe?

Ken

Painting insides is old school method of sealing porous cases &or to provide faster thinner oil layer drain off so oil don't heat as much - as this oil layer does nothing to help cool the cases.

milfordite said:

Herb is pretty good at figuring things out. Years ago he was running some huge carbs on his racer that flew in the face of convention, but they worked!

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I have a 650ss that Herb pulled out of a scrapyard then donated to the Ontario Vintage Motorcycle Association. They restored it then raffled it off. A few years later it dropped a valve and Herb got the bike back for repair. Herb told me that while he had the head off for the repair he couldn't resist reshaping the intake ports "the way we do them for the Commando race engines" After reassembly he noticed that the clutch, which held fine before the porting, would start to slip when the motor hit about 4 k rpm. Job well done Herb! :mrgreen:
Years later I bought the bike and noticed the clutch slip. I replaced plates, tried running it dry, replaced springs, but it simply would not hold. Finally I installed a Newby belt drive and dry clutch. With the springs set for moderate lever pull, even that had some slippage when the engine hit 4k rpm.
I tightened the springs down to the point that the lever pull is just tolerable and now it just holds with the Newby dry setup.
For 650ccs , that little bike packs a helluva wallop when it hits the powerband.
Herb definitely knows how to get power out of a Norton twin.

Glen

Doug MacRae said:

Hey John; the ports are 35mm and the carbs will be same 38mm Mikunis that we used before. However, when measured exactly inside, those carbs are only 37.5 mm- Herb has some that he bored out to 39 so we will try the 38's and then see if the 39's do any better on the dyno. Herb says that with the Fullauto head, there is loads of material around the ports so going to 35mm was no problem, he could go even bigger- with a stock head you would probably be already broken through at 35mm.

Ken, Herb is using stock lifters with a 3" radius and the cam is a Megacycle SSS

Tom, we will be going to Stay Tuned but don't know when yet, stay posted

The port measuring tool shows exactly the same distance at both ends, a very simple tool that I am sure was around when the pyramids were built

-Doug

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Hi Doug,
I am running 36mm on the LSR 500. Just curious what main jet size you are using and needle you are running in your 38's? Did you have to change out the needle from the one that they were sent with?

Thank you,
Paul

Hey Paul. Just for you and anyone else who wants to run 38mm Mikunis, here are the specs of what we run for the 750;

Twin Mikuni 38 mm carbs-
slide- 2.5
needle- 6F9
needle jet- 166 Q-2
idle jet- 25
float needle- 3.3
main jet 250 (to start with)

I asked Herb to look up in his notes what he ran with twin 36mm carbs, here are the settings-

Twin 36mm carbs-
slide- 3.5
needle- 6DH4
needle jet- 159 Q-5
idle jet- 30
float needle- 3.5
main jet- 200 (to start with)

Herb did mention to me that at altitude on the salt flats this would have to be leaned out, especially the main jet and needle jet.
Mikuni do have a tuning chart that lists all the increments of needle jets etc.

Thank you Doug, very much appreciated from both you and Herb!
Keep us posted on the Dyno results.

Hello Doug, thank you very much for that.
Do you know if settings would be a lot different for a 850 (with PW3)?
All the Best,
Bruno

FWIW, I ran a pair of 38 mm Mikuni flat slides on the 920 in the ex-Jim Schmidt monoshock Norton racer back in the day, and used main jets from 250 to 270, depending on course and conditions. If I can find the rest of the notes, I'll post more details.

Ken

Hi Bruno- I would think that it would be a pretty close starting point for an 850. You would probably be a stock 828cc anyway and my '750' would be actually around 765cc, they are not too far off.