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Judson 40-Horse Rebuild - 83mm/Cam/Rocker Upgrade
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kostya.lyt
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PostPosted: Fri Dec 31, 2010 5:08 pm    Post subject: Judson 40-Horse Rebuild - 83mm/Cam/Rocker Upgrade Reply with quote

I'm going to be "freshening" up a buddy's Judson supercharged 40-horse. I'm picking up a set of 83mm P&Cs for it, as well as a really mild cam and some 1.1 rockers. What cam should I get for it? I'm thinking an Engle 100 or equivalent. Also, what else do I need to take into account in terms of the supercharger? Carb jetting? I just picked up an LM-1 to play with.

Thanks in advance for any advice!
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glutamodo Premium Member
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PostPosted: Fri Dec 31, 2010 8:00 pm    Post subject: Reply with quote

What size is the engine now? I don't know if it's true, but in the past I've heard that combining a Judson with the big bore kit is not a good combination - the extra displacement isn't matched to the boost you get out of the supercharger.
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kostya.lyt
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PostPosted: Tue Jan 04, 2011 10:51 am    Post subject: Reply with quote

It's currently a bone stock 40-horse with just the Judson.

Is it lack of volume due to the supercharger, or do they usually run poorly due to incorrect carb adjustment?
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glutamodo Premium Member
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PostPosted: Tue Jan 04, 2011 10:56 am    Post subject: Reply with quote

From what I was told, the volume doesn't match with the big bore.
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John Moxon Premium Member
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PostPosted: Wed Jan 05, 2011 5:38 am    Post subject: Reply with quote

If you run it on a big bore 1385cc and you get the jetting right it will still give you a modest gain in performance.

Most problems arise when the owner tries to compensate for an apparent lack of boost pressure by overdriving the Judson. Their theory is you need to spin the Judson faster to make up for the extra 200ccs chamber capacity. However the downside of this is spinning the Judson faster creates more heat through more friction of the vanes in contact with the chamber wall. The heat-sink fins on the blower body aren't large enough to channel away the extra heat quickly enough and the temperature climbs accumulatively til meltdown.

Jetting? PM "Peppe" here, he's experimented with a Judson on a 1385 so could have a few things of use to you.
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kostya.lyt
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PostPosted: Wed Jan 05, 2011 7:06 am    Post subject: Reply with quote

Thanks John! I'll make sure and send him a PM.
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PEPPE
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PostPosted: Sun Oct 29, 2017 1:43 am    Post subject: Re: Judson 40-Horse Rebuild - 83mm/Cam/Rocker Upgrade Reply with quote

i used a 2231 CB cam, too much overlap and fuel economy goes down. remember that the supercharger extends the RPM capabilities also with stock cam.
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Snydr
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PostPosted: Sun Oct 29, 2017 10:30 pm    Post subject: Re: Judson 40-Horse Rebuild - 83mm/Cam/Rocker Upgrade Reply with quote

Thanks Peppe! I guess I’m to blame for this thread getting ressurected; I followed the advice and reached out (PM) to Peppe about jetting. Good info but ended up not being as applicable to running a Judson on a 40hp 1385 Big Bore.

I get the over driving and over heating on the Judson to get more into the larger cylinders. But what if one were to just install the Judson on a 1385 without modification to the Judson’s gearing/rpm? Would there be a risk of damaging anything? It would run as normal, just with lesser gains in performance?
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thomas.
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PostPosted: Wed Nov 01, 2017 12:34 am    Post subject: Re: Judson 40-Horse Rebuild - 83mm/Cam/Rocker Upgrade Reply with quote

It would still turn at the same speed so you can run it on your 1385. It will just make less boost. When my 40hp was a 1200 I was getting around 6 pounds boost when I was running a Judson. When I rebuilt the engine and went to the larger 1385 it struggled to make 4 pounds. closer to 3 really. I also tried to spin it faster. It didn't work for me. It made the cast iron Judson get much hotter and with that came the detonation. Photo from gallery when I had it installed. I used two crank pulleys together with a two inch longer belt.
There is a plug on the bottom of your Judson . If you take the plug out you can replace it with a fitting for a boost gauge if you didn't know.
Also if you are not aware. The throttle linkage is set up for a 28 pict series carb. If you want to run the 30 it needs welded and re-sized. There was a thread just recently about this. If you weld you can do it yourself. If not George Folchi is the go to guy.

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