General Category > Bike Builds, Rebuilds And Restorations Only
1975 850T Survivor Project
cmice:
Past few weeks were busy sourcing and cleaning up a seat pan, and getting a custom seat made at Corbin which is about 1.5hrs away from me. https://www.corbin.com/ridein/index.shtml
You can tell which is the good seat pan, and which is the lost cause.
Metal Prep, then POR15 clear base coat, and then Duplicolor top-coat.
I won the prize for the oldest-foam of the year. After we discussed what I was looking for, the basic parameters of the seat, it took less than an hour to block out the basic seat shape which we refined from there. Tweaked the height, the position of the rear butt-stop, the scoop-out of the seat base and how the base transitioned into the sides. The foam was then completely taped up with masking tape, and we marked out a design (based on a design I liked). Colors, textures, stitching, piping, bottom turn, logo stitching. It was really a comprehensive process. We broke for lunch, and when I came back, viola - seat...
cmice:
The big update I have is I took him out for his first ride today. It was fantastic! I was going to grab some video but couldn't figure out how to mount the gopro so I said to-hell-with-it and I'll try to get something interesting later. Too many things to be worried about for a first ride anyway. So here's a photo of where we stand as of now...
Let's start with the good stuff...
First, the chassis and suspension are surprisingly good - even shockingly good. Nimble but really stable, no wobble, head-shake or frame flex. I didn't really push it, but it did go down some very not-straight roads and hills with less than ideal road surface in places. Front dampers were replaced with new but original spec dampers. The one nasty fork tube I replaced with a good used replacement. The rear shocks are originals and are pretty ok. I honestly didn't expect it to be so comfortable and capable, but it's just great.
Next, the engine pulls like a train. It's really surprising how smooth the torque delivery is, and the gearing really suits it well. I was keeping the revs and throttle opening on the modest side as we're still seating the rings and breaking in the engine. But I'm really looking forward to being able to open him up more. Also, turns out, I did know what I was doing when I put the gearbox back together along with the re-shimming process. No clunks or crashes, just nice and smooth. Most importantly, no leaks anywhere! Given this bike has been parked since 1985, I made it a point to replace every seal and o-ring I could get to.
Lastly, the look and the sound. It sounds great with the Dunstalls - maybe a little boomy, so we'll see over time whether they stay. But wow it's a symphony when you're out there. On a relatively short ride with a friend to a local pub, got a couple of comments and thumbs up on the "antique" bike and nearly as antique owner.
In terms of the to-do list, which I may or may not keep up here...
I replaced the right start-kill switch when the OEM shorted out to the bars (released the magic smoke). I picked this switch from a Tomos scooter because I like the look of it, and it should visually match a "Lego" style lemans left hand switch when (not if) my left switch dies. The Tomos switch is wired backwards from new, so kill is on and run is off. Irritating but maybe consider it an anti-theft device for now.
It's having a problem holding a steady idle. Symptoms are lean pops at idle, and high-then-falling idle like an air-leak. The dellorto rebuild kits I used didn't have the o-rings for the mixture screws and I thought I saw somewhere that they aren't important. I think they are, so I'll try putting them in and see if that solves it.
The alternator struggles to top the battery up. It's putting out amps but with all the incandescent lighting plus the sealed-beam front light, that's just a lot of draw. I'm going to swap the sealed-beam for an H4 style lens and use an LED headlamp bulb - that should drop the 10A draw down to 1.5A.
The clutch bite point seems really narrow for as much lever travel as is afforded. It seems like of the, say, 3 inches of total lever travel that the initial bite to full engagement is all of 1/2inch. If I mess with the cable adjuster I can move that 1/2inch forward or backward on the lever, but widening the zone doesn't seem to be an option. It's not a huge deal and may be just getting used to it, other things to worry about...such as...
The brakes are...well...bad. The rear brake is surprisingly good, but the front does not feel like it'll be there when you need to do a panic stop. I replaced the rubber lines with braided ptfe, and used new (old stock) pads. Solid lever feel and not spongy, but you've got to put a firm handshake on it to get even modest braking out of it. Two finger braking is not it's deal right now. I'll try bedding the front a bit more, but I think realistically a dual-disc conversion is in the cards, but I was already planning on that anyway.
That's it for now - was just a great day today, and thanks for listening.
Antietam Classic Cycle:
The VHBs used on Guzzis (and Moto Morinis) didn't have o-rings on the mixture or idle speed screws from the factory, and I've been running all of my VHB equipped bikes without any for the last 42 years.
The LED headlight should help considerably with the charging issue, an LED brake light bulb will help too (in more than one way). I like to run as "big" of a battery as possible (ETX30L) and an adjustable, solid state voltage regulator will help optimize output. A 450 watt alternator kit from EME eliminates the issue once and for all...
The stock PS15 front master cylinder is ill suited for a single F08 caliper. There are several "easy" ways to get better front brakes: 1) Replace the PS15 with a PS12 off of a later Tonti (T3, Convert, etc.) or even a PS11. 2) Replace the F08 caliper (38 mm pistons) with an F09 (48 mm pistons). 3) Add a second disc, F08 caliper, etc. and stick with the PS15 master cylinder.
cmice:
--- Quote from: Antietam Classic Cycle on May 08, 2026, 09:43:27 PM ---The VHBs used on Guzzis (and Moto Morinis) didn't have o-rings on the mixture or idle speed screws from the factory, and I've been running all of my VHB equipped bikes without any for the last 42 years.
--- End quote ---
Yeah - is a theory of mine - as I think about it, the thread on the adjuster screw is pretty fine and probably seals pretty well on its own. Will pull the carbs and go back through them, check float heights and all that. Back to basics, as it's a pretty simple setup.
--- Quote from: Antietam Classic Cycle on May 08, 2026, 09:43:27 PM ---The LED headlight should help considerably with the charging issue, an LED brake light bulb will help too (in more than one way). I like to run as "big" of a battery as possible (ETX30L) and an adjustable, solid state voltage regulator will help optimize output. A 450 watt alternator kit from EME eliminates the issue once and for all...
--- End quote ---
Ordered the my regulator just now, and will track down some LEDs for front and rear.
--- Quote from: Antietam Classic Cycle on May 08, 2026, 09:43:27 PM ---The stock PS15 front master cylinder is ill suited for a single F08 caliper. There are several "easy" ways to get better front brakes: 1) Replace the PS15 with a PS12 off of a later Tonti (T3, Convert, etc.) or even a PS11. 2) Replace the F08 caliper (38 mm pistons) with an F09 (48 mm pistons). 3) Add a second disc, F08 caliper, etc. and stick with the PS15 master cylinder.
--- End quote ---
Lots of options - the F09 swap may be the simplest and cheapest. 2nd disc gets pricey when you add up the caliper, the hub spacer, disc, extra hose and distribution block change, plus the weight. Just rebuilt the PS15 and other masters don't look right (to me) and are price-equivalent to swapping the caliper out. Gotta mull this over but nice to have the options laid out like that - thanks Charlie!
Antietam Classic Cycle:
You're welcome.
I use these LEDs in the taillight and turn signals:
https://www.amazon.com/dp/B074GPX2Q8
https://www.amazon.com/dp/B074RFSFVT
I've installed this LED sealed beam unit in two customer bikes:
https://www.amazon.com/dp/B0BNT4V2VC
There are lots of others that are less expensive, but I like the look of the Peak lens better.
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