1980 SG Back From The Dead – AKA Dad’s bike

[Mike G]

Now the fun part! I never cared for the stock front brake and since everything was toast anyway I decided to do the FZR rotor and blue spot caliper conversion and replace the MC with an 11mm unit from a Honda.(Thank you eBay for all the parts.) I mocked everything up to determine the correct disk spacer thickness to center the rotor in the caliper, I think it was 0.515” IIRC, as I didn’t want to use spacers in the bracket. MotoLana has a 10mm spacer that would have saved a bunch of time making the spacer but would have required additional spacers (I needed 13mm total) and I wanted to use my recently refurbished lathe.

For those who like machine tools. It’s a 1946 Logan Model 820 10x24 I found on Craigslist. It was pretty tired but in decent shape. I figured I could pay someone for the spacers or make them myself and learn how to use a lathe in the process.(never used one before) I’m also thinking of replacing the rear wheel with an 18” XS400 wheel because I like the look of the 18, in which case I will need more spacers. Here’s how it looked when I picked it up.

I tore it down and stripped it to bare metal. It had probably 6 or 8 coats of old paint.

Then repainted it the original color.

A few parts were broken and some of the bronze bushings worn out so I repaired or replaced all the dodgy parts and got it humming again. The hardest part was cleaning all the crud out of the headstock bearing. Replacements are expensive and by all accounts not as good as the originals so after much soaking/cleaning/soaking/cleaning it finally ran smooth. Here it is finally "done". Not really done as I still need to repair the original half-nuts so I currently can't cut threads on it.

The above is the real color, the one above makes it look more blue.

 

[Mike G]

Unfortunately dad never got to ride it. It was supposed to be his to ride when he came out to visit but his health started failing shortly after I bought it.

 

[Mike G]

Anyway...back to the brakes. I bought some aluminum plate from McMaster (did I mention I love that place?) to make the disk spacer and caliper bracket. I started with the spacer as it was harder and I was itching to actually make something on the lathe. I made a mandrel out of a scrap piece of shafting from work and cut the corners off the plate to get the shape closer to round.

And made my very first round thing!

Here's the finished product.

Now it's time for the bracket.

 

[Mailman]

Now the fun part! I never cared for the stock front brake and since everything was toast anyway I decided to do the FZR rotor and blue spot caliper conversion and replace the MC with an 11mm unit from a Honda.(Thank you eBay for all the parts.) I mocked everything up to determine the correct disk spacer thickness to center the rotor in the caliper, I think it was 0.515” IIRC, as I didn’t want to use spacers in the bracket. MotoLana has a 10mm spacer that would have saved a bunch of time making the spacer but would have required spacers and I wanted to use my recently refurbished lathe.

For those who like machine tools. It’s a 1946 Logan Model 820 10x24 I found on Craigslist. It was pretty tired but in decent shape. I figured I could pay someone for the spacers or make them myself and learn how to use a lathe in the process.(never used one before) I’m also thinking or replacing the rear wheel with an 18” XS400 wheel because I like the look of the 18, in which case I will need more spacers. Here’s how it looked when I picked it up.

I tore it down and stripped it to bare metal. It had probably 6 or 8 coats of old paint.

Then repainted it the original color.

A few parts were broken and some of the bronze bushings worn out so I repaired or replaced all the dodgy parts and got it humming again. The hardest part was cleaning all the crud out of the headstock bearing. Replacements are expensive and by all accounts not as good as the originals so after much soaking/cleaning/soaking/cleaning it finally ran smooth. Here it is finally "done". Not really done as I still need to repair the original half-nuts so I currently can't cut threads on it.

The above is the real color, the one above makes it look more blue.

You have to ask if guys here are interested? Haha! I’m surprised we don’t have a forum section for machine shop tools and old tractors on here. The guys love all that stuff. Great job on the lathe, it looks like new!

 

[Mike G]

I started with another piece of plate and KevC’s excellent drawing of the bracket. I printed it full size and center punched all the hole centers, radius centers and tangent points and played connect the dots.

I got it functional to make sure everything fit correctly.

I drilled out all the holes and cut the rest out by hand with a hacksaw and shaped it with files.

And Bob's your uncle...

 

[Mike G]

Now on to the master cylinder. After looking at the VintageBrake chart for proper brake ratios I made a handy little spreadsheet and decided 11mm should work the best. I poked around on-line looking for likely candidates without much success and one day while looking around on eBay I saw a Nissin MC with 11 (11mm) cast in it for a Honda Shadow. A quick search on partzilla and there are quite a few Hondas with 11mm master WITH a mirror mount.(unfortunately RH thread so I can’t use the XS750 mirrors I wanted to or I need an adapter)

It only needed a quick teardown and clean-up, it was very clean inside, and ready to install. The only other issue is that the Shadow’s have 1” handle bars and the XS has 7/8. Another trip to McMaster for a bronze bushing and we’re in business.

 

[Mike G]

No way would the original brake line fit and it is 40 years old anyway so I bought the parts and pieces from Earl's, or whatever they are called now, and made up a braided stainless line. No picture of that by itself though but you can see it in some of the pictures of the finished bike. A little front brake bleeding and front brake is finished. I always thought the original disks were on the heavy side. Every time I picked one of them up I would think how heavy they are. I did some searching on the forum and saw that a 5mm Maxim disk is a direct fit so a little time on eBay and...

 

[Mike G]

I rebuilt the MC and caliper but I still need a replacement hose, I bled it with the old hose anyway to make sure I didn't have any problems and adjusted the pushrod and switch now all works as it should.

 

[Mike G]

Next in line was to replace the missing fuse box with a blade style fuse holder.

I also removed the RLU and jumpered the connector and did the 5twins wiring mod to use the old headlight indicator as a charge light. Thanks 5twins works like a charm.

 

[Mike G]

I rebuilt the petcock and made up a 2 foot tall standpipe (much more pressure than normal) out of some vinyl tubing and it leaked like a sieve!! Did a little more digging in the forum and saw the hint about bending the aluminum disk on a socket. Problem solved, didn't lose a drop in two days.

I took the carbs apart and they were pretty clean, all the jets were stock and I replaced all the questionable bits except the rubber pilot plugs which I didn't have. I ordered up a set and some shaft seals and if the carbs give me any problems I will put them in then. Sorry, no pics but you have all seen carbs taken apart about a zillion times.

 

[Mike G]

A couple of new XS1 style grips from dads parts bin and a set of standard bars from a member on one of the old, defunct, forums years ago and it's starting to look like something.

 

[Mike G]

It didn't have any air filters, just the metal cages and no media, so I made up a set using the Briggs air filter per Pamcopete. Thanks Pete!

And decided to add another air inlet to the back of the filter cover. (just cuz there were a set of used rubber tubes in dad's old stuff)

Ok, here's the nerdy part. I calculated the area of the carb inlet vs the area of the two tubes and adding a third tube made it equal. And yes I know the carb can pull air from the other side but I liked the idea of each housing having enough area to supply one carb. Turns out a 7/8 spade bit makes the perfect size hole to add the tube and hold it firmly even though the plastic in that area is thinner than where the other two tubes are mounted

 

[Mailman]

Super nice work on the front brake! Damn!

 

[Mike G]

Thanks for all the positive comments. The bike wouldn't be near as good as it is without all the tips and tricks from this forum.

 

[Mike G]

When it got to this point it was time to start it up for the first time in almost 20 years. I don't have a battery for it so I hooked up some jumper cables and spun it with fresh oil and the plugs out to get some oil around. I then kicked it through with the kill switch and the choke on a couple of times, kill switch off and it started on the first kick! I think maybe dad gave me a little assist on that one. It's not running great but it runs so the ignition works. I checked the spark and it was reddish and looked weak so I got a set of Honda MP08's from eBay and now the spark is nice and blue. I'm glad it didn't smoke as even the 10-20 seconds it was running in the basement stunk the place up pretty good!

So now we're caught up to the present...

I moved it up to the garage and started it up yesterday. The charging system is working fine. I checked the brushes and they have plenty of life left but I did swap them to even out the wear. There is something going on with the carbs. Once it warmed up it idled well and revved up nice when blipping the throttle but I tried the dead cylinder method to set the idle mixture and the right screw does absolutely nothing. It's totally closed and it idles fine. The left one doesn't start to sputter until about 1/2 turn out so both seem to be running rich which the plugs agree with as they are black and sooty. I checked the float level using the clear tube method and it's about 4mm below the flange (not the gasket surface) on the carb body which should make it lean not rich. The diaphragms drop very slowly so I don't think I have bad choke plunger seals.

I'm taking the carbs off today and will replace the old pilot plugs with the new one I have and do the throttle shaft seals and check the float level again and see what I find.

 

[5twins]

The plugs will be black if you used the choke when starting. It takes several miles of running down the road to burn them clean again. For tuning you might want to get another set. Start the bike with the choke and warm it up, shut it off and change to the new clean plugs, then start it again with no choke to get a better plug reading.

Did you replace the little o-rings on the mix screws? They're important for the screws to function correctly. These BS34s are so pollution mandated, the mix screws don't have that much of a perceived effect as you adjust them, not like the mix screws on the older carb sets. The one that doesn't do anything until about 1/2 turn out sounds about right, the other that doesn't do anything at all isn't. Did you remove the mix screws when you previously cleaned the carbs? You have to do so to do a proper cleaning of the passageway leading to the screw. You must also insure that the other 3 passageways leading from the pilot jet into the main bore are clear .....

 

[Mike G]

Yes, when I cleaned originally I took the mixture screws out to clean and installed with new O-rings. I have the carbs out and the pilot rubber plugs were tight in the passage so they aren't the problem. I'm going to clean out the pilot jet and passages again and make sure the pilot air passage is completely clear.

 

[Mike G]

For anybody looking for a fitting to fit the float bowl drain to do the clear tube float level check, I found a fitting on eBay that worked very well. I put one of the harbor freight O-ring kit O-rings on it and no leaks.

 

[Mike G]

All passages and jets are/were clear. I do have a question though. Is the mixture screw tip supposed to protrude into the carb bore when it is bottomed, like maybe .020"? The reason I ask is that the left screw, the one that is behaving normally, protrudes in that far but the right one didn't when it felt like it was bottomed. I turned the right one in farther and, while there was more resistance, it did go in another 1-1/4 turns until it really was bottomed, at which point it was also protruding into the bore about .020". If this is correct then I think I found the problem. The right cylinder didn't stumble because it wasn't bottomed. There were no marks on the tip of the right screw so the only thing I can figure is that there was gunk in the threads that made it stiff enough to feel bottomed out when it wasn't. I worked the screw in and out a few times and now it goes in easily.

This is what the left needle looked like and now the right one matches.

Hope that was it...

 

[5twins]

Yes, they will protrude like that when bottomed. Looks like you found the issue, mismatched settings on the mix screws. The BS34s are sensitive to that. It can cause popping, stumbling, etc. I would set them both at 3 turns out and fine tune from there. Keep them both the same if possible, that is, if adjusting, turn both in/out the same amount. The BS34s usually like somewhere between 3 to 3.5 turns out.