1981 gs750 (gs750e) Retro Racer project

[LarsKroghStea]

The guy I bought the bike from told me he put carbs from a GS1000 on the bike. The two sets I have are identical, and I measured the front opening (towards engine) on the ones that are on the bike and they measure 32mm. Both butterfly valves are stamped with the "box" and the number 135. Seems they are both GS750 carbs after all

I've adjusted the pilot screws and the bike is now easier to start, but still runs lean. The spark plugs are light grey, low rev pulls are slow and uneven, and there are the occational pop in the exhaust. When I had the carbs off, I did a new "bench sync". I've read that the level should be equal in all four carbs when using 4-1 exhaust, so I guess a bench sync is OK for now.

I've read through the Factory Pro CV carb tuning guide several times, and I've concluded that the float hight is wrong. I'm pulling the carbs again tonight as I might have compressed the needle spring when measuring float height. The guide says increments of 1mm, but I may be way off. I'll start with 22,4mm -1, which will give me max fuel level. Then I can at least see if I can get some color on the spark plugs. I'm getting anxius from always driving the bike lean, and if this doesn't help there must be something else wrong. The bike pulls great at high rpm/full throttle (high vacuum) so I'm guessing fuel delivery from the tank is OK.

I also took some pictures of the pistons with a USB "endoscope" type camera connected to my phone. There's no pitting on the pistons, and there is little carbon buildup. I guess the valves are in the same condition and that compression is OK. I will test later if changing fuel level doesn't help.

[LarsKroghStea]

When I tested the bike, it felt like it was running lean, and when I checked the plugs that was confirmed. The carbs have been cleaned, but I didn't remove the pilot screws as they were stuck, and someone has partially mangled the slots in them. I managed to get the two outer screws out, but I will have to take the carbs off to get the last two out.

The screws were full of white oxydation, and the springs looks like this:



Luckily I have a spare set of carbs, as the previous owner put GS1000 carbs on the bike. He moved the gs750 jets over to the gs1000 carbs, and I've no idea how smart a move that was. The bike runs very well above 5k, but doesn't run well below that.

The pilot screws off the gs750 carbs were in great shape, and the springs were shiny as chrome. I'm moving them over to the 1000 carbs, and will go through the tuning process.

I'm also ordering a set of new o-rings, so sometime during the winter I will disassemble dem completely and clean them in the ultrasound cleaner (just bought one, so I didn't have it when I cleaned them the last time. Until then I'll just clean and use the screws from the 750 carbs. I've measured them, and I'm pretty sure they are the same size. I mounted them with some light grease on, so they wont get stuck between now and full cleanup.

[salty_monk]

Ha.. I've heard (and done) of brazing before but never with Tig! Learn something new every day I guess!

[LarsKroghStea]

The tube I ordered for the pivot bolt arrived today:



I went for 316 seamless stainless steel. It's more expensive, but feedback from other buyers indicated that cheaper steel tends to be handeled with less care and produced to poorer tolerances. I've also heard of people recieving seamless tubes that are not really seamless. The tube I got seems very well made.

The 750 pivot bolt slides easily into the tube but without any wiggleroom. The bushings from the 1100 would need pressing or slight hammering with a plastic mallet, but I will instead sand down the ends of the tube ever so slightly, or else I'm afraid I'll never get it apart if I need to change the bearings.

[LarsKroghStea]

I've been looking for solutions for a new gas cap. It needs to be low profile so it doesn't interfere with the flipover lid. I'm thinking something like this:





I haven't really TIG-welded anything since I made the seat some years ago, and I don't feel confident in welding in the bung without burning holes in the thin sheet metal. After some gooogling I've decided to try out something called Silicon bronze TIG brazing (https://www.youtube.com/watch?v=rGDs3ZJErkI&t=669s). You may know what it is already, but for me it's a new concept. It's like TIG welding, but with bronze filler. The metal to be joined is not melted, just the filler. Sounds like low risk welding, and maybe an easier way to learn how to TIG-weld better.

Bronze brazing is often used in custom bicycleframe building, because it doesn't warp or stress the metal to be joined. Looks cool to

[LarsKroghStea]

So, this is the solution to the clip-on problem: SpeedyMoto makes adjustable clip-ons with a good range of adjustments. They're pretty expensive, but the good news are that their replacement tubes are 22mm. SpeedyMoto also explicitly states on their website that they recommend them as replacements for other clip-on clamps.

They are made with a 14 degree angle, and will suit my setup well.

[LarsKroghStea]

My clip-ons have a pretty steep angle of 9 degrees. Add more rake to that, and the sum amounts to bad ergonomics. This can be fixed with clip-ons with an adjustable angle like I had on the old fork.
I haven't decided on any brand yet, but I'm going to order something like those pictured below. I would prefere some with more offset (the bars are in front of the fork tubes - makes more clearance between bar and tank), but those are adjustable between 6 - 9 degrees, and I want the option of havng them almost flat.

[LarsKroghStea]

Finally, I had my first real ride with the new configuration. This is the first time I've really gotten to try out the new fork and front wheel. It works really well, and the brakes are awesome.
Winter is coming, and this was probably the last trip this year. I'll take a little break, buut there's a lot more to do.

Finishing the front fender.



Mid ride picture:




Arriving at my dads house, after an hour of riding.



I learned a few things on this ride:

• The clip-ons need to be angled more towards the back. The current angle is wrong for my wrists
• Possibly a new tink lid. The rubber gasket was old and hard as plastic.Gas was flowing everyhwere when I was breaking. I made a new gasket, and it almost cured the problem. Will look into replacing the lid with a quick-lock alternative.
• Swap swing arm.
• New upholstery. I will pay someone to do it, as I've already done it myself and I want a better version.
• Remake the housing for the buttons. Preferably in aluminum as I hope to finally test my anodizing equipment.
• Make side cover for right side.
• A lot of cleaning up bolts and elctrical connections.

Extra note; I made a bracket for the speed sensor. Tested with my multimeter and all, but it didn't work correctly and I almost couldn't get the bike over 40 kmh. It may be problem with where it is grounded, and I need to go over the wring. The sensor worked fine the last time I uset it.

[LarsKroghStea]

A couple of weeks ago I made a temporary licenseplate-holder to check out placement and angle. I was planning on using it this spring and make a better one later. It turned out to be way too flimsy, so I had to make another one.

The flimsy one:



The new one. It's not pretty, but if I like it I'll sandblast it and make it a bit nicer.

[LarsKroghStea]

I bought a 6mm stanless steel rod, and made a pretty sturdy front bracket:





It doesn't look like it in the pictures, but the front and back ends of the fender is the same with as the tyre. In the middle, it is a little bit narrower. I dont mind, as most of the water is thrown off the center of the tyre thread.

I used the original HEL rubber protection to attach the brake line to the fender:

[LarsKroghStea]

Lots of stuff going on lately, and before I could finish the Ducati fender I came by another front fender that suits my build much better:



It came with som braces and clamps. I didn't like the clamps, and will swap them with rubber lined clamps. I'll use the rear brace, but will have to make a new front brace because it's too short for a 19" wheel. I'll pick up a length of 6mm stainless steel rod tomorrow along with a pack of clamps

[LarsKroghStea]

The swing arm has arrived, and I've taken some measurements.

First of all; it's very light:



I haven't weighed the steel one, but I would guess the weight is almost half.



The inner bushing is 16mm (difficult to measure exactly).



And the pivot bolt is 14mm.



I would guess I could just buy a length of steel tubing with ID=14mm and OD=16mm (1mm wall thickness). Easy to get hold of in 304 stainless steel, and as it'll just sit between the bolt and the bushing (not directly on the needle bearing) I'm pretty sure that will be strong enough

[slayer61]

I love the attention paid to wiring pinch bolts

[LarsKroghStea]

The front fender is a more modern look than I wanted, but will have to do for now.



I've bought som flat aluminum rods, and will cut them a little longer than the originals.

[LarsKroghStea]

I've changed some of the bolts already, and today the bolts for the lower triple arrived:

From this:



To this: