1981 gs750 (gs750e) Retro Racer project

[LarsKroghStea]

Not much wrenching today, but I've been at my dad's and picked up the rest of the parts and some tools. He also handed me down an old pillar drill:
IMG_20200506_213845 by Lars Krogh-Stea, on Flickr


I'll use that to drill holes for the safetywire.
IMG_20200506_220255 by Lars Krogh-Stea, on Flickr


I also got my safetywire pliars:
IMG_20200506_220245 by Lars Krogh-Stea, on Flickr


And my smaller torquwrenches:
IMG_20200506_220303 by Lars Krogh-Stea, on Flickr

[LarsKroghStea]

The shocks are back in working order Next up is safetywiring of the rotors and rear sprocket. Some of the safety tabs are in bad shape and one of the screws in the front disc came loose. Before i do anymore testdriving I'll have to go over the whole bike and refit the screws with with correct torque and loctite per manual. There's been too much jumping back and forth over several years and I have clearly forgot where i've test-fitted parts and where I've done them up correctly. Safety first (from now on)!

[LarsKroghStea]

I guess it's when you start riding that the errors you've done come back to bite you.. I thought the ride was extremely harsh, and when I went out yesterday to bounce the shocks.. this happened.

I thought the hash ride was because of the thick oil and the cold weather, but I could just as well ridden with steel rods for shocks
I feared the worst..

that I had to buy new ones.


I took them apart to see what was wrong. Apparently the vibrations from running with thick cold oil rattled loose the end screw (1m) from the rod (3). Don't mind the arrows. That made the whole valve sink to the bottom and the spring pulled the rod through part 1c, wich is what it bottoms out on when I bounce the bike. 1c rests on 2a and that tube rests on the shim 2c on the bottom of the shock body. The only part with som visible damage was on 2c on one of the shocks. Some markings and it's bendt, but very little. I'm reusing it as it doesn't have much valving function.


Dempere by Lars Krogh-Stea, on Flickr


The internals, washed and end screw torqued to spec with a dab of blue locktite. Filled up the shock with new SAE 5 oil.


Dempere by Lars Krogh-Stea, on Flickr


The cool thing about having built a home gym, is that I've apparently also built a pretty safe and easy way to compress springs


Dempere by Lars Krogh-Stea, on Flickr


Dempere by Lars Krogh-Stea, on Flickr

[LarsKroghStea]

Spendt most of the day gardening and working on my home gym.. both me and my sons miss going to the gym in these Corona-times. Did get the time to buy the hood-locks though. Here are some pictures of how i envision the fastening device for the rear seat. I'm putting some rubber between the seat and the frame to prevent vibration and to put the hood-lock under tension so it won't rattle. I will also have to test which position is best.. I'll either drill and tap the square tubing or drill two metal pieces to clamp over the square tubing. We'll see.


Setefeste by Lars Krogh-Stea, on Flickr


Setefeste by Lars Krogh-Stea, on Flickr

[LarsKroghStea]

Today I'll also throw in a picture of a great deal. I have and old (2007) Shark carbon Composite helmet. It fits me perfectly and I haven't found any other helmet I'd rather use. It was quite expensive, but I got a good deal on it as I bought it, and a full Goretex outfit plus boots and gloves, together with a used Kawasaki ZX7R. Okay, I'll post a picture of that too:
1909837_22450845914_8814_n by Lars Krogh-Stea, on Flickr


At the time I thought that was the coolest bike you could have. Much cooler than the new ZX10R. It was large, pretty heavy for what it was (about 200kg) with about 120 hp. But the sound was like a racing car, and everything was making rattling or metal noises. That was when I realised that I'm never going to buy a new fuelinjected smooth riding bike. I wanted the rawness. But, I digress.. The point is, that I only had the black visor for my helmet. Someone (that's an even longer story) scratched up the clear one. The black visor is not road legal and impossible to see through at night or in tunnels. A new original visor costs about a 100$. Yesterday I found that a chainstore nearby sold some low cost helmets from a manufacturer that had copied the snap-on visor attachment that Shark uses. And they were selling out the rest of the spare visors. I bought two clear ones and two gold/mirror for about 10$. Both are awesome. The gold mirror gives good visibility, but it's impossible to see in through the visor. They look like this:
Snapchat-1984076064 by Lars Krogh-Stea, on Flickr

Next part of the project is to buy a set of car hood latches and use them to make a fastening mechanism for the rear seat:
Panserlås by Lars Krogh-Stea, on Flickr

[LarsKroghStea]

Well, I learned a few things this week. Very useful info about fuel flow.
I like your side cover work too.

Thanks man And I really like this forum for all the helpful people and all the good ideas I've picked up.

[Buffalo Bill]

Well, I learned a few things this week. Very useful info about fuel flow.
I like your side cover work too.

[LarsKroghStea]

Did a short test run yesterday, and the bike pulls good through the gears. Didnt' get the engine fully warm I think, because there was a "scoffing" sound in the front wheel. Couldn't se anything, so it might be brakes, but I'm leaning towards bearings. I think I ordered an Allballs set a couple of years ago, but I can't remember if did the switch..

Next task anyway, is to make make fastners for the seat.

[LarsKroghStea]

Excellent. I'll be fitting a replacement petcock shortly and haven't been too impressed by the size of the outlets of the ones I've seen.
That, and filters. I've always had a filter, but they've been car-sized ones, as I've got plenty of room to fit them, having the single carb. Even so, it pays to check fuel flow every so often just to make sure they're delivering what they should.

Maybe I'll install an empty glass filter, just so I can visually inspect the flow..

[Grimly]

Excellent. I'll be fitting a replacement petcock shortly and haven't been too impressed by the size of the outlets of the ones I've seen.
That, and filters. I've always had a filter, but they've been car-sized ones, as I've got plenty of room to fit them, having the single carb. Even so, it pays to check fuel flow every so often just to make sure they're delivering what they should.

[LarsKroghStea]

Rough rule of thumb is about half a pound of fuel per horsepower per hour and that will provide a comfortable figure to work within.
Or, if you want to get metric on its ass...
https://en.wikipedia.org/wiki/Brake-...el_consumption

Awesome! If my calculations are correct, that amounts to 0,44liter/minute. I managed to fix the biggest petcock, and when I flow tested it, I got 170ml/30sec with fuel filter and 230ml/30sec without filter. It's an easy choice then to ditch the filter. Now that I'm getting 0,46 liter fuel/minute I'm taking it out for a ride tomorrow

Here's a comparison of the petcocks. I didn't realise the difference before I opened them.

IMG_20200421_171648 by Lars Krogh-Stea, on Flickr

IMG_20200421_171922 by Lars Krogh-Stea, on Flickr


I sanded down the gasket and the bakside of the valve, flipped the gasket with the sanded surface in (opposite to the picture) and drilled holes for nuts/bolts. Now it works as intended
IMG_20200421_163650 by Lars Krogh-Stea, on Flickr

[Grimly]

Rough rule of thumb is about half a pound of fuel per horsepower per hour and that will provide a comfortable figure to work within.
Or, if you want to get metric on its ass...

https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption

[LarsKroghStea]

Well.. I've done a couple of comparisons with regards to flow of fuel. I'm starting with three pictures. You can see the combinations of filter+hose/hose/no hose. Time to flow is 30 seconds and measurements are in milliliter. The reason is this; when I tested the bike last fall with the little one liter fueltank (last picture) it took off like a rocket. Ever since that I've not managed to get it to run properly. I'm guessing it runs lean, but I didn't think it would need that much fuel or be that sensitive to variations in fuel hight (I'm guessing). Anyway, here are the flow tests:


Hose and filter (90ml in 30 sec):
IMG_20200419_190656 by Lars Krogh-Stea, on Flickr


Only hose (110 ml in 30 sec):
IMG_20200419_191027 by Lars Krogh-Stea, on Flickr


Only petcock (110 ml in 30 sec, same as with hose. I'm not holding it completely upright)
IMG_20200419_191409 by Lars Krogh-Stea, on Flickr


This is obviously not enough flow. I havent changed anything else since the test run, and I'm running new white paper filter and have new intake boots between plenum and carburettors. All tests are done whith tank lid off, so there's no vacuum that hinders flow. Tanklid on/off only differs 5ml or so.


This is the small test tank I used last year:
IMG_20200420_184926 by Lars Krogh-Stea, on Flickr


As you can see, it flows over 2.5 times as much as with the hose and filter:
IMG_20200420_184910 by Lars Krogh-Stea, on Flickr


I blame the petcock for this. It's a repro Honda cx500 petcock to fit the cx500 tank. AFAIK the xc500 has two carburettors, and maybe thats the reason it copes with lesser flow. Or maybe the repro-petcock is crap.. I have one more petcock. Also repro but different design. I've drilled out the rivets on this one, and will try to modify it for better flow.


What do you guys think? Anyone know how much the petcock wil need to flow per minute to keep up with full throttle?

[LarsKroghStea]

Thanx


Installed the speedoconverter and tested it yesterday. Worked almost as I hoped. It was a bit shallow and I had to shim the lid a bit to get it working. The worst thing though was that the hexagonal holes that were intended to keep the nuts from spinning wasn't working properly. I think at this small size, the holes and nuts would need to be square to keep the nuts from spinning.
As a signal pickup though, it worked flawlessly, and I'm going to make a revised housing at a later date.


Throwing in a couple of pictures as usual. The first one is from the finished left sidecover (now with rubber edge protection) and one of me and the bike just before I rode it home. About an hour long journey. It still runs as it gets to little fuel, and I blame the petcock. Will test other solutions to this problem, as it must be sorted before I take another trip. First I'll take a short test run with the small white plastic tank to verify that it indeed is the petcock. The third photo is just for fun


IMG_20200418_190938 by Lars Krogh-Stea, on Flickr


Første tur (2) by Lars Krogh-Stea, on Flickr


IMG_20200418_201004 by Lars Krogh-Stea, on Flickr

[LarsKroghStea]

So, I went to pick up the last 3D-printed part. It was a little bit skewed, but I don't mind as I'm going to sand and paint the parts anyway. I think the whole setup looks awesome, and I'm a little bit proud to have designed my own 3D-printed parts (I know I'm a little bit biased ). Anyhow, I present to you the analog to digital speedometer converter

IMG_20200416_204315 by Lars Krogh-Stea, on Flickr

IMG_20200416_223222 by Lars Krogh-Stea, on Flickr

IMG_20200416_223337 by Lars Krogh-Stea, on Flickr