1981 GS750E (GSX750E) Rat Cafe Racer

LKS

Member
Nice. I'm only guessing but it looks like you'll mount that little piece on the bars maybe? or is it lager than it looks and will go around a fork leg?
Thanks :) It goes around the forkleg (35mm). I'll try to place it behind the headlight, facing slightly towards the tank so the cable wont kink. If that doesn't work I'll make a new center piece with the housing at an angle.
 

LKS

Member

ridesolo

You only bear responsibility for your own actions
I like the large one. To me it has a "serious" look rather than the "added on as an afterthought because I have to have one" look that the small one has.
 

LKS

Member
Got the fuel problems sorted today :) Firstly, there was a slight kink in the fuelhose. Secondly, and more important, the fuel cap venting mekanism wasn't letting air in and out of the tank. Fascinating how fast the vacuum stops the flow of gas. Now it runs as smooth as it did with the small plastic tank I used for the test run. The petcock is still too tall (can't get the tank to sit low enough and line up with the seat), so I'll have to change it out one day. I'll save this for task for later.
 

LKS

Member
Also got the first sidecover done (not with the final paint..). I've had those perforated stainless steel sheets laying around forever and finally got around to use them. I wanted to be able to remove them easily and for that reason I've kept the original mountingpoints on the frame.

First I fired up the lathe and made a "push-button" for the bottom mountingpoint:


Then I took made a cardboard template and cut the perforated steel into a loose fit:
Påska by Lars Krogh-Stea, on Flickr

Påska by Lars Krogh-Stea, on Flickr

I'll line the edge with an edge protection profile like this:
96520-K1367-Kantenschutzprofile-Edge-protection-profiles-Form-C by Lars Krogh-Stea, on Flickr

I used the same profile to line the backingplate for the licenceplate:
Påska by Lars Krogh-Stea, on Flickr

I shaped two pices of the same perforated steel to the back of the sidecover and pop riveted them in place, also drillet and riveted the "pushbutton" fastener:
Påska by Lars Krogh-Stea, on Flickr

Did a quick "paint-job" and mounted the cover. The fit is prettyr tight and there is very little room for vibration. I'll go over the edges and fine trim them when i get the edgeprotection profiles:
Påska by Lars Krogh-Stea, on Flickr

Next weekend it's time to fit he speedomoter, and then I'll get to drive it home. That will hopefully speed up the process significantly :)
 

LKS

Member
Today I measured the "speedo A/D converter" and redesigned the housing to not be so bulky. I saved a lot of space by flattening the inside of the housing so that it only builds 1mm from the forkleg. Top pictures are the old ones, bottom two is the file I sent to my friend for printing:

Speedogearhus_huset v3_4 by Lars Krogh-Stea, on Flickr
Speedogearhus_huset v3_3 by Lars Krogh-Stea, on Flickr
Speedogearhus_huset_kort v3_5 by Lars Krogh-Stea, on Flickr
Speedogearhus_huset_kort v3_2 by Lars Krogh-Stea, on Flickr
 

LKS

Member
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
 

LKS

Member
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
 

LKS

Member
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?
 

Jimbonaut

Well-Known Member
DTT SUPPORTER
I'm late to the party - damn this bike is cool. Nicely done mate, really dig what you're building. I'll be making some side covers too soon - I like how you made yours a lot. Cool :cool:
 

LKS

Member
I'm late to the party - damn this bike is cool. Nicely done mate, really dig what you're building. I'll be making some side covers too soon - I like how you made yours a lot. Cool :cool:
Thanks! I fixed the petcock today, so now I can hardly wait to take it for a test ride tomorrow :)
 

LKS

Member
At last the bike runs as it should :) 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, preatty 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$. Yesterday I found that a chainstore nearby sold some cheap helmets from a manufacturer that had copied the snap-on visor attachment that Shark uses. And they were selling out the rest of the spare visors. I bought two clear ones and two gold/mirror for about 10$. 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
 

LKS

Member
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:
 

LKS

Member
Thanx! The rear tyre is a 150/70-18. The rear hub is from a 77-79 GS, the only ones with both disc and spokes at the rear. It was pretty hard to find, but finally found a guy in the US that had three of them on the shelf. Probably had them there since the 80s. I ordered the rim and 6mm shorter spokes from Richard Hoyland at Central Wheel Components Ltd in the UK. Awsome service :) In the US I guess one would order theese parts from Buchanans. Laced and trued it myself which isn't as hard as many make it out to be. To get the chain to not rub on the wheel even if it's laced at the center, I did a 520 conversion with the narrowest D.I.D chain I could find. The rear sprocket is for a Suzuki DR 750 and the front sprocket is for various 90's Kawasakis. The front wheel is a standard GS750, but with GS1000 calipers as they will clear the spokes. I have a 2005 GSXR750 front fork and R1 monoblock calipers that I plan to use in the future with a Cognito Moto hub. I'm saving a wider front for that.
 

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