1980 Suzuki GN400 - cafe conversion

[ex119x]

I'm in the La Crosse, WI area.

I guess there is at least one member on here close to you, I live just north of Menomonie, so about 90 miles or so. I went to UW-LaCrosse a long time ago and lived in Sparta in the early 2000s and worked in Chaseburg.
Of course, you have the best riding roads in the state around you and don't need anything bigger than a 250 to really enjoy those coulee roads. I have ridden many, many of those roads on a 400 to 600 bike and you don't need more.
I did a quick tour of Marketplace and see that there are 2 $200 GN400s listed. One in Camp Douglas and one in Spring Green. I would get them both and build 2 bikes out of the three so you and your daughter each have one and you have spares to test parts with and to keep them running. Suzuki GS450 rear wheels will match the mag wheel on the GN so again you could easily get an 18" rear wheel.

I would not bother with the 750.

 

[Maritime]

I guess there is at least one member on here close to you, I live just north of Menomonie, so about 90 miles or so. I went to UW-LaCrosse a long time ago and lived in Sparta in the early 2000s and worked in Chaseburg.
Of course, you have the best riding roads in the state around you and don't need anything bigger than a 250 to really enjoy those coulee roads. I have ridden many, many of those roads on a 400 to 600 bike and you don't need more.
I did a quick tour of Marketplace and see that there are 2 $200 GN400s listed. One in Camp Douglas and one in Spring Green. I would get them both and build 2 bikes out of the three so you and your daughter each have one and you have spares to test parts with and to keep them running. Suzuki GS450 rear wheels will match the mag wheel on the GN so again you could easily get an 18" rear wheel.

I would not bother with the 750.

this is good advice

 

[Untame]

I guess there is at least one member on here close to you, I live just north of Menomonie, so about 90 miles or so. I went to UW-LaCrosse a long time ago and lived in Sparta in the early 2000s and worked in Chaseburg.
Of course, you have the best riding roads in the state around you and don't need anything bigger than a 250 to really enjoy those coulee roads. I have ridden many, many of those roads on a 400 to 600 bike and you don't need more.
I did a quick tour of Marketplace and see that there are 2 $200 GN400s listed. One in Camp Douglas and one in Spring Green. I would get them both and build 2 bikes out of the three so you and your daughter each have one and you have spares to test parts with and to keep them running. Suzuki GS450 rear wheels will match the mag wheel on the GN so again you could easily get an 18" rear wheel.

I would not bother with the 750.

Awesome! The one in Spring Green... well... having communication problems with the seller. Kinda grumpy. But Camp Douglas is closer to me. Haven't seen that one yet (I can't find it -- can you message me with a link?). I did find an 18" GS425 matching mag wheel on Ebay, but the GS450 mag wheel I found was a 17".

Yes, the roads around here are spectacular. I live on a small farm tucked back in the coulees (near Galesville), so these are my roads. This is exactly the type of riding I have in mind.

Thanks for the tips.

 

[ex119x]

A 17" rear would work, too. There are lots of good 17" tires available.
https://www.facebook.com/marketplac...wse_serp:08ca9c65-942c-4a31-9a45-11131be933c6 is the one in Camp Douglas. It is on Facebook listed as a Suzuki gn, but now I think it might be a 125 not 400.
As I have been thinking about it and that your kid wants to own the bike and spend her money on it, I would do the minimum that will have it roadworthy and safe at minimal expense. That being the case I would put a good tire on the front, rebuild the front forks with new oil and seals, rebuild the front caliper and master cylinder, install better bars that fit her along with new grips and cables as needed. There are some good 120 x 16 rear tires available, like the Bridgestone BT46 or SC. Finally, get some longer rear shocks to raise up the rear for better handling and look. Then get after the cosmetics that you want. All of that can be done on a budget, done over time and will show continuous progress over the winter.

Then, work on the second GN for yourself and get as involved as you want. I might have a spoked rear wheel that might work, if you can make spacers and change bearings. I have a couple of XL500 wheels, CB350 wheels and a mystery Yamaha wheel. I probably have a stock XL500 carb that would work and some megaphone mufflers, too. As you get into it, you are welcome to any of the misc. parts I have laying around. I would just be happy to get some of them out of my garage. Just some things to think about as you move forward. It looks like Galesville is about an hour and a half from me.

 

[Untame]

I found someone who has a 1980 GN400 owner's manual. It says tire pressures should be 25 front, 28 rear. This sounds reasonable, but my VIN tag says 32 rear. What gives?

 

[ex119x]

That is 45 year old recommendations for old style tires. I am sure it would be safe, but sounds a little low to me. I would follow the recommended pressure from the tire manufacturer, or if it were my bike I would consider 28 - 30 front and 30-32 rear and see how it felt.

 

[Untame]

That is 45 year old recommendations for old style tires. I am sure it would be safe, but sounds a little low to me. I would follow the recommended pressure from the tire manufacturer, or if it were my bike I would consider 28 - 30 front and 30-32 rear and see how it felt.

Sounds good.

But I'm trying to figure out what the front pressure should be as specified on my VIN tag. It is rubbed off, and I am having a reproduction made. It matters almost nothing, but my OCD wants to get it exactly right.

 

[Untame]

Had a nice day yesterday, so I degreased and pressure washed the frame. Got it jigged up with the forks and a shock to verify the reported factory geometry.

After several measurements I am confident that my GN400 has 31 degrees rake, and the axle leads the headtube centerline by 62mm. This comes out to a calculated trail of 112mm.

I also mocked up the engine and sprocket so I could check swing arm clearance with an oversized rear shock (360mm instead of 320mm). We're all good.

 

[Untame]

Got an 18in GS400X rear wheel on Ebay. Should be here next week.

 

[doc_rot]

This is a good cheap solution for the rear, I'm glad a member here had this info. I mentioned a while back that the GN400E looked like it had a 18" rear makes sense that Suzuki had other bikes with the same wheels.

I agree with ex119x - The best solution for anyone that is new to bikes and building them, is to make the bike safe and road worthy and get some seat time first. May turn out you don't like riding bikes and an original bike will almost always sell for more and faster than a custom one. I also agree with the idea of small changes incrementally for dialing-in suspension, theory only gets you so far for getting it just right. However when you start talking about radical changes like removing 3.5" of fork travel from the front, theory becomes relevant to keep things in a desirable range.

 

[irk miller]

31 degrees of rake and 4.5 inches of trail is going to handle like a small chopper. It's gonna turn slow. Sport bikes are in the 23.5 - 25 degree range with 3.75 - 4" of trail range. A Beull XB12s is on the extreme side @ 21 degrees/3.3".

 

[Untame]

31 degrees of rake and 4.5 inches of trail is going to handle like a small chopper. It's gonna turn slow. Sport bikes are in the 23.5 - 25 degree range with 3.75 - 4" of trail range. A Beull XB12s is on the extreme side @ 21 degrees/3.3".

Yeah, I got the GN400 because of the 400cc thumper engine (and it was very cheap and available). It has some drawbacks as a donor bike to a cafe racer project. The big one is the geometry (another is the 6v electrical system). In 1980-81 I suppose the market was leaning toward chopper/cruiser so Suzuki brought out their SR400 alternative slung low with more rake.

With a series of small modifications I am working to wrestle the geometry back toward street bike:

- 18-2.15 rear wheel (instead of 16in)
- 100/90-18 front tire (instead of 3.60-18) gains over 1in of height to add trail so I have room to reduce rake
- 110/80-18 rear tire (instead of 4.60-16) gains 1.5in of height to help reduce rake
- 360mm rear shocks (instead of 320mm) adds clearance for larger rear tire while further reducing rake
- Front fork tubes moved up in clamps 35mm (1 3/8in)

These changes net me the following:

- 27.13 degree rake
- 95mm (3.74in) trail
- 54.5 wheelbase (instead of 55.5) - not trying for this, but it is a consequence of rake adjustment

 

[Untame]

Here is the geometry problem I am working on now....

I want to install a flat seat loop and modify the existing seat platform so that it is parallel to the ground (right now it slopes toward the rear, then kicks upward).

With 80mm of total shock travel the rear tire will hit the seat pad (top of the 1in seat loop). I am considering adding a 3/4in rubber bumper to the shock pistons to limit the shock travel to 60mm. (Note - because of the angle of the shock, the wheel travel will actually be greater than 60mm.)

 

[Untame]

I need to pick out a seat so I can have the right measurements to install the loop. Anyone have a recommendation for a good "value" (balance of quality and price). Looking for something brown with diamond stitching and a rear hump that can be painted. I have seen a couple I really like in the $400 price range (Tuffside and OC Cafe Racer), but ...

On the other hand Amazon has a bunch of Chinese seats for under $100. Anything in the middle that represents a good value?

 

[pidjones]

I had a Vietnamese seat on my RD400c that was pretty good. Look just like the original. They also make tons of custom seats. There is a contact in the USA, but they are built in Vietnam.

 

[Untame]

I had a Vietnamese seat on my RD400c that was pretty good. Look just like the original. They also make tons of custom seats. There is a contact in the USA, but they are built in Vietnam.

Do you have a link or company name?

I know from business dealings that Vietnam has excellent leatherwork at low prices.

 

[Untame]

Took the front wheel apart. Spokes are good but ugly. Nipples should be replaced. Recommendations for refinishing the spokes?

(Spoke kit is hard to find.)

 

[Untame]

I think we will go with this tank on Amazon for $76. The other tank was far too long.

Judging by the Amazon reviews on these Chinese tanks, it looks like a crap shoot to get one without dents.

 

[Untame]

Got my daughter into the shop today (finally - had to tear her away from "Gardenscapes"). She had her first go-around with the blast cabinet. We are cleaning up the aluminum bits with glass bead. Did the front hub and top tree clamp. She seemed to enjoy the experience. While she did that I started cutting the vestigial tabs off the frame.

Her tastes are morphing... now she is thinking about a silver frame with British Racing Green fairing/tank/seat cowl with "electric red" stripes and S logo. Might set the red accents off with silver edging. I'm sure she will have more new ideas before we are done!

 

[pidjones]

Be careful with the glass beads. When they hit, they shatter and create glass dust that can lacerate nasal and lung linings, inviting infection. I prefer aluminum oxide, although it doesn't leave as pretty a finish. Using glass, be sure to let the dust settle before opening the door, and vacuum up any leakage.