GS500 Camshafts and Carbs into a GS450

[pete]

Certainly could be, I think I only need to make up about a 1mm diameter or so difference. Trying to find some of that locally is the big question...

[pete]

Actually is this the stuff? If so I can duck out at lunch tomorrow and get some probably:

http://www.jaycar.com.au/Service-Aids/Tapes/Other/Aluminium-Foil-Tape---50mm/p/NM2860

[Chuck78]

Were the carb spacings identical between the original 450 carbs & the gs500,carbs? I was planning to build resleeved cammed built up 502cc GS425 next winter, & running the gs500 carbs (pre-2001 slingshots). Another member I have been chatting with about his similar gs400 449cc wiseco build had just got some early gs500 carbs for his 78 gs400 & sent me a picture of them mouth to mouth, & the gs500 carbs were slightly wider intake boot spacing than the 1978 gs400 carbs. I figured all 400/425/450 carbs would bevthe same spacing, but with the cylinder spacings being slightly different, maybe not so... With a different intake boot setup or potentially altering the linkage/choke setup/fuel tee/etc, maybe the 500 carbs could be narrowed .47" I believe is what he told me.

Any thoughts???? With the 2.8lb slingshot flatslide carbs being far superior to the 6lb stock carbs, the extra work is very tempting!

[tkent02]

Actually is this the stuff? If so I can duck out at lunch tomorrow and get some probably:

http://www.jaycar.com.au/Service-Aid...-50mm/p/NM2860

Looks like it, but I think it comes in thicker versions. Might take quite a few wraps at .04mm to get your required .5mm thickness, but for temporary use I bet it works OK.

[pete]

Just remembered we're one team member down for the next 2 months, so no chance of me getting out to get some tape and lunch... I think I might stop procrastinating and just bite the bullet and order the new boots/clamps/O rings. The dealer I buy from doesn't have the boots or clamps in stock but it's usually only a day or two delay... if I can get them on before this weekend then hopefully I'll have time to feel it out during the commute and hopefully sync the carbs again on the weekend.

[Big Rich]

Pete, are you planning on getting new GS500 boots? Just want to make sure.....

Chuck, I measured the spacing when I put 500 carbs on my 450 and they were identical as far as I could tell (same spacing on a GR650 as well). I assumed the spacing was the same for the 400 & 425, but have never been near one to measure......

[Chuck78]

Well when the time comes (475cc or 502cc custom pistons & megacycle cams + head work), I think I will buy a set of GS500 carbs & try to adapt them by narrowing them first, 2nd bet is to adapt different boots, although I really don't want to disrupt the path of the airflow by offsetting the carbs outwards almost 1/4". That may gave other performance side effects as best as I can speculate.

[pete]

Yep Rich, ordered 01 500 boots, O rings, and clamps yesterday. Not in stock so they're ordered from Suzuki Australia, hopefully there's not too much of a delay.

When I pulled in the drive way yesterday afternoon she was idling a little high which she hadn't done previously... sorta almost like a hanging idle... and we all know what that typically indicates!

As far as spacing goes, with the 01 500 carbs there are two long bolts that go the entire length of the carbs and screw in from the left and there are two T's that join the carbs, one of the overflow at the top and then the fuel T at the rear. There is also another spacer between the carbs at the rear.

So to widen them you would need to sort out 2 T's, a spacer, and maybe get longer bolts depending how far you need to go.

You can just see the head of the long screw underneath the stack in this photo:




The other option would be to get adapter plates made up (or make them yourself).

Bolt the carb boots to some aluminium plate which is rotated 90 degrees or so from the head mounting bolts, then bolt it to the head.

The intake hole in the plate could be cut then slanted towards the carb and engine intake... I don't know any other way to try to describe what I'm thinking... I'm not sure if that would have a negative effect on air flow into the engine or not...

[Chuck78]

As far as spacing goes, with the 01 500 carbs there are two long bolts that go the entire length of the carbs and screw in from the left and there are two T's that join the carbs, one of the overflow at the top and then the fuel T at the rear. There is also another spacer between the carbs at the rear.

So to widen them you would need to sort out 2 T's, a spacer, and maybe get longer bolts depending how far you need to go.

The other option would be to get adapter plates made up (or make them yourself).

The intake hole in the plate could be cut then slanted towards the carb and engine intake.

I believe the GS500 carbs are too wide for the 1977-1979 gs400/425, not too narrow, so a narrower set of fuel (& vent?) Tees would need to be sourced or made up, about 6mm narrower on each side of the tee if that is possible. So the carbs would need to be made about 12mm closer together if that is possible. Do you mind looking at yours & telling me of any major problems/obstacles you see in attempting that, especially with the throttle linkage & choke setup? Is it a single shared throttle shaft on the butterflies of both carbs???

[Chuck78]

On the GS425, there are already some thick (9/16"?) Thick adapter spacer pieces boltled between the head and the carb boot. I was wondering what those were on there for. I suppose it would be possible to rework those & maybe even tig weld some extra material onto them (tricky, as it's cast Aluminum) in order to be able to bore them out at an outward angle, outward toward the rear, & use the TIG add-on metal to fill in the inner rear area that the old carbs occupied. I assume these spacers are factory & have some sort of intake boot o-ring groove. Making your own would mean they would have to have a darn goid seal in the form of a gasket capable of handling cylinder head temperatures, unless you had a mchinist capable of maching a nice groove in for intake boit o-rings.

You absolutely would not want to make the new carbs angled down from the boots, as this would mess up the flow of air/fuel mixture. More modern heads like the Chevy vortec/LS series(& our tscc & tdcc Suzuki engines I believe) use a raised intake runner design so the air/fuel mixture has less bends to make as it enters the cylinder with more of a straight shot with less angle than an older head design.

[Chuck78]

swapping gs500 carbs onto a gs400/425

The schematics for 78-79 400's & 425's show an aluminum spacer & gasket bolted to the head, called an "insulator." So if making an adapter, you already have a gasket to make this work. The only thing to do is put the intake boots on the gs500 carbs & hold them up to the head and see if the bolt holes in the head will terribly interfere with the wider placement of the gs500 boots& carbs. It may even be possible to countersink the bolt heads on the spacer so that the intake boots could slip over them slightly as long as it wasn't too close to the intake boot o-ring.

If that adapter idea was total no-go due to bolt pattern interference, then you could search ebay or better a local parts place or Japanese bike junkyard for a set of factory Katana or GSXR intake boots that had the right carb size & close enough offset. With patience, research, & maybe buying a few wrong boots, you should be able to come up with something that is a bolt-on.

[pete]

For some reason I thought the carbs were narrower... not sure why...

Best bet is for me to try for some photos. I'll have the carbs out of the boots when I do the 500 boot replacements so I'll get some photos then although they won't be the best. I have limited time to do this stuff at night so I'll be leaving them attached to the throttle cable while I replace the boots.

I'm hoping they'll arrive today so I can do them tonight but I'm not sure if that will happen yet.

With the adapter, I was thinking slanted slightly left/right for each side, not up or down... but no not the best solution.

[theironlung1976]

I THINK im the dude Chuck was talkin about w the 78 400 doin the carb swap... If not, i just so happen to have a 78 400 and im doin a carb swap on n sent Chuck a pic of the carb spacing bein different... Lol.

I got the spacing difference figured out. 2 custom "t"s r needed. One for the vent, one for the fuel inlet. U could probably get away w takin the oe lower fuel inlet "t" n use it as the upper vent " t" w some tubing n pinch squeeze clamps after the width is lengthened. No pressure, just a pathway for fumes. 2 tie brackets n choke link rod need to b lengthened .474". The lip on the left side carbs throttle shaft needs to b lengthened .474" n shaped to allow for sync adjustment. My "t"s r being turned as we speak. Ill send a pic when theyre done. The rest is simple weldin. The bottom tie bracket holdin the carbs together hits the cam tensioner by the way. Needs to b relieved to clear it. Petes later carbs have a different bracket system n choke setup... N kinda looks easier to overcome. Im gonna do a thread on it soon. Just waitin to have all the shhhtuff together for pics before i do it. Stay tuned Chuck!

Pic is of my old 400 carbs next to the 500 carbs.

Didnt mean to impose Pete... Just wanted to get the info out there if someone was lookin for it. Anxious to see where yer jetting settles in to a sweet spot.

[theironlung1976]

And since Pete n Rich hit on this earlier, just figured id show how light these r... Compared to my old carbs anyways.

[theironlung1976]

Crazy! This swap is worth it in more ways than 1.