GS500 Camshafts and Carbs into a GS450

[pete]

I've been thinking of putting GS500 camshafts into my '82 450 for a while but had never really had that extra bit of drive to do it.

However just before Christmas I discovered tears in my carb diaphragms and long story short I need new carbs as the JBM diaphragms won't work in these particular carbs. Genuine replacement diaphragms with slides are way too expensive... $AU95 each plus a lot of shipping from eBay US or over $AU200 each purchased locally.

A set of 01 GS500 carbs turned up about 5 minutes from me here for $150 so I bought them and he has camshafts as well for $50 so I bought them as well. Both look to be in good condition going by the photos but I will see when I physically have them in my hands.

So, providing these really are 01 model carbs, it should be a nice upgrade.

The only things to sort are the choke cable and air filters as the K&N's on my stock carbs won't fit.

The seller has a choke cable that I'm hoping he will throw in so that should sort that

I'd really like to run velocity stacks with some sort of filter except I can find no 60mm diameter ones locally, so it looks like I need to get some cheap dodgy pods that will do a lot of breathing but not so much filtering... not ideal but the best I can find here locally. I don't want to go the K&N lunchbox on these... big, ugly, and way too expensive.

Going by info on the GS Twins site I can start with 20 pilots, 65 mid main, and 145 main jets. It just so happens the main jet is the same as the stock 450 carbs so I have several different sizes available already, so I just need to buy some pilots and mid mains.

Anyway, if anyone has any other tips on these swaps I'd be happy to hear info, I know Big Rich has done the carbs at least.

I'll keep the thread up to date with how things progress... it'll be at least a week before I can get them in as I need to give the carbs a once over and get the jets etc.

[tom203]

If this plan fizzles out (or you need backup), this carb cleaning guy near me has (or had )this item

http://maine.craigslist.org/mpo/4794450487.html

[pete]

Cheers Tom, the annoying thing is the rest of the carbs are fine, it's just the diaphragms. Oh well, this way I can get a bit of an upgrade in the bargain so I won't complain!

[Jedz123]

My concern is the power band of the GS500 and the Redline of your GS450. I know the GS500 has to wind out to 10K mark to generate it's maximum HP where as redline for a GS450 is 9.5K(I believe). Since Cam shaft's dictate your location of high end power I'm afraid you'll hit red-line before getting into the meat of the power dictated by the Cam profile. You could just bring the engine to 10K but I would be afraid of over exerting the 33 year old components.
Also not sure of the year but the GS500 stopped using a gear drive off the exhaust cam to drive the tach. No gear means you won't be able to use the stock tach.

My 2 cents...

[pete]

I only typically play in the 6K to 8K range when twisting the wrist and the one time I had the 450 on the dyno (more for fueling than power figures) peak power was just before 8K RPM, so I don't think that will be an issue. I do understand what you're saying though!

I have an Acewell dash on her as well, so I can set the tacho to flash as a shift indicator, so that might be a safe option.

That also negates the need for the tacho drive on the camshaft, I've had that blanked off for a few years now.

[Charlie G]

Pete,

I have a set of 450 carbs I bought years ago and you can have them for the shipping. Year unknown. If you just want the diaphragms thats ok to. Let me know if you interested and I'll pull them apart and take some pictures. Seems to me one of the floats is bad or odd....? Give me a PM.

cg

[pete]

Cheers for that Charlie, but hopefully I won't need to! Got my hands on the 500 carbs and cams over the weekend along with throttle and choke cables.

I had some issues with the cheese head float bowl screws (surprise surprise) so I slotted them with the dremel and the impact driver made quick work of removing them.

The insides are nice and clean and there is not a hint of anything in any of the jets, so I won't need to dismantle and soak thankfully. I know I'll probably get grief for saying that but these haven't been sitting long and the fuel was drained, so I'm pretty confident they're good to go.

I ordered pods yesterday and will order jets today and my house mate is going to pick me up some stainless allen head bolts for the float bowls, so the carbs should be good to go in once those bits arrive. I just need to cut some fuel hose and vacuum hose to suit.

At this stage I'm hoping to take Friday off work and if that works out I'll give her a service and swap the camshafts out at the same time as I need to do valve clearance checks anyway. I'll check clearances before swapping the cams and then again once I've done the swap.

[Jedz123]

The GS500 Carbs are a great upgrade for any 80's GS twin. IN fact I'm considering running GS500 carbs on my GR650... But maybe down the road a bit. I want to see how it runs with the stock carbs after the port match job and pods.

[pete]

Yeah I'm hoping this will not only fix my issues but also be a nice upgrade. They are also a lot lighter!

Jets ordered yesterday and hopefully everything arrives today so I can do the swap tonight. Very keen to be able to open my throttle again!

[Jedz123]

Keep us posted! I look forward to hear about your results!

[pete]

Jets and pods arrived yesterday, so last night was carb night. 3.5 hours and lots of cursing later they're in for better or worse. I could only run it for 5 seconds as it was 10:30pm when I finished but she did at least run... after wondering why the float bowls had no fuel and realising I must've needed to hit reserve as I was pulling into the driveway yesterday


There are two issues... the idle knob interferes with camchain tensioner and the right hand carb mixture screw is going to be incredibly awkward to get to also due to the camchain tensioner.

I'd highly recommend looking into GS500 intake boots for the head as well as the ports on the carbs are slightly smaller than the 450 ports so I had to use some alternate hose clamps to get a good seal on them. If the boots are slightly longer that would also resolve the camchain tensioner/idle knob issue.


I had to swap the idle knob with the one from the 450 carbs which also meant cutting down the spring on it which makes it a bit less effective but it seems to work. Hopefully there's enough adjustment left to be able to get a good idle setting.


If I cut some length off the stock 500 knob it will work much better, but I can't see a way of safely getting the plastic knob off to do that yet.


After all that the GS500 throttle cable is identical to the GS450 cable despite different part numbers...


I reckon I save half a kilogram with these new carbs too! Way lighter than the stock ones...

Should be an interesting commute today!


Jets installed as a start; 20 pilot, 65 mid main, 145 main as per info I've seen on the GS Twins site:





Nice new stainless allen head bolts with anti seize to replace the cheese head float bowl screws:





GS500 carbs on the left (inlet side), I reckon she'll breathe somewhat easier:





Cheap and dodgy but should do the trick until I can source something better like velocity stacks:





Installed:





The painful idle adjustment... no longer interferes with the camchain tensioner but nearly touching the starter motor cover:

[Big Rich]

Looks good Pete!

I flipped the CCT on mine so the "bulk" of it points to the left side. Not a huge help since it is just as close to my pre-2000 carbs, but I always reached for the idle adjustment from the right side and the CCT would always singe me.

I would have to double check my jetting, but I know I went smaller than what was recommended on the Twins site. But remember: I also have the K&N lunchbox filter which probably flows differently than your current pods.

Speaking of K&N lunchbox ......mine was a direct fit onto the GS500 carbs, but special attention was needed to the fuel lines coming from the petcock. Nothing major, but taking the K&N on and off was much easier with the tank removed since the lines were RIGHT up against the air filter.

Did you notice the difference in weight of the carbs themselves? The stock carbs felt like they were made of pig iron when I held both.....

[pete]

Good to hear from you Rich! I was hoping you'd chip in...

The idle knob has been fixed by John (john82q) and his lathe magic, much shorter but still looks like stock:



I've spent way too many hours trying to get these right... and got led up the garden path by the left Dynatek coil breaking down once the bike got hot. It would idle fine but as soon as the rev's got up she'd start stumbling and eventually drop to one cylinder.

Consequently I have a completely stock ignition system again...

The reason I'm so glad to hear your comments Rich is that I've been on a wild goose chase to get rid of the flat spot and the fact that she feels like she starts to die at full throttle. I've lost all of my time for full throttle plug chops due to the coil issue, so I have to do my tuning based on the commute to work... and that just doesn't work!

What I've been doing is thinking I'm too lean based on popping under deceleration and what I determine to be a flat spot... I had a last ditched attempt of doing a dodgy and reaming out the stock 115 mains that I'll never use again. They're probably the equivalent of a 185 or 190 now...

Anyway, on the way to work yesterday the two times I got briefly to full throttle it felt like it was dying off even more, so I figured that was way too rich... then I saw the email update from you and it dawned on me that I was probably too rich across the board. I have not tried these carbs with anything close to stock jets...

So, last night, stock 60 mid main went in, and I dropped the main to 132.5 which is probably still too rich but I'm still trying to avoid going too lean!

I have left the needle at one notch richer than stock.

So I'll see how she goes today but I should get out Saturday morning which means I should be able to get a full throttle plug chop done finally.

As for the weight difference in the carbs, oh yeah that is a huge difference!! These are so light in comparison...

I also haven't done the camshafts yet, wanted to make sure I understood the carbs and jetting first before going down that path...

Edit: I neglected to mention that I went back to stock pilots last week as I'd already determined it was too rich at idle, and I also have the mixture screws 3 turns out at present.

[Big Rich]

A bad coil, huh? Well, at least you know what the problem is.

I didn't get a chance to dig up my jetting info yet. But seeing that you have the 3 jet carbs and mine are the older 2 jet carbs, the jetting numbers wouldn't match up anyway.

Going off of my memory, the GSTwins site recommended 140 mains for my intake / exhaust setup and I went with something around 132.5 (remember, my memory absolutely stinks!). I am running the stock GS500 pilot jets for certain..... I believe they are 37.5 for me. The US needles aren't adjustable so I have one or two washers under the clips to richen them. The one thing that helped me out a bunch was checking and double checking the float heights using the clear tube method. If the float bowls weren't filled to the brim, it made a significant difference.

[pete]

Yeah that bad coil had me so confused... so glad that it presented itself properly finally and I'm now back to just tuning carbs like I should have been many weeks ago...

I had a trouble free run to work and back yesterday but one brief stumble and I swear it still felt a little on the rich side so I've dropped the mains last night to 127.5's, see how she goes today. I'm set for a ride with the Kat boys Saturday morning so hopefully I can squeeze in a plug chop or two and get a more accurate idea.

I haven't found any suitable diameter clear tubing to check the float heights with that method yet, but best I can tell with measuring they seem ok... they're quite awkward to check compared with the 450 carbs.

Oh and Rich, with these carbs, they have two throttle cables, push/pull setup. The pull cable is identical to the 450 cable so that meant it was nice and simple.