GS500 Camshafts and Carbs into a GS450

[pete]

Got out with the Kat boys Saturday morning and got a proper true full throttle plug chop done at last. Plugs are a little on the white side of grey so the 127.5 main is a little lean, so I will go back to the 132.5 mains. It could be that I need 130's but I'll wait and see before buying more jets.

There is also some snap crackle and pop during deceleration with a closed throttle, so I also need to wind the mixture screws out half a turn to start with.

I hope I don't have to raise the needles any further as these horrible plastic needle holders just don't like having the needles any higher than they are now in the middle position. That's the one thing I really don't like with these carbs...

[Mekanix]

Might want to consider a dynojet kit if anything just for the needles. They have quite a bit more taper near the end.

[pete]

I hadn't considered that... usually the dynojet stuff is just ridiculously expensive here but that was thinking of the 450 carbs where it would've been a special order, haven't looked at the 500 stuff but I could possible get it on eBay or Amazon at a guess.

Right now I'm trying to track down velocity stacks and some sock filters to fit them... found a couple of stack options but not having much luck with sock filters with a large enough diameter to go over the flared ends of the stacks.

I really need to get rid of the dodgy pods...

[Steve]

The US needles aren't adjustable so I have one or two washers under the clips to richen them.

Did you only add your washers under the clip?

If you left the stock nylon spacer above the clip, your jetting is unchanged.

The height of the needle is determined by what is ABOVE the needle, so you need to replace that thick nylon spacer with a few thinner washers that have less total thickness.

Any washers added below the clip only add preload to the spring, pushing the needle up harder, but that does not change the position.

.

[hillsy]

Did you only add your washers under the clip?

If you left the stock nylon spacer above the clip, your jetting is unchanged.

The height of the needle is determined by what is ABOVE the needle, so you need to replace that thick nylon spacer with a few thinner washers that have less total thickness.

Any washers added below the clip only add preload to the spring, pushing the needle up harder, but that does not change the position.

.

I think Rich means shimming under the clip on the needle, not putting a washer under the plastic retainer.

[Big Rich]

Any updates Pete?

[pete]

Sorry guys, I've been a bit slack and haven't logged in for ages!

Update wise, I found some velocity stacks to fit the carbs but have had to dodgy up a bit of gutter mesh to go over bell mouth until Unifilter release some new rally pods they have coming which should fit them nicely.



I only got my first run with the stacks on Saturday and I actually overheated her by running too lean, but that was with the needles at the mid point. I have since raised the needles. I think I lucked out and did no damage as she seemed fine once cooled down again. That's the risk you take when the only real testing is the commute... I'd love to have a bit more time for tuning runs.



Jetting wise, I'm now running stock pilots, needles two notches richer than stock, and 132.5 mains.

After lifting the needles there is still crackling on decel so I'm still lean somewhere... I'm beginning to think the 132.5 mains are still a bit small as she feels great at low to mid throttle, but once you get past that I swear she's lacking something. I'll probably get the 137.5's in later this week to check.

[pete]

I should add I haven't put the GS500 camshafts in yet, next service is something like 1000km's away so I'll check the valve clearances and if everything looks good I'll slot them in then.

I'd like to get close with the jetting as is now first though.

[Big Rich]

Where did you find velocity stacks Pete? I've never seen them for the 500 carbs...

Sorry to hear you're chasing your tail with jetting again. But think of all the experience you'll have after doing it over!

[tkent02]

Pete, just curious what you think of the power, throttle response, etc? Is it worth doing for the performance improvement alone?

[pete]

I'm not worried about re-doing jetting Rich, I'm just happy to be moving forward at last after dealing with dodgy diaphragms and then dodgy pods...

I ended up finding two sources of stacks that suit 60mm carb inlet diameter, one locally here in Aus and one place called Speed Moto in the US.

Speed Moto had only one in stock and they don't look as well made as the ones here, only catch being the ones here had no way to mount as they're fairly generic.

http://www.jntperformance.com.au/index_i6515601.html?catId=269035

So I slotted them so I could clamp them down and that did the trick nicely.



They have a huge (for the 450) bell mouth of 99mm which is why the difficulty in finding sock filters to go over the top, but Unifilter have said they're releasing ones to suit up to 100mm. They were supposed to be out in March but have been delayed.

I upped the pilot and main jets last night... 20 and 137.5 respectively. I'll be happy if I end up a bit rich so I know where I'm at with the jetting.

I'll be heading out again Sunday morning so I really need to get some more fuel in there so I can get a proper feel for how she's running now.

Tom, to be honest it's hard to tell right now given it's been so long since I had a good ride with fully functioning carbs, but it is getting better all the time. Saturday was my first ride other than the commute with the stacks on and up to half throttle she felt absolutely awesome.

The biggest difference I have noticed with the stacks is that it has smoothed the throttle out quite a bit, not so jerky from a closed to partially open throttle for example.

Once I get rid of the lean bits I expect even better again.

She's definitely stronger up to that half throttle stage at the moment but I don't really know if it's more power as such or just better throttle response and fueling due to a smoother air flow.

Quite a while ago she was dyno'd and had a bit over 32hp at the rear wheel, so once I get this sorted I hope to get on the dyno again and see where the AFR is and get a new power reading.

Overall I'm happy I put the 500 carbs on and am happy I chose to go with the stacks, despite the need for fiddling with the jetting.

Oh, and the noise... the noise is quite addictive

[pete]

Question... anyone directly compared the 500 carb boots with the 450 carb boots? Measurement tells me the 500 carbs have a slightly smaller engine side diameter than the 450 carbs and I think this is allowing a slight vacuum leak on the right carb as that plug always seems a little leaner than the left plug no matter what I do nor how many times I sync the carbs.

Just wanna make sure I'm on the right track before shelling out $100 for the 500 carb boots, O rings, and clamps.

Oh, and can anyone confirm they're a bolt on to the 450 head? I can't see why not but thought I should check...

Incidentally I upped the mid mains and mains last night as she still feels lean when I get to probably half throttle and up. I haven't had a chance to do any plug chops lately but I'm hoping to get some done this Saturday. In the meantime I'd much rather be rich than lean...

[tkent02]

Measurement tells me the 500 carbs have a slightly smaller engine side diameter than the 450 carbs and I think this is allowing a slight vacuum leak on the right carb as that plug always seems a little leaner than the left plug no matter what I do nor how many times I sync the carbs.

Pete, have you tried increasing the diameter of the carb temporarily with some of that aluminum tape around the carb?

[pete]

Nope didn't think of that! Although I'm seriously thinking of swapping the boots regardless... one thing I noticed when i did get them to sit in properly (or the best I could) is that the spring for the butterfly and the vacuum port sit hard up against the rubber boot which doesn't seem right to me.

And looking closer again I reckon the boot is clamped down so much that it is starting to deform and bulging a bit. I'll try to get a photo or two to see if I can demonstrate what I'm trying to explain.

I had a great ride yesterday and she felt strong all through the rev range finally but still popping under decel with a closed throttle and if I held the throttle at say 1/8 or so then cracked it there was a period of nothingness/hesitation before she started to pull again.

In comparison, holding it at around 1/4 throttle then cracking it was a pretty instant increase in acceleration.

Unfortunately despite marking the throttle positions I got so carried away with the fun I forgot to do any plug chops... however that behaviour at closed throttle reaks of being lean still to me... where the rest of it just felt good.

[tkent02]

And looking closer again I reckon the boot is clamped down so much that it is starting to deform and bulging a bit....

however that behaviour at closed throttle reaks of being lean still to me... where the rest of it just felt good.

Sounds like the bulging boots leaking may be the only problem, or at least the main one. Try the tape.