D-Mac project GS550 - more carb issues

[D-Mac]

D-Mac,

Maybe I missed the answer earlier in the thread, but what size main jets are you running?

I am running the Dynojet 155 mains (kit came with 150s and 155s - these are in Dynojet sizing). Others who have jetted this model/year bike successfully have recommended running them. I also installed the air jet from the kit and the needles (3rd clip position down).

Mains wouldn't be interfering with idle/low speed circuit though, right?

[tkent02]

I am running the Dynojet 155 mains (kit came with 150s and 155s - these are in Dynojet sizing). Others who have jetted this model/year bike successfully have recommended running them. I also installed the air jet from the kit and the needles (3rd clip position down).

Mains wouldn't be interfering with idle/low speed circuit though, right?

Yes, on CV carbs they do effect them.
Try smaller jets.

[D-Mac]

Yes, on CV carbs they do effect them.
Try smaller jets.

I'll install the 150s then. Good to know.

[tkent02]

What is the standard Mikuni jet for that engine?

[BigD_83]

What is the standard Mikuni jet for that engine?

92.5 according to "The Chart"

http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html

[tkent02]

So 120 something you want in Mikuni specs, who has the DJ conversion? I still think you main jets are way too big.

[D-Mac]

Yup. 92.5 Mikunis.

Here's another potentially-important thought.....

I installed the air jets that came with the jet kit. Almost no one seems to mention them. As I recall from when I re-built the carbs (it's been a year), they press in and you put a tiny dab of glue on them to help hold them in place (they go in over top of the stock air jet as I recall). They stick out a tiny bit on the back of the carb inlet - on the right side looking into the carb from the airbox side.

I did find one post where someone with a nearly 80s GS550 with pods indicated that "they often aren't needed."

Do you think I should try and pull them back out? Anything that reduces air would end up enriching the mixture a lot, right?

Hmmmm......

[D-Mac]

As I understand it...

Dynojet Main 155 (currently installed) = Mikuni ~145
Dynojet Main 150 (also came with my jet kit) = Mikuni ~135.5

Got that off the web.

[BassCliff]

Hi,

There are tons of Mikuni-Dynojet conversion charts on the web. I have a copy of Mr. salty-monk's conversion spreadsheet on my little website. It does the calculations for you.


Thank you for your indulgence,

BassCliff

[tkent02]

Not sure but I believe those air jets only have an effect at very high RPM and full throttle, to adjust the mixture at really high power. Your main jets appear to be many sizes too large, which would do exactly what you are seeing..

[BigD_83]

I agree with tkent.

You mains seem to be about 10 sizes too big. I'd think with that pipe and pods you'd only need to go up to a Mikuni 115 (DJ 122) or 120 (DJ 128).

P.S. Cliff, the link to the spreadsheet gives a 404 error

[D-Mac]

I agree with tkent.

You mains seem to be about 10 sizes too big. I'd think with that pipe and pods you'd only need to go up to a Mikuni 115 (DJ 122) or 120 (DJ 128).

P.S. Cliff, the link to the spreadsheet gives a 404 error

Thanks for the advice, and I agree that my mains sound too rich, but I'm still baffled by the fact that at least a dozen folks with a similar stock setup have had luck with this kit on the 80 and 81 GS550s with the exact same setup I have. Most actually ran the 155 mains, and a few preferred the 150s. Despite the missing at idle, the bike did seem to rev freely from 1/8-full throttle the last time I ran it. It still needed choke to start too.

It does sound like the mains are too big though. Before I start ordering new mains and trying to decide what to keep and what to ditch from this kit (among other things), I'm probably gonna install the smaller mains from the kit, lower the floats to be better within spec, and try again.

[CafeRookie]

I know this is 10 years old.... but any update on this?

[BigD_83]

D-Mac is no longer active on the forum, so unless someone knows them personally, I'm afraid we're not going to hear back