GT750 carbs on a GT550

[Alan H]

I can't post page 21 of the original J/K manual, but that's what Suzuki says. The taps changed L onwards.

[Vintageman]

I sure wish I had a Kawasaki two stroke : Avenger, s1(would make s2), s2, s3 H1.

Markush
Did your air box mod dampen sound say versus just removing snorkel?

You have the later Needle jet from later GT250A. http://www.oldjapanesebikes.com/mraxl_G ... etins.html" onclick="window.open(this.href);return false;

Accept, you are 4 step up on main. Not sure that snorkel mod makes that much of a difference. I ran my gt380 without it and really did not change jetting (maybe did a little and I should have moved up 2.5 maybe 5.0). Did you cut the air box larger?

An engine can run several jets too rich on main before your butt can discern. Yes I know we don't want the infamous lean melt down The only issue is you have too low fuel to oil injection ratio (myth? think about it)... little oil mixed in the tank fixes that. Plug chops on two stroke for me is too fuzzy a criteria or I just never do it right.

Here's the thing I won't get: piece of mind. That is I will always wonder if I got the jetting best it can be. Unfortunately if I make this change that's how it will be no doubt, But I have nice close starting point. thanks guys

Mike. First try with 77 GT550 jetting works great. I am sure it does. Could it be better? maybe - maybe not. You would have f with it. why bother

Markush:

How many different jetting combinations did you try before you settled on that combo?

Well you guys have convinced me GT550 carbs over my 26mm to start. I'll compare Needle Jet size to needle jets to see how Mike and Markus compare.

Don't you hate when people say your jetting varies but, then the manufacture sells ten of thousands of a given bike model all with the same jetting? And, you know each bike has some manufacturing tolerance variations too. I suppose the key is to have a well centered jetting and proper tools

Great Job with gt550 carbs on gt380 guys. As I said before the GT380 cyl intakes is ready and willing for them from my research too.

Markush with X7 pistonswhat is the highest usable rpm you get 9000RPM? Will it pull OK just under 4000 rpms?

Fun stuff

[yeadon_m]

Hi there,

My GT550 carbs on my GT380B are indeed the 1977 jetting. It feels very nice, as mentioned.
If I had any reason to tinker with the jetting I would do so (in fact, if there was a flat spot or any concern it was too lean I couldn't rest for tinkering!) but honestly, more by luck than anything I've done, it feels spot on and is a joy to ride.

I've retained the stock airbox complete.

Cheers!
Mike

[markush]

Hello!

Did your air box mod dampen sound say versus just removing snorkel?

It is a tiny bit louder than with the original snorkel, but quieter than without any.

How many different jetting combinations did you try before you settled on that combo?

First, I have tried many settings on my GT250 racer. It runs with GT250A-28mm carburetors on RamAir cylinders with adapted inlets. Because of the open air filter I ended up there at #112.5 main jet. GT250RamAir and GT380 cylinder are largely the same. This also applies to the carburetor body of GT250A and GT550, and I have some of the GT250A-needle jets and needles in apparently usable condition, so I immediately took these and I was sure, with them it would work on the GT380. I started with #95, which worked not at all with WOT. #100 was OK for riding, but the B9ES(!) spark plugs looked too bright, so I go with main jet #105 now and the other settings stated above. If we want it more precisely, we have to measure with a lambda probe. I will try this sometime soon at the 380.

Markush with X7 pistonswhat is the highest usable rpm you get 9000RPM? Will it pull OK just under 4000 rpms?

It also revs higher, if you don't shift, up to fourth gear also to about 9500. Below 4000 the engine pulls a very little but not at full throttle. With stock pistons it does from 3000rpm on, also in 6th gear.

bye
Markus

[Vintageman]

My gt250A had first jetting O-2 (not O-0), but since chambers I ran 95 main (not 92.5). Stock air box. More that 95 too rich. 100 main I would at times foul plug. I think a "hotter" (Gt250A 29.5mm Ex versus 32.5/33mm on GT380) engine gives a stronger signal and thus don't need as much jet?

I have three new 172-O2 (could drop needle a clip then O-0 ish) . If I go this route, I as you may have a few runs before OK, but just main jet.I do like you thinking about gt250A jetting



Mike. I believe you too. I would have to buy 169 series Needle Jet for no 172s anymore. Sure that will work as stated before. Dang P4 versus O0. That's 8 size diff on needle jets. Need to compare Jet needles

Both of you have piece of mind that all's near perfect!

But I plan to port Ex just a little too (want to drag race )

Fun Stuff

Someday check your MPG if you think of it