Suzuki GT750 Neuvo Retro Cafe Racer

[tz375]

Jets are cheap, so that's not a major issue, But I would be tempted to lift the needles again and see what difference that makes. If that improves things even slightly I'd try Z-6 needle jets http://www.mikesxs.net/product/48-0654.html" onclick="window.open(this.href);return false; and drop the needles back down and see if that does the trick. They are available from MikesXS.com and if you try them, don't forget to buy a few extra O rings http://www.mikesxs.net/product/48-5020.html" onclick="window.open(this.href);return false;. If you have spares you will never need them and if you don't, one will run off the bench and hide or get cut fitting it.

The O rings are still available from Suzuki - at least they were the last time I checked.

Larger Needle jets will make a significant difference at the bottom end and they may be too rich but it's worth a try.

[tz375]

Jets are cheap, so that's not a major issue, But I would be tempted to lift the needles again and see what difference that makes. If that improves things even slightly I'd try Z-6 needle jets http://www.mikesxs.net/product/48-0654.html" onclick="window.open(this.href);return false; and drop the needles back down and see if that does the trick. They are available from MikesXS.com and if you try them, don't forget to buy a few extra O rings http://www.mikesxs.net/product/48-5020.html" onclick="window.open(this.href);return false;. If you have spares you will never need them and if you don't, one will run off the bench and hide or get cut fitting it.

The O rings are still available from Suzuki - at least they were the last time I checked.

Larger Needle jets will make a significant difference at the bottom end and they may be too rich but it's worth a try. The difference in annular area is +18% at the root and +2% at WOT.

The dyno suggested that Jemco pipes were way more lean as the slides lifted than the 3 into 1 pipe.

[Rassie]

That sounds like a good fallback plan to me. I will see how the washers work, but honestly if it fixes the problem I am going to leave well enough alone. As it stands right now I would say the surging problem is about 80% better than before. If the washers give me the other 20% I am stopping there.

If I may ask why you suggest these specific (z 6) needle jets. Is there are reference to what is in the stock GT carbs so we can at least compare it that way or is the % you quoted the only thing we can go on?

[tz375]

That's a secret and if I told you I'd have to kill you

Stock BS40 needle jet is Z-0 and bought a bunch of different jets to find a useable alternative. MikesXS happens to sell that jet which fits our carbs and I worked out teh difference in area versus the stock Z-0 NJ

[Rassie]

Nice

If the washers don't work as expected then I will definitely go that route. I think the 18% at the bottom can possibly be overcome by going back to the stock pilots @ 145 or maybe one size down 142.5 if they do prove to be too rich at the root. What do you think?

I am installing the washers today and plan to ride the bike about 50 to 60 miles tomorrow.

[tz375]

Those percentages represent the annular gap between the needle and jet like a small doughnut. At idle, there is little to no flow from that orifice and as revs and air speed increase, the needle jet becomes more important. The implication is that mixture from say 1/8th throttle up will be richer with that needle jet compared to stock. At higher throttle openings the extra area remains constant but it becomes a smaller percentage increment over a larger base.

It will be interesting to see if smaller pilot jets are required or not. I suspect not, but I suspect that the mixture screw setting may change.

Have fun on the ride. We'll be interested to hear how well that needle adjustment works.

[Rassie]

Just so you can get an idea how the washers fit and their size, here are some pictures. I installed them this afternoon.

[Rassie]

Bottom line is that the washers did not make much of a difference if any. I was out riding with Ringding and I asked him to ride my bike to get a second opinion and he felt that it ran quite well and that I should try the airjet mod next. Ringding feel welcome to add here. While at it I also did a quick plug check as in the picture below. I am at the point where I think I have done what I can and it runs well enough. I will take out the washers and do the air jet mod. May also go to the 122.5 jets to see what happens. But that will be all I am planning right now.



Here is a nice picture of beauty and the beast, Ringding's beauty and my beast

[Rassie]

Here is a video so you can hear it run..

http://www.youtube.com/watch?v=JUYp2ni6 ... EQ&index=1" onclick="window.open(this.href);return false;

[Suzukidave]

Sounds bad a$$

[RING_DING]

Oh yes it is! Just to make you all jealous, I had the pleasure of riding the Threesome for about 10 miles yesterday. The sound is just incredible. Throttle response is very crisp. There is still some surging, so I think perhaps the airjet mod is worth a try at this stage. The top-end kick from the chambers is significant, way different from the 3-1 setup I have on my Red bike. Brakes & suspension are well sorted....feels like you are on a modern superbike.
Rassie, we need to find a deserted airfield where we can do some more "performance testing"

[Rassie]

Oh yes it is! Just to make you all jealous, I had the pleasure of riding the Threesome for about 10 miles yesterday. The sound is just incredible. Throttle response is very crisp. There is still some surging, so I think perhaps the airjet mod is worth a try at this stage. The top-end kick from the chambers is significant, way different from the 3-1 setup I have on my Red bike. Brakes & suspension are well sorted....feels like you are on a modern superbike.

Rassie, we need to find a deserted airfield where we can do some more "performance testing"

I like the performance testing idea...

[CJF]

I love the sound of that exhaust!! Think I may be adding a GT750 to my garage in the future.

[tz375]

Ring_ding,

Just a hint, don't put any cash or pink slips on the line. Not that I have dyno tested both pipes or have any opinion on the matter. Just sayin'...

That would be fun though to see roll on performance differences

[RING_DING]

TZ, no worries.....I'm certainly not betting the family jewels on this match! It would be an interesting experiment though, as between Rassie & me we have stock pipes, Strader 3-1 and Jemco 3-3.