Project 74 GT550

[r3tro74]

72 and 73 are the same but the are not interchangeable with the 74 thru 77 tanks which are also the same, The 72-73 tanks had a much more rearward petcock mounting placement due to the carb mounting position and extended fins on the head. I trial fitted a 73 tank on my 75 and the tank hit the frame and lacked about an inch of going all the way down at the rear. The later tanks won't fit the earlier frames, once again because of the petcock mounting placement. It was moved over an inch forward and would hit the head f for the fins that were chopped off in 74.
So, the 72 and 73 380 and 550 tanks were ide

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ntical as are the 74 thru 77 tanks.

Great info. Thanks
The carbs are back together with linkage repaired. Its running way better now.
I figured out how to get the last bit of air out of the brake. The m/c resovoir has a hole in the center that allows fluid to get the ports in the casting. The ports are off set to the rear of the hole in the resovoir. Air was taped under the resovoir and was sluicing back and forth. Temporarily rotating the m/c lever side up on the bar and bleeding allowed air to come out from under the resovoir

[Scorch]

Great build, r3tro74, thanks for sharing. Got any pics of the painted parts?

[r3tro74]

My wife is out of town with the camera. Hopefully I'll get some pics and video up this weekend. I still have some finishing touches and tuning.to do. I to get insurance, etc.

[Allan k]

How much did that jemco exhaust cost ya?
I want a set like that for my 550 too!

[r3tro74]

How much did that jemco exhaust cost ya?
I want a set like that for my 550 too!

http://jemcoexhaust.com/downloads/Jemco ... atalog.pdf" onclick="window.open(this.href);return false;


The catalog shows the gt750 but does not show the gt550- youll have to call him and ask. Mine were slightly less than the set for the 750. I did not opt for the nickel plating. Was planning to paint them black or aluminum/silver but after seeing some various preserving techniques such as Mop-n-glow, WD-40, or gun oil, I kinda like the raw welded up look.

[Allan k]

How much did that jemco exhaust cost ya?
I want a set like that for my 550 too!

http://jemcoexhaust.com/downloads/Jemco ... atalog.pdf" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;


The catalog shows the gt750 but does not show the gt550- youll have to call him and ask. Mine were slightly less than the set for the 750. I did not opt for the nickel plating. Was planning to paint them black or aluminum/silver but after seeing some various preserving techniques such as Mop-n-glow, WD-40, or gun oil, I kinda like the raw welded up look.

Me too!
I did sent him an email yesterday...hope to hear from him Soon.

[r3tro74]

Got any pics of the painted parts?

I forgot I needed mirrors, so hopefully track somthing down in a few days. One of the original mirrors has the coveted "S" symbol on it, they just look way to tall on it- like moose antlers.
Everything works- charging, signals, brake light, speedo, tach, etc. Starts and idles good, no insurance for a couple more days so how it takes the gas remains to be seen...
I'll post some video this weekend

[Coyote]

GOOD JOB

[r3tro74]

Here is a video of her idling in the front yard. I ran around the block a few times. I have some more tuning to do. She seems to idle fine but likes constant acceleration. Even just a slight bit of accleration and she feels smooth. however, when trying to maintion a constant speed , bucks and pops a bit. right now I'm running 105 mains (stock was 97.5), 30 pilots (25 stock), original needle jets and slides with the needle in the bottom groove (stock was 1 groove up).

http://www.youtube.com/watch?v=qL_5Vn4L ... e=youtu.be" onclick="window.open(this.href);return false;

[r3tro74]

I had a couple of hours to play around today. I reviewed the topics "low speed tune/crackle or not" and the "gt550 jetting with chambers". I marked off the throttle in % openings as was sugested. (taking some extra care here to make sure that my marker tape didn't hit the kill switch would have saved me some aggrivation ) It seemed to be most noticible 1/8 to 1/2 throttle opening. a slight increase in throttle at any speed would momentarily smooth it out until the RPMs raised up to an equlilbrium state then crackle/buck untill adding a little more throttle- same thing 1000 more rpm of smoothness then crackle/buck.
It seemed rich at idle- no raw fuel but rich exhaust smell. I put the stock pilots back in and set to air screws to max idle. It takes off better now and the crackle/buck seems less noticable, but still needs improvement. I swapped out the pod filters for the stock air box and could not feel any difference at all.
I wanted to use what I already have in an attempt to diagnose before buying more wrong stuff so decided to experiment and removed the carbs again and put the needles back to the stock position. A little more of an undertaking than swapping out jets. The kids woke up from thier nap before I could get it all back together. Its forcasted to rain tomorrow so hopefully i'll get a chance to work at it some more and get her straightened out..

[Allan k]

Just saw the video.... Sounds great!

I just wanna know how the hell you Can run it at only 1000-1100rpm idle!

Mine wants minimum 2000 to have steady idle..

[r3tro74]

GOOD JOB

Just saw the video.... Sounds great!

Thanks for the encouragement!

So its back together with the stock air box, pilot jets, and needle in the stock position. Kept the 105 mains. The air screws are best at ¾ to 1 turn out. It’s raining on and off all day. I did get out on the road and its running great. I stayed under a ¼ throttle or so because I didn’t want it coming out from underneath me on the wet roads. It spins right up and holds steady speed without the crackle/buck. It does crackle between shifts (I’m fine with that because it sounds great). Maybee dry roads tomorrow and I can go for an extended ride and check the plugs to be sure I'm not too lean now.

http://www.youtube.com/watch?v=2dlohPKB ... e=youtu.be" onclick="window.open(this.href);return false;

I just wanna know how the hell you Can run it at only 1000-1100rpm idle!

Mine wants minimum 2000 to have steady idle..

OK if you mean that with the idle speed screw bottomed out it won’t idle down, that happened to me on my first set up. I used the “Suzuki GT 2 stroke late model carb manual” and the “VM Manual” to set these things up. The Suzuki manual stated to set the idle stop screw 1 ½ turns out and then set the individual throttle valves. Mine would not idle lower than 2K due to the idle stop screw bottomed out and would not allow further adjustment. The second time around, I placed the idle stop screw 2 ½ turns out then set the individual throttle valves.
If you mean that it stalls under 2K then something is probably not exactly even between the cylinders – timing, throttle valve opening, plugged up jets, or exhaust, float height, etc.. I spent a bit of time setting all these things, rotating the engine and rechecking, rechecking the zero of my indicator, etc. Wearing "reading glasses" helped out a lot.

[macdogg]

R3tro74,

Awesome build great color choice, you have inspired me to put off buying my dual purpose bike, and instead put the $$ into my 72GT550, hopefully I will beable to pick your brain on various issues that may/will arise.

Cheers
MacDogg

[r3tro74]

Thanks. I changed my mind a few times on the color. I'm happy with the way she turned out. I originally planed to do the paint myself. I was talking to a neighbor who works at a local auto body shop. He offered to do the paint for about what it would cost me to do it myself. I purchased the deals from reproductiondecals.com. I emailed "Deb " a few times who was going to do a color change on the 74 GT550 set (no extra charge to change 1 color). I ended up getting the set for a 74 gt380 because it already came in grey and i could cut the "tails" off the top to use on the seat.

[r3tro74]

Great work. How did you polish the motor cases ? What did you use and how did you go about it ?

If you are asking about the engine case halfs, cylinders, and head - they are not polished. I soda blasted them. I had an old "speed blast gravity feed blaster" no pic, but you can google it. I shelved a while back because it never worked real well, but after reading other posts about soda blasting I thought Id give it a try. A couple of $3 jumbo boxes of baking soda from Meijers and it was done