engine numbers ??

[aussie gt]

Can anyone help. engine no 4099 is a K model????? I have read that 1974 model starts at 43041 and 1973 starts 31357 cheeers

[Fritz500]

What model of Suzuki?

[oldjapanesebikes]

I'm guessing GT750 eh ? Info is available here. Numbers for other models are here.

[aussie gt]

Thanks for the reply, it looks like a gt750 k 1973 model cheers

[Suzsmokeyallan]

Just bear in mind that if it had been a 74 engine you would not be able to attach the oil pump cable fitting to the threaded post on the top crankcase since there would be none there.

[aussie gt]

Hi suzsmokeyallan, so there is a different in the cabling between 73 and 74 models ?? The carbs are different. Another question, are the barrels on the J and K models the same. Cheers

[tz375]

Yes and no.

Early 72 had bolt on rubber intake manifolds and late 72 had spigots that look like all later barrels, but without the WATER COOLED badges inset into the sides.

72 and 73 had AMAL type slide carbs and used a 4th cable to operate the oil pump. 74 on used Stromberg style CV carbs with a push pull cable arrangement and throttle shaft, so the pump was changed to use a pull rod from a crank on the right carb throttle shaft

[Suzsmokeyallan]

To add to that bit of info Richard posted, the port timing on 72 and 73 barrels was based more towards lower end torque delivery and less on higher rpm power output.
The 74 barrels are supposed to have a similar porting layout as the 72 and 73 barrels, so being they have the liquid cooled recesses, this makes them a one year specific version of barrel.
From 75 to 77 the port timing and header pipes (no cross over tubes) were changed for less low end torque and more high end output, which gave these engines about three HP more.

[tz375]

And just to expand on that a little. The big drop in low end performance from 74 to 75 appears to be almost entirely related to the intake floor change.

So for a performance motor, grab an early block and raise the exhaust to gain top end and leave the intake alone to keep more bottom end. The change in intake floor tips at around 5500 revs and the combo of earlly intake and late exhaust looks like the best overall.

[Suzsmokeyallan]

tz375

the combo of early intake and late exhaust looks like the best overall.

Now why didn't Suzuki think of that.

[aussie gt]

Thanks for the info, at this stage i am trying to get enough parts together to build a standard 73 motor, but i do have questions about the info. tz375 whats intake floor change???. How do you raise exhaust ports and leave the intake alone? cheers

[aussie gt]

Bought bottom end motor from ebay with k model nos today. So i went looking for id plate i pulled off the frame when i got it power coated last year (hidden away in my spare parts bins !!!) to check how far away the ebay motor number was from the ordinal motor number. I could not believe my eyes when the ebay motor no was the same as the ordinal ID no. So after years apart the motor and frame came together again. CAN NOT BELIEVE IT, HOW LUCKY CAN YOU BE.

[tz375]

No way Jose

Early barrels had the exhaust port roof 42.5mm down from the top and the intake port floor was 101mm down IIRC. MAB were 40.0 and 104 respectively.

If you grind the roof on the exhaust to 40.0 and leave the intake floor alone, you get more top end with almost no loss of bottom end torque. At least that's my theory and I'm sticking to it - until I change my mind.

[aussie gt]

thanks tz, So you get a air die grinder and go for it. No probs with the exhaust port being bigger? You do not have to fill the bottom of the exhaust port? cheers

[tz375]

Porting the exhausts is easy. The roof needs to be raised. You can take it up to 40mm like later motors or venture another mm or two and widen the ports by 2mm either side. Keep the roof as a nice curve and don't be tempted to square it off. The rings really appreciate a gentle curve and remember to slightly chamfer the port at the bore to make life easy for the rings.

The floor of the exhaust port will be slightly below the piston on most stock cylinders and that's OK. The critical dimensions are height and width. The floor doesn't do a lot of anything in the exhaust port. As the piston goes down, it's only at BDC for the smallest amount of time and by then, the gas has for the main part already left the building.

Intakes are almost the opposite. It's the bottom of the port that flows most as the piston rises to open the door. Lowering the intake floor drops hp below about 5500 much more than it adds above that speed. That's why I like short intake events