Standard Suzuki GP125 specs.

[TZ350]

For what its worth here are our measurements.

Measurments taken using large protractor from the Warehouse.

On a Standard Suzuki GP125.

Bore 56mm Stroke 50mm 15hp at 8500 Rpm Carb 24mm. MJ 90 to 97.5

Inlet opens 145 BTDC closes 55 ATDC.

Exaust opens 91 degrees ATDC Duration 178 degrees.

Area of exhaust port is 85mm# and 64% of bore width.

Exhaust port diamater at the flange is 36mm.

Trans1 opens 120 degrees ATDC Duration 120 degrees.

Trans2 opens 120.5 degrees ATDC Duration 119 degrees.

Boost opens 122 degrees ATDC Duration 118 degrees.

To work out duration, subtract opening degrees ATDC from 180 and multiply the resultant by two.

Ie., Ex opens 91 ATDC so 180-91=89 and 89*2=178 Duration.

People have had very good results adapting an RG250 chamber to the GP125.

Others have used part of the header section from the RG250 pipe and welded their own cones onto it to make the rest of the pipe. Use 1.25mm sheet. This gives a heavy but strong pipe that can be rigidly mounted and survives bucket racing crashes, easy to weld too.

From the backroom boys. , and .

[F5 Dave]

They claimed 15hp at the crank I guess. In UK the then newly introduced learner rules were for 12hp. The GP125 frustratingly made 13hp. So Suz UK contracted an engineer to make a restrictor. He came up with a suitable turned washer that fitted in the top of the carb limiting travel.

He then started seeing customers wanting to de restrict the bikes (removing said washer). Then sold them back to Suz UK & thus being paid 3 x for the same work.

[CM2005]

Isn't the allowed carb size 26mm? See you at Mt Welly for the 2hr TZ!! Have fun in Taumaranui on the weekend!

[TZ350]

They claimed 15hp at the crank I guess. In UK the then newly introduced learner rules were for 12hp. The GP125 frustratingly made 13hp. So Suz UK contracted an engineer to make a restrictor. He came up with a suitable turned washer that fitted in the top of the carb limiting travel.

He then started seeing customers wanting to de restrict the bikes (removing said washer). Then sold them back to Suz UK & thus being paid 3 x for the same work.

Thats interesting, has the ring of truth. I remember a previous post where you said "HP measured at the sales broacher", how true, the workshop manual says 15hp, and yes, I gues it would be at the crank by the Marketing Dept.

That might explain why after working on my bike and getting it running well it only showed about 12hp, thought I had made a mistake with my work and lots of my friends enjoyed the joke that I had tuned it to a standstill.

Later after a lot of development I was dissapointed to think I had only gone from 15hp to 18hp. But 12hp to 18hp at the rear wheel is a much better achievement. Thanks F5 for the insight.

[TZ350]

Isn't the allowed carb size 26mm? See you at Mt Welly for the 2hr TZ!! Have fun in Taumaranui on the weekend!

24mm max for F4 125 air cooled two stroke.

[Slingshot]

They claimed 15hp at the crank I guess. In UK the then newly introduced learner rules were for 12hp. The GP125 frustratingly made 13hp. So Suz UK contracted an engineer to make a restrictor. He came up with a suitable turned washer that fitted in the top of the carb limiting travel.

My Haines manual has this to say on the matter:

Late GP125 models have a circular plastic ring fitted inside the throttle valve, to restrict the amount of throttle opening. This modification was necessary to comply with the government regulations on 125cc machines introduced in 1982.

[bucketracer]

Cool, actual verification.

[bucketracer]

To work out duration, subtract opening degrees ATDC from 180 and multiply the resultant by two.

Ie., Ex opens 91 ATDC so 180-91=89 and 89*2=178 Duration.


From the Team ESE backroom boys. , and .

Thats interesting allways wanted to know.

[F5 Dave]

His name was Leon Moss & a regular tech input via JR in PB mag back when what they said was worthwhile. Sadly killed in his car by a run away trailer I think.

[koba]

Cheers for putting that info up!
Very interesting.
If I ever have the MB engine apart I will get a cheap protractor and post the same infor for reference.

[F5 Dave]

Ok I’ll start you off

Inlet, 360 deg.

[diesel pig]

If I ever have the MB engine apart I will get a cheap protractor and post the same infor for reference.

The port timings for the MB100 (H100A in the book) and H100 (H100S in the book) are in the Haynes manual. I will post them up if I come across my photocopy of them.

And here's a fun fact not one port timing is the same between the MB100 and H100.

[koba]

Ok I’ll start you off

Inlet, 360 deg.

I made the reeds better yesterday, the casting was shit im sure I must have gained at least 0.00012 horsepower!

Anyway I did notice looking down the inlet that I could see lots of piston skirt, does it actually close the inlet when it is standard, even tho it has reeds?

The port timings for the MB100 (H100A in the book) and H100 (H100S in the book) are in the Haynes manual. I will post them up if I come across my photocopy of them.

And here's a fun fact not one port timing is the same between the MB100 and H100.

Shit man, Im confused already!

[F5 Dave]

There are fingers around the sides of the barrel that feed the transfer area & hence the crankcase to the inlet is potentially 360. Of course the reeds close so this is not really the case. The inlet is in need of a two sided reedblock. Easiest option is cut ~ 1cm off an old air cooled yam & get it tig'd on (just corners so don't distort everything) & Devcon the join, then hog it out so the block fits on, use the yam inlet & you're away.

Sensible option is not to open the inlet too wide or you'll break skirts when the piston or bore wears.