Over bore a GP100 bucket?

**TonyB** · 11th July 2005, 14:53

I'm looking at buying a Suzuki GP100 to go bucket racing with. I know there also used to be a GP125, and I also know they shared the same conrod, so I guess it's safe to assume the gearbox etc was the same.

I'm picking that the barrel and head are the same for both, and that the 100 just has a bigger sleeve, which would mean it can be over bored to 125cc. According to a website I found, the 100 has a 50mm bore, and the 125 has a 56mm bore.

Can anyone tell me if I can indeed bore the 100cc barrel out to 125?

**speedpro** · 11th July 2005, 15:56

I don't know for sure but I'd doubt it. It may even be cheaper to buy a 125 barrell rather than bore the 100cc one out 6mm. Plus the transfer ports are probably different. Going from past experiance(with TS100/125) I would expect the barrels to be able to be swapped but don't bet on the gearboxes being the same. It'll work OK just might be different. The GP is an OK bucket racer with plenty of potential for power, the gearbox might be a disappointment if you REALLY start getting into it.

**TonyB** · 11th July 2005, 16:18

Yeh, I noticed the gears seem fairly widely spaced, but given my 'abilities' as a rider I think it'll be a loooong time before that becomes a problem.

I'm not overly mechanicaly minded, but as the stroke is the same (only the bore changes) I thought maybe the ports would be the same? Mind you, I suppose the depth of the port would decrease by 3mm which wouldn't help the performance.... Hell, I don't even know how a rotary valve 2 stroke works

Do they have ports in the bore??

**speedpro** · 11th July 2005, 16:31

Giving the clutch a hiding can overcome powerband versus gearbox inadequacies. Just check out F5 next time he's down your way. It's nothing to worry about.

Guys up here have GP125s going OK. Someone down there will be able to do the basics for you. I'd try for a 125 barrel, fresh piston, get the motor going good, ride it a bit, and then some basic stuff like a bit more compression.

If the motor is running well and you have good tyres and brakes it'll be sweet.

**diesel pig** · 11th July 2005, 21:44

The gp125 barrel will swap straight over to the gp100 bottom end and would be easier (and in the long run cheaper) than boring the gp100 barrel but remember you will need the gp125 head too to match the bore.

**speedpro** · 11th July 2005, 22:50

Originally Posted by diesel pig

The gp125 barrel will swap straight over to the gp100 bottom end and would be easier (and in the long run cheaper) than boring the gp100 barrel but remember you will need the gp125 head too to match the bore.

I see the old Yokohama tyres cartoon has been ressurrected. I've got a 4 X A4 size original drawing on my wall.

**TonyB** · 12th July 2005, 08:19

Thanks for the advice guys. I've just done a wee deal with Russell (111) to lease one of his GP100's for the rest of the year. I just need to check the rules, as Russell is pretty sure the 125 2 strokes have to be proddy racers.

TonyB is going Bucket Racing!

**Bren_chch** · 12th July 2005, 12:33

yeah get 111, dont lease that fuker i was on, i rekon its cursed!!!!

**speedpro** · 12th July 2005, 15:38

Originally Posted by TonyB

Thanks for the advice guys. I just need to check the rules, as Russell is pretty sure the 125 2 strokes have to be proddy racers.

TonyB is going Bucket Racing!

They must remain air cooled and use carburation equivalent to a single 24mm carb which typically is the stock carb size. Even with these constraints they can be made to be competitive, especially on kart tracks where peak horsepower is not so much of an issue. The disc valve 125s seem to fare better with the 24mm carb than piston port motors. Jim Steadmans "Kawa125/RG400 barrel" hybrid only has a 28mm carb and there aren't many that will get past him in a straight line, or round corners for that matter.

If you have a bike sorted to ride that's good as it gives you time to collect bits at good prices while still being able to race.

**TonyB** · 12th July 2005, 15:57

Cheers speedpro.
I'm pretty sure the GP100 has a 22mm carb. Not sure on the GP125.
If I can't get a 24mm carb that will actually fit, is there any point in going to 125?

**diesel pig** · 12th July 2005, 18:45

[/QUOTE]
simple you get a gp125 carb they are 24mm!

**speedpro** · 12th July 2005, 18:46

Originally Posted by TonyB

Cheers speedpro.
I'm pretty sure the GP100 has a 22mm carb. Not sure on the GP125.
If I can't get a 24mm carb that will actually fit, is there any point in going to 125?

The Yanks summed it up pretty well with "You can't beat cubic inches". If you get a 125 barrel get the carb off the bike at the same time.

**gav** · 12th July 2005, 19:19

simple you get a gp125 carb they are 24mm![/QUOTE]
So you must as well just buy a complete GP125? Any advantage having a GP100 over the 125?

**dangerous** · 12th July 2005, 20:30

Originally Posted by TonyB

TonyB is going Bucket Racing!

Ya bloody bugger, my bucket days are over for a bit and they hardley began..... LOL, I have to peal the lid off the motor for some serious repair work

Its just not 'dangerous' enuff running on 1 pot