Intro and a question.

[NickMcDonald]

Hey all. I guess I better introduce myself. Im Nick, Ive been riding a mere 6 months on my 77 cb550f. Absolutely loving it.

Ive recently picked up an old 3ln fzr250 frame for the purpose of bucket racing. I sourced a suzuki gt125 twin for the engine and im attempting to somehow mate the two to form a passable track abortion. Im not terribly clued up when it comes to bike setup, and Im wondering where a good spot for the engine would be. Im assuming I'd want to keep the weight fairly low? But how far forwards/back would I want it? Again, Im assuming centrally regarding the bikes overall weight? Feedback much appreciated.

Cheers, Nick.

[Henk]

Nick

You should probably talk to the ESE guys, I'm pretty sure they have exactly what you are building in the fleet. Come to buckets next Sunday, I'm sure they'll be there. I can point you in the right direction if you can't work out who they are, I'll be the guy with a concrete left arm.

[Rick 52]

Hi
The chain rout will tell you !
With using a 12 - 13 tooth front sprocket the diameter is small and gives you limited options ..Keep the engine as far back as poss this helps with chain tension when the rear end moves up and down.

[NickMcDonald]

Cheers Rick. Yeah I did a quick search and found a page detailing the need to keep the drive sprocket way back. I guess thats a start then! Ill definitely try make it to the buckets next sunday, and Ill keep my eyes peeled for the aformentioned concrete armed Henk. Muchos appreciatos.

[koba]

Ricks advice is good. If there is a bit of room to go further forward, do it. As long as everything still works with the chain run and length.

GT is a cool engine.

Be mindful that the rules stipulate a 24mm carb area for a 125.
You can exceed this easily with 2 carbs, in fact it may not be strictly legal as standard.

However, a single carb on a 125 twin is a great thing because each pot takes turns. Sure, there will be some loss of efficiency with a manifold but if it is made carefully you effectively have up-to a 24mm carb for each 62cc pot.

[Buckets4Me]

Hey all. I guess I better introduce myself. Im Nick, Ive been riding a mere 6 months on my 77 cb550f. Absolutely loving it.

Ive recently picked up an old 3ln fzr250 frame for the purpose of bucket racing. I sourced a suzuki gt125 twin for the engine and im attempting to somehow mate the two to form a passable track abortion. Im not terribly clued up when it comes to bike setup, and Im wondering where a good spot for the engine would be. Im assuming I'd want to keep the weight fairly low? But how far forwards/back would I want it? Again, Im assuming centrally regarding the bikes overall weight? Feedback much appreciated.

Cheers, Nick.

bloody good on ya
chambers is building something very similar but with an rd125 ?? yamaha twin

E.S.E have 2 3ln's but both have gp125's in them
there is some picks on the E.S.E thread of both TZ's and chambers bikes in the build (go back 200+ pages)

[NSR143]

Hey all. I guess I better introduce myself. Im Nick, Ive been riding a mere 6 months on my 77 cb550f. Absolutely loving it.

Ive recently picked up an old 3ln fzr250 frame for the purpose of bucket racing. I sourced a suzuki gt125 twin for the engine and im attempting to somehow mate the two to form a passable track abortion. Im not terribly clued up when it comes to bike setup, and Im wondering where a good spot for the engine would be. Im assuming I'd want to keep the weight fairly low? But how far forwards/back would I want it? Again, Im assuming centrally regarding the bikes overall weight? Feedback much appreciated.

Cheers, Nick.

3LN is the way forward unless you are extremely rich like Rick. He says my 3LN is too heavy, I am thinking of chopping my leg off but I don't think it will help me catch him regardless. But with a 125 twin you should have a good power to weight ratio. Good luck.

[speedpro]

The 2 stock carbs combined exceed the allowable single 24mm equivalent. However, I have seen a very simple manifold made from a copper plumbing T-piece and 90deg angles that very nicely supplied two cylinders from a single central carb.

[NSR143]

The 2 stock carbs combined exceed the allowable single 24mm equivalent. However, I have seen a very simple manifold made from a copper plumbing T-piece and 90deg angles that very nicely supplied two cylinders from a single central carb.

surely we should consider 'standard' carbs are OK unless he starts kicking everyones arse????

[speedpro]

I'm pretty sure that nobody would complain if he turned up with stock carbs. I wouldn't. As long as he was aware they were illegal and didn't expect anything other than to get a ride.

[speedpro]

I've got a 3LN chassis as well and it's a great ride. Check the "#6" thread. Plenty of room for carbs, or in your case another cylinder. They handle good, stop good, and are comfy for us more mature types.

[jasonu]

I'm pretty sure that nobody would complain....

I have already lodged a protest with Peter Ramage. He told me he will get right on it...

[Grumph]

I have already lodged a protest with Peter Ramage. He told me he will get right on it...

Yeah, after the two years worth of shit arising out of this years nationals....and they're barely started yet !!

Re engine placement - the final drive sprocket should ideally be in line with the swingarm pivot and rear axle at about 1/3 of the rear wheel travel and as close as possible to the pivot.
As a general rule the further forward you move the motor, the higher in relation to the pivot it should go...a little work with pencil and paper will show why.

[NickMcDonald]

Good point raised by koba regarding the use of a single 24mm carb. I was actually planning on just rocking the two factory carbs for now. Im almost certain they exceed the two 17mm carbs rule, but I figured it wouldnt be too much of a controversy for now considering Ill be lucky to get around a track without ending up on my ass. Whats everybody elses thoughts on using a well designed single carb manifold for a twin?

Ive got a fairly decent idea of how I want the motor to sit. Ill have a browse through that colossal ESE thread and see what I can dig up. Cheers all.

[F5 Dave]

Yeah just run it how it is but when its sorted change it over to keep within the rules. Search GT125 on this section & you will find the math done several times. You could sleeve the carbs or buy a 24 & manifold it.

GT isn't a small engine, but either is FZR so it will sort itself out as long as you have the chain so its just lying on the top of the swingarm at rest with a small sprocket. Ideally you'd have the sprocket touching the swingarm, but you need to keep the weight near the front a bit as well so a compromise can be up to 4" forward of this point, but that can cause issues with longer travel bikes & chain tightening up means running it loose on some bikes so it doesn't go over-tight as the SW goes over parallel pivot (tightest point)