Suzuki 2 Strokes

dgoodsy wrote:cool! (not the waiting part, but the part about raising the exhaust ports.)

Being a noob to modifying 2 strokes I had to google how raising exhaust ports affects performance. I read that it trades off a little low end grunt for some top end power. What is your plan for an exhaust system?

I am going to run a 3-1 system to try and keep the "stealthy 2-stroke" look.

I have a spacer plate (3mm lift with the extra gasket) under by jugs, and with my Jemco pipes, and 34mm VM carbs, and 3 mm removed from rear piston skirts, I am putting about 80 HP on the ground, revving hard up to 8K. If you raise the ports, and use a 3 into 1, you're gonna break even and basically get stock power. 3 into 1 typically only revs to about 6K. Don't get me wrong, it'll still be fun.


Lane

you got it in one, Lane

the idea is to get standard GT750 power using the 3-1 system.

garry55 wrote:you got it in one, Lane

the idea is to get standard GT750 power using the 3-1 system.

I hope you are using an MAB cylinder. That's what I have, and it works well.



Lane

no - I am using a "J" motor - slide carbs and all.................

The slide carbs area must.



Lane

I have 2 sets of slide carbs - 32mm and 34mm. Will probably save the 34's for the track bike.
Not looking for out-and-out performance from the road bike.

Stock zinc 32s or real ones??

Stock OEM carbs are heavy and long but they are less tall than aftermarket carbs. Almost all 32mm and larger carbs are too tall to clear the clutch side crankcase. There are some 34mm small body snowmobile carbs around that clear and there are other options available. Some guys mill the early block to raise the downdraught angle. Others use angled carb adapters. Another fix is to cut a section out of the top crankcase half and weld it back in as a concave curve.

The last option - for lazy people is to let the carb drain bolt rest on the crankcase but that tends to cause fuel frothing and related problems.

I have one set of stock carbs and one set of Keihins. The stock carbs should fit OK - I haven't tried the Keihins yet. Also have a couple of sets of the later stock CV carbs which may be OK for road use?

Correct. BS40 carbs are OK up to around 100HP as per Bob Prior. His makes around 95 RWHP IIRC and that's on stock OEM carbs

In which case I will build the later motor for this project and utilise the stock CV carbs - I think they transition better than slide carbs for road use.
The XR11/73 project can run the slide carbs as that is primarily for track use.

For the street, my preference is late 72, 73 or 74 barrels ported on the exhaust side to better than MAB specs with stock (but cleaned up) intake timing. Tests show early motors made more torque and analysis suggests that the later intake timing hurts more than the exhaust timing helps, so go for both - port and older block.

It's your bike...do what you want. I rode a 72 with a 75 engine using the 72 carbs and it was a wheelie machine. Power wheelies were easy, and made me laugh until the rear tire blew out....another story. My bike, as is, does power wheelies if I want it too, but I'm not a wheelie king, so I don't do it much.


Lane

you used early carbs on a later motor?
are the inlet manifolds compatible? (I don't have a set of post-J/K manifolds to check).

Yes. All late J and K on barrels had the same diameter intake stub and will take K inlet rubbers which allow you to fit J/K slide carbs on any motor.

J/K slide carbs have a 43mm outlet OD which is the same as regular VM34, TM38 etc. TM32 are 40mm OD as are small body 34s but they can be sleeved up to fit into a BS40 intake rubber. Lane (rngdng) let me into that secret.