Lawn-Boy Model 'E' Twins (mockup)

[Russ2251]

Is it actually better to run a (mixture corrected) 2-stroke with open pipes or with a possibly restrictive muffler?

An unmuffled 2 cycle will produce more power/rpm than a muffled one.
An expansion chamber is not really a muffler but actually takes advantage of exhaust pressure waves that emanate from combustion chamber.

It makes me wonder if I could've pulled more beans out of my snowmobile engine if I ran a pipe instead of the Harley muffler

Just a pipe would be much better.
This article will help:
Expansion chambers explained
A properly tuned exhaust can do more for a 2 cycle engine power band than porting.
It could be said that this is analogous to putting a bumpy cam into a Briggs 4 cycle without ever having to disassemble engine.

 

[KingCobra]

You like pink Russ?

Ummmmm Here is one of Russ's karts I had to rescue! Now to paint it lavender

 

[Russ2251]

shouldn't your tie-rods be in front of the frame?

Depends on design. My 1 wheel drive kart has tie rods in front.
Azusa placed them as pictured. Plenty of room for feet to rest on floor pan:

 

[Russ2251]

Another hijack.

 

[jr dragster T]

Dont worry about the hijacking Russ. We try not to respond to hijacked threads lol. So hows the dual lawnboy kart coming? Pilots licence in yet?

 

[Russ2251]

Have hit some snags. I will post an update soon.
Thanx for asking.

 

[jr dragster T]

Cool hope to see some video footage of this thing soon. I hate those little snags that get in the way that present a huge probelem.

 

[gocartkid]

I've been gone for a while so I missed the start of this project.....but all I can say is WOW!!!

And I have an identical frame just laying around too....

 

[Scorch3]

oh i know the snag, small problem, easy solution, small part, big shipping?

 

[Russ2251]

Some problems solved...now Nº2 CDI pack is flakey

Twin linkage is now complete, synchronized, and functioning as it should. Will no doubt need some tweaking once both engines are up and running.
Total weight of kart is now at 148.8 lbs. Not bad considering that original single engine one wheel drive kart was 98 lbs.
Engines only weigh in at 25 lbs. each with custom mount. Compare to clones at 33.8 lbs.
Wanted to post vid of initial start-up, but one CDI pack failed (start side).
No real problem here...an easy fix.
A couple of quarts of a TCW3 mix will be used for running in engines before switching back to full synthetic racing oil.
Should have it up and running Monday with vid to follow.

 

[Russell ATV]

What was the power rating on those engines? I think you mentioned a gear ratio of just over 4:1, so based on the MAx RPM (you will likely reach it), what do you calculate as top speed?

If you are like me, I do not think a helmit will be involved, so I wonder how long you will keep your foot in the throttle. Things get squirelly beyound 50MPH. Little things like balancing the tires become necessary.

It is going to scream.

Russ Barrow
Russell ATV

 

[Jerryburger]

Should have it up and running Monday with vid to follow.

....this is going to be cool! I was wondering when this would be finished!

What was the power rating on those engines? I think you mentioned a gear ratio of just over 4:1, so based on the MAx RPM (you will likely reach it), what do you calculate as top speed?

Stock, he was at 6.5hp per motor. If they can hold 7000 rpm, and (I'm ASSuming a few things here), he has 13" dia tires and a 4.5>1 ratio, that'd be 60 mph.
I see no reason why he WON'T hit 60, unless he doesn't have the room, or the motors won't hold at that rpm.

 

[jr dragster T]

I'm not sure if the motors will hold 7000 rpm for very long. I suppose tests will show. Great job Russ!

 

[Russ2251]

I'm not sure if the motors will hold 7000 rpm for very long.

This is the real unknown. Best I've turned is just under 5.5k rpm (single engine) and only because of short length of parking lot.
Virtually everyone who has driven the original, remarks how it's still accelerating before being forced to hit the brake.
Original kart (not DuraForce) was clocked at 42 mph with a car (backed up with speed calculator).
DuraForce is clearly faster.
Top speed/rpm with twins? Who the hell knows.
I'm more impressed with torque than with mph. Something about the smell of burning rubber I guess.

....this is going to be cool! I was wondering when this would be finished!

Not really finished yet. Vid will simply document initial cold start and adjustment of carbs. Chains will not be installed at this point.
I no longer have access to a dyno, so horse power will remain a mystery. Advertised hp is 6.5, but does not take into account increased compression ratio, larger than stock Tillotson carbs, and straight pipes.
If I absolutely had to estimate hp....my educated guess would be 7.5 to 8 each or 15-16 total. This number might be conservative...or dead wrong.
http://www.youtube.com/watch?v=0C8-I8rVAaQ
Original kart numbers (not DuraForce):

 

[Russ2251]

Should have it up and running Monday with vid to follow.

As usual...the picture has changed.
10+ inches of snow predicted through the next solar day.
Long Island summers are about the best on the planet, but when it snows...well...it just plain sucks.

 

[jr dragster T]

Sorry Russ looks like we sent you some snow. I hope you like your present from me. We still have 5' snow banks everywhere.

 

[BradenM]

It hasn't snowed in my city for several decades

 

[Jerryburger]

Sorry about the weather,Russ. Here, it gets too f*&^ing hot to be outside for at least 4 months out of the year. Figures....

I think the motors should hold. My reasoning (extremely flimsy in the cold light of reality) is that in The Olde Days, people used to run 11" wheels with 5.1 or as short as 6>1 ratios using existing utility motors (and rev the piss out of 'em to boot.) Those old Clintons, and (can't remember any others off hand) the rest of those 2 strokes worked pretty well in that role... not being modified much past porting/breathing.
Mechanical-Durability-wise, if the motor has a 2.5" stroke (Duraforce I believe is shorter) and spin it at 7000 rpm, you have a piston-feet per minute of 2900 ft. per minute... well under the "Oh My Gawd, She's Gonna Blow!" speed of 4000 ft per minute. (For comparison, a stock Harley Sportster can spin 6000 rpm, or 3900 ft per minute, and still have a 2 year warranty.)
So, all this guestimating comes down to, are they (Duraforce motors) obviously a bad design or poor quality of build? Doubtful. A person who pulls one of these things apart would quickly see the obvious.

Now I'm on a roll:
Since each motor is driving it's own wheel independently, it'll be no more likely to lay rubber than with the single-engine kart, because the same motor is driving the same tread-patch... BUT, acceleration is going to be ridiculous. It'll still do those lift-wheel spins around corners like before, and it'll hit the torque peak of the motor(s) much quicker.
Sorry about all the blathering, but I love this stuff.

 

[jr dragster T]

Since each motor is driving it's own wheel independently

both engines are attached to a live axle.

 

[Kevin Noah]

I think you're going to be amazed at the quickness of your build. Lower # of sprocket (62-64)could propel you to 75mph and faster. Is this the first dual you've ridden? Hold on tight.