Lawn-Boy Model 'E' Twins (mockup)

[freakboy]

well if something would go that would go before the flywheel.

 

[jr dragster T]

I highly doubt Russ is going to blow anything up in his engines. He really knows his stuff and the only modifications done AFAK are carb and a higher compression ratio. Typically engines like this as long as the power keeps getting to the rear wheel its not going to blow.

EDIT: Russ, Your going to blow a flywheel!

 

[Jerryburger]

Maybe all the "Yer Flywheel's Gonna Blooooow!" people died. That article you posted on exploding flywheels was from the early 1900's......?
I think the motors will run out of their powerband before they grenade. Or maybe hole a piston, but that would take some doing. My Dad, back in the 70's had a Honda CB100 (his first bike) and was trying to keep up with friends on the freeway. Well he DID keep up a pretty good speed, but after a few miles, the top of the piston burned through about a quarter inch hole in the dome. He replaced the piston and rings and it was fine.
Since Russ says it richens up on the top end, that would negate the overheated piston crown.
I'm still voting for the 54 tooth on the back. It'll still jump off of the line.

 

[Russ2251]

I'm still voting for the 54 tooth on the back. It'll still jump off of the line.

I'm hoping your right Jerry.
I have a pair of unused 66 tooth split sprockets I may bolt up this afternoon.
If I end up losing a significant amount of torque...the 72 toothers will go back on.
As stated earlier, I'd rather have the torque.
As everyone knows, there are trade-offs when screwin' around with ratios.

 

[jr dragster T]

I think if you ran the 66 tooth rear you would still have plenty of off the line power and a higher top end.

 

[Rickracer]

I ran a 15 tooth clutch with a 63 tooth axle gear behind my (12 hp?) GX240, it didn't have great take-off, but it was decent. With twins, it would have been great, and I'd have probably wound up dropping some rear teeth to keep the motors from over-revving on the race course.

 

[Russ2251]

I have been running that same ratio.
I was using 17 tooth clutch with 72 driven sprocket or 4.23:1.
With 66 tooth sprocket ratio is now 3.88:1.

 

[Jerryburger]

I've upped the ratio (taller) on some of my projects, and since the motors "come on cam" at slightly higher speed with the taller ratios, the kart/bike/whatever seems to be quicker. Not quite as jerk-your-neck off the line, but I'll trade snappy on the first 20' for the better rush afterwards. (There's a point of no return, obviously, but judging by the way your kart jumps up to top speed so quick, you can definitely take advantage of a taller gear.) It's all subjective though. (my 2c.)

 

[Russ2251]

Made some changes to engine and drive-line resulting in a new speed record.
New Boyesen carbon fiber reeds (thanx to Crazycart) and 66 tooth driven sprocket.
Difficult to tell if reeds actually did anything. Time will tell.
Smaller sprocket definitely helped as the numbers show.
Still jumps off the line which kind of surprised me.
Expected to get some bogging, but did not happen (reeds???). Power seems the same or perhaps a little better than before.

 

[Rickracer]

The reeds should give you a crisper idle, more midrange, and probably a few more rpms on top end. You could probably go up in gear some more too,

 

[Russ2251]

Less than one mph to go....!

 

[Rickracer]

Have you actually measured the rollout of your tires? Might be more than the number in the calculator, my 12x8x6s rollout to about 38".

 

[Russ2251]

Have you actually measured the rollout of your tires?

Yup...within 1/10th".
It's pretty close.

 

[Jerryburger]

Too bad you don't have a GPS. Those things are handy for this sort of stuff. I lucked out and found a cheapy on ebay.

 

[Russ2251]

Too bad you don't have a GPS.

I have one, but it tells me I'm only goin' 17 MPH. Hell...my governed clone does 21 MPH.
Something about where I'm running I guess. Not a clear shot to satellites.
Surrounded by high hills, large buildings, trees, etc.

 

[Jerryburger]

Yes.... here in AZ, we are 'blessed" with what mostly resembles MoonScape, which gives better GPS performance. How is it going with "The Twins" ? That last video of you flying down the street was cool. I'm still guessing you'll bust 60mph easily- and the fact that you're doing it within the confines of that parking lot makes it even cooler.

 

[Fast Eddie]

Great read. Was looking for a pair of newer, more common 2 strokes to repower my kart (see end of 1st post in Project Rupp Dart restomod) and I think these may be the key. I have a L-B Duraforce mower and love it. Two questions though:

1. Did you make or adapt a different flywheel shroud? Mine is integrated into a huge plastic engine cover. I've seen smaller shrouds on Commercial L-B's, but not sure if they are DuraForce engines.

2. Is there an electric start Duraforce? I know some L-B's have electric start, but not sure on DuraForce. (twin electric start motors would be too cool).

 

[Russ2251]

and the fact that you're doing it within the confines of that parking lot makes it even cooler.

Cool nuthin'...it's friggin' scary!!! After running just a few minutes, I'm out of breathe!!! Can you say adrenalin rush?

Did you make or adapt a different flywheel shroud?

What you see is underneath the "huge plastic engine cover" which is only decorative and incorporates the fuel tank. No difference between the commercial L-B's and the home owner machines...just minus the shroud. Otherwise identical internally and externally.
Three phillips head screws and two carburetor hoses (fuel supply and primer) and it's off.
Of coarse the recoil handle must be removed and then replaced after shroud is removed.
Tie a knot in cord BEFORE removing starter handle...otherwise recoil will have to be disassembled to retrieve cord and spring rewound.
Electric start was available. I remove them and chuck 'em out. Too much weight.
2 or 3 pulls (5 if dead cold) and I'm running.

 

[Fast Eddie]

Thanks Russ. All great news.

Do all DuraForces have provisions for an electric start or do I have to find a specific motor? Not too worried about weight, it's just a fun kart. Is there an alternator incorporated? Is the wiring pretty simple?

 

[Russ2251]

Do all DuraForces have provisions for an electric start

All bolt holes are there for starter, but flywheel is different from non-electric start. Flywheel must have teeth to engage with starter pinion. Non-electric does not have teeth. There's also a bunch of other stuff in there to accommodate a starter.

do I have to find a specific motor?

Would be far less expensive in the long run to have a DuraForce that is complete with starter and associated parts. To convert from non-elecric can get real expensive real fast.

Is there an alternator incorporated?

None of mine did. Unknown to me if any DuraForces had an alternator.
Not sure if an electric start would fit on my kart. Plus I have no room for a battery.
My twins are a tight fit as they are. Both are configured for manual start.