Huge accidental horsepower!

After working on my S, I went for a test ride down a quiet paved road. I was able to hoist 4th gear wheelies with no clutch. :naughty: I was quite amazed. 14/47 gearing.

While putting the bike away I noticed that I forgot to put the air cleaner side cover back on and my petcock was on prime.

I put the cover back on and the gas to ON. No more 4th wheelies. :naughty:

Is there anyway to get that perfomance back? Is it just a matter of more fuel and air? Is this what a larger carb will do? My carb is a DJ stocker with 3x3 cut.

Thanks for your help.

The fuel on prime had nothing to do with the horsepower. Regardless of where the valve is set the tank will feed it faster than the jets in the carb can take it. Infact most of the time gas is not flowing down the gas line. It only flows down the line until the float bowl is full and then the float shuts off the gas to the carb until needed.

I don't think haveing the petcock on the prime position has anything to do with it?. Sounds like your jetting is to rich?, (you don't say what you pilot,main,needle,or fuel screw are set at??). The extra air seems to have caused the increase. I'd look at your jetting, but beware that temps, humidity & alltitude also effect jetting. :naughty:

maybe is too lean with all that air rush into the carb

lean = bit more power

but hurt the machine.

25 pilot, 4th clip, 140 main, 1500ft

So should a bike run as well with the air filter side cover off as on? Or vice versa?

I agree about your jetting being to rich. If your bike is jetted right, by leaving the side cover off should make it run worse, because it will be to lean. The petcock position has nothing to do with your symptoms.

maybe is too lean with all that air rush into the carb

lean = bit more power

but hurt the machine.

This is true and more syptomatic of a two stroke engine. On a four stroke engine ... they need to just be right ... weather they are rich or lean ... they will tend to run flat.

I have found the s petcock is a real performance factor...but mostly when wide open. When the carb is wide open the vacumm signal is too weak to keep te valve open for adequate fuel flow. Running in prime will enhance your performance if running much above half throttle.

But 4th gear wheelies is pretty hard to believe. I will have to do some testing of my own. If opening the side shows a positive performance gain (which it might)...I will have to modify the side cover. Of course I will buy a second one to use when the possibility of deep water is a factor.

But it makes sense that if the engine needs more air that it is getting...that you will see a good performance gain from supplying it more then it needs...(especially if you can force it in like with a turbo or supercharger). The more air and fuel in...the more power out. Also...the more air you can get out of the engine leaves more room for more to get in. That's why a bigger free flowing exhaust is important.


This post reminds me of the awesome feeling of riding your sled on that cold morning, tons of new power, incredible throttle response, everything is running perfect, and then.......... BWAHHHHHHHHH, BWAHHHHHH. CLUNK.

Melt down. :naughty:

Definitely lean. I'd guess your "real" power level is somewhere between the "accidental" power and what you have now.


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