New Pipes of 33BHP restricted 650 Dragstar

[LivetoRide]

Hi guys, got a technical question for you....

I've got a 33BHP restricted 650 Dragstar, and I've been thinking of putting after market pipes on it to get rid of that standard whisper it makes with the factory pipes and get it more umph. Spoke to someone today about it, and they said because it's 33BHP restricted, I should wait until I can unrestrict it before changing the pipes because "it'll mess with it".

I've been looking at some pipes on eBay previous to this, and messaged the guy asking if I need to re-jet the carbs to put them on, and he said he didn't and no problems, so probably no need.

Will this change because my bike is restricted to 33BHP? And why? Can anyone explaining what this "messing" is, and how severe or unsevere it is?

Thanks for your time, and happy riding!

Rich

[Ttaskmaster]

The reason factory pipes are so quiet is because they have several baffles in the silencers that slow down the airflow, by making it 'hurdle' around before exiting.

This creates back-pressure in the engine, which makes it run efficiently.

When you put loud pipes on, these have fewer baffles, or possibly even none at all. Consequently, your back pressure drops and you end up with too much air running through the system.

You therefore need to upsize the jets in the carb to compensate and restore the balance. This is true of all bikes, restricted or not.

Don't believe anyone who tells you you don't have to re-jet. Every mechanic I've ever known advises re-jetting. It's not a particularly hard job, either.

Restriction has almost nothing to do with it, especially if you correct the balance with the proper jets.

[HoughMade]

I'm in the U.S. where we do not have such things (can't say it's a bad idea, though), but it is my understanding that the "restrictor kit" is just a plate that chokes off the air available to the engine. It has a hole much smaller than the intake manifold inlet. If that is the case and the bike is currently running smoothly, I highly doubt that the larger pipes will need much jetting, but it is possible.

The reason is that the 2 components that affect airflow are the intake tract and the exhaust tract. If the original pipes are designed to work well with the unrestricted 650, on a restricted one, it is likely that the exhaust is not providing a great deal of backpressure (there is much more to silencing an exhaust than restricting flow, so the quietness is not a good indicator of restriction). On a restricted engine, the intake tract is so choked down that I doubt that opening up the exhaust will increase airflow that much. It is possible that re-jetting will be necessary, and it would certainly be necessary on a non-restricted engine, but I kind of doubt it as is.

That being said, if it were me I would leave it as is for now because I imagine that it would be a bear chasing a decent tune when changing components on a restricted engine. The turbulence caused and the fact the carb isn't in its sweet spot with a restriction will cause some unpredictable results. I would wait until I could de-restrict it and do the mods then.