Post by ZRX Gremlin on Feb 1, 2009 10:40:29 GMT
An hour in the shed was all that was needed to completely transform the performance characteristics of my GPz 500.
How much?? :broke:
Well, just say that this job runs at the right price.
Not too sure that I understand all the science behind this mod but all I had to do was drill a 1" hole in my airbox and open the pilot screws a tad and Whoosh!!! :burnout:
The Gpz500 has the peculiar characteristic of behaving more like a 2 stroke than a 4. Rough idle, poor accelleration up to about 7K then wallop, in comes the power . This is what probably makes this bike so learner friendly while at the same time being interesting enough to keep more experienced riders happy.
More power can be released with this simplest of simple mods. Basically, to comply with emissions regs, the bike runs a little lean at tickover and then it gets too rich everywhere else particularly up top. What this mod does is richen the mix for lower engine speeds and leans out at the top end.
Quoted from the EX 500 owners site:
Hole drilled, screws turned, lid and gloves on and it's out for a test ride.
Bike starts easier with less choke and tickover settles down very quickly. Tickover is now smooth and even as against the characteristic apparent misfire every 10 seconds or so. All 500s do this, not just mine.
From Gremlin towers it's about 50 yards to the nearest T-junction in either direction and instaed of the motor stumbling at low revs over this short slow speed distance, it picks up immediately. Our estate roads are all 30 mph and instead of keeping the revs above 4k as usual I allow the motor to labour a bit. It's a whole lot smoother without the normal buzzes and rattles and feels as though there is a lot more power there even at these low revs.
Onto the open road so I give it the beans as usual. I get to the magic ton mark surprisingly rapidly with no effort at all. Slowing back down to more sensible speed I try a couple of top gear roll ons from different speeds. Big improvement there too, especially from the lower revs. Bike now pulls smoothly from tickover to redline with none of that peakiness we had before and I'm sure I've released a couple of ponies in doing so.
Is this like rejetting and removing the snorkel on Rex I ask?
Next up will be some experimentation with pilot jet settings as I still use the stock air filter. there is some debate on that site as to whether the K&N really is that much, if any, better than stock in any case so I'm not really expecting any gains yet. It feels about right now and I'm sure an ignition advancer (5 degrees) to make the most of our British fuel will really smooth things out.
In short I'm absolutely gobsmacked at the performance and apparent power increase that this simple mod has given me and I wish I'd have found out about it sooner.
That poor little bike has been gasping for breath its entire life and I didn't even know. :violin:
How much?? :broke:
Well, just say that this job runs at the right price.
Not too sure that I understand all the science behind this mod but all I had to do was drill a 1" hole in my airbox and open the pilot screws a tad and Whoosh!!! :burnout:
The Gpz500 has the peculiar characteristic of behaving more like a 2 stroke than a 4. Rough idle, poor accelleration up to about 7K then wallop, in comes the power . This is what probably makes this bike so learner friendly while at the same time being interesting enough to keep more experienced riders happy.
More power can be released with this simplest of simple mods. Basically, to comply with emissions regs, the bike runs a little lean at tickover and then it gets too rich everywhere else particularly up top. What this mod does is richen the mix for lower engine speeds and leans out at the top end.
Quoted from the EX 500 owners site:
I continually remind everyone that the airbox/filter system is not about airflow or maximizing airflow. But a pressure balance. More correctly a negative pressure balance. Weather one filter or another flows more freely than another means nothing.
The Engine determines the airflow, by it's displacement. That is for every two revolutions of the engine 498cc of air are drawn through the filter, no more no less. Even if the is No filter whatsoever.
Now you do need a filter, which one is best. For that you'll need to find another expert, but once you choose one, Here's what happens.
The filters restriction creates a bit more vacuum in the carb venturi area which causes the atmospheric pressure on the gas in the float bowl to have an easier time forcing fuel through the various jets and orifices. This causes the mixture ti enrichen (over no filter). SO to obtain proper running you need to make some adjustment.
OK starting with a stock EX with a stock airfilter. Here we have a engine that was tuned to pass EPA rules. That is very lean @slow speed. and somewhat rich everywhere else.
To help the rich on top we lower the airbox pressure with 1" hole Then we lower the float bowl pressure with a looser filter (KN) then we open the pilot screws to allow the lower pressure in the float chamber to push enough fuel to improve the low speed running.
The Engine determines the airflow, by it's displacement. That is for every two revolutions of the engine 498cc of air are drawn through the filter, no more no less. Even if the is No filter whatsoever.
Now you do need a filter, which one is best. For that you'll need to find another expert, but once you choose one, Here's what happens.
The filters restriction creates a bit more vacuum in the carb venturi area which causes the atmospheric pressure on the gas in the float bowl to have an easier time forcing fuel through the various jets and orifices. This causes the mixture ti enrichen (over no filter). SO to obtain proper running you need to make some adjustment.
OK starting with a stock EX with a stock airfilter. Here we have a engine that was tuned to pass EPA rules. That is very lean @slow speed. and somewhat rich everywhere else.
To help the rich on top we lower the airbox pressure with 1" hole Then we lower the float bowl pressure with a looser filter (KN) then we open the pilot screws to allow the lower pressure in the float chamber to push enough fuel to improve the low speed running.
Hole drilled, screws turned, lid and gloves on and it's out for a test ride.
Bike starts easier with less choke and tickover settles down very quickly. Tickover is now smooth and even as against the characteristic apparent misfire every 10 seconds or so. All 500s do this, not just mine.
From Gremlin towers it's about 50 yards to the nearest T-junction in either direction and instaed of the motor stumbling at low revs over this short slow speed distance, it picks up immediately. Our estate roads are all 30 mph and instead of keeping the revs above 4k as usual I allow the motor to labour a bit. It's a whole lot smoother without the normal buzzes and rattles and feels as though there is a lot more power there even at these low revs.
Onto the open road so I give it the beans as usual. I get to the magic ton mark surprisingly rapidly with no effort at all. Slowing back down to more sensible speed I try a couple of top gear roll ons from different speeds. Big improvement there too, especially from the lower revs. Bike now pulls smoothly from tickover to redline with none of that peakiness we had before and I'm sure I've released a couple of ponies in doing so.
Is this like rejetting and removing the snorkel on Rex I ask?
Next up will be some experimentation with pilot jet settings as I still use the stock air filter. there is some debate on that site as to whether the K&N really is that much, if any, better than stock in any case so I'm not really expecting any gains yet. It feels about right now and I'm sure an ignition advancer (5 degrees) to make the most of our British fuel will really smooth things out.
In short I'm absolutely gobsmacked at the performance and apparent power increase that this simple mod has given me and I wish I'd have found out about it sooner.
That poor little bike has been gasping for breath its entire life and I didn't even know. :violin: