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Hello ! I was wondering if anyone would have some information to how I could increase the HP on my little 425. I am getting some POD filters put on to do away with the airbox. Was wondering what kind size of jets would be sufficient with more air flow ? Any help would be much appreciated ! :cool:
 

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Discussion Starter #4
It is a 1979 GS 425, wondering if I need to increase the gas flow (bigger jets) if I put the air pods on the bike after. If so what size should I go with.
 

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It is a 1979 GS 425, wondering if I need to increase the gas flow (bigger jets) if I put the air pods on the bike after. If so what size should I go with.
Mistake #1: You assume that adding "air pods" (I think apple gonna sue somebody) automatically increases airflow. In most cases it does not, and in the rare cases it does, it depends on the quality and type of filter used. If you bought the cheap paper mesh style pod filters that look like this:

10113154.jpg

the only thing they are good at is teaching you that not all motorcycle parts are created equal and that it is really easy to waste money when you don't know what you are doing. Chances are you are having problems because there is an inner rubber lip inside the filter that is probably blocking the CV carb intake port.

s-l300.jpg

see that oval port at the top and those two little holes on each side of the carb intake? those need to be unobstructed. Most motorcycles, even the dumb boring commuter ones have GP technology in them (albeit outdated GP tech) and the airbox isn't like an aircleaner on an old chevy - removing it doesn't usually remove restriction, but it does make drive-ability worse.

Mistake #2: you are asking the wrong question. You are asking what jet size you need for some mod you did that nobody knows anything about but you. What you should be asking is what are the signs that I need to adjust the carb jetting and settings on my bike? And then you need to describe how it rides. Chances are you don't have to touch your carbs because those pods didn't make a difference, but if you did, you would look at your plugs to see if your bike is running rich or lean, and you would notice a stumble at the transition from different points in the throttle (as the bike transitions from the idle circuit, to the slow jet, to the main jet).

SO let's start again. Why do you think your bike needs a re-jet? is it behaving differently? if so what is it doing.
 

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I have not put any POD filters on yet. I was just asking a question seeing if anyone has had experience with them or it..thats all. I know these bikes can get kinda funky removing the original air box set up. So if there's a way for in creased HP even if its small I was asking if I should rejet it.
 

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It's unlikely you'll be able to improve power much with basic "bolt ons" (exhaust/carb mods). You've got to remember the amount of research the engineers put into making the bike perform well across the entire rev range. One thing you can improve on however is the handling (tires, suspension) and brakes. Those will give you a more noticeable improvement and level of enjoyment
 

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Fitting pods will not improve performance because they do not increase air flow therefore no jetting changes needed.

There are all sorts of ways to improve performance of your bike and in no particular order:
Bigger bore
Increase compression
Higher lift/longer duration camshafts
Gas flow (porting)
Make sure wheels turn freely, no binding/dragging brakes
Reduce weight
Reduce drag - lower bars etc
and so it goes on.

Back to the original question: most pod filters are no improvement at all and many restrict airflow either overall or they cover that bean hole slot that allows the slide to rise. Removing teh airbox not only hurts that flow side of things but makes the bike noisier and less easy to ride for a number of reasons.

The GS500 is a more modern version of your bike and could be a nice upgrade if you really like the Suzi twins. A way better and cheaper alternative in the long run is any one of the latest crop of 250-500cc twins. They are very affordable and handle and brake and go so much better than any old twin from back in the day.

Suzuki Cycles - Product Lines - Cycles - Products - GSX250R - 2018 - GSX250R

https://www.kawasaki.com/Products/2017-Ninja-300-ABS?cm_re=MOTORCYCLELANDING-_-PRODUCTTHUMBNAIL-_-PRODUCTDETAILS

2018 CBR300R Overview - Honda Powersports

https://www.yamahamotorsports.com/sport-heritage/models/sr400

https://www.yamahamotorsports.com/supersport/models/yzf-r3

Those may be more than you want to spend, but they are new and reliable and are easier to ride and cheaper than adding cams and porting etc etc to an old bike. Just a thought.
 

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all the above
you are getting great advice from seasoned expert racers and tuners
thev stock airbox can be fitted with a free-er flowing filter element and the lid to the airbox can be modified or removed
you can do your own testing to see if improvements are made and if the carb tune is on
all that takes is a few new sets of sparkplugs and a deserrted road you can speed on ,preferably slightly uphill
i know what you are wanting and that is the open look in the center ,you want to be like everybody else ,huh ?
go ahead pod that gs
you want a shitty running bike don't listen to us
i dare you ,i double dare you to be different
instead of pods maybe fab some custom side panels
the gs is a good engine basically 2 850 jugs (think an 850 with a cylinder hacked off each end)with the same dohc configuration
the other thing about pods is the strange sounds ,the airbox hides all kinds of weird noises
do not cut the exhaust pipes short and put shorty muffs on there that is a sure hp killer
last question do you actually want to ride ?
 

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Discussion Starter #10
all the above
you are getting great advice from seasoned expert racers and tuners
thev stock airbox can be fitted with a free-er flowing filter element and the lid to the airbox can be modified or removed
you can do your own testing to see if improvements are made and if the carb tune is on
all that takes is a few new sets of sparkplugs and a deserrted road you can speed on ,preferably slightly uphill
i know what you are wanting and that is the open look in the center ,you want to be like everybody else ,huh ?
go ahead pod that gs
you want a shitty running bike don't listen to us
i dare you ,i double dare you to be different
instead of pods maybe fab some custom side panels
the gs is a good engine basically 2 850 jugs (think an 850 with a cylinder hacked off each end)with the same dohc configuration
the other thing about pods is the strange sounds ,the airbox hides all kinds of weird noises
do not cut the exhaust pipes short and put shorty muffs on there that is a sure hp killer
last question do you actually want to ride ?
It actually not what Im wanting (A CRAPPY RUNNING BIKE). I actually was just wanting to know if there was any benefit to the pod or even anything else more so when it comes to the air intake I guess? I have massive respect for everyones input. So what ive gathered is NO on the Air pods. Leave it stock. Have any of you herd or had good experience with velocity stacks? Once again im just asking..
 

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if you take a look at the rubber tubes that run from the carb to the airbox, you'll notice that they are velocity stacks (designed to provide the best power delivery across the usable rev range)

Now the velocity stacks you're thinking of (generally aluminum) are really only appropriate for use on a racetrack. They can require a lot of knowledge and tuning (using a dyno or experience) to get performance improvements out of. Things like length and diameter need to be factored in. The major problem with using them on the steet is that even with mesh filters on them, they do nothing to protect the motor from contaminants.
 

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Discussion Starter #12
if you take a look at the rubber tubes that run from the carb to the airbox, you'll notice that they are velocity stacks (designed to provide the best power delivery across the usable rev range)

Now the velocity stacks you're thinking of (generally aluminum) are really only appropriate for use on a racetrack. They can require a lot of knowledge and tuning (using a dyno or experience) to get performance improvements out of. Things like length and diameter need to be factored in. The major problem with using them on the steet is that even with mesh filters on them, they do nothing to protect the motor from contaminants.
Thanks for the info! So what ive gathered is don't touch the original set up! lol. I am totally fine with that. What about exhaust set up? I know I could get a MAC 2 in 1 for it. But would that take away from the power it currently has? I know usually it will add hp if its a 2 into one.
 

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velocity stacks as a performance do not apply very well to the type of carb you have
the stock air tubes to the airbox are optimised as well as they can be
but the fact that the cv carbs have such a large diameter bell mouth pretty much negates optimal velocity stack tuning
because the optimum is a continuation of the intake port diameter from the carb on back
this is done to a tuned length which can be calculated to catch the 3rd wave of the natural sonic pulse in the port
mainly in relationship to the intake cam duration and target rpm of a tune
WesCooley1980YoshSuziGS1000.jpg
and also an image of a superbike basically your engine times 2

notice the small diameter of the stacks at the carb
the slide valve carbs like on the early gs 4's are similar to race carbs in that respect (the bellmouth closer to intake port size than on cv carbs )
read up here on stacks and tuning
Velocity-of-Sound Intake Runner Length Calculator
 
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