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Discussion Starter · #1 ·
Would anyone like to explain how this arrangement works?
Air to the carb intake is going to find the easiest path.
This means it will avoid going through the filter and route through gaps in the covers and the leaky internal stuff.
I am seriously thinking of modifying the plastic cover, in order to fit velocity stacks...long 4 1/2", no mesh.
Similar to this:
http://www.youtube.com/watch?v=Ooj9zFLc4nc
 

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Zener diode

Don't forget that the zener is mounted inside the airbox so that it stays cool via the air flow over it. If you stop the air flow, you could fry the zener. It will need to be mounted somewhere else.
Mark
 

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Discussion Starter · #3 ·
Thankyou Mark, but I have an electronic rectifier/regulator, with heatsink mounted on the rear metal panel.
My air filters are a poor fit, as are the plastic airbox cases.
Just curious about how this arrangement draws air through the filter.
To me, it seems this weird set-up is completely useless, as are the rubber carb hoses,
This not an air-tight system, so why not fit velocity stacks which will channel air in an efficient manner?
 

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OIF side panels

I quite agree about the air filters. My '74 didn't have them when I bought it in 1977 and I took them out of my '72.
I have a set of velocity stacks to go on mine some time. I will probably fir retro panels to do it though.
 

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Caulky,

First, BRAVO!! on your baking tray conversion. I actually enjoyed the Hell out of your little video. It made me laugh when I thought about all the custom tools they sell for shaping sheet metal and you did this with a couple of hammers and a few slabs of wood.

I'm not crazy about running an engine without an air filter. Granted, those air boxes are not the best sealed beasts in the bike-world, but they are much better than nothing at all. I would strongly consider a filter on the end of your stacks. I would suspect that GPZ has seen engines after they've run without filters. I've seen some non-Triumph engines with nicely shaped conical cylinders.

Why wouldn't you just eliminate that entire air box assembly, and go with pre-OIF air filters? Hate to see your sheetmetal skills go to waste like that but if you remove the entire air box, you'll have plenty of room for filters.

And if you are that good with a hammer and a baking pan, I'm sure you could hammer out a couple of pre-OIF side covers for that bike.
regards,
Rob
 

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OIF airbox is junk

lets face it the oif airbox in 71-72 are all metal and dont really fit that well..mine were cast so poorly and finished that when put together over a filter there where gaps around the edges...so the air get in the engine unfiltered....great design huh?.

I know they were trying to meet noise regs of the time and lots of people like to pitch them for the 'retro' 60's look.....plus I had put mikuni's on and barely fit with the stock airbox only after shotening the manifolds as much as possible.......soooo I filed them and did some whittling, used the rubber carb boots from a KZ400 that matched the mikuni and t120 air box cover...put in a set of UNI filters and it is all good.....
 

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Hi Caulky,

The best person to ask here is Plewsy, he's the one that did the video.
(You can see the side panels on a few of the videos he's posted on this forum)

Sorry Plewsy for blowing you cover :)

Webby
 

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Caulky,


I'm not crazy about running an engine without an air filter. Granted, those air boxes are not the best sealed beasts in the bike-world, but they are much better than nothing at all. I would strongly consider a filter on the end of your stacks. I would suspect that GPZ has seen engines after they've run without filters. I've seen some non-Triumph engines with nicely shaped conical cylinders.

Or you could try a pair of K & N filters ?

Webby
 

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Discussion Starter · #10 · (Edited)
Maybe velocity stacks with gauze? No grit, bees, flies, etc.
Bumble bees hurt at 60mph, ask me how I know.
I was thinking of the grub-screw on Amals...3 inch I think.
Depends on your location I s`pose.
In hot dusty environments, it would quickly take a few thou off of everything.
If I remember correctly my old `57 `twenty-one just had a small trumpet, no filter.
Anyone?
 

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Coming from a 2-stroke background I am a little confused about all this air filter talk. I have my own jettting issues at the moment, and am running WITH standard airboxes (71 twin) but WITHOUT filters.
I am tossing up my options and would like to get it straight in my head the normal jetting changes necessary when running 1) velocity stacks, 2) repro round ones with chrome 3) airbox without elements

I there are no changes necessary it is either a testament to the flow of the stock airbox system, or It just doesn't matter on a 4-stroke.

derek 'not afraid to ask the silly ones' myers
 

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Discussion Starter · #12 ·
I dont really know if the jetting will be affected.
I think the mixture would be a little leaner.
As far as I know, each particular engine needs to be tuned individually, because the length of the inlet and exhaust also affects it.
There`s no `standard` set-up, as I understand it.
A bit vague but the only way is to run what you have and tweak as neccessary.
 
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