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Author: Subject: AIRBOX problems on Bike Carbs
bikecarbfred

posted on 20/9/14 at 06:59 PM Reply With Quote
AIRBOX problems on Bike Carbs

New to the forum. Hello all.

Polo 1.4 16v on CBR600's

Before box.
Carb slide flutter
25-40% throttle: around low 14's AFR
50% + throttle going into the main JETS (150's): Between 12 and 13.5

So I decided to make an airbox to reduce the oil temperatures, make it run leaner through the main jet.
(I had a front grill cold feed before I went onto carbs and temps were around average 50 degrees.
With carbs they were on average 60-65.

I made a 2.9 litre volume airbox. Around 30cm x 9.8cm x 9.8cm
The trumpets were well inside the box. No restriction to the emulsion tubes.
I used a ramair 80mm induction pipe going to the front grill as I had before.
I used a ramair foam filter with 75-80mm neck which was squeezed in the front grill.

So I thought. Well this will work. Not quite.

After airbox:
No carb flutter
10% throttle on cruising 16's
25-40% throttle: around 15.5's
50% + throttle going into the main JETS: Between 12.5 into low 14's
Temperatures were down between 5 and 10 Celsius on cruising. I would say around 7 to be accurate.

So I thought this is good. My work is good. Temperatures are down and the wise decision of using 150 jets is paying off with the airbox.

Now time for the performance gains.

I hammer it in 1st gear , switch to second and here the induction Roar!! The burp burp, ups... AFR showing 10. Damn!
Too rich. What's going on?

I realise there's air flow problem. Air starvation at the high revs!!

Lmao. Cheesed off to the max as I don't get it.The only thing I have not done to the book is there is a kink in the pipe which I had to make to fit. Picture below. Can someone kindly spare me some of their precious time to help me please.









[Edited on 20/9/14 by bikecarbfred] spelling

[Edited on 20/9/14 by bikecarbfred] pictures

[Edited on 20/9/14 by bikecarbfred]

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tul214

posted on 20/9/14 at 08:08 PM Reply With Quote
I am no expert but i had cbr600 fx carbs on my 4a-ge engine. I fitted an air box and had it set up at Bogg Bros.

He used 140 jets.

I would also say that your airbox looks quite small. Here's mine;
Description
Description


It was linked to a piper cross filter at the grill that can just be seen here;
2
2






1.6 Raw Super6 sold

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bikecarbfred

posted on 20/9/14 at 08:43 PM Reply With Quote
Thanks for the reply. Mine was setup at boggs without the airbox.

The picture is deceiving.
Mine over hangs on each side over the vac covers by 1cm and is a full square so I have a feeling in terms of litres it is the same as yours.Not as long but square.

Can I ask what pipe size you used please? Also what litre engine.

I have my foam filter in the high pressure zone grill.

[Edited on 20/9/14 by bikecarbfred]

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tul214

posted on 20/9/14 at 09:11 PM Reply With Quote
Think the intake hose was 70 or 80mm.

ETA - it was a 1600cc 160bhp Toyota 4a-ge motor

[Edited on 20/9/14 by tul214]





1.6 Raw Super6 sold

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bigrich

posted on 21/9/14 at 11:38 AM Reply With Quote
I did think still airboxes should be in the 5 to 7 times engine capacity volume to work without restriction. cant think where that snippit of info is from but seems to be logged in my head from somewhere, would make your 2.9 litres appear very small and restrictive. this seems to back up your own findings with air starvation or making your current jetting very rich for the airflow you now have

Rich







A pint for the gent and a white wine/fruit based drink for the lady. Those are the rules

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bikecarbfred

posted on 21/9/14 at 04:52 PM Reply With Quote
Round 2:

Decided to make a bigger one and re-route a new pipe. 5 to 7 times bigger seems physically impossible.
I make one this time 4.5 litres as opposed to the 2.9. Picture below.





It's a beefy thing. Again the results are lean driving slow and the AFR drops like a plane in "stall" just at the press of 100% throttle.

It's like a instant starvation like you could not believe. At this rate I could make it three times bigger and it would not change much.

I am starting to wonder if it is the ram air from the font that's causing a pressure problem?
Do I route all the breathers in the induction box? I feel very sure it's a pressure thing.

The box is so big I could get 4 individual pipes for each cylinder and route that to the grill with a pipercross filter.
There is something happening at the box...

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se7ensport

posted on 22/9/14 at 08:05 PM Reply With Quote
Looking at the size of it there should be enough volume if your filter is up to it, I'd be tempted to try without a filter for a test run once up to temperature.

I had a similar size airbox on a 2.0 pinto but used a remote filter without any issues.

Regarding the little 2mm vacuum tubes, they need to be blanked off - golf T's works well.

carbon airbox
carbon airbox


Description
Description


[Edited on 22/9/14 by se7ensport]

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bikecarbfred

posted on 22/9/14 at 09:18 PM Reply With Quote
I have tried it without a filter and the exact same reading. The foam filter I use is super.
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matt_gsxr

posted on 22/9/14 at 10:17 PM Reply With Quote
So if it isn't the airbox, or the filter, then what about that pipe with all those ribs in it?

I don't know the numbers on smooth bore versus this rough texture, but it can't help.





http://jpsc.org.uk/forum/

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tul214

posted on 23/9/14 at 04:42 AM Reply With Quote
Not sure the ribs will effect it as the total volume of air in the hose will be more than the air box.

As many have said before, your really need these setting up properly. Can you get back to Boggs?

Also, what about your fuel pump.....these carbs often dont like the facet type pump and need to run on a bike pump for best results.





1.6 Raw Super6 sold

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Norfolkluegojnr

posted on 23/9/14 at 07:51 AM Reply With Quote
have you tried leaving the box on but taking the hose to air filter off?

worth fitting a pressure gauge to the airbox to track what the airflow is doing?

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