Homemade airbox

[Vloukole]

Hi guys

I can’t seem to find an airbox for my 78 GS550 so I decided to make one. It is still raw metal. Will sand and paint later.
What do you guys think?
Could it be too restrictive?
All the flanges are 40mm OD and 37mm ID.

 

[Nessism]

Looks like some nice craftsmanship.

Be sure to use a quality filter, not a generic Chinese cheapy, which can be restrictive.

 

[Vloukole]

Will do. Thank you

 

[Vloukole]

Does anyone think I should set my carbs up like it is running with 4 pod filters? Just as a starting point?
I am running stock jets and needle position at the moment.
1/4 throttle is fine but anything above that and the bike bogs down.

 

[zed1015]

That small single carb filter won't flow enough air to serve the demands of all four cylinders and the actual air box needs more volume.
The size of the airbox would probably be fine for blow through forced induction and the tapered ends folllow plenum design for pressure equalisation to the outer cylinders but for normally aspirated the whole set up will be restrictive especially at higher rpm's as you are now experiencing.

 

[Vloukole]

Update:
I remove the homemade airbox and installed pod filters. The pod filters have those dreaded shoulders. I bought silicone hose with 40mm ID and 50mm OD. I cut 15mm pieces and used them as spacers inside 50mm pod filters to bypass/remove the shoulders. Now they are straight through/no shoulder like a proper set of filters.

I jetted the carbs according to the guide for pods.
I am running stock pilot jets, jet needle clip one notch lower and 95 main jets.
Bike is running WAY better. Little bit of a flat spot half throttle and WOT.
Think I am going to shim the needle rather than lowering another notch. Also going up to 97.5 mains.

Would love to have the stock airbox but it is a little scarce here(South Africa).

 

[zed1015]

Update:
I remove the homemade airbox and installed pod filters. The pod filters have those dreaded shoulders. I bought silicone hose with 40mm ID and 50mm OD. I cut 15mm pieces and used them as spacers inside 50mm pod filters to bypass/remove the shoulders. Now they are straight through/no shoulder like a proper set of filters.

I jetted the carbs according to the guide for pods.
I am running stock pilot jets, jet needle clip one notch lower and 95 main jets.
Bike is running WAY better. Little bit of a flat spot half throttle and WOT.
Think I am going to shim the needle rather than lowering another notch. Also going up to 97.5 mains.

Would love to have the stock airbox but it is a little scarce here(South Africa).

Your GS should have Mikuni VM22 mechanical slide carbs.
For running pods or stacks etc you are best fitting air corrector jets.
These enable the best performance with no flat spots and require no other carb settings, needle position or jet changes except for the usual increase of the main jet for upper throttle openings.
Air corrector jet kit for MIKUNI VM22SS ONLY. SUZUKI GS550, KAWASAKI Z650 import | eBay

 

[salty_monk]

If you have a flat spot at WOT that is main jets... that's the starting point.

 

[zed1015]

If you have a flat spot at WOT that is main jets... that's the starting point.

Most likely using cheap pods that are resricting the top end and also maybe masking the main air jet and pilot jet passages in the mouth of the carb.

 

[Vloukole]

My bike has VM carbs.
I used 50mm pod filters and made reducers from silicone hose to eliminate the shoulder that sometimes cover the air jets etc.

 

[salty_monk]

If you have a flat spot at WOT that is main jets... that's the starting point.

I'll say it again... you need to get the main jet set properly before you move to any of the other circuits.