venting Hitachi "SU" carbs

[lostforawhile]

How are you guys running the bowl vents to these carbs on non stock air cleaners?  I have a set off of a 510 SSS on an 86 Accord, that I'm working on,  it's a long story, but I'm trying to figure out the best way to run the bowl vents, I went to a lot of trouble to hide the original Charcol canister and make it functional, simply because I dont want my small garage stinking like gas all the time, and I hate wasting gas to the air, you know it's not cheap anymore. I was thinking of making something cool out of aluminum to run both bowl vents to, and venting it through a purge valve off of a later model Honda,  I could hide it somewhere, basically it opens to the air when you apply 12 volts, and it's designed to handle fuel vapor,  theye are everywhere at the yards, if I go simple and just run a hose back to my air cleaners, I just run the fitting outside of the velocity stack area on the air cleaner? I dont want to put it in a low pressure area, and have fuel siphon issues,  these are small air cleaners, looking for ideas,  I'll post some pics later of the air cleaners so you can see what I'm talking about 

[lostforawhile]

any ideas?

[vanmansam]

I am also wondering as I just built a set of carbs+l20b and put them in my 510 and there arent any ports on the air cleaner, and currently have both vents completely open.  I have heard suggestions of running clear vinyl tubing or fuel hose down to some open area in the engine bay so the ends just point at the road.  

[Ratwagon1600]

I've run two different systems previously when I've been running Su's.

 

The first as Vanmansam alluded to was to run two seperate fuel lines from the bowls down to the chassis rail. I used two p clips (one for each line) and had the lines hanging slightly below the bottom of the rail. Definitely not aesthetically pleasing, but functional. Just need to make sure if you use this method to route the lines away from the exhaust as much as possible.

 

The second method was to run two lines into a catch can similar to this.

 

 

This is not the original setup, but should give you an idea and is my preferred option for both looks and functionality.

[lostforawhile]

I would think they need some sort of filter, as air does move from the vents to the bowls to equalize pressure as the fuel level drops, if they were just open dirt would find it's way to the bowls, I'm leaving towards the Honda purge valve as this would close the vents when the car is off, and prevent the fuel in the bowls from evaporating

[Ratwagon1600]

OK, if you think you have the solution, why ask for advice?

 

Do whatever you want, I'll waste my useless advice on more deserving people.

[lostforawhile]

OK, if you think you have the solution, why ask for advice?

 

Do whatever you want, I'll waste my useless advice on more deserving people.

I'm listening to your advice,  I'm just thinking of different scenarios on how best to make this work is all, if I didnt want anyones advice I never would have posted this thread, putting some theory out here and seeing what I can come up with, I'll go take pics of the air cleaners in a minute 

[lostforawhile]

I havent drilled the mounting holes yet,  I need an old gasket for a pattern to get the holes right. Pegasus racing has the foam available in a bunch of different grades, this was just some old filter foam,used to put them together. 

 

[oldskoolvws]

I would think they need some sort of filter, as air does move from the vents to the bowls to equalize pressure as the fuel level drops, if they were just open dirt would find it's way to the bowls, I'm leaving towards the Honda purge valve as this would close the vents when the car is off, and prevent the fuel in the bowls from evaporating

 

 

I'm not too familiar, but on my MK1 VW, when I did something similar, on super hot days, the fuel would expand in the tank and go up the equalization tube and run out the gas cap because it couldn't vent. It sucked bad. I wound up releasing to atmosphere.

[lostforawhile]

I have the same issue with having a sealed tank, but I was able to figure out a way to make the canister still work like factory, I used a  fuel injection canister with a tank connection but no carb connection, I built mountings for the entire thing and put it on the front cross member, out of sight. I might have enough room on the back plates of my air cleaners to weld on a half of a steel coupler, and connect them directly to the vents, I do like the catch can as if there was an issue with a float, the gas would go to the can and not on the ground or the motor

[bonvo]

does the fuel  tank have a return line nipple? thats what im gonna do with my su's is run the vents to the return line on the tank making it a closed system 

[lostforawhile]

no return line, if you have a sealed tank you'll have pressure in the tank, and I would think that would back up into the carb bowls? 

[converted_to_datsun]

I had the same idea about running it to a return line but apparently it's not a good idea. Makes them not function properly. I ran mine streight down. It overflowed once but you can tell when they're overflowing cause it'll stumble at lower rpm's. as long as your floats aren't taking on fuel overflowing shouldn't be a problem. I have seen people run the vents back to the firewall and along there. Prolly a cleaner place to put a catch can

[wayno]

I havent drilled the mounting holes yet,  I need an old gasket for a pattern to get the holes right. Pegasus racing has the foam available in a bunch of different grades, this was just some old filter foam,used to put them together. 

 

 

Make sure you drill the suction piston vent hole also on each SU carb, as you need 3 holes on each one of these filter housings.

If you look real close on the face of each SU carb, you will see which one is the vent hole.

I would pipe the bowl air vents to the back of each carb air fliter housing, it is such a short hose that way, that it can almost be hidden.

[lostforawhile]

yea the factory velocity stacks I picked were too big,so I have to replace the backs on the air cleaners, I'm just going to use the short stacks that will fit and have to redrill the holes anyway, I know about the vent, thats the issue with these 

[lostforawhile]

this is what I think I'm going to settle on, they will fit  inside of the air cleaners, other then having to clean  up the sharp edge on the lathe, they look decent. I'll just make some new backing plates for the air cleaners with the correct size center hole, then line these up to drill the bolt and vent hole http://www.ebay.com/itm/SU-H-4-HD-4-HS-4-Short-1-1-2-Ram-Pipe-/330922831543?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4d0c89aeb7

 

[lostforawhile]

copied from my three geez facebook post

 

breather tank is almost done, this will mount on the firewall between the carbs, and gets one of those small filters on top, wondering what the extra fittings are? I needed a place to run the carb bowl vents, so I drilled the ports right into the billet bracket, this will get two 45 degree fittings on the end, -3, which are the really small lines, the straight fittings were just to check the threads, each carb gets a line run to the bowl, and a -6 line runs out the bottom of the bracket out of sight, I'm going to mount a late model civic canister purge solenoid out of sight down on the firewall, when the key is on, the carbs are vented to atmosphere. when the key is off the bowls are sealed. This stops fuel from evaporating out of the bowls. I didnt have the fitting to the valve cover on in this picture, it has to be tig welded on tomorrow

 

[lostforawhile]

if it helps anyone, I found that pegasus racing has -3 and -4 hose ends that are BSP thread,  you can make up ptfe fuel and vent hoses that screw directly into the carb fittings,  bsp on the carb end, npt or whatever you want on the other  ends, this gives you the possibilty of direct fit custom lines, they have more metric and oddball AN fittings then I have ever seen 

[cimarronlibre75]

I SeeU Carbs!