Two barrel carburetor conversion

[westgl]

I realize this is a older post.

But it may help someone in the future.

Redlion is a weber Carb and parts source.

I have Not tried this yet.

I bought a setup from them last year though i was going to use it.

I did a lot of research into a single carb, setup.

I decided that instead of a progressive Weber two barrel carb that I would go with a 38mm dual synchronous throttle bores.

What i mean is, One two barrel carb with two 38mm bore's that both open at the same time.

I wanted both Carb bore's to open at the same time to provide a little more Ooomph.

The intake manifold is a VW type IV.

Note this part number is not a WK297, it has the 38DGES Carb.

The type IV manifold is the smallest, as it is very compact.

Look at how small that center manifold section is.

The end's where the manifold tube make that curve/bend they would be cut here at the necessary length and would go into the stock manifold's and manifold rubber and clamped.

I had two thoughts for heating the manifold.

1. To use Resisters like I used on a 1971 Porsche 914, to heat the manifold. (I hate to use anymore electric than i have to on these old low power electrical systems)
2. Weld a tube ( it can be a 180 degree horse shoe shape) across the intake manifolds close to right under the carb, then run a Radiator coolant line from thermostat outlet to carb heater into one side and out the other, does not seem to difficult.

I had also thought about taking the heat shield in back of the radiator and in front of the Carbs off, and letting the heat go through to the carb then adding back a another heat shield just under the frame tube to keep the heat out of the intake, and pass under the carb , but on to the manifold.

Another possibility was to have a heated intake, a welded tube on the header that with a choke lever/cable that could be turned on and off, to be used as a air intake preheater

I bought the carb setup with a Electric Choke.

But i ended up rebuild the carb's for that bike, and still have this new carb setup waiting for a victim.

I just found a 75' GL10 for $40.00. this may be the one.

I just have a hard time not using the stock carb setup. Especially on a 75'

If the carbs on the 75' are schlitz, I consider it fate.

But I also have a pair of 34ICT's on my shelf waiting for a victim too.

 

[78AzWing]

Take a look at the single carb setup for the Type III.

And if you experiment with both the synchronous and progressive, you will probably find that the progessive works better for the GL1000 engine.

The 38/38 is just too much for them. It is also why the 38/38 wasn't used on VW engines of 1600cc and smaller. The 32/36 works better for these applications.

You already have water tubes running across the top of the engine. If you can get the manifold tucked down close to them, they may provide enough heat. Remember there is not a whole lot of room between the real gas tank and the baffle behind the fan, or from the bottom of the faux tank and the top of the engine. All this stuff has to fit in that area..

You might consider mounting the two 34ICT's. Randakk carries a set of manifolds (or did) that may work with them.
The only thing about using two carbs is figuring out the throttle linkages. :moped:

 

[badorderbob]

Hey Z, long time :music: ,.....I can add, I tapped into the the thermostat housing before the thermostat and at the end of the tee piping, right before the x-over pipes. This provides current thru whatever you purpose to use to heat the maifold and out when the thermostat opens. You can also put in a shut-off inline valve. This is what I'm in the process of doing, I took an alminum block, drilled out and sealed it, heat chamber. This will be attached to the bottom of my plenum, {CI. conversion manifold} with an inline shut-off. I am still profectting it. I also agree with Z, 38's will be too much also. The best to use is a Weber 32/36, but the one Randall uses, two on each side is a sweet set-up also! Just trying to add my $.07 worth!! Good Luck!!! :laptop: Bob

 

[78AzWing]

Hey Bob.

Not riding much anymore.

Too many injuries to the left leg, and it won't hold up a bike any more. :fiddle:

 

[westgl]

If Randaak uses 2ea 40mm carbs,

that's 4ea 40mm butterfly's or 4ea x 40mm = 160mm of venturi area.

A single 32/36 progressive carb is 32 + 36 = 68mm of venturi area.

2ea 34ict carb's = 68mm of venturi area.

A single 38/38 sync. carb is 76mm of venturi area. this is only 10mm more venturi area than 2ea 34 ict's

Now if the correct jets are available, you should be able to make the 38/38 work.

I realize that 32/36 you are running around on only 32mm until about half throttle.

Is there some on this board or another board that has tried a single 38mm sync carb.

 

[Anonymous]

I've found that heat is a absolute requirement with a single-carb conversion (for the manifold itself) in allowing the mixture to remain in suspension from throttle valve to intake valve.
I've also found differences in drivabillity between a single throat and a dual throat progressive carburetor. No problems with either, just differences in how the bike operates using one carb or the other.
One thing I'm absolutely convinced of at this point; ...a heated manifold is the only way to go. I've tried most reasonable designs and with any of them, heated interior surfaces of the manifolds plenum area, runners and the fuel tract as a whole benefit from the application of heat. Keeping the fuel mixture in suspension is critical as I know it. A retired GM Powertrain employee who has experience in induction design pointed this out to me and the known problems common to other unheated manifolds disappeared once I heated my manifold.

I find nothing wrong with a well tought out single carb conversion for a old GL.

 

[Anonymous]

If Randaak uses... butterfly's... 160mm of venturi area...

Need to know: Auxillary Venturi and Choke sizes plus all the additional set-up and tune information.
Bore openings alone are pointless without knowing the rest of it.

A big non-fixed choke Weber carburetor can be choked-down and set-up for our small 1000cc engines.

A big fixed choke Weber carburetor cannot be choked-down and properly set-up for our small 1000cc engines, hence all the set-up problems associated with the 32/36 DGV's on these forums.

Weber suggests the following initial set-up for 1000cc engines @ 5K RPM:
28/30DGV with 21/22mm chokes and 4.50/4.00 aux venturis
28/36DCD with 23/24mm chokes and 4.50/4.50 aux venturis
32/32DFT with 22/22mm chokes and 4.00/4.00 aux venturis

New DCD's are 36/36 only and too large, as are anything larger. I know of only one NEW 28/36.
New DGV's are fixed-choke @ 26/27mm employing a secondary idling circuit that must be dealt with. Out of the box most all set-up parts need to be changed (jets, e-tubes, etc.) and even then it will perform less than optimal.
New DFT's are available as listed.

The ideal single-barrel, single carburetor application has a 31mm bore opening with 25.5mm choke = Brosol H-30/31

I've set-up information here. I'm still setting the page up though... I've never any time to stay on it.

 

[78AzWing]

I think you should probably call them throats instead of chokes.
To me the choke is the metal plate (butterfly valve) at the top of the carb throat that closes the throat off for cold weather starts.

And I never had a problem with the progressive 30/36 or the 28/30 as far as setting one up to run a small engine.

set up is the same for a boxer four as an inline four.

 

[Anonymous]

I think you should probably call them throats instead of chokes.
To me the choke is the metal plate (butterfly valve) at the top of the carb throat that closes the throat off for cold weather starts.

And I never had a problem with the progressive 30/36 or the 28/30 as far as setting one up to run a small engine.

set up is the same for a boxer four as an inline four.

... in the Weber, the throat is the venturi.
...Weber chokes are removeable parts if not of a "fixed"-choke DGV/DFT-style design.
...Many Weber venturi's have removeable auxillary venturi's (kind of a pre-choke) - the DGV does not.
...Many Webers have a "Choke Throttle Valve" or the butterfy valve as you know it. - the DCD does not.
...though you cannot replace a throat or venturi entirely, some Webers allow to greatly modify the venturi's bore opening-to-closing restrictive properties (chokes and aux venturi's) allowing use of what would normally be a carburetor that is too large if being compared to that of a fixed-choke design, as in the 32/36 DGV.
The "Big Carb" problem comes in the form of too low of air-speed through the venturi, or throat to properly activate the bleed circuits(s) that control atomization of the fuel. Large bore/fixed-choke carbs on small engines don't work well because of this.

...as mentioned by the OP, a 28/30 apparently came with his CC conversion, who I imagine either took Webers advice and applied the correct carburetor for the application, or calculated it themselves. Either way, you should have no problem with your set-up because of it.

I thought you run the same set-up? Set-up is the same, yes...

A new 32/36 DGV is just too big of a carburetor for someone new or old (but especially new) at trying to go with a conversion on their own and right out the gate. More trouble than they are worth. There are better alternatives.

I pulled this thread from the front page of a Google search. Someone new to this conversion stuff will be doing the same. Might as well cut the headaches out for him up front eh..

 

[78AzWing]

You want progressive carbs, not simultaneous ones. And most of them also have non-removable chokes.

 

[Anonymous]

You want progressive carbs, not simultaneous ones. And most of them also have non-removable chokes.

Yes, all new Weber downdraft progressive carburetors sold today are of the fixed-choke variety, ....except for the DCD36, which is not physically sold in the US (thank the EPA) but can be had from Anthony @ Fast Road Cars in the UK..