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styroman
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PostPosted: Thu Nov 10, 2016 12:36 am    Post subject: Dual Motorcycle carburetors project Reply with quote

I have posted as a separate topic, information about my VW Trike rebuild project. The engine on the trike is built using a 1600 dual relief case, 1300 cylinders, and 1200 heads; and it was done for fuel economy, so the original builder could economically tour the United States as part of his bucket list.

Since I have it all apart anyway, and because I already know what the cold weather does to my dune buggy here in the Pacific Northwest, I decided to go with dual carbs on the trike.

Looking around, it seems no one has manifolds for a dual carb installation on 1200 flatheads. I found one company in Europe that has them, but they are expensive, and are made for 34mm carbs. I'd have a Grand into that kind of conversion, and 34mm carbs are just too big for the flathead ports.

So, for a few weeks I chewed on the matter, researching all the time, and have come up with what I hope will be an awesome dual carb setup for my trike, and would also work with later single ports, by using larger motorcycle carbs.

Here is an image of my project trike, in case you have not seen it in the volksrod/other/trike index. I will post gallery photos of my carburetor project below.
Image may have been reduced in size. Click image to view fullscreen.


Last edited by styroman on Sun Nov 13, 2016 4:36 am; edited 1 time in total
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styroman
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PostPosted: Thu Nov 10, 2016 12:55 am    Post subject: Re: Dual Motorcycle carburetors on 36hp project Reply with quote

I thought this would be interesting enough to have its own topic; as I have seen many requests on The Samba for information about putting dual carbs on 36hp engines.

The first two photos show the carbs mounted on reducing ell hoses. I plan to sacrifice this manifold by cutting the flanges off, leaving an inch of tube on each flange so the hoses can be clamped onto them.
Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.


I plan to use stock motorcycle throttle cables on the carburetors, and have chosen this one becaus it has an additional inline housing length adjuster:
Image may have been reduced in size. Click image to view fullscreen.


I purchased two pair of carbs. One pair are straightforward slide carburetors, and are purely cable operated. The second pair have a butterfly valve and vacuum diaphragm operated slide and metering jet, which should make them more economical going down the road. Both pair of carbs are 24mm, essentially the same ID as the VW manifold flanges.
Image may have been reduced in size. Click image to view fullscreen.


I am also going to plate off the stock fuel pump, and am installing a 1.5-2 psi electric fuel pump. In this photo is also shown the throttle cable splitter I am going to use to operate the two carburetor throttle cables, using a single Harley style handgrip cable.
Image may have been reduced in size. Click image to view fullscreen.
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styroman
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PostPosted: Thu Nov 10, 2016 1:09 am    Post subject: Re: Dual Motorcycle carburetors on 36hp project Reply with quote

I will cut the hoses down to a minimum usable size; and, if necessary, put a support strut under the carburetors, attached to the shroud bolts directly below.
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PostPosted: Thu Nov 10, 2016 2:45 am    Post subject: Re: Dual Motorcycle carburetors on 36hp project Reply with quote

I like where this is headed.
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toiga
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PostPosted: Fri Nov 11, 2016 4:43 am    Post subject: Re: Dual Motorcycle carburetors on 36hp project Reply with quote

Hi, what kind of carburetors are you using? This is a interesting conversion!

Keep up the good work
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jaxdream
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PostPosted: Fri Nov 11, 2016 12:26 pm    Post subject: Re: Dual Motorcycle carburetors on 36hp project Reply with quote

Styroman please be aware you are giving up your heated from exhaust intake . These VW engines like a heated intake or else icing Might occur. This a problem especially with T4 engines when carb (s) are used . If you make them short enough , you might luck out. Your project , good luck with it. Letting the head heat them might work out , just be aware of the non-heating issues . Research the elimination of heated intakes , might find a solution .

Jack
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styroman
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PostPosted: Sun Nov 13, 2016 4:44 am    Post subject: Re: Dual Motorcycle carburetors on 36hp project Reply with quote

jaxdream wrote:
Styroman please be aware you are giving up your heated from exhaust intake . These VW engines like a heated intake or else icing Might occur. This a problem especially with T4 engines when carb (s) are used . If you make them short enough , you might luck out. Your project , good luck with it. Letting the head heat them might work out , just be aware of the non-heating issues . Research the elimination of heated intakes , might find a solution .

Jack


The main reason I put dual carbs on my dune buggy is the cold weather. Buggies and Trikes have no engine compartment to keep the intake manifold warm in cold weather; but these exposed engines seem to have a problem with condensing fuel in the intakes, particularly on the low end in cold weather. The exhaust tubes do not keep the manifold ballast warm enough by themselves to prevent fuel condensation.
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modok
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PostPosted: Tue Nov 22, 2016 9:51 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

Above 40f you don't need any heat. Just adequate velocity. Below 40 F some heat is needed, but not very much.
Do not exceed intake 1.25 MCSA, save for a few inches straight out of the carb.
If you follow that, it will work, GREAT

If you don't, well, you can apply heat, to whatever degree Razz
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styroman
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PostPosted: Wed Nov 23, 2016 12:30 am    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

modok wrote:
Above 40f you don't need any heat. Just adequate velocity. Below 40 F some heat is needed, but not very much.
Do not exceed intake 1.25 MCSA, save for a few inches straight out of the carb.
If you follow that, it will work, GREAT

If you don't, well, you can apply heat, to whatever degree Razz


Now see, you made me do the research. Sure enough, temperature related fuel condensation does not begin to happen in typical automotive manifolds at temperatures above 40.

As I look back, my issue with my dune buggy was not entirely about condensation, but also the time delay. When I put the dual EPCs on, it lost all its lag and blubbering. Throttle response is now clean and immediate, even in cold weather.
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PostPosted: Wed Nov 23, 2016 1:02 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

love what you are doing. but i would run 1300 heads and run weber icts. simple . short manifolds . no need for heat. dependable. good mileage.no tuning issues. like i said i love the idea. but may be a bitch to tune?and a lot of work. just thinking out loud.
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styroman
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PostPosted: Wed Nov 23, 2016 5:15 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

sgmalt46 wrote:
love what you are doing. but i would run 1300 heads and run weber icts. simple . short manifolds . no need for heat. dependable. good mileage.no tuning issues. like i said i love the idea. but may be a bitch to tune?and a lot of work. just thinking out loud.


It looks fairly simple from this end of it, but time will tell. I am really wanting to stay with the original designer's intent, to have a 50-60 mpg touring bike. I might even size the carbs down to 21mm, or 18mm.

I think I am weighing the problematic nature of dual carb linkages with the seasonal adjustments of slide operated carbs. There are a lot of scooters out there running dual slide carbs that require little to no adjustment; and the install of a cable splitter is far simpler than installing and adjusting linkages to a pair of ICTs.

It is enjoyable none-the-less.

If it does not work, or is too troublesome, 1300 heads will be my next option.
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styroman
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PostPosted: Wed Nov 23, 2016 6:05 pm    Post subject: Re: Dual Motorcycle carburetors on 36hp project Reply with quote

toiga wrote:
Hi, what kind of carburetors are you using? This is a interesting conversion!

Keep up the good work


Hi,

I have two sets of carbs to try: The first is a set of 24mm Oko PWKs, common to motorcycles and scooters. They are a slide operated performance carburetor. The second set are Keihin PE carbs, also 24mm. The PE carb fits the same applications as the PWKs, but are butterfly/vacuum operated slide carburetors. with electric choke, for more conservative and fuel efficient use.

I am beginning with the PWKs because of their ease of setup. If all goes well, I will try the PEs, which will require metered manifold vacuum and wiring to operate (the choke will operate on the same wire as the ICT I took off)

I purchased two full sets of jets for this project, as I do not know what the VW engine will need to run well. The nice thing is that both the PE and PWK carbs, of all manufacturers for this size and up to 30mm, use the same jets.
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styroman
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PostPosted: Wed Nov 23, 2016 6:14 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

While I am planning on cutting up a sacrificial intake manifold to make this dual carb setup, I am also cogitatin' on casting or welding up a pair of aluminum manifolds instead. I can do either in my home shop.
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PostPosted: Sun Nov 27, 2016 4:04 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

styroman wrote:
While I am planning on cutting up a sacrificial intake manifold to make this dual carb setup, I am also cogitatin' on casting or welding up a pair of aluminum manifolds instead. I can do either in my home shop.


Oh, boy! As I cogitated some more, I stumbled upon some motorcycle intake manifolds I think will work with my 1200cc heads. I may be able to give up the ideas of using silicon hoses as manifolds, or casting or welding up new manifolds in my shop.

These manifolds look like they will lay flat over the intake ports on the 1200 heads. Their port size is a perfect match, but their bolt pattern is 12mm too narrow. Because they have a lot of thickness to the bolt flange, I am going to try slotting them and bolting them on with thick flat washers under the nuts, such that the washers center them over the port on flat gaskets instead of crush rings. Their design will point the carbs straight out from the heads so that I may not be able to use a stinger exhaust.
https://www.amazon.com/gp/product/B01EA32D5C/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.


The carb face of these $7 manifolds is a typical chinese/japanese/korean scooter design that accepts a rubber carburetor hose adaptor to clamp the carb into.
https://www.amazon.com/gp/product/B013LHVG7O/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.


They are all coming from China, so I will be waiting a few weeks for them to arrive, but I have plenty of other stuff to work on til then.

When they arrive, I could simply grind the manifold mounting face to a round shape, so that I can rotate them to face aft, and clamp them down with something like a chevy distributor clamp to hold them centered over the ports.
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styroman
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PostPosted: Sat Dec 17, 2016 8:13 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

styroman wrote:
Oh, boy! As I cogitated some more, I stumbled upon some motorcycle intake manifolds I think will work with my 1200cc heads. I may be able to give up the ideas of using silicon hoses as manifolds, or casting or welding up new manifolds in my shop.

These manifolds look like they will lay flat over the intake ports on the 1200 heads. Their port size is a perfect match, but their bolt pattern is 12mm too narrow. Because they have a lot of thickness to the bolt flange, I am going to try slotting them and bolting them on with thick flat washers under the nuts, such that the washers center them over the port on flat gaskets instead of crush rings. Their design will point the carbs straight out from the heads so that I may not be able to use a stinger exhaust.

The carb face of these $7 manifolds is a typical chinese/japanese/korean scooter design that accepts a rubber carburetor hose adaptor to clamp the carb into.

They are all coming from China, so I will be waiting a few weeks for them to arrive, but I have plenty of other stuff to work on til then.

When they arrive, I could simply grind the manifold mounting face to a round shape, so that I can rotate them to face aft, and clamp them down with something like a chevy distributor clamp to hold them centered over the ports.


They arrived. They look like they will fit. I am going to use the VW 34mm compression ring; but I am going to also use a gasket and Permatex #2 to seal the deal. I might grind the head flange to a round shape, and fabricate something like a pair of Chevy distributor clamps to locate it and hold it in place. If that seems unstable, I could sleeve the inside of it with thin aluminum tube, so that the tube extends into the head to locate it. The ID of this manifold and the head are nearly identical.
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Image may have been reduced in size. Click image to view fullscreen.
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PostPosted: Sun Dec 18, 2016 4:12 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

So, while I was assessing the use of these new components for the dual motorcycle carburetor conversion, which I think will work nicely, my concern is still about the carbs pointing towards the tires, and prohibiting the use of a stinger exhaust. I cannot modify these manifold to turn them aft, because it will not allow enough height and reach for the carbs to fit over the cooling tins.

A little more poking around the internet and I found some mandrel bent elbows of 1.25" OD 6061-t6 aluminum tube, 1.125 ID. I could cut the legs on these to a precise length, then make a flange/foot of aluminum plate that would have all the function of the stock foot, and could be MAP welded to the tube. This would allow the carbs to both point aft.
Image may have been reduced in size. Click image to view fullscreen.


So, I think this, plan C, will be my first plan of attack; and if they do not work out I will go back to plan B, using the short cast aluminum motorcycle manifolds above. I have pretty much scrapped plan A, utilizing silicon hose as a manifold.
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PostPosted: Tue Dec 20, 2016 1:38 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

As far as I know all dual carb conversion manifolds include provisions for a balance tube running across the engine interconnecting the two manifolds. You might need to modify these to allow use of a balance tube.
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styroman
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PostPosted: Tue Dec 20, 2016 1:55 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

alanhall wrote:
As far as I know all dual carb conversion manifolds include provisions for a balance tube running across the engine interconnecting the two manifolds. You might need to modify these to allow use of a balance tube.
Thanks Alan,

I will keep that in mind as I proceed. Multi-carb motorcycles use them too. I installed dual carbs on my buggy, without a balance tube, and it seemed to tune alright and run up and down the driveway nicely. I have not had the opportunity to road test it yet. I might need to do it to that rig too.
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PostPosted: Tue Dec 20, 2016 2:41 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

alanhall wrote:
As far as I know all dual carb conversion manifolds include provisions for a balance tube running across the engine interconnecting the two manifolds. You might need to modify these to allow use of a balance tube.
Doing some research on balance tubes, it seems there is a science to getting them just right when used. They are often tuned to soften intake pulsing. I am getting too old to learn all this stuff.

It also appears that some installers omit the balance tube when they are able to get an acceptable tune without them.

Anyone out there in Samba-land have some knowledge of these things?
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PostPosted: Thu Dec 29, 2016 11:28 pm    Post subject: Re: Dual Motorcycle carburetors project Reply with quote

styroman wrote:
So, while I was assessing the use of these new components for the dual motorcycle carburetor conversion, which I think will work nicely, my concern is still about the carbs pointing towards the tires, and prohibiting the use of a stinger exhaust. I cannot modify these manifold to turn them aft, because it will not allow enough height and reach for the carbs to fit over the cooling tins.

A little more poking around the internet and I found some mandrel bent elbows of 1.25" OD 6061-t6 aluminum tube, 1.125 ID. I could cut the legs on these to a precise length, then make a flange/foot of aluminum plate that would have all the function of the stock foot, and could be MAP welded to the tube. This would allow the carbs to both point aft.

So, I think this, plan C, will be my first plan of attack; and if they do not work out I will go back to plan B, using the short cast aluminum motorcycle manifolds above. I have pretty much scrapped plan A, utilizing silicon hose as a manifold.


So, there I was, posturing and posing over the best way to proceed with mounting these motorcycle carburetors up, and I decided to save myself a whole lot of work and proceed by modifying the original intake manifold. As I looked at the manifold I realized that I could cut enough straight tubing out of it, to weld onto the stock 'feet', so that I could simply slip a silicon hose over it to mount the carbs.
Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

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