Making manifolds

[Ed_Bobber]

Morning from the UK

Couldn't see how to post this in the unique carburation topic - I've never been very good at driving the internet.

Hopefully a simple question, I'm moving over to Weber downdraft style carbs on my 83 GL1100 and need to make up the manifolds - the cost of buying the Randakks kit and shipping to the UK seems a bit much - and was wondering if there was any reason why you couldn't make the section that bolts to the engine case in one piece rather than 4 independent pieces, as I'd have through this would make the welding easier and lesss likely to be misaligned. I'm 3D printing test pieces beforehand to ensure it is as exact as I can make it before having the elements laser cut.

Thoughts appreciated, Ed

[gltriker]

Welcome to the Club!
I don't know anything about Weber intake manifolds design.
You may find something of interest if you scroll a lìttle farther down to the bottom of this page to see an additional 5 Similar Topics

Keep doing the same Similar Topics search at the bottom of each successive page you visit, too.

[Whiskerfish]

Greg F did some interesting design work that may give you some thought here viewtopic.php?f=47&t=43563#p452208

[5speed]

tagged for pics of your manifolds when you are finished.

[Ed_Bobber]

These are the protoypes, one of which is seated on the mating plate of the Weber carbs.

The other one is a mock-up which I will try on the engine later today to see how it lines up. I have made a payout using gaffer tape first, then a friend and I played around with Fusion360 to create a printable shape.

Will let you all know how it works out.

[ericheath]

I think Randakks have a slight taper towards the head to keep speed up. That is one thing that set his apart from most homemade sets.

Having messed a little with some, if I could, I would set the carbs forward some. People who are long legged tend to bang their knee on the rear carb. That complicates it some.

[Ed_Bobber]

Yes, I was aware of the taper, that's something for whoever actually ends up making these, but the port holes on either end are different sizes so it makes sense to try it. I've done some MIG welding but not sure I've got the chops for a tapered pipe, I'll leave that to a pro.

Interesting point about moving them forward, might have to think about that

[gregforesi]

Alright...here I go.
The lower plate must provide spark plug access and so Randakk and his fabricator decided on separate pieces. I agree with that. The 4 pieces are identical so only one design is required.
The upper plate must allow for the swing of the accelerator pump linkage. The mid cutout that Ed_bobber shows in his first image is also a feature of the Randakk manifold.
The Randakk manifolds do have a taper at the top of each tube to account for the 40mm bore of the Weber throats. A proper swage tool would be an elipse since the tubes come up to the top plate at an angle. Good luck with that. Round is close enough. The swage needs to be done before the angle cut on top of the tube is made.
If you have a cylinder head to use as a jig for tack welding the parts together, that is a beautiful thing.

If I was going to do this I would move the carbs away from the shelters by about 25mm to provide more clearance. Randakk and I talked about that and he felt that it made the parts too difficult to make. I respectfully disagreed as it is simply a case of the tubes being longer.

This is the side-draft manifold that Whiskerfish mentioned. This was originally what I intended for the bike but with side draft Weber DCOE's instead of these stock Keihins. I ended up making the tubes by shaping potting foam and then finishing them with paint and wax. Then I fiberglassed over the foam. It runs like a stock GL1000 which is definitely not as quick as the Weber setup. It looks pretty cool though. Kind of like a B-17 coming down the street. I'm fairly confident that no one has any idea what they are looking at. I run the bike with these on it for about a month a year and then I miss the growl (and performance) of the Webers and put them back on. I seem to recall that the only change I made to the Keihins was to drill out the idle jets as the stock ones were too lean.

[Rat]

Whew …

Gord

[CYBORG]

i love that bike!!!!

[5speed]

your bike is wicked...
where did you get the white faces for the tank gauges?

[Whiskerfish]

your bike is wicked...
where did you get the white faces for the tank gauges?

BOTY ten years ago. Really nice build even in person.

[digschopper]

Ive pondered 1 into 2 manifolds on each side, using 2 big side drafts, maybe 38s. The top would bend 90° for the carbs. Never seen it done.

[5speed]

Ive pondered 1 into 2 manifolds on each side, using 2 big side drafts, maybe 38s. The top would bend 90° for the carbs. Never seen it done.

I've wanted to put a holley 4 bbl on mine..

[digschopper]

5speed,you may be as crazy as i am. Thankfully.