'Vw carburetor on 85 xj700

Im attempting a custom carb setup ..single barrel VW carb
Or a ford single off a 6 cylinder
..ive heard it works well if you get the jetting close and choke right..anyone ever attempted this or anything similar. .
strictly for fun and a cool factor

 

Im building custom manifold
4 into one

 

I used a Ford Escort throttle body on mine... took a few tries to build the manifold I wanted, though. Injectors are right up by the ports and angled to fire down towards the intake valves.

What are you guys doing for the manifold?

 

Pvc tubing for testing purpose
I would like to get clear pvc for the final product
if I can find some gas friendly lol
its light weight

 

I don't think PVC will take that kind of heat.

 

Also, after a bit of EGR and/or PCV, the inside of clear tubing probably won't be that pretty anymore.

There are some other plastics that can handle higher heat (obviously, since many new cars have plastic manifolds). PVC starts to break down at 140C/284F. I once tried to use it for part of the coolant loop on a VW Golf. Didn't last long.

 

One member here (orange-n-black) made a pvc manifold for his carb conversion, and it melted due to gas fumes dissolving the plastic. Search for his "Simple carb fix" or something like that.

 

Ill post a pic of the manifold .
Almost done..and yes I figured the gas may eat the pvc ...not sure though todays plastics are pretty resistant..?for temperature the pvc part will probly be 6 to 8 inches from the block.m carb is going out one side by the tank and your knee
wont fit underneath. .thanks for any input all is appreciated

 

What are you doing for the 6 to 8 inches between the block and the manifold? The carb holders are only about 1 inch of that.

As to gasoline resistance, there is no "today's plastics"... PVC is still PVC. It's rated for moderate effect by gasoline. https://www.google.com/url?sa=t&rct...srUI9uo_ZGvRP7_rA&sig2=_cbpzHlWqSEFlRxAC8e3vg

If you want to use today's plastics, you need to look for other compounds than PVC.

 

Right on ..this is really just a test mainly for flow I planned on using rubber hose for the remaining 6-8
Inches my thought is that I could figure in equal length tubing easier and the manifold wouldnt get as hot
I have 2inch extensions coming off the carb holders

 

OK. Sounds interesting. Pictures?

 

Hopefully fire it up tomorrow
see how much scavenging is goin on.
i may do all copper tubing
Also have some of this pvc soaking in gas..im just gonna leave it
see how long before its useless

 

Interesting. I'm curious to hear how it's going to sound with those very different runner lengths.

 

Seat I made last week
stainless steel ..lambskin

 

Ill let yah know how it goes

 

Those runners are so long throttle response will be in minutes . Usually they use accelerator pumps to compensate for loss of vac don't think it will work up hill gonna puddle. Hopefully it will work for you but do not be surprised if it does not. Watch 1 2 and 3 make sure if it does run you don't hole a piston. i do not believe there will be any gas getting to them. I saw someone try this with a small holley 4bbl told him it was not gonna work when it did not he went to 2 of them 1 on each side. Best of luck

 

What do you think if I had a choke setup for the individual ports?
You think it would help

 

I think that you'd be much better off with a double-Y arrangement that places the carb between #2 and #3.

 

I agree.

 

Well i got it all hooked up
it started quite easily and actually idled quite nicely around 1800-2000 rpm
Im drawing vacuum from #4
And so far it is looking ok with the plugs
granted ive only let it idle for ten minutes three times
oddly enough the throttle response seems somewhat normal
Im keeping my eye on everything

 

What I would be most concerned with is how the different runner lengths are going to interact at different speeds.... like if resonances and standing waves lead to starvation of one cylinder at certain engine speeds. When you see manifolds like yours in production designs, the shared tube or box is much larger than the runners.

Cool to hear it's running, though. Allows you to eliminate a number of concerns from your tuning process.

 

Imo 1 and 2 will definitely starve and run too lean. 4 will always run too rich. The set up doesn't allow for slowing the fuel to 4 enough to not starve 1 and 2. I could be wrong.

+1.

Gary H.

 

If you made a box plenum chamber with stubby outlets matching into the head inlets, and sat the carb directly on top - would there be enough headroom for the carb, including some form of intake filtration? A low-profile carb is probably available from something, and if necessary, a low-profile flat-section bend from the top of the carb to an air filter.
With your current arrangement, I can see you might have horrible fuel drop-out issues when it gets a bit colder.

 

Ok fellas did a redesign
built 2 individual equal length steel box plenums fed directly from the bottom center and am still using the 1965 pict 28 vw carb
Testing is going well ..plugs look great.....no cutting out.....dunno may be onto something here

 

Carb isnt on in these pics

 

Have you seen mine? - it really is simple. Only reason I didn't try a one-piece cross-ways plenum was the lack of height ot the top rails. You have a ton of room there.

 

Seems like a lot of manifold run. Does it hesitate when you crack the throttle?

 

Where can I find that pic
I looked ? Can you load one up on here id like to see it..thanks dave

 

The throttle response is

 

Is what?

 

Throttle response is nice
Surprisingly

 

Amazing! Just seems like a lot of run and curves the fuel and air to navigate for positive throttle response.
Seems like an interesting mod though. SQLGuy did his fuel injection a while ago and that was impressive

 

I'd be curious to see how wide it is with the air filter , from a sitting rider's point of view.

 

I would think that a manifold like mine would work pretty well with a good sized MC carb (44mm or so) in the place of the throttle body I have in my setup.

 

I would like to see that!

 

Were the adjustments minimal once you found the right manifold/throttle body setup?

 

Well, there was a lot of learning involved before I got to that point. Part of that was because I had one of the first batch of 10 Microsquirts made. There were problems with the VR conditioning that they didn't solve 'til long after I had replaced the whole circuit. Initially they didn't believe those problems existed. Then they had a cure that made no sense. They finally did fix it in a later revision, though. Idle control was also a challenge, as was warm-up (most of the Megasquirt warm-up curves are idealized for water cooled engines).

This is my second manifold design and third fuel rail design. I did work out a lot of the tuning on the first manifold, and things were smoother with the new design - as well as easier to install and more elegant. I haven't done any dyno work with the newer manifold, though, so I can't say how much of a difference it made in power; it does certainly feel like it runs better.

It's hard to say how difficult or easy it would be if I were starting with the solution I have now and just needed to tune it. And there's still the question of how much better (if any) an ITB solution might be...

 

Here's a less pretty picture of what the manifold looked like during construction. Gives a better idea of how the pipe pieces fit together. These are regular copper pipe fittings, mostly 45 degree pieces, since a pair of those can make a wide variety of curves. The intake port flanges are cut from brass sheet, and the throttle body flange is cut from a thicker copper sheet. Copper and brass allow for fairly forgiving assembly and tweaking with silver content solder and a propane torch.

 

That manifold is so cool looking!

 

A piece of art !

 

A piece of hack, more like. But it works, and it looks much better with paint on it!

 

Nope, the copper looks cool! That could be the start of a decent theme ... instead of chrome, copper!

 

Here's a post - more pics available if needed.
http://www.xjbikes.com/forums/threads/single-carb-mod.30257/page-6#post-472411

 

Steampunk!!!!

 

Looks pretty good for a piece of hack if you ask me. I couldn't have done that in my wildest dreams. That's what makes this site so great is all the great ideas and people with real talent helping everyone. You are a very talented individual sir! Thanks for your insight and help with things like this.