Custom Manifold for 6 Carburetor Setup

[ARiskyCvt]

Beautiful!!! can't wait to see the finish product! keep up the good work.

[pkz]

Drilled and tapped the throttle shaft today. Tested out the throttle mechanism using a pair of pliers- everything lined up pretty well. Then I cut out the holes where the header interfered and was able to set everything in place- only to realize I drilled the head-mounting holes in the wrong location. I used the exhaust-intake manifold gasket as a template to mark the holes, and accidentally used the exhaust holes. Fortunately it wasn't anything that wasn't fixable. Drilled new holes, and the old ones aren't in the way of anything- I'll probably cut them off later once I get to making everything look nice.

 

Gareth- how did you secure the bottom half of the head-mounting flange? There are no holes for the original manifold- the original manifolds are .5" thick and are held in using a thick washer that also holds the header/exhaust manifold in place. Right now my carbs are only held in by the top few bolts, which I'm sure is just asking for a vacuum leak down the road.

 

And finally, some pics:

 

 

 

Tried starting it this evening- ended up setting the carbs on fire with starter fluid- scared the heck outta me. it was freezing in my driveway... Tomorrow I'll take another look once it's light out. I suspect I have fuel leaking from somewhere, but it's impossible to see in the dark. I can already tell I'm going to have to rework the T-fittings to accept the fuel lines better- they keep falling off way too easily.

Edited December 16, 2015 by pkz

[Gareth. J.]

Carb spacing looks good, will the sealant on the fuel tee's last? A fuel leak above the headers would be bad news.

 

I made the manifold flange from 12mm ally plate to match the thickness of my stainless headers flange. It secures the same way as the factory setup.

 

If you have trouble with different thickness flanges can you weld on extra strips of metal where the manifold nuts and washers need to go?

Edited December 16, 2015 by Gareth. J.

[pkz]

Got the car to start yesterday- wouldn't rev under a few thousand RPM without sputtering out and dying though. I'm going to weld on extra material for the manifold washers to compress to the head today- then try again.

 

I also reconsidered using permatex sealer on the fuel fittings. I think I'll be better off grinding down the diameter of the plastic T fittings so that the original O-rings fit back on. From what I've heard, anything that relies on a permatex sealer alone (ie not in addition to a threaded connection) to seal will eventually fail. 

[Gareth. J.]

For the fuel tee's could you use 'JB Weld' to permanently seal them into the carb bodies?

 

Great progress, keep going!

[pkz]

After grinding down the T- fittings I don't have any fuel leaks (the stock O rings seal really well) and since the carbs are all pretty secure and the T-fittings are squeezed between two adjacent carbs, so they are very secure. Without jb weld the T's are free to swivel, which makes installing fuel lines much easier.

I welded on some extra material to the head-mounting flange, so the header washers hold the flange down nicely. Thanks for the advice gareth, it worked great.

My engine idles decently now. I'm going to install a vacuum fitting for the brake booster on the rear manifold tube.

I'd like to set up ignition timing advance- like most webers, the mikuni tm40s don't have vacuum ports, so I'll have to come up with an alternate solution. From some searching the archives I have a few options:
1- set up a vacuum log on my intake manifold. Ideally for this to work I'd need to use at least 3 tubes to prevent vacuum pulsing.
2- Run an electronic distrubutor (123 ignition etc). This would be the way to go but they're pricy, and maybe not completely necessary for a N/A setup. To my understanding, these run about 400$ for a standalone ignition setup.
3- Change the mechanical advance curve (new springs). I might not be able to achieve the level of control that the vacuum advance offers, but this would be pretty simple and may be a good "close enough" option.
4- Run the existing system with no vacuum advance and adjust the timing accordingly. Drivability under 3K rpm will suffer, as well as gas mileage.

Given that this is a street car, My first choice (unless there are other ideas) is to change the mechanical advance. My current distributor has a crane cams xr700 optical pickup but it otherwise stock (I'll do some more reading and figure out what year).

 

EDIT: Still weighing my options on ignition advance. Read this post about vacuum advance on the Zcar forum. http://www.zcar.com/forum/10-70-83-tech-discussion-forum/286774-pure-mechanical-timing-2.html . Mechanical advance will probably result in something less streetable than I'd hope for.

Edited December 19, 2015 by pkz

[pkz]

I set the initial advance to 10 degrees today and the engine idled really well. Started tightening the distributor clocking bolt and my distributor support snapped. It wasn't a clean break- definitely fatigue, so I guess I'm lucky it didn't fail while I was driving. I flipped around the plate and drilled a hole in the other side of the distributor support so I could hold the distributor in place- until the replacement comes.

 

I spent some time setting up the throttle linkage today- I kept as much as the existing linkage as I could, without drilling or cutting it at all. Just in case this setup isn't drivable within the next couple weeks I want to have the dual flattops (and their throttle linkage) usable so I can drive daily. Not planning on it coming to that though.

 

I ordered a wideband O2 sensor which should be here in a few days. Then I'll be able to dial in the tuning much more efficiently. Throttle response right now is pretty sluggish.

 

PS- video coming in the next couple days

[pkz]

[sharedmedia=videos:videos:286]

 

Got the video up! Sorry it took me so long. The wideband sensor goes in tomorrow. 

[pkz]

I accidentally started a welding fire in my garage in January when welding on a bracket which was going to hold the existing Z throttle shaft in place. I learned the hard way just how important it is to have your fire extinguishers checked- mine didn't work and left me scrambling. I put the fire out with a hose in my backyard, but not before it roasted my fender and alot of my engine wiring. The old flattop carbs went back on the car for a while in an effort to get the car back on the road as soon as I could. Since I had the six carbs off the car I decided to spend some time to clean up the setup. I bought a spectre throttle cable which I'll run directly to the throttle arm. I also made the slide throttle positions relative to one another- Originally I had the single throttle shaft tapped and screwed in the individual slide mechanisms, so the mechanism wasn't adjustable (couldn't think of a surefire way to make it adjustable at the time). Now I've used set screws to hold the slide mechanism to the throttle shaft. In order to adjust them, I have to loosen the set screw, then retighten when they're set correctly. Not quite as easy as with triple webers or stock carbs, but overall not too difficult.

 

I decided to repaint the intake as well. After using a grinder wheel to clean up some of the rough edges from before, I taped off the area where the carburetors mount to the upper plate, then used a few passes with vht paint from oreilly. I'm really happy with the results.

 

 

 

 

 

 

 

Edited May 11, 2016 by pkz