Two carbs are better than one

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Model T Ford Forum: Forum 2016: Two carbs are better than one
Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth in Alabama on Thursday, March 31, 2016 - 12:48 am:

I've been busy with school but have found time here and there to fool with getting my new 4 valve Rajo installed. Still have a ways to go with making sure everything fits and lines up but couldn't help myself and snapped a couple pics.







I'm going to get it all hooked up and intake painted and see how it does hopefully this weekend. My only concern is the intake might be a wee bit big, I may do better 1" pipe instead of 1.25" pipe. I visited my parents house in Georgia and my dad has the welder there so I had to make the intake with just the head and some measurements. I think it turned out about like I pictured in my mind. Although if make another one from smaller pipe I'll raise that equalizer tube and swap the carbs front to back so the linkage can be smaller and simpler.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Thursday, March 31, 2016 - 03:03 am:

Nice work. Here comes the "but". All the factory type installations have a "balance tube" between the runners. Probably closer to the carbs. I believe it really helps in getting the carbs balanced for flow. If yours runs good then please ignore this. I'm willing to learn from your experience


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Thursday, March 31, 2016 - 03:06 am:

I see you have a tube but I think it may not be big enough! If it runs ok then of course it is!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Thursday, March 31, 2016 - 09:02 am:

You can get it to run OK with individual runners if the carbs are carefully synched. I used to have a pair of mercury manometers for tuning my Japanese four cylinder motorcycle. Made a huge difference.

I think the balance tube adds performance due to making the effective plenum area larger, and allowing all cylinders to pull from both carburetors. This will give an increase in torque, but you would still benefit greatly from synching the carburetor flow with a manometer.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John McGinnis in San Jose area, CA. on Thursday, March 31, 2016 - 09:33 am:

Wonder where it is going to break off first.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth in Alabama on Thursday, March 31, 2016 - 10:45 am:

Thanks for the input Les, I'll let everyone know how it does once (if?) I get it started up. If I end up having to remake the intake over again I'll beef up the balance tube.

Royce - how does that work? I am guessing it has to do with flow through the carbs but would have no clue how to go about balancing them.

I'm wide open to any input or suggestions.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Thursday, March 31, 2016 - 11:25 am:

I tried balancing two carbs, but couldn't quite figure it out.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Terry Woods, Richmond, Texas on Thursday, March 31, 2016 - 11:32 am:

Steve, Did you try balancing them on your head?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Thursday, March 31, 2016 - 11:37 am:

Here's a do it yourself twin carb synchronizer: https://www.youtube.com/watch?v=Y_WDF6glD5k


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael Snyder on Thursday, March 31, 2016 - 11:45 am:

haaaa! i just spit my coffee reading this !! thanks Steve...


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Thursday, March 31, 2016 - 01:46 pm:

Here is a four manometer setup on eBay. It is similar to what I used to have except mine was made for a twin, even though I used it on a four:

http://www.ebay.com/itm/Motion-Pro-Carb-Sync-Tool-Synchronizer-Motorcycle-Carbur etor-Syncpro-5mm-Adapter-/131548774986

Basically you tap into the intake manifold and make sure that you have the throttle blades adjusted so that each pair of cylinders is receiving the same amount of mixture, as measured in inches of mercury. You check it at idle, then at mid range, then at full throttle. You have to make the linkage adjustable so that you can get as close as possible - it will not be perfect at the end of the day without a balance tube located close to the head.

If you go on You Tube there are lots of videos of folks using these and other vacuum gage type devices to accomplish the same thing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Zibell, Huntsville, AL on Thursday, March 31, 2016 - 02:42 pm:

Seth,

If you install vacuum ports in the intakes I have the necessary equipment to balance the carbs. I do it all the time on motorcycles. Idle sync isn't as important as open throttle. You want the sync dead on at about 1/2 throttle, and close is good enough for idle.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, March 31, 2016 - 04:31 pm:

All the 2 carb MG's that I used to own had the balance tube between the 2 intake manifolds.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Thursday, March 31, 2016 - 05:43 pm:

Well, another interesting thread that prompts a question for Les or Royce, or anyone else knowledgeable in carburetor type things,......

Lets suppose for a moment that it is easy to synchronize two carburetors (which it's not) on an in-line 4 cal. engine (I'm remembering here, several British cars with twin SU's) and lets also suppose that they will stay synchronized for long periods of time (which they probably will not). If this was the case, would the balance tube still be necessary?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Thursday, March 31, 2016 - 05:46 pm:

4 cyl,....NOT 4 cal,......dang auto correct thing,....!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Thursday, March 31, 2016 - 05:50 pm:

Harold
I think James has answered your question. My experience is that twin carb SU's stay synchronized quite well. I have a '58 Jaguar and have had really minimal problems


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Thursday, March 31, 2016 - 06:11 pm:

.....at least not with the carburetors, huh? Thanks Les,....harold


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Zibell, Huntsville, AL on Thursday, March 31, 2016 - 10:27 pm:

From my experience on motorcycles, a balance tube on intake isn't necessary. A balance tube on split exhaust systems will increase savaging and help to get a fresh charge in the cylinder.


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