4 valve Rajo and an OF.

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Allan
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4 valve Rajo and an OF.

Post by Allan » Sun Feb 02, 2020 11:46 pm

A friend has a speedster fitted with a pair of swayback NH Holley carburetors. In rebuilding the exhaust system, he is looking to simplify the setup. The car has a 4 valve Rajo head, but the camshaft is unknown. Nor has he any knowledge of the pistons used without pulling plugs and having a look. I have a good OF Stromberg carburetor on the shelf, and it would be a simple matter to make a new inlet manifold to suit it for his application.

The questions are;
Will an OF be sufficent to give optimal road performance for a 4 valve Rajo equipped car?
Will it out perform the current NH's, which are rigged such that the second carburetor only comes on line under heavy throttle?

Allan from own under.


Joe Bell
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Re: 4 valve Rajo and an OF.

Post by Joe Bell » Mon Feb 03, 2020 7:28 am

Not enough air and fuel, it will run it but restricted on air flow for the size valves in the head. I have the twin NH's on mine and do like the way it performs, you need an equilizer tube between the two carbs to make it work right. Just my thoughts!


StanHowe
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Re: 4 valve Rajo and an OF.

Post by StanHowe » Mon Feb 03, 2020 2:14 pm

IMHO, the OF is not carb enough for the setup. You would be far better off with an MB-1 Stromberg, a 4 series Zenith or a couple other sidedrafts. OS-1 Stromberg's are good and depending on the RAJO model, some people run OS-2 Strombergs or HP5A Zeniths on them. If you are stemwinding you don't want either one of those, they can be hard to start. They also can be difficult to get to idle well with that big a carb. HP5A's with a venturi reducer will work but there are HP4A's or HP4U's that are great for those, they will start well, idle well, and will make use of about everything a 4 valve RAJO will do.


Harry Lillo
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Re: 4 valve Rajo and an OF.

Post by Harry Lillo » Mon Feb 03, 2020 3:41 pm

I realize the initial question related to the flow capability of the OF carb with a 4 valve RAJO.
I have run OF, Winfield as well as NH singles on a hot flathead engine. In my opinion as single OF will not flow enough to keep the 4 valve happy.
I am just finishing up a 4 valve RAJO engine and have some similar questions.
The engine has a 290 cam, 1 :1 rockers, log manifold and DU4 spark.
My choice is a pair of Windfields.
I am also interested in knowing how the progressive linkage worked on the present setup.
A good friend had a nice twin carb log manifold on an overhead. He started out running a single rear carb until he finished rebuilding the second carb. The engine ran way too warm and he could not resolve his heating problem until he got the second carb on. The front two cylinders were running way too lean and 3 and 4 too rich.
I have considered progressive linkage to run on one carb until I need more jam, but am reluctant to do so because of this experience. Any experiences from others on this?
Harry


Topic author
Allan
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Re: 4 valve Rajo and an OF.

Post by Allan » Mon Feb 03, 2020 7:28 pm

I suspected the OF might be just a bit lacking on a 4 valve Rajo, but had to ask. What about a pair of OF's? Thank you for your list of alternatives Stan. I'll have to list them in my little black swap meet book and keep my eyes open.
The owner had a new set of headers made to tidy up what was on the car when he purchased it. When these were fitted, the car ran like crap, lacking power and response. On checking, I found that the throttle linkage on the first carb was fouling on the header and he was only getting 2/3 throttle!
Now he wants to tidy up the whole thing. The current intake manifold has the NH's in line with the two ports on a tube manifold which places them almost down on the frame rail. This car still runs on gravity feed. However, the runners to the carbs are around 8" long. Those runners, and the balance tube are 1.25", with the balance tube almost up at head port height, but the runners necked down at the carb end.
He wants to drop the rear tank down to near the original height, and is prepared to run a fuel pump, so we were looking at making a new intake manifold and eliminating some of the length of the runners, reducing the size of the balance tube and lifting the carb/s at the same time. Looking for guidance here.
I was surprised to read that the pair of NH's would do the job. The progressive linkage set-up is interesting. Until around 2/3 throttle, only the front carb is working. The path to the rear two cylinders is quite tortuous, but apparently it works. With loads of throttle the second carb comes in. There is a rod with an adjustabe stop connected between the two carbs. As the first carb is asked for more, the rod slides and the stop engages to open the plate on the second carb. I have not seen/heard the car running to see just how much the second carb contributes. If it works well, a good tidy-up of the linkage mechanism may be all that is needed.

Allan from down under.

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TonyB
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Re: 4 valve Rajo and an OF.

Post by TonyB » Tue Feb 04, 2020 1:10 am

I have an OF on the speedster and on the 14 touring and I think they the very best carb for the T.
However I have close friend with a four valve rajo and we have tried number of carbs with varying degrees of success. All were trial and error and it’s been a fun ride over the last 5-6 years. However I can state categorically that the OF at 1 1/8” is too small for the full performance you can get with the four valve Rajo. Right now the rajo has a Stromberg M1 at 1 1/4” and the owner thinks it’s both the best looking and best performance carburetor he has tried.
So there in a nutshell is five years of playing with different carbs, we may be wrong, we may be last but it’s been great fun getting here.
Tony Bowker
Ramona, California
1909 Touring, 1914 Touring, 1915 Speedster, 1924 Coupe.


Aussie16
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Re: 4 valve Rajo and an OF.

Post by Aussie16 » Tue Feb 04, 2020 5:08 am

Allan, My Rajo 4 Valve came with from what I can remember was a fairly big SU carb. It had a very simple inlet manifold and used pretty simple throttle controls off the standard rhd control shaft. It serviced the big inlet valves well. SU's are readily avaialable. Search 4 valve Rajo on the forum. there was good coverage fairly recently of a chap with a 4 valve Rajo that initially had twin NH carbs then swapped for 2 bigger accessory carbs. Thing ran very quick when sorted. http://www.mtfca.com/discus/messages/59 ... 1462740130


Topic author
Allan
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Joined: Sun Jan 06, 2019 7:21 pm
First Name: Allan
Last Name: Bennett
Location: Gawler, Australia

Re: 4 valve Rajo and an OF.

Post by Allan » Tue Feb 04, 2020 6:37 am

Warwick, can you recall if the SU mounted with 2 or 4 studs? 2 studs = 1 1/2". 4 studs = 1 3/4" or 2". A single carb is much easier to work with!

Allan from down under.

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