Carburettor Config Questions

[mosu]

Hi all,

I just purchased a sort of frankenstein 1974 Spider with a 1608 motor transplant. It seems like the previous owner put it together from a combination of parts from the two model years. It still has the DHSA carb, but it looks like it was mounted to the single plane manifold. The manifold has a single large inlet under the carb, and seems pretty compact, and from descriptions on the forum it sounds like the single plane. At any rate the secondary diaphragm housing is bent and cracked and probably leaking vacuum like mad.
Following popular wisdom I decided to go for a DMSA, but the only one I can find is a core for $150 at C Obert & C. I have little carb experience, so I'm wondering if going for it is the right move. The gentleman there is kind enough to give it a quick look for cracks and non-binding shafts, but is it enough? For the guys with more experience, is this too risky to pay for? Any advice would be greatly appreciated in how to proceed to replace my tired DHSA.

Alex

[manoa matt]

This was taken from Brad Artigue's article:

"The DHSA was used on the 1438 and 1608 motors. Vehicles imported into the United
States received the 26/34 DHSA1 and the 28/36 DHSA2. The numbers refer to the
primary (26 or 28) and secondary (34 and 36) barrel sizes.
The DHSA is a progressive two-barrel carburetor with a vacuum operated secondary.
This secondary throttle opens when the primary throttle is fully open. This opening is
controlled by a diaphragm mounted on the side of the carburetor and linked to the
secondary throttle shaft (refer to figure 9 in the previous section). The different DHSA
models are directly interchangeable with each other and with the DMS and DMSA
carburetors.
The DHSA has a mechanically operated choke, meaning that a cable connects the choke
plate to a knob. The driver pulls the knob, activating the plate, and restricting airflow into
the carburetor.
There are two additional small diaphragms that are electrically activated by the position
of the clutch. These devices are also attached to fast idle speed controller, electronically
linked to the clutch assembly and to a switch on the transmission. When you shift into
or out of 3rd, 4th, and 5th gears the controller keeps the engine speed around 1500 RPM.
The actual speed at which the controller engages is set by a switch in the engine
compartment.
The diagrams on the following pages show the exploded views of the DHSA carburetor.
For a description of the operation of the carburetor refer to the section on the DMSA.
The DMSA is operationally similar with the exception of the vacuum secondary."

"The DMSA was used for a single year (1974). It is virtually identical to a DHSA except it
lacks the vacuum operated secondary. DMSA has a mechanically-operated secondary
and the largest primary and secondary throttles of any carburetor installed on the
Spiders. The advantage over the DHSA is there is no time lag during heavy acceleration
for manifold pressure to pull open the secondary. The DMSA is a slightly larger
carburetor than the DHSA2; this was to accommodate for the larger 1756cc engine
introduced in 1974. The DMSA and DMS are popular upgrades for DHSA owners. Problems with the
vacuum-operated secondary unit (typically stemming from a misunderstanding of how it
works) would lead to cars that ran poorly. The DMS, with a direct mechanical
connection between the throttle plates, eliminated these problems. As DHSA
carburetors wore out they were often replaced with brand new DMS units."

Basically with the single plane manifold you need a mechanicaly opperated secondary, like the DMSA. The single plane manifold may not provide optimim performance with the vacuum secondary of the DHSA. The 34 DMSA would be an improvement for your car and provide more power, but as stated it was designed for the 1756cc and may need to be jetted down for your 1608cc. Another alternative is the 32ADFA, also jetted for the 1756cc motor. They are plentiful, rebuild kits are readly available, and there is plenty of information on them including diagrams and a workbook.

[mosu]

Thanks Matt, that's what I was thinking of too, but I didn't know I had to jet down for the motor. I guess it makes sense. The jets in my current carb can be transferred over to a new Weber I'm assuming so I don't go around guessing?

Also, was I correct in identifying my current manifold as single plane from the "one big hole" description I found somewhere (probably in Brad's article too)?

[manoa matt]

You may or may not have to jet down, I don't know. However starting in 74 with the emissions regulations, the carbs were jetted down to lean out the mix to meet US emissions regulations.....so.. a carb jetted for a 1.8L that is already "jetted down" may work on your 1.6L. You'll have to play with the air fuel mixtue screw and read your plugs to tell for sure.

[SpiderHead]

34 DMSA..... no better single carb was ever put on a Spider.

There are the twin IDF's... honestly more fun to fiddle with, and they look so cool!

That 34 DMSA has low rev grunt that the smaller twin carbs lack. With it you will get better economy in town, at lower revs, but will suffer economy on the highways, where the twin carbs come in to their own.

Don't switch out your carb, just get it jetted properly. Or, if you do... might I suggest those fun to fiddle IDF's?



-Ryan

[mosu]

Spiderhead, I want to buy the DMSA, that's what I'm asking people if it's a good idea to buy a core for around 150 and regasket it or it's too much of a risk because of cracks, frozen throttle shaft, etc.

Also, am I correct that my manifold is the single plane one if it has a single hole where the carb bolts in?

Right now I have a cracked DHSA bolted to what I suspect is the single plane mani, so the car's slower off the line than a mental retard doing calculus