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Strangeflow 02-22-2010 01:20 PM

Anyone ever modify and atomic four?
Mainly carb. mods, I am thinking about fabbing a new intake manifold to use a sidedraft or downdraft carburetor. Has anyone ever done anything like this or tried?

nolatom 02-22-2010 01:46 PM

Then a hotter cam, shave the head, tuned exhaust....

The "Nuclear" Atomic 4 ;-)

tommays 02-22-2010 02:14 PM


I have found that soaking the carb in a 20 dollar can of carb soak and putting in a new needle a seat pretty much makes it work perfect and its got the correct requried flame arrestor

Going Wile E. Coyote on any gas inboard opens a real ungly can of worms ;)

As the intake and exaust manifold are one water cooled piece it would be a lot of work for something that works :)

Strangeflow 02-22-2010 03:56 PM

Hmm, okay. Mine runs great right now but has a lot of corrosion, it is also raw water cooled.

I was going to do a diesel swap but due to the economy I picked up a freshwater cooled atomic for $45. I am going to rebuild this one and swap it in this spring.

The reason for me asking is that I see the updraft carburetor as the 2nd worst aspect of the engine (in between it being gasoline powered and it having points, though an electronic ignition is in the works.)

I have the machining skills to fab a new manifold but don't want to waste the effort if I am headed into uncharted waters so to speak.

I don't think I'll go full nuclear,for the cost i may as well just go diesel.

bljones 02-22-2010 04:18 PM

I've never really thought much about hopping up an atomic 4, but now you have me thinking...
A downdraft or sidedraft manifold and carb set up would likely give you some clearance issues. That is the one benefit of the admittedly goofy updraft carb, you can tuck it in beside the block where it is out of the way and approximately 177% more difficult to access.
if you've got the width, a side draft SU might be a decent match, but then you have to create some sort of bellcrank throttle linkage, and then you start scratching your head over the cam set-up, and I don't think anybody does custom bumpsticks for A-4s.
I'd probably look at simply mproving flow by porting, polishing and matchporting the manifold and head, and maybe changing the ratio of the rockers. Maybe deck the head a little to raise compression from the seriously low 6.3:1 . But seriously, if your A-4 will drive your boat at hull speed now, well,...

xsboats 02-22-2010 05:10 PM

There is a replacement downdraft carb available for the Atomic 4 . I put one in my Alden back in the 90's for $180 . It was a bolt on installation with no mods needed. I think I got it from Hale Marine. The flame arrestor from my old updraft fit on it as well.

ViribusUnitis 02-22-2010 05:11 PM

What about a EFI or even electric engine control system?

A TBI MAP system should be fairly easy to arrange. And it would probably be MUCH better than a carb. Start up quicker, be more efficent, etc.

Would you pay a couple hundard for that?

tommays 02-22-2010 05:36 PM

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Amazing but IF you can do simple repairs on a lawnmower you can go through and A4 and make it run

sailingdog 02-22-2010 06:32 PM

I'd point out that adding an EFI system is probably a really stupid move. The bilges on most small sailboats are prone to getting wet...and keeping the engine as simple as possible is probably a good idea. Replacing the distributor cap, rotor and points with a hall-effect distributor might be a good idea, as that is going to be more reliable...but electronic fuel injection, not a good idea IMHO.

nickmerc 02-22-2010 06:55 PM

I added electronic ingnition last winter to my A4. I found that for the same price as two sets of points and condensers I was able to but the electronic ignition. It took about an hour to swap out the ignition and it was well worth it. My engine runs smoother and I do get better fuel economy. Plus there is little to no maintenance to worry about. I got mine from Moyer for about $100.

As said before if it already drives the boat at hull speed there is not much need for more power. However, if you can have a more reliable and efficient engine, that may be worth some upgrades.
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