Marine carb replacement

[Bubba1235]

I am in need a for a carb for my 351 Windsor (square bore 4bbl. 600 CFM electric choke)

I am doing my best to find a "marine" carb but when I look on a number of sites I see that most of the ones advertised as "marine" have vacuum secondaries.

How can that work when a marine engine has little to no vacuum at anything above idle?

 

[Bondo]

Re: Marine carb replacement

Ayuh,....

ALL Marine 4bbl.s are Vacuum secondaries.....

The Edlebrock AFB Clones are Great Carbs for the money spent....

 

[chiefalen]

Re: Marine carb replacement

What year is that 351 windsor?

Cause i think oem was a vacuum choke.

Electric choke was added latter maybe.

Or a different carb changed on to it maybe.

 

[a70eliminator]

Re: Marine carb replacement

Marine engines have just as much vacuum as any other engine, my 351W pulls about 18" at idle. The vacuum drops to 0 when you open the throttle because you've just opened a big hole in the top of the engine, the carb. The vacuum secondary throttle plates are now being sucked open by the lower pressure beneath the carb, the vacuum diaphragm has a spring in it that limits the amount a pressure needed to open the secondaries which is adjustable by choosing springs with different pressure values.
I think I said that right .

 

[wca_tim]

Re: Marine carb replacement

I've had good luck with a couple of the edelbrocks and for a little over $300 its a hard option to beat.

I've bought a couple of them (a 600 and a 750) and wouldn't hesitate to do so again.

I'm getting ready to try a Holley double pumper with mechanical secondaries to see how that fares, but for general use I've been very happy with the edelbrock 1409 and 1410 carbs and know several others that are as well.

 

[Maclin]

Re: Marine carb replacement

It is not manifold vacuum that opens the secondaries. On Holleys it is the draw thru the primaries that pulls against the diaphragm and opens the secondary plates. On Eddys and QJ's the secondary bottom plates are opened mechanically and it is the draw of air from the secondary side that pulls open the top plate.

 

[WizeOne]

Re: Marine carb replacement

...in other words, it is the absence of vacumm that open the secondaries (subject to diaphram spring pressure as noted) not the presence of vacumm.

 

[rthomas]

Re: Marine carb replacement

ive been running a 1405 for a while now, the nice thing about that is being able to add a pcv valve and do away with the tubes that foul the spark arrestor. btw the e-brock/afb is a fully mechanical carb, the only porpose of the upper butterfly in the secondaries is to create an instant of vacuum to quickly get the fuel up to the venturies so you get less of a flat spot when you open them

 

[wca_tim]

Re: Marine carb replacement

1405?? That's not a marine carb!

 

[mkast]

Re: Marine carb replacement

Cause i think oem was a vacuum choke.

What is a vacuum choke?

 

[Fishermark]

Re: Marine carb replacement

The Edlebrock 1405 is the performer carb - an automotive carb. Not to be used. The Edlebrock 1409 is the marine version. That's the one you want.

 

[John_S]

Re: Marine carb replacement

The Edelbrock 1409 and 1410 have secondary butterflies that are mechanically linked to the primary butterflies. The secodarys start to open at about 2/3 primary opened, and fully open at wot. An air door controls how much air/fuel flow through the secondarys. From a standstill when you hit the throttle to wot, the primarys and secondarys will both be wide open. Only minimal airflow will occur in the secondarys until the engine creates enough vacuum to open the air door. On these Edelbrocks the secondary air door is controlled by a counterweight. Q-jets use the same principle, except the secondarys are controlled by a windup spring, which unlike the Edelbrocks can be adjusted.

Holley uses a vacuum diaphram, that opens the secondary butterflies when the engine vacuum overcomes the spring in the diaphram module. Holleys are adjusted by changing the vacuum spring, with one of a different opening rate.

 

[dan t.]

Re: Marine carb replacement

concerning holley vacume secondarys,if engine vacume overcame the spring in the secondary vacume pot the secondarys would be open at idle when vacume is highest. what realy happens is a small passage goes from the primary venturie to the secondary vacume pot.the more air flows thru the venturie the stronger the vacume siginal .the spring controles the opening rate

 

[John_S]

Re: Marine carb replacement

It has been awhile, but I believe the vacuum port for the secondarys is above the primary butterflys, such that the primarys need be significantly openned to get a vacuum to start to open the secondarys. Holley's spring tuning kit includes represenative graphs of the different color springs and their beginning and fully opened points.