carburetors, what are you guys using

guglielmo6160 · Post by **guglielmo6160** » Fri Apr 01, 2011 10:41 pm

my 350 Merc, is using a two barrel Rochester, having some issues with dripping down the barrels while she is idling, carb is rebuilt, and I notice some huge jets in the bowls.
Was wondering what carbs you guys are running, and has anybody else noticed this whle at idle ,
thanks

rossjo · Post by **rossjo** » Fri Apr 01, 2011 11:32 pm

Quadrajets - only way to go ... good fuel economy and great performance.

prowlersfish · Post by **prowlersfish** » Sat Apr 02, 2011 7:07 am

for a 2 barrel carb Rochester is your best bet . I also have seen Holley and ford/autolite carbs used on ford marine engines with 2 barrels .

as a general rule on 4 barrel engines your will find Rochester ( Q-jet ) and Holley's on GM engines , Holley's on fords and Carter AFB ( elderbrock now) on Chrysler marine engines .

I would stick with what you have as fitting a other type can be a pain. and the Rochester 2 barrel is one of the better ones

But what ever you do . You must use a marine carb as they are vented differently a auto carb would be a ticking time bomb .

alexander38 · Post by **alexander38** » Sat Apr 02, 2011 7:55 am

Had the same trouble with my stbd one. Bought a re-man and took the old one part and found that Serria didn't put the carb filter in and a pc of rubber from a dining fuel pump and gotten in the float seat , also don't over look a bad fuel pump causing this. And like the King said don't go to a different one you can bring in new troubles and drive your self nuts .

guglielmo6160 · Post by **guglielmo6160** » Sat Apr 02, 2011 8:29 am

the carb and the engine are both full marine, as this was a complete drop in unit, the carb although was new(rebuilt) Im sure, I also went through it myself, everything checks out especially the float level and there is no debris at all in the carb. Now I have to point out that this engine is using an electric pump, which is fitting to the right front of the engine. In my experiecnce to much fuel pressure will also cause this dripping int he barrels, while running.
What I did was shut down the fuel pump while the engine is running and about two seconds the dripping stopped, due to the decrease in float level. But Im not quite sold on that repair yet. And of course once the pump is plugged back in it immediately starts dripping all over again,
this is causing a rich mixture with raw, un atomized fuel being dripping into the manifold. , not to mention the price of fuel and what Im wasting.
so I guess the next step would be a fuel pressure gauge , and possibly a regulator.
Im guessing between 2-4 lbs should be a normal setup for carbs..
again, my experience is with older automobiles not marine, but Im applying the same principals to this set up,
I was just wondering if anyone had this particular problem with a Rochester before, as it is a super simple carb.
thanks (excuse my spellilngs, as its early,,lol)

rossjo · Post by **rossjo** » Sat Apr 02, 2011 10:44 am

Fought the same issue son the 454 in my 26. Finaly foudn the fuel pump had loots its pressure regulation and would build up pressure at speeds over 1,200RPM. Replaced it (mechanical, belt driven Mercruiser unit) and all was well (now I'm dealing with 100 gallons of old corn fuel, which I plan to separate & "polish").

Yes - 4-5psi MAX pressure! You can get a regulator from Summit racing

If you're happy with the power, keep the Rochester marine 2-barrels (it was a marine eigne purchase, correct)?

If you want more power, you can change the manifolds and put a 4-bbl on. The Qjet is very economical because its a "spread-bore" meaning its 4 venturi are different sizes (2 sizes). The 2 primary venturis are small (smaller than you 2-bbl probably), while the secondary venturis are very large (when you get that need for speed).

All other 4-bbl carbs (Holley, AFB, Motorfraft) are "square-bore", meaning all 4 venturis are the same size.

alexander38 · Post by **alexander38** » Sat Apr 02, 2011 11:04 am

Aah yes a pump that's pumping to high a psi will cause this, mechanical or elec. I found that out last yr. The fuel pump on my Onan 6.5 mcck went bad I thought it was the carb, pump the elec gas pump was not shutting down when it should've and not letting the float seat .

Captain Blast Off · Post by **Captain Blast Off** » Sat Apr 02, 2011 11:50 am

Seems as though everyone has had this problem; I installed an adjustable regulator and a guage took care of the problem.

Word of advice... do not get a cheap one many will leak. Read the reviews of whatever you buy. I reccomend Holly I think they have one for around $65.00 on Amazon.com that will adjust from 2 psi to 6.5 psi.

Good luck.

Steve

alexander38 · Post by **alexander38** » Sat Apr 02, 2011 1:39 pm

Cheap = boom

guglielmo6160 · Post by **guglielmo6160** » Sat Apr 02, 2011 7:52 pm

when has anything marine been cheap? if we were looking to save money, we wouldnt be into boating

jimbo36 · Post by **jimbo36** » Sat Apr 02, 2011 8:20 pm

Rebuit carb? Most carb kits do not come with a new float. Floats can become saturated and cause the problem you refer to. One of my Q-jets is doing this and I am rebuilding and replacing the float as well.

jimbo36

prowlersfish · Post by **prowlersfish** » Sat Apr 02, 2011 9:06 pm

I agree on the float issue

alexander38 · Post by **alexander38** » Sat Apr 02, 2011 9:36 pm

Hey guys seems he found the trouble, to much pressure and its keeping the needle from seating

Paul · Post by **Paul** » Sat Apr 02, 2011 9:42 pm

You have a 2 bbl on a 350cid MerCruiser? What HP is the engine rated at? It seems to me that there should be a 4bbl on that engine.

rossjo · Post by **rossjo** » Sat Apr 02, 2011 9:46 pm

the foam floats have got to go - brass only! Can't believe they still make them.

Fired up the Cummins today - started/ran like a top ... cruise tomorrow.