blown1500

I go with Tinkerboater. If you run over 7 or so psi, the needle and seat take a real beating and will give problems. 6psi is enough if you can keep this pressure at full throtle. If you loose over 1/2pound, you need better fuel supply.

blue thunder

More pressure has a similar effect to increasing the needle and seat size. Say the float is 1/2 submerged with 7psi. Change this to 8psi and the float may need to be 5/8 submerged to supply the requisite seat pressure to stop the flow. Therefore, the higher pressure got you a higher fuel level in your float bowl. If you then lower the float so the fuel level is in the same place as with 7psi, you achieve your 5/8 submerged float (at 8psi) but do not change the a/f ratio.


Make sense?

BT

CESSNA

Just my 2 cents worth called my engine guy today and he said
he does see change in the a/f ratio when he changes the pressure I only have this to go on don't know who is right but thats all I found out

Vinny P

I still don't see how raising the level of fuel in the bowls ( by raising fuel pressure ) will richen the mixture. If the floats are adjusted properly with 6 psi, then you add pressure to 7 psi, I will go along with this causing a slight increase of fuel in the bowls. The fuel still has to pass through the jets. The jets still have the final say as to the amount of fuel that enters the manifold. To me, float height has more to do with having enough supply for the engine to suck fuel in at higher rpm's and loads. If the floats are low, you run the risk of sucking the bowls dry causing a lean condition. If they are too high, the fuel can overflow out the vent tubes.

Dennis Moore

There are tubes inside the metering blocks that reach down into the fuel. These tubes have holes drilled through them (emulsion holes). The holes are designed to pick up air and mix it with the fuel on the way to the boosters. A high float level will cover some of these holes creating a rich mixture. The float level needs to be exact to keep these air holes uncovered. Everybody should pull apart a Holley metering block once and follow the fuel circuit, it is very interesting and explains a lot of the problems related to Holley four barrels!
Dennis Moore

Hot Boat

Ok I have a worked 850 Holley punched out to a 920cfm . i am running a Holley black marine pump threw a stock merc water filter and size 8 An braided steel lines from the tank to the carb. Its set at almost 8 psi but at WTO she drops to just under 7 psi. How bad is this??????? and what should I do to correct it????? This is on a 454 with a small blower. so I gather that fuel is important.

Mbam

I won't run more than 5 PSI at full throttle, found that any more and the carb will dump fuel when landing from a wave or running hard in rough water. Makes for a black transom and soft throttle response.

The key is a fuel pressure regulator, assuming of course you have adequate supply to the reg. If worried about enough fuel in the bowl, (only a problem on big blower motors) run dual needle float bowls.

Hot Boat, the 1 psi drop is pretty normal.

Did some work with clear bowls and TV camera on the dyno, the higher pressure will raise the fuel level.

formulaF302

I'm having some kind of fuel problem and am running Holly red marine fuel pumps....where to these fall into this pressure equasion with Holley marine 830 annular carbs? they are a 4150 body? Glenn

bobby daniels

well at least Dennis and Marc understand what I'm talking about
above

As marc said the 1 lbs is normal or o.k. and f302 what type problem are you having ??

formulaF302

I'm having a problem with the rear 4 plugs on each engine running pure black, and getting a smell of gas in the bilge after shutdown. I'm assuming fuel is dripping down the manifolds after shutting down as the engine heat rises and expands the fuel in the bowls...I've got "puddling" of fuel in the cast grooves in the manifold, but don't know if I'm getting this condition while running, or only from idling back into the marina after the back of the boat sets back down....thereby increasing the angle on the manifold floors and sending all this raw gas back to the rear cylinders. I MIGHT be zeroing in on myproblems now though. Just got off the phone with my engine guru....he said I should have minimum of 8.5 power valves in the carbs in light of the cams he put in them. I just checked and found I only have 6.5's. That combined with float set too high in primary side could be causing this per him.......