What causes fuel pressure to rise to the point of needing a regulator?
 

What causes fuel pressure to rise to the point of needing a regulator? Motor is 1985 merc 260 Carb. I am just trying to get a handle on this. I have been having some carb issues and I am down to where if the carb is not the problem too high fuel pressure is. Thanks

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

If you have the stock Merc mechanical fuel pump , it's unlikely the pressure would increase. I'm running Carter mechanicals (140 gph)on my 540s and they are internally regulated for 7 psi. I also have 4 pressure gauges , 2 electrical on the dash and 2 mech. right at the carbs for a second opinion and they never change.
If you're still battling the idle problem , it's more than likely the float level or the needle and seat. It seems the common problem here is the fact that this problem appeard with the rebuilt carb...right?

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

ok so now the guys at the carb shop are pulling it apart again and rechecking everything. My problem before the carb rebuild was that the secondaries in the carb where sticky and weren't opening all the way and who knows what else was sticky also in the carb. It had a rough idle after running a 30 min run and lost a bunch of top end speed.So I had it rebuilt, ran it, ran very smooth for 10 minutes on the hose and then it puked with what seemed like a flooding condition. I saw some fuel exit the exhaust also. I then shut off the fuel valve and the carb burned the fuel that was in it fine. turned the fuel valve back on and it flooded and stalled immediately. Thanks Mo

Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Check the tangs on the floats. Especially if the floats are nylon.

I bought a problem HP 500 carb that flooded the owner's engine soooooooo much the he got rid of it.
Turned out to be weak tangs on the float that control the inlet/float valve.
You could set the fuel level but after a few minutes the tangs would bend out of shape again from the fuel pressure (6psi) and fuel would come out the J tubes..
The newer black floats (Nyglene?) have much stronger tangs. :D

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

BTW: HP500 carb is a 4150 Holley, but I have seen the same problem with a Carter 2 bbl

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Thanks I'll mention that to the carb guys. I appreciate it.

Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

RickR, Just spoke with the guy rebuilding the carb and he says that's what he rebuilt the carb with. The new newer style black floats. It'll be ready by 4:00 today so hopefully I just got a bad set in the first rebuild. I'll let you all know how it goes. I'll install and run tonight with crossed fingers. ;)

Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

The Rochester QuadraJet is also known for the float becoming "logged" (saturated) and not having the correct bouyancy specs.

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

ahh haa. So it could be this is a POS to begin with ? Is there a solution? or just replace the carb with a Holley or edelbrock? Thx

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Actually, the quads aren't really that bad a carb. If he used the newest style float, you should be OK there. I didn't know if you were still using original parts.

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Ok Dave and thanks, We'll see if there is any difference tonight when I try it out. My fingers will still be crossed. ;)

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

It's a PIA problem , but one that should be able to be fixed easily enough :cool:

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Check your fuel system upstream of the pumps, especially within the tank. If there's a leak in the fuel pickup, usually at the tank outlet fitting, air will get sucked into the fuel line and cause the carbs to seem like the pressure is too high. You must have solid fuel, not fuel with air bubbles being pumped to the carb(s).

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Thanks, I'll check it out JohnJan. The carb was freshened up again today with a new needle and seat. The float is brand new(the new style). Since I don't want any more disappointment today I will run the engine tomorrow.

Mo, we know for certain it's a PIA problem, How easy to fix? We shall see. Thanx

Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Just to be certain John Jan, If there is a leak from the fuel tank to fuel pump, especially on the tank fitting, there would be some fuel leaking at the fitting, correct? If not how else would I knowthere was a leak? Thanks

Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

:D :D I know that feeling :( :(
I've been fighting a somewhat similar problem. My engines start fine (cold) and run fine. Shut the off and restart...they fire as soon as the starter engages :cool: . Let them sit for a hour or two and I have to crank and crank and crank and crank and crank and crank and when they finally fire they start like they are flooded. Ya know , like 1 cylinder at a time , then 2 then 3 etc. Carbs have been done by a couple of people. One suggestion which I haven't tried ,mostly because the season is quickly expiring up here , is wedge plates under the carb's to get the level since my boat sits low in the back. I tried the soak test on the trailer and hose so it was level and it did seem better :rolleyes:

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Mo, I feel your pain, Does someone actually make these wedges? Or do you have to fab it yourself.

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Ok, didn't stall out today. :) Ran it on the hose for about 20 min. I put some seafoam through the engine(decarbonizer). About how long after a decarbonizing should I still be seeing a smokey exhaust. Today' it seemed to alternate smoke between both pipes. I will take it out and run it today or tomorrow for the real test. Thanks for your help

Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

I did notice Idle was a little on the high side (around 1k) Is there a way a layman can adjust it with out calling in the pros?

THX

Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

JGB - the experience I had was similar to yours, the float bowls would presurize to the point of fuel spilling over the discharge nozzles into the venturi a few settings after starting the engine. Nobody could figure out why. The Holley tech line guys went so far as to tell me that what I was describing was impossible.

I inspected the lines all the way back to the tank and the tank fitting/pickup tube itself. The pickup tube was an aluminum pipe basically jammed into a tapered thread fitting. From compressing the aluminum into the taper a crack in the pickup tube was allowing air to be sucked into the fuel line at any time that the fitting was not covered with fuel. The fuel pump would fill the bowls with air which would effectively pressurize the bowls. This was the case with the stock carb, rebuilt carbs, whiz bang blueprinted carbs, whatever.

I posted something wayyy back then and several guys acknowledged similar problems and found leaks internal to the tank.

Once I welded a SS tube to the fitting my boat was all of a sudden very easy to dial in and rock solid reliable. Carb calibrations became a set it and leave it forever deal.

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

That seems strange that the bowl would become "pressurized" with air... carb bowls are vented... I can't understand where the excess pressure would come from... but... what may be happening with the air mixed in with the fuel in the line... is the air expands when it soaks up some heat from the engine after stopping... and the pressure rises... much like vapor lock... and it forces more fuel into the carb than what it needs... check to see if the line from the pump to the carb is isolated from the heat... I think the problem is not in the carb.... but in the fuel system before the carb.

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Ok, I am starting to get confused here. After I installed the rebuilt carb it is NOW running fine with the exception of the 1k rpm idle and alternating steamy exhaust. I ran for 15 + min shut if off, started right back up running smooth. So How can I adjust the idle on the carb? Thanks for your responses. I appreciate it. Should I still be checking for problems in the fuel system?


Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

You might want to get a manual.
What kind of carb and engine?

There is a idle stop screw which you adjust with the throttle cable removed.
Then adjust throttle cable to correct length (slight tension pushing throttle closed.

BUT you will also want to adjust the idle mixture screws to get correct fuel/air ratio.

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

I believe Moroso does( from what I hear)BUT I'm not sure about dominators

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Steam coming out of exhaust is not a carb problem, as long as it is steam. It is cooling water boiling in the exhaust stream. Swapping sides is pretty common too.

Adjusting idle mix and idle speed are a screwdriver away. A vacuum gauge is handy for adjusting idle mix if you aren't comfortable with adjusting by ear.

All fuel systems have a pressure regulator. Your stock mechanical pump has the regulator inside it.

Carb bowls are vented to the intake area above the venturis. Bowl pressure will stay around atmospheric unless you have a very restricted flame arrestor, in which case the bowls may see a bit of negative pressure, partially leaning out the over rich fuel mix (but not enough to make up the difference for the lack of airflow). There's no "normal" situation that will create any positive pressure in the bowls.

Vapor lock or air in fuel lines can act mighty odd though.

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

A lot of mechanical fuel pumps "regulate" the pressure just by how strong the spring is... I've seen electric fuel pumps with a pressure release valve built in. In automotive applications I've seen pumps with a relief tube that returns fuel back to the tank... but I've never seen that on a boat....... :chimp:

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Thanks Reed, Rick, Mo, and Mcollinstn

Much appreciated ,

Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

here's an update for the boyz.

Ran the Cigartette 20 today. I saw top speed 54 (gps speedo) @ 4500 Rpm spinning 25 p clever. I think I am real light on the RPMs for a merc 260(350SBC) Was told the engine put out 320 hp, was told it has a mild aftermarket cam ( don't know what though),was told it ran in the 60s, I don't think I can believe that but that's another issue. Anyway the 54 mph is an improvement from 51 by rebuilding the carb. However, the engine still ran rough though started and idled ok but the engine itself seemed to stutter somewhat like maybe only 6 or 7 cylinders working. I am still seeing smoke from the breathers. Compression test to come. wish I had the coin for a brand new drop in. Oh well, I guess that's boating for ya.


Thanks again for all your help guys, Look at it this way with your help we saw tangible results of gaining back 3 mph. I think that's pretty good considering there could/is something else wrong with the motor. Thanks again.


Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Jim,
Yep, that's boating. Hope ya get it worked out.

Now, a little off topic, but still applies:

The average 350 chevy's torque is non existant compared to the big blocks. As long as your carb and timing are right, a 350 with 320 hp is probably peaking at 5,000 to 5,200 rpm(hp wise). Even though a 454 with 330hp would push that boat just fine at 4,600rpm's, the 350 is going to want to get to 5,000 to realize it's potential.

My guess is a 23p mirage will get you right there in that boat - 5,000rpm at 65mph on the average speedo, and 60+- on GPS.

I've had great luck picking up nice props on E-bay for $200 or so and selling them for same or more when I didn't like 'em.

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Thanks hangtime, so I am right in assuming that 4500 rpm ain't cutting it for my 350. If I see 60, that's almost perfect for the twenty. The boat previously had a mirage 23 and the previous owner opted for a 25 clever with the alpha ss drive. Until I get the engine running good I'm not ready to screw with props. Supposedly with the 25 cleaver it got intot the 60's , I still think it is tough to belive but that is what I have to go on. I'll certainly keep all of my OSO friends posted as to my progress. though right now it very difficult to have much optimism if any. I am sure all here can understand and sympathize. Thx

Jim

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Don't think I've ever seen the Alpha SS drive - if I did it was too long ago. Got any pictures handy?? It's gotta be alot more effcient than the trs/trans setups the bigblocks used.... A 454 with 425hp with a trs would turn a 25" mirage to 5,000rpm or so, and a 27" to 4,700.

The X-dimension on two different years was also different from the factory on these two boats. The '79 was 1+" deeper than the '82....

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

here is the alpha ss

Re: What causes fuel pressure to rise to the point of needing a regulator?
 

Looks like they just "nose coned" it. I presume it's all one casting. Is the water pickup any different than a standard alpha? Boat must run a good bit different than the 454/TRS setups!! They have so much weight on that narrow transom, that when you slow down to come off a plane, you have to be careful not to let the wave crash over the transom!! --the wave will come right on in over the rear seat if you just kill the throttle - pain in the ass. Your boat must be 300lbs+ lighter back there.

I've always heard the alpha's do OK as long as you don't "stroke" or "boost" that small block - "more hp is OK, just don't add lotsa torque".......Enjoy