Reed Jensen

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.

JGB

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

RickR

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.

mopower

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

mcollinstn

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.

Reed Jensen

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.......

JGB

Thanks Reed, Rick, Mo, and Mcollinstn

Much appreciated ,

Jim

JGB

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

Hang Time 27

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.

JGB

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