Last post on Sep 14, 2007 at 4:23 PM
You are in the Speed Shop Tuning and Modification
What is this discussion about?
Chevrolet S-10, Performance Mods
#19 of 26 Re: BLACK OIL [drcarp]
Sep 11, 2007 (11:02 pm)
I had a couple of additional thoughts that might speed up the process of sorting out this puzzle. Does the engine have a stock fuel pump? If the truck now has a fuel pump that puts out more pressure than the stock pump, the carb needle and seat may not be able to handle the increased pressure. In such a case, it is necessary to install an adjustable fuel pressure regulator between the pump and the carb. There is no need to spend big bucks for this item. Holley makes several adjustable pressure regulators which sell for less than $30. I would recommend their PN #12-803 'max pressure regulator.' It can be set to limit fuel pressure to any level between 4 1/2 and 9 psi.
I also would like to know if any other modifications have been made to the engine. I'm particularly interested in any changes to the intake manifold, camshaft, cylinder heads, valve train, and pistons. You say it makes about 350HP; where did those numbers come from? Has the engine been dyno'd?
Also, since the engine has 20,000 miles on it; has it been turning the oil black for that whole time, or has this just begun recently. If it only started happening recently, can you correlate it with any changes or new parts that have been installed? Has this carb been on the engine the whole time? And has the carb ever been taken apart?
I'd appreciate any details you can provide.
#20 of 26 Re: BLACK OIL [drcarp]
Sep 12, 2007 (8:33 am)
When I woke up this morning, a light bulb lit up in my head: S10s made in 1986 and later all had fuel injection, and used an electric fuel pump which is mounted inside the gas tank. This pump produces over 30psi pressure. So, if it's still in place after your V-8 conversion, that high pressure fuel injection pump is just drowning your poor carb with excess fuel. The carb on your 350 engine is designed to work with 4 to 9psi fuel pressure. The fuel injection pump is putting out so much pressure that it wouldn't be practical to try reducing it with a pressure regulator. Instead, I would suggest simply removing the fuse for the S10's stock electric fuel pump, or disconnecting the power wire that goes to the pump at the gas tank. (Be sure you don't cut the wire for the fuel gauge, and that you insulate and secure the cut power wire, because it will still be electrically live.)
If there is a mechanical fuel pump on the 350 engine, then it should be able to draw the fuel it needs through the disabled electric pump. But if you installed an electric pump anywhere that's higher than the tank, it may have trouble pulling fuel up to the engine. Electric pumps are made to push fuel, but they are not good at pulling fuel from a lower point.
There are now lots of after-market electric pumps out there which produce very high pressure, and are made to be used with fuel injection systems. Those of us who have carburetors on our engines have to be careful not to use that kind of pump, because it will create severe flooding problems.
#21 of 26 Re: BLACK OIL [zaken1]
Sep 12, 2007 (5:25 pm)
IF HE IS USES THE EDELBROCK 600 WHICH I HAVE USED A NUMBER OF TIMES ON SMALL BLOCKS UP TO 400HP I HAVE HAD MY BEST LUCK AT ABOUT 4LBS. OF PRESSURE AND YOU CAN CHANGE JETS,SETUP SPRINGS,AND METERING RODS WITHOUT REMOVING THE CARB OR ANY LINKAGE.
#22 of 26 Re: BLACK OIL [okko1]
Sep 12, 2007 (7:53 pm)
Thanks for the tips!
#23 of 26 Re: BLACK OIL [zaken1]
Sep 13, 2007 (6:11 pm)
THERE IS A MECHANICAL PUMP ON THE TRUCK NOW. THIS WASN'T THE CASE A YEAR AGO. YOU ARE SO RIGHT ABOUT THE PUMP IN THE GAS TANK WHICH WAS REMOVED AFTER BLOWING A CARB.THE PUMP RUNS AROUND 4# PRESSURE. THANKS FOR ALL THE KNOWLEDGE COME ON DOWN TO LAKE OKEECHOBEE AND GO FISHING.
THANKS TO ALL
#24 of 26 Re: BLACK OIL [drcarp]
Sep 14, 2007 (10:36 am)
Sounds like we both have been on the same trail, but something still is going on to turn your oil black and suck all that fuel. If the mechanical fuel pump has a leak in the diaphragm, it can pump gasoline into the crankcase. This will make it look like the oil level is not going down, but the oil is gradually being replaced by gasoline. In that kind of situation, I've seen an engine blow the valve covers off when the gas in the oil exploded. If you unbolt the pump from the block, it may be possible to spot a leak; if you can see or smell any gas on the engine side of the mounting flange. Or, you can substitute a low pressure electric fuel pump for the mechanical one, and see if the problem goes away.
One other possibility is that someone left out the check ball, and/or the weight in the accelerator pump discharge nozzle. This would make the pump nozzle act as a siphon, and pour fuel into the engine when it was running. If you take off the air cleaner and look into the carb with the engine speed held steady at about 2500 RPM, there should be no fuel coming from the pump nozzle, unless you speed the engine up.
And, of course, it there is a sound insulating blanket on the underside of the hood, and it is too close to the air cleaner or it is loose; it can be pulled against the air cleaner by the force of the incoming air; which makes it act like a choke that is on all the time.
When I used to live in Kissimmee, I would have been happy to drive down there and go fishing, but since I moved back to California after the hurricanes began, it's now too long a drive.
#25 of 26 Re: BLACK OIL [drcarp]
Sep 14, 2007 (1:17 pm)
Along with the points I raised in the preceding post, there is one other test that's worth doing. With the engine off, take off the covers over the metering rod assemblies, and note the height of the top of the rods. Then start the engine, and see if the rods move to a lower position when the engine idles.
If the metering rod assemblies are always in the up position when the engine is running, then the carb will supply the richest possible mixture at all times; and this will grossly overfeed the engine with fuel.
If the rods did not move down, then they are either stuck, or the rod control pistons are not getting any vacuum. If you can press down on the top of the rods, and they move down easily against their spring, then they are not stuck. In that case, the vacuum passage to the piston well is blocked; either by gasket cement, or by an incorrect or improperly positioned carb mounting flange gasket.
#26 of 26 Re: BLACK OIL [zaken1]
by MrShift@Edmunds HOST
Sep 14, 2007 (4:23 pm)
Whatever he does he'd better do it quickly. Having gasoline washing your cylinder walls and bearings is NOT GOOD! This could end up being a relatively low mileage engine.