CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
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I am having a fuel pressure drop problem that is driving me crazy:
After driving the car for once a week for about a year without any problems, I started having problems with the carb puking fuel out if the primary vent tube occasionally, causing the engine to die. After waiting a few minutes, it would start and run for a few miles until it would happen again. I replaced the regulator (Holley) with an Aeromotive non bypass style reg. and that problem stopped. Then, after warming up, my pressure reading on the reg gauge would gradually fall to zero after warming up. I dropped the tank, pulled out the stock pump and fabricated a steel line sump/filter, but with the same pressure drop problem, I then replaced the holley blue pump I have near the tank with a Mallory Pro Comp 110 pump-same problem. Suspecting vapor lock near the factory TPI filter, I deleted the filter and made a heat shield out of aluminum plate to cover where the filter used to be since I have dual exhaust that stops before the rear end with 2 flowmaster 40 mufflers (about 2 inches from the old filter location). I have tried letting the car idle without the gas cap on since it is the stock non-vented cap, but the same problem is occuring. After letting the car idle for a few minutes tonight, the pressure dropped to 3 psi. I have a cheapie Mr. Gasket clear filter right before the regulator and can gradually see it dry out as the car warms up.
The car was previously a TPI car before I converted to a carb last year.
Anyone have any suggestions or am I missing something obvious?
Thanks for any help!
__________________ '86 IROC
carb'd 350 (0.040 over)
Holley 750 HP, comp solid roller XR286R cam
Cola crank, Oliver rods, Mahle flat tops
Pro Comp 210cc heads
700R4 3500 stall
ford 9" 4.10 gears
sounds like some of the fuel lines are too close to the exhaust. When it dies out touch all the fuel lines and I would imagine the ones closer to the front are heating up too much. IMO you need to run a return style regulator and this will be less of an issue. I like the mallory 4309 for a budget minded person.
__________________ 2011 chicago world of wheels placed in super street class
Best Engine '11 Thirdgenfest
Best Modified Camaro Thirdgenfest '05, '07, '11 Second place Camaro Modified '06, '08, & '10
MFBA March 2008 Featured Calendar Vehicle
I have a mallory bypass regulator and it does the same thing. After I set the fuel pressure, when it warms up it goes down to zero. The regulator is new and I am using a walbro 255 intake pump. Any ideas?
I have a mallory bypass regulator and it does the same thing. After I set the fuel pressure, when it warms up it goes down to zero. The regulator is new and I am using a walbro 255 intake pump. Any ideas?
are you checking it with a crappy 1.5" guage or with a real quality guage? the little cheapies will fluctuate pressure readings based on heat.
I have an 89 camaro, it was a tbi but I switched it over to a performer series carb. At first I had the same problem with it dieing out, then after about a minute it would run for a short while. All I did was add a fuel pressure reg. that was my problem, so I got a mechanical fuel pump w/out a regulator and it runs fine. Good luck and hope this helps!
The factory feed line is the larger 3/8" line. The return is the smaller 5/16" line.
That Summit regulator in the picture looks a LOT like the Mallory return-style unit. I have used several and they hold onto the fuel pressure setting like a pit bull. Never a single issue with fluctuating pressure.
Don't assume your gague is reading correctly, especially if it's a liquid filled gague. Many have reported they don't show correct pressure when they get hot. Personally, I use a REMOTE gague to get it away from underhood heat.
Last, your see-though filter will never show much more than about 1/2 full. They always have a lot of empty space when you're idling and fuel flow through it into the carb is near zero. It looks like there's nothing flowing becuase your carb is barely drizzling any fuel into the engine at idle. The air pocket in the filter NEVER goes away unless it's mounted absolutely vertical (nor doesn that air pocket cause any restriction to fuel flow). That's just the nature of the beast.
I don't have a see through filter. I am using the factory filter near the tank. The regulator is the mallory unit. The fuel pressure gauge is from summit.
I have almost the exact same setup as LilJayV10 now with a Mallory 4309 regulator using the TPI fuel lines (3/8" delivery, 5/16" return) and am still having the pressure drop problem. I put heat wrap around the lines from the header collector up to the steering column with no luck there either. The clear filter is before the regulator and will jam tight with fuel (bubbles work out within seconds) when cold and then gradually have bubbles accumulate after a few minutes of run time. I understand the gauge I have may be unreliable and will try using another gauge I have, but the performance above 4,000 rpm is nonexistent when hot. I ran it at the track this week and it crapped out after the launch and I had to short shift through the gears to make it through.
The lines aren't getting that hot (now, anyway). Today I drilled a small hole in the gas cap, cleaned the plastic vent near the tank and hooked up another gauge after the engine was hot. It showed a steady 6psi even after the engine cooled down where the cheapie gauge on the reg fluctuated from 6.5 to 4psi after hot.
So either the gauge has been wrong all along and I need to do a lot of carb rejetting after changing from the GM 58cc alum. heads to the Pro Comp 220cc or one of the many things I did fixed the original problem. The filter was definitely running out of fuel in the beginning, but I didn't think of hooking up the alternate gauge until today, so I don't have a true baseline to compare with.
Thanks for all the input, I should have this car in the low 12's or high 11's when I get all this ironed out.
__________________ '86 IROC
carb'd 350 (0.040 over)
Holley 750 HP, comp solid roller XR286R cam
Cola crank, Oliver rods, Mahle flat tops
Pro Comp 210cc heads
700R4 3500 stall
ford 9" 4.10 gears
I am having a very similar problem as noted above running 383, stock tank that has been converted from electric pump, 110 gph mechanical pump, no fuel regulator, and running through the stock 3/8" fuel line with no return line. The car falls on its face by 5000 rpm and I can't get the plugs to darken up no matter how big of jets I jet up to. I am leaning twords a fuel starvation problem. What could I do to with my current setup to correct this?
I am having a fuel pressure drop problem that is driving me crazy:
After driving the car for once a week for about a year without any problems, I started having problems with the carb puking fuel out if the primary vent tube occasionally, causing the engine to die. After waiting a few minutes, it would start and run for a few miles until it would happen again. I replaced the regulator (Holley) with an Aeromotive non bypass style reg. and that problem stopped. Then, after warming up, my pressure reading on the reg gauge would gradually fall to zero after warming up. I dropped the tank, pulled out the stock pump and fabricated a steel line sump/filter, but with the same pressure drop problem, I then replaced the holley blue pump I have near the tank with a Mallory Pro Comp 110 pump-same problem. Suspecting vapor lock near the factory TPI filter, I deleted the filter and made a heat shield out of aluminum plate to cover where the filter used to be since I have dual exhaust that stops before the rear end with 2 flowmaster 40 mufflers (about 2 inches from the old filter location). I have tried letting the car idle without the gas cap on since it is the stock non-vented cap, but the same problem is occuring. After letting the car idle for a few minutes tonight, the pressure dropped to 3 psi. I have a cheapie Mr. Gasket clear filter right before the regulator and can gradually see it dry out as the car warms up.
The car was previously a TPI car before I converted to a carb last year.
Anyone have any suggestions or am I missing something obvious?
Thanks for any help!
Since the OP already removed the stock in tank pump and replaced with a plain line and external pump - would he have a need for a return-style regulator?
And LilJayV10 isn't using any return lines, so the return-style regulator isn't doing him any good either (look at his pic). In fact, it looks like LilJayV10 is using the return-style regulator wrong! The RETURN line is supposed to go in at the bottom of the regulator, not the feed line. Since he isn't using any return line (it's not connected in his pic), he should have his feed line going into the side of the regulator, and the exit line to the carb out the other side right? Not sure LilJayV10 is connected correctly - on those regulators the feed goes in the side, and the return goes out the bottom back to the tank, and the regulated fuel exits the other side to the carb.
So LilJayV10, I'm confused as to what you've got connected where and how it's working at all.
Since the OP already removed the stock in tank pump and replaced with a plain line and external pump - would he have a need for a return-style regulator?
A return style regulator is good a good choice for anyone with an external electric pump. By returning unnecassary fuel back to the tank, it is less stress on the pump, keeps the pump cooler and also creates a CONSTANT pressure to the carb. With deadhead styles, it is possible that the carb can cause a pressure drop by using the fuel in the bowls and the pump not being able to fill the bowls fast enough. Anyway, did you ever get this straightened out? I have a mallory 140gph pump with their 4309 return style regulator and a prepump filter... high flow. I ran into a problem of too much pressure. Ended up beign that the fuel return line is supposed to be the same size as or larger than the feed line. Also if you are using a mallory pump with their regulator, the pump needs to be modified, need to take off the jam nut, unscrew a bolt, take out a spring and replace it with a spacer. Also like everyone else is saying, a liquid filled gauge will cause false reading depending upon temperature.
Goodluck!
