I am going through the 2 G tri power setup on my roadster just to clean up inside,change gaskets etc after 3 years of unleaded fuel. Got kits from Quadrajet which has parts for several different models. The base gaskets(carb to manifold) include a very thick one about 1/2 inch thick compared to the regular gasket which is only maybe 1/8 inch thick. The thick one has a different texture or coating on it also whereas the thinner one is just regular carb gasket cardboard. Under what cir***stances would you use this really thick one?
It acts like an insulator. I actually add phenolic ones under every carb. The only drawback to a phenolic is needing 2 regular gaskets.
I'm in the process of installing a 4 deuce setup on my SBC midengined Corvair. The only thing I have found is that it insulates and stops boiling out the bowls. The ones I got with my carbs are a little over 1/4 inch thick...….Still not sure I want to use them
Paul...........a mate down here has a triple set on his newly acquired roadster, where did you get the kits and have you found any hiccups or issues with doing this.......I wouldn't think that there should be but he hasn't played with multi carbs before tho' I think it shouldn't be any great problem..........thanks....Andy Douglas
Andy If they are Rochesters the first thing is to find the serial numbers on the carb. You will find these on the body of the carb just below the fuel inlet(RHS). I bought my sets from Quadrajet in USA and they have various kits for different models. The important thing is that only the middle carb has idle screws. I bought special bases for mine that have the front and rear blocked off for idle screws and I also bought the very professional linkage from Hot Rod Carbs: http://hotrodcarbs.com/store/ If he has carbs with idle screws front and rear as well there is a bit of work involved to modify them so that they are not primary ones. With Quadrajet you gets lots of parts in the kit that can be used on a range of carbs so there will be leftovers!!!
Paul, thanks for the reply.........his car has had the triples on it for a few years so I think it may have the proper setup as it has a progressive linkage and operates on the centre primary carby but it doesn't appear to have had much maintenence done so he's thinking about putting kits through them which shouldn't be very difficult.........I'll mention to him about the serial numbers and to also check re the bases, as to what sort are there....sounds like that Quadrajet place maybe the go for kits..............thanks, andyd
Not sure what advantage I will get using these thick gaskets. It is in an engine bay with no sides or hood. we are in a temperate zone with temperatures in summer around 30-35 Celsius. I have never had a problem with fuel boiling in the bowl. Engine runs very cool. If I did use them do I need a regular gasket top and bottom as well??
No. Just one or the other. I'm guessing you bought fits-all kits , that are used over many applications and years. The later models tended to use the thick base gaskets more often. I don't know the actual reasoning behind it. That being said, I can't see the harm in using the thick ones. We know it's not a resto, seeing that SBC's never came with 3x2 's , so that wouldn't be a concern.
Paul, I'd be inclined to use the insulators, however if you haven't had any issue with fuel vaporisation then maybe not, tho' I've always thought that any way to reduce the temperature of fuel in the carby is a good move but as you say it is an open car so keep them for use later if need be...........oh, and spoke to the mate with the triples and his runs on the centre carby which is the only one with the idle screws, the outer carbs have had the screw holes soldered shut, also his carbys are all the same serial numbers, starting with 704, which are apparently early/mid 70's 2G's.........gave him the details re Quadrajet, he p***ed on his thanks..........andyd
I use this gentleman's parts ,Charlie Price, Vintage speed.The carb will absorb heat, make fuel percolate ,and will be hard to start.Now , without hood sides , thats a different story. He also has a very informative youtube series where he build's primary and secondary carbs. Best of luck.
I have pulled the carbs apart and replaced just gaskets,new needle and seats and reset the float levels and drops as per specs given to me by Larry at Hot Rod Carbs. All looked good but front carb leaks fuel from the venturi when it is just sitting there not even running. Fills up over the ****erflys. If this is happening when it is driving then we have excess fuel being used but not needed. Will pull the top off AGAIN and recheck settings.
I had very good results using overhaul kits from the guys at www.pontiactripower.com - They have a lot of parts for and experience with the Rochester 2G carbs... The best results I got putting all carb components into the ultrasonic cleaner after dismantling... I was not able to get all the crud form the carbs p***ages manually before and the carbs never ran truly well prior to teh US cleaning...
If your fuel line enters the front carburetor first, this may be from too much pressure building up in the line from heat. This is very common with the factory Pontiac tripowers, with the fuel block on the front carburetor. Since the front carb relieves the pressure, the other carbs do not leak. Only occurs AFTER the engine has been running, not during the run. The solution is a return line from just before the fuel enters the carburetor back to the tank. Jon.
If you don't have the exhaust p***age at the base of the carb in the intake it probally won't matter.
I have a three port fuel block on the firewall and the front carb is the last in the block to get fuel. Ran it this morning for just a few minutes and didn't leak.PS I am not using that red fuel line anymore. Went to a safer black webbed line.
The new fuel lines may be better insulators. Will be interesting to see if it leaks after it gets hot. Jon.
Ran it in the garage this morning for several minutes and could see a small amount of fuel on front carb. Let it heat up for 10 mins and switched off. Fuel started dripping out onto ****erfly's again. If I open the front carb after stopping engine and let fuel out then it stops leaking. I can't remember why but I put a fuel pressure regulator just below the fuel block. However it is one with a minimum setting of 4.5 lbs. So I have wound that right out (anti-clockwise)to maybe get lowest pressure but that didn't really help. I think a stock pump is 3-5 lbs anyway and this is reading 4.5lbs although the gauge does have lower numbers on it. I think a tri-power set-up only needs 3-5 lbs. Also attached a new photo of fuel lines but they have been on there for a couple of years at least. The fuel comes in on the LHS with rear carb first to get fuel. Maybe just some more adjustment on the float settings. Larry had the front and rear at drop of 1.75 inches and level setting at 0.91 inch. Centre carb is 1.75inches drop and 0.75 inch float level. I hardly ever open it up anyway so next thought is go to a 4 barrel. It wouldn't have the same visual appearance for the period that the car is built to though.
Watched the videos from Charlie Price and very imformative. I reset the float levels front and rear and now will have to wait and see. He talks about that percolating in the carbs if not set right and leaking fuel down after **** off.
The following is copied from the "Troubleshooting" section of my website: A common complaint today is fuel dripping out of the throttle body by the throttle shaft AFTER the engine is switched off. While a number of issues may cause this problem, by far the most common issue is the volatility of modern fuel. Mechanical fuel pumps have a check valve which prevents fuel from moving back to the fuel tank. The problem is as follows: (1) After the engine is switched off, heat from the engine heats the fuel in the fuel line. (2) The expanding fuel (increased volatility) creates pressure in the fuel line from the pump to the carburetor. (3) The check valve prevents the fuel backing up through the fuel pump. (4) The pressure increases to a point the float/fuel valve combination in the carburetor cannot withstand the pressure. (5) An amount of fuel (usually from a teas**** to a couple of tables****s) flows into the fuel bowl of the carburetor. (6) This raises the fuel level in the bowl above the main discharge nozzle(s). (7) Fuel flows through the main discharge nozzle(s) and drips onto the throttle plate(s) which is/are closed, and exits out beside the throttle shaft(s) dripping onto the intake. Possible solutions: (1) IF POSSIBLE, AVOID ETHANOL LACED FUEL! Sometimes you can buy real gasoline at a marina (2) Buy the lowest octane name-brand fuel that does not ping or detonate in your engine (the higher grades often have more ethanol) (3) Install a “vapor return line” (take a look at return lines used on many factory air-conditioned cars) End of copy. On a tripower, generally only one carb will leak, as the carb leaking will relieve the excess line pressure. You can move the leak from carburetor to carburetor by slightly changing the float settings. Jon.
With an open engine percolation isn't such a big thing. Just lower the float a tad in the front carb until the problem goes away. I measure the to a point on the float and bend the tab to lower by fixed amounts, like .020 or so until it acts right. I've found those old Rochesters need individual attention and what you're experiencing is normal for them.
Thanks for that detailed information. That explains exactly what has been happening. Over here we don't have ethanol automatically added to the fuel. I use 98 octane(no E) and probably could go down to 95 octane. Will using that thicker gasket in the Quadrajet kit be a help and do I use it just by itself or need regular gaskets each side as well? I am using a stock SBC fuel pump that just has fuel in and fuel out and no other fitting for a return line?
I reset the float level at .75 inch(was recommended .91) and now after a few minutes of and with the engine still running it leaks fuel and then switch off and more fuel leaking down probably more than before(front carb only). Looks like that wasn't the correct setting. Float drop is 1.75 inch.
Try a regulator with a lower pressure setting. I had a similar problem with 2G on my A. Bringing the pressure down to about 2.5 psi made it go away. After a couple of failed Mr Gasket regulators I switched to a Holley 12-804, and that has been the last bit of problems I've had with that.
Are you running a triple 2g set up. Your avatar with the Model A pickup looks like only 2 carbs? What is the standard pressure on a small block chev fuel pump. I think maybe 4-6. I cannot see a make on either the pump or the regulator. Pictures attached. My info sheet from carb guy said around 4- 5 psi on tripower but you say it worked OK with 2.5. My current regulator is a 4.5 psi up so I don't think it will go below 4.5. So if the standard pump is 4-6 lbs the Holley 12-804 must be able to reduce the PSI from standard 4-6.
While the thicker mounting gasket MIGHT marginally help, the thin gasket is not the culprit here; the culprit is engine heat heating the fuel lines. As to the fuel pump, some checking might turn up a stock SBC fuel pump for air conditioned cars that does have provision for a return line. But even this may not help the line pressure after the engine is shut down. But note the fuel line from the pump to the fuel block goes right under the headers! You might try insulating the fuel line from the pump to the block, and also the individual lines to the carbs. Not saying you should leave it this way, but it might verify the problem. Once the problem is known, you can then think about a solution. And I know the following violates the rules of vintage hot rods, but consider the fuel volume of your arrangement versus the method used by the manufacturers of running a hard line from the pump to a block on the front carb (or the center carb on Chevrolet), and short lines from the block to the others carbs The more fuel line volume, the more pressure from heat. Jon.
Yes, it does sound more like a fuel pressure problem. I'd bet if you plugged the line to the front carb then the next carb will exhibit the same problem. Another mentioned the Holley 12-804 regulator, I agree that that is the one you need. Set it 3lbs or less and you should be good to go. I believe you said you had the 12-803?, if so you can get a regulator rebuild kit for the lower pressure and just replace the spring under the diaphram (Holley #12-807) by taking the top off the regulator.
There was an earlier thread about the same problem, with video. The cure was a byp*** line on the carb side of the fuel pump with a small orifice. The orifice was small enough that it did not affect operation; but let the post shut down heat caused fuel expansion to bleed off. https://www.jalopyjournal.com/forum/threads/dripping-stromberg-97s-after-motor-shutdown.1013921/
It's a dual 2G intake, not triple. 1 primary, 1 secondary. Standard pressure will vary by engine. On mine the pressure was up to 9 psi. I believe the pump was probably aftermarket. Since then I've replaced that pump with another aftermarket pump from NAPA. I don't know what the max pressure is of this pump, I haven't run it without a regulator. But 2.5 psi is plenty of pressure. All your doing is ***uring that the float bowl is full, and there is a reserve supply of fuel in the fuel block and in the lines to keep the float bowl full of fuel when the engine is under a load. Also, pumps don't make pressure, they produce flow. Keeping the float bowls full requires flow, not pressure. Yes, the Holley 12-804 is able to regulate the pressure from 1 - 4 psi. https://www.holley.com/products/fue...regulators/carbureted_regulators/parts/12-804
Hudson48 - a bit more information that may, or may not be useful: First, it would make good answers MUCH easier if we knew WHICH Rochester 2G carburetors you were using, and some specifications about the rebuilding kits. While there are different measurements for different carbs, a common float adjustment for the Chevrolet carbs is 0.75 inch MEASURED FROM THE GASKET OF THE BOWL TO THE LOWER EDGE OF THE LIP OF THE FLOAT. Rochester released a number of different fuel valves for the 2G series carbs, with fuel orifices from 0.086 inch to 0.118 inch. Chevrolet carbs from a late 1960's 350 or early 1970's 400 would use the 0.118 orifice. Pontiac specified the 0.086 valve for use on the end carbs for the 421 Pontiac, which was probably the thirstiest of the factory tripowers. The smaller valves in the end carbs were to minimize issues such as you are experiencing. Even with the smaller valves, tripowers STILL often experience issues such as yours with modern fuel unless the return line is used. Because the cheap FLAPS kits are designed as "one size fits all, works well on none"; the FLAPS kits in the USA generally contain the larger orifice (cheaper than having multiple kits on the shelf). You might check the orifice of the fuel valve in the leaky carburetor. Jon
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