This is the first carb I have touched in years. Even then, it was a Rochester MonoJet. I could use a little help! The carb in question is a 5071 according to the numbers on the air horn, along with teh numbers "7832" and "7002" on the body. It was tuned and operating fine on a 350 with a Performer RPM intake and GM HEI distributor. THe motor had a mild cam. It is now on my 350, stock intake, RV cam, points ignition. It starts and idles fine for about 25 seconds, then starts to load up. It floods and dies after about 45 seconds. I've started with the idle mixers set at 1 1/2 turns and worked my way down to 3/4 turns, which is as low as I can go and it still idle. The fuel pressure is regulated at 5 psi, and I've tried as low as 3 psi. All vaccuum ports have been capped. What else could I be looking at? Thanks Evan
Can you see gas dripping down the primaries when it's running? If so it may have some crap in the needle and seat.
With the truck not running, and the electric fuel pump on, it does not dribble. Do I'd imagine it's not dribbling when it's running.
Looks to be this series, guess I got the number from the wrong spot. It actually looks to be the same as a 4160, just spreadbore.
You might have to change the float levels. Also those carbs are kind of noted for popping the power valves.
list 6210? The float adjustment is inside, and they also sometimes leak at the outside of the float bowls, where the plugs are installed in the ends of the fuel passages. I'm not to keen on this series of Holley carb, although it's been a long time since I messed with one.
Probably a power valve problem, especially if you had a backfire at sometime with it or a possible float flooded with fuel or sticking needle/seat.
do you have the externally adjustable floats? If you do then it's pretty simple to set or check. Many have suggested power valve and I'd agree with that idea as well. If the power valve diaphram is cracked then she'll sip fuel through the vacuum circuit for the power valve. Does it burp fuel up through the vent? If so then you need to look at the whole float, needle, seat, fuel pressure thing before going any further. If it's not burping fuel out the vent but still loading up then your float system is probably working but it's drinking fuel from a passage that's not supposed to be open. Try gently turning both idle mixture screws all the way closed while it's running and loading up. if you can't kill the engine by closing the idle mixture screws then it's drinking fuel through a bad power valve or you may have a bad gasket situation on the float bowl face allowing fuel to leak into the accelerator pump passage. If you somehow have the wrong gasket or a broken gasket around that accelerator pump passage then it can drink fuel through the squirt ports. Power valve is more likely than that scenerio though. Good luck.
The holley spread-bore - not my favorite carb either. What you are describing is raw fuel going into the engine. The way raw fuel will enter the engine is from floats being a tad high or blown power valve. With the floats a tad (this is a scientific term and means a few thousandths) high the fuel will flow excessive in dribbles (another scientific meaning non-atomized) out the boosters and these dribbles can't be lit off by ignition and floods the engine. They will generally dribble briefly after the engine is shut off and you'll see excissive fuel leaking around the throttle shfats. When flaots are just a tad high the needle and seat will function as normal so by running the fuel pump without the engine running will mislead you - ok? The blown power valve is one of those 'usual suspects' kind of thing. It can happen with engine backfire - i have no doubt. I also happen to have the vacuum tester for the power valve and i can tell you that in 20+ years of checking blown power valves the next blown one i find will be the first one. Whatever your real problem with the carb will have to do with fuel drying up in the bowl and the residue/gum that is left is plugging a passage - perhaps the air/emulsion passage for the idle circuit so that the idle is overly rich? raw fuel? kinda thing when (almost all the fuel circuits have air emulsified into them to help atomize the fuel droplets and not form dribbles). I think all you need to do is get a good rebuild kit from a proper carb shop - those napa etal kits have poor quality componants - and some carb cleaner spray cans from Walmart (the best i have used) and spend an evening with your carb torn apart.
Thanks everybody. I've got my grandpa on his way out to take a look with me.He built the carb about a year ago for my brother's truck and tuned it then to the other engine. Maybe he can shine some light on it. I've since thrown my QuadraJet onto the truck, and it won't even start. One week into this carb fiasco, and I'm getting a little irritable!
I am thinking power valve as well. It may need a different number power valve with the different cam and intake setup. Take a vacuum reading when the engine is idleing, use your vac gauge to trim the carb until it makes the most vacuum it can. Now take that number and divide it by two. That is the number power valve you are going to need or pretty close to the right number. Also how is your choke working, is it comming open after the engine starts to warm up?
Question: My holley's highest vacuum reading at idle is 17. Does that really mean that I should be using a #8.5 power valve? Carb came new with a 6.5 power valve. Carb is a Holley 390 4160, List 8007 4 bbl. I also read about dividing the highest vacuum reading at idle by 2, but found it hard to believe. I am at sea level. Here's a post below about this on another site about a fellow who had a "flat spot" when accelerating.; Re: Holley power Valve info: -------------------------------------------------------------------------------- If the PV is too low of a number, then if you slowly tip-in the throttle, you get a loooonnnngggg flat spot, until you push it far enough to where the vacuum drops low enough for the PV to open, at which point it suddenly clears up and begins to act normal. Holley's instructions, to use a PV that's half of your idle vacuum, are WRONG. They will ALWAYS lead you to choose too low a PV number, which in turn will force you to use too large jets, too much pump, etc. Ignore them. Keep raising the PV number until that flat spot clears up. In your case, I'd add a 95 and a 105 PV to your selection; and delete the 55. It's only going to make it worse. Once you get the PV right, put the pump back like it was, because you won't need to "crutch" the otherwise inadequate fuel delivery problem with it anymore. Here's another viewpoint on Holley power valves: Member Join Date:Nov 2009 Posts:92 How do I tell what size power valve I need? To properly size a power valve, take a vacuum reading at idle and if it is above 12" for a standard transmission a 6.5" will be safe to use. For automatic transmissions take a vacuum reading in gear at idle and if the vacuum is below 12" divide that in half for proper size. Example 9" of vacuum in gear at idle will require a 4.5" power valve.
Here's the Holley video re: Power Valves. Be sure and watch the entire video. Excellent info. http://www.youtube.com/watch?v=6vKlAnKdcB4
I can't ever get it to run long enough to even get a vaccuum reading. Just put a new power valve in it and it backfired the first time I cranked it. A new power valve, "backfire protector," and rebuild kit are on order from Summit. My garage is locked up and I WILL NOT BE RETURNING UNTIL I HAVE CALMED DOWN AND HAVE GOOD PARTS!
Get a genuine Holey rebuild kit for your carb and carefully rebuild it after cleaning it really well. Make sure you rebuild the accelerator pump also. Make sure no internal parts are missing from the carb. Install a set of new spark plugs so you know it's got fire power.
19fordy No one as answered your question so let me try. The vacuum by two equation is not an exact science it is a starting place, it is affected by a number of variables. Here is an example, I have a 4160 that I altered the venturies, to increase to CFM rating. The engine in question actually makes 14 inches of vacuum @ idle. I tried a 7.0 power valve and ended up going back to the 6.5, the carb just works better with the 6.5 power valve. 6.5 is pretty standard for an off the shelf 4160. I would try an 8.5 but be prepared to drop to an 8 or rise to a 9. Here is a tid bit about power vales, all newer holleys have a power valve protectors. I started noticing them on off the shelf holleys in the later '90s. If you open your holley and it does not have a protector (you will notice a brass busing in the hole that goes from the base to the power valve, they are cheap and easy to install. The last time I purchased one they came in a package of two for 7 bucks, they may go as high as 11 bucks now. Anyway I was reading a service bulletin about a year ago about alcohol and holley carbs. To paraphrase, while all new holleys come with alcohol resistant pumps and needles they have not yet found a way to make the power valve alcohol resistant. Even if your holley engine does not backfire your power valve can go by the wayside it is a good idea to keep a spare on hand, it is also a good idea if you do not spring for reusable gaskets to rub your gaskets down with chapstick before assembly. That will make them reusable, or more reusable.
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