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Run a fuel pump volume test. see what you get and le t us know Jay 6155
Last edited by intergrated j 78; 03/16/15 10:12 PM.
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How do I do that?
It's a new pump, filter and sending unit.
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Thanks, guys. Appreciate the advice and help.
I'll tear it down tomorrow and find out what's in it. Take some pics too.
couldn't do it today. Had to power wash the patio after work to keep the wife happy...
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To run a pump test you'd have to have a pressure gauge on yer line and while the engine is running the gauge would show if the pump is holding pressure. Least that's the way I've done it anyhow.
Last edited by TJ's Chevy; 03/16/15 11:43 PM.
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Ok. I'll pick up a combo gauge today. Found one at Harbor Freight for 15 that does both fuel pressure and vacuum.
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Well... 20 inches of vacuum at idle. Powere valve is a 6.5 (From memory). Obviously there's a problem there.
I'll pull it apart and check the guts after the kids go to bed.
Last edited by gbauer; 03/17/15 08:29 PM.
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6.5 power valve. Obviously way low.
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gbauer,
With your carb troubles, I checked again what is in my 390 Holley.
Its a List 6390, a 4150 so it has both metering blocks. But the primaries would be the same. Not sure about the air bleeds as I don't know your List #### or what your bleeds measure.
I ran shootouts with my 390 Holley, stock 250, powerglide 3.08, both Clifford and Offy intakes. To get a good 60ft I would just STOMP on the 390 right at the line. If I hit a bad patch it would spin the right rear a little, no hesitation at all. Secondary opened up nearly all the way, and this carb won several of the carb/intake shootouts. It is well set up for sure:
Pri #51 main jets
Pri .028" PVCR (hole sizes in the metering block, you gotta know those!)
Power valve 6.5 or 8.5 not sure, that doesn't make much diff.
Squirters are .028 yup that's plenty for the stock cam.
You know the squirters have NOTHING to do with your full throttle or cruise mixture - they only operate like a squirt gun (actually like a mechanical fuel injection assist) while you are mashing the pedal. With the pedal in a steady position, the squirters do nothing at all.
Sec #52 main jets
Sec .031 PVCR
That is about equal to a 4160 plate with a .056 hole, a #3 plate has that size hole. Drilling them isn't quite the same but would be close.
Sec spring was either yellow or purple one.
If you can set your carb like this its gotta be close, except again I don't know how the air bleeds compare.
Timing was about 12 initial, 32-34 total at 3000-3500, somewhere in there.
Total timing cruising including vac was maybe 40-45 degrees, much more than that it will surge & buck as you describe.
Hope that helps, if not I'd try a different carb, you need a spare anyway!
I ran lots of carbs on that little 250: Autolite 4100s (440 and 500cfm), Autolite 4300 (440cfm), Carter 625cfm, Edelbrock 600cfm, Rochester 4GC 470cfm, Holley 390 and 450cfm. IIRC I even tried a Holley 600 on it, too big but it would run and cruise down the road ok. I rejetted some of them for the shootout but they would all run and drive right out of the boxes, not the kind of trouble you are having.
How do I know what metering block I have? Here's Some pics:    I have no idea what size main jets I have so I'll just replace those too. I plan on going down to the #28 squirter. I have a good #28 and a good #35. both with tubes and brand new Holley parts. Power valve is NOT broken and it looks like I did the vac test wrong: I connected it to the lower vac connection on the carb by disconnecting the trans vac line. (auto trans) I don't know if that would have made a difference or not though. I can't start the car right now because a) the carb is in pieces, and b) it's loud and I don't want to wake up my kids. If the sizing can be done with the reading I have then the power size should be 10.5. From the research I just did online 1) the metering block doesn't match up with squat and 2) if I were to guess I'd say the jet should be a #52. Should I change the metering block out or what? But, the real question is: would any of that cause the problems I'm having?
Last edited by gbauer; 03/17/15 11:28 PM.
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The pics are of the front block. We are referring to the rear block. It will have a plate instead of jets.
On the block you have pictured is the main jets. They are screwed in and have # stamped on their edges.
A 6.5 PV is just fine. A 10.5 will be open almost all the time and cause poor fuel mileage.
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OK while you're in there:
* On the carb air horn there should be a number, like
LIST 6390
or
LIST 8007
And then a 3 or 4 digit date code, can you read those?
Then on top of the metering block there should be another number, like
6946
That might tell us what goes together.
To measure the PVCR holes you have to take that power valve OUT, then there are 2 small holes drilled in the metering block, they will be about .028" or so. Worth doing while you're in there so you know whats what and if anybody was in there playing with it.
The jets should be stamped with a number on the side.
I used to be able to read them from a mile away but now I use a magnifying glass. Of course, make sure nobody drilled em else who knows what size they are.
On the main body, there are 4 brass inserts inside the choke horn area near the boosters. These are air bleeds, it would help if you can measure those too. The inner pair are the main air bleeds. On my 6390 carb they are .000" ie not drilled. The outer pair are the idle air bleeds, they are .067" on my 6390 carb.
Also, while the metering block is off, clean it with gasoline, thinner, acetone, blow every hole with lots of air, anything you have. Cant hurt and is sometimes the problem.
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On the fuel pressure test - while youre teeing in the gage, what I do if any doubt is, run the fuel pressure gage all the way out, snake it thru the hood and hook it in the center of the windshield with the windshield wiper or something.
Make sure the fuel lines wont get cut by the hood or other, you don't want a gas leak under pressure, that's why you don't run the gage into the car ever.
I then take the car out and floor it on a long run, watch or film the gage with a camera. Lots of old iron will have fuel supply problems after say 10-12 sec at full throttle. Unless its REALLY bad, that is not likely your problem (yet) but good to check while you have the gage on it.
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If it's the plate I think it is...  The pic makes it look like everything is full of cracks but it isn't.
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More pics and jet sizes. Jets have a "512" stamped on them. Pics of various stampings:      Any guidance you guys can give is appreciated.
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Ok its a List 8007.
Made on the 284th day of year "0" (either 2000, 1990, maybe 1980, that's all you can tell)
The 512 jet is a 51 Jet, the '2' is for close tolerance.
Next you need to get behind the power valve and measure those 2 small holes, the PVCRs.
Metering block is 7240, not sure if that's right or not, sounds close.
Right in the center of the metering plate (secondary), there should be a 1 or 2 digit number stamped, like "34" or "59", can you find that?
Another thing to be sure of, I think I got my 390 Holley cheap cuz it ran like crap, wouldn't idle at all. Turns out the base gasket (base to main body) was the wrong one, the holes didn't line up right. Or even an old gasket can shrink, so check that carefully too.
I don't see anything else obvious right now!
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34 in the metering plate.
I don't have a good way to check the hole diameters behind th e power valve but I did use some welding wire. 25 fit, 35 didnt. Seemed to be right between the two. Maybe closer to the 35.
New gaskets, no holes covered.
Last edited by gbauer; 03/18/15 09:11 AM.
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Sucked it up and reached out to Holley via their website. We'll see what they come up with.
I almost wonder if it's the secondary float. I bought a new one since that one was plastic and I don't trust it like a good brass float. The other was brass.
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The black Nitrophil floats are the ones to use.
Inliner Member 1716 65 Chevelle Wagon and 41 Hudson Pickup Information and parts www.12bolt.com
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It was a beige one in there.
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gbauer
If I remember right You can use a torch tip wire cleaner. ( they are gauged sizes) Or metric drill, Numbered drill bits to check the size.
Larry/Twisted6 [oooooo]  Adding CFM adds boost  God doesn't like ugly.
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I'd do that if I had either one...
I'm almost positive it's a 28. Like I said my .025" weld wire had some wiggle and the .035" was way too big.
I'm very close to being done throwing money at this hoping to find the problem. If after Holley gets back to me verifying the plates and I replace the power valve Jets And it still doesn't work I'll take it to a local carb guy and shake the dust off my wallet.
I kinda need to do that anyway for a couple things: new muffler back (too loud and it rubs), an alignment and just a second look over before we take it on our 10 year anniversary trip next month.
She's close to right. So close.
Last edited by gbauer; 03/18/15 09:00 PM.
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The way we ran a fuel pump volume test was shut the car off, remove the fuel line, hook up a hose to the line, run the hose to a container and start and run the engine at idle for 10-15 seconds or until it run the carb dry and quits. Then see how much fuel you pumped. I have seen pumps put out pressure but little volume. Not likely with a new pump, unless there is trouble with the line to the tank. Jay6155
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Well I think I got it!
I put in my 10.5 power valve, slapped in a #37 squirter, changed the float to a brass one, fired it up and drove it pretty hard.
I re-tested the vacuum at idle, this time in gear (duh!) and got 18 lbs. Ideal power valve is 9.5 then. I think my 10.5 is probably close enough.
No more stumble. No more surge. She's running pretty good now. Lit up the one wheel good too.
I still seem to be down a bit at 90% throttle and above but that might be a power pump cam adjustment. Thoughts?
I didn't test the fuel pump yet. I know the pump is good so I'm thinking I should try blowing out the fuel line. Is there a check valve in the fuel line or any reason why I couldn't squirt some air through it without dropping the tank?
(come to think of it I believe I can disconnect the fuel line right before the tank and blow through it with an air hose)
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If you have 18" (inch) of vac, how do you come up with the idea that a 9.5 PV is ideal?
Great to hear it is running better. You are learning how to tune a carburetor.
I suggest hooking your vacuum gauge up and drive it around. If the PV is too high of a #, the PV will open when you do not want it to. Causing poor fuel economy. I bet with cruise RPM you will see around 15". With slight throttle input, the VAC with drop below 10.5 really quick.
Could the power at 90% throttle be a engine thing? Is this a stock engine? Meaning the cam/ head.
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Great news!
No ideal rule for power valves, that is a good starting point but it depends on how lean your main jets are and how much vac advance you run too. Adding more main jet or more vac advance, you can usually delay the power valve ie use a smaller number.
But, that's a detail - if it likes a 10.5, give it a 10.5.
At 90% throttle the pump squirter is pretty much out of the picture, so now I would start doing the paper clip test -
Clip on, rev to 3000, then back off, pop hood & see if the clip moved any. Snug the clip up again against the secondary housing. Try again, go up to 3500. Etc, then 4000, 4500, 5000 if you want.
This way you can see when the secondary STARTS to open, then when it is FULLY open (if ever), then worry about the air/fuel mix.
Easiest way to richen it unless you have a bunch of secondary plates around is richen the primary jets. Really have to clock it somehow since seat of pants can fool you - usually richer feels faster because of the initial kick, but at some point richer becomes slower.
Then you can put in a richer secondary plate, and put your lean primary jets back in for mileage and to avoid carbon buildup in traffic.
Sure, you could disconnect the gas line back at the tank and blow forward, that's what I'd do. Pump test under load would still be good to make sure the whole system will feed under a long pull at full throttle. Should be fine at your level but that is a good check.
Glad to hear the good news.
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I'm certainly no expert in carb's, but to clarify, you are not simply revv'ing the engine to various rpm's, you are driving and putting the engine under load to said rpm's correct? As I'm pretty sure revv'ing an unloaded engine to various rpm's in neutral will not open vacuum secondaries.
To follow up with that, you are really testing two systems, the "when it opens" and the "rate it opens". The "when" is vacuum dependent, and on anything other than Q-jet's I'm not sure how to change the "rate".
On my old 400 powered Firebird and my Centurion's Buick 455, both engines pull(ed) over 15inHg at idle and I tuned the Q-jet secondaries to not open until 5inHg. On engines that pull decent vacuum, my opinion 5inHg is a good starting point for balancing economy versus power. That way the secondaries weren't opening on every hill I encountered. At least for 6.6L+ engines =P
Last edited by TheSilverBuick; 03/20/15 11:57 AM.
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I think I might toss in my 6.5 valve and see what Happens. Also want to try my 28 squirter and a weaker spring.
One at a time and I'll find the best mix.
Seems like a lot of trial and error with carbs, huh?
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Just put an 850 cfm holley on there and forget yer troubles. HAHA!
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...in exchange for all new and exciting troubles?
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Seems like a lot of trial and error with carbs, huh?
With a wide band O2 reader, less guesswork, less tuning required. You will know exactly if it's too rich, too lean etc. MBHD
12 port SDS EFI 
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I think I found my problem right here...  All that work for this?
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It doesn't take much. I had to tear the carb in the boat apart because of a tiny paint chip in the wrong place. Primary or secondary float?
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I think I found my problem right here... All that work for this? At least you found it. Good find! MBHD
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..I'm more impressed with the camera on my phone than actually finding the problem...
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It doesn't take much. I had to tear the carb in the boat apart because of a tiny paint chip in the wrong place. Primary or secondary float? Primary.
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I'm getting ready to take the car on a little trip for my 10 year wedding anniversary with my wife. Part of the preparation was a new muffler. The old was (Flowmaster 10) was WAY too loud for anything over 30 minutes in the car.
I took it to a good shop to have it done. They put it up on the lift and opted to change it from the Y all the way back because the previous shop did such a poor job. Now there's no rubbing at all and it's much better tucked in than before. I'm now running a single 2.5" Flowmaster 44 series. It's the same sound just half as loud. No more drone.
Wish I went this way to start. I highly recommend the 44 to anyone looking.
No pretty pics this time. Maybe later.
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Fixed the brake problem I was having last night, installed an oil pressure gauge, and putzed around with the carb again.
I just can't seem to get the carb right so I'm taking it to a pro later today to tune it.
Now I'm having a heck of a time starting it. Just won't fire unless I squirt starting fluid in the carb. Once it fires she runs OK but not right at idle. Get the RPM's over 1,500 and she pulls really strong though. I think I have the secondary and power valve right. Just not the primary side. Might be timing. I just don't know anymore.
...sometimes you gotta just step away and let an old hand show you the ropes properly I guess.
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Finally found out why I could never get the tune right!
My powerglide always shifted a bit rough but I was told "they all do that" and just assumed they all did that. Turns out the hose between the hard line and trans was, well, missing.
Replaced the hose, reset timing, reset idle air, changed to a #28 squirter and off I went! Problem solved!
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Good! You are learning how these old cars work. FYI the first gear band needs adjusting once in a while on Glides.
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Good! You are learning how these old cars work. FYI the first gear band needs adjusting once in a while on Glides. what do you mean? Is this something that requires dropping the trans? How would I tell if it needs adjusting? It's shifting extremely smoothly now and not slipping. The machine shop guys all said the engine seems to be like new in that it has excellent vacuum (18+ lbs) and is very quiet. I didn't really believe the car only had 28k miles but I'm starting to think it just might now. No real wear on the pedals; tons of original parts that normally wear out; etc, etc. I do know the car was only driven 1500 miles from 1998 to 2013 after a restoration. It sat for a couple decades before that collecting rust, and started life in Bethesda, MD where people don't drive much.
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I just looked up the adjustment band.
...and I'm adding something else to the to-do list now...
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