Will do Larry! Thanks for the help. I'll report this weekend when I have time to tackle all these hoses.
You guys remove the filter in the carb for the qjets? I have an inline filter in my car from Rob mc. And his pump. It is the pre pump filter. Interesting thread here
I have a pre pump filter in the 1/2" line, and another in the -6AN line from pump to Q jet. No filter in carburetor. I have the CV products pump.
Thanks Larry I have 1/2 line too and inline filter on frame rail Also filter in carburetor which I always thought was a restriction
Well, turns out there was more of an issue than I thought. I pulled the carb and disassembled everything to find that three of the brass tubes (air bleeds?) that were are supposed to be on the top plate were busted up. 2 bent pretty bad and one fell off all together. Also, there wasn't a hanger for my needle, it was just resting fully in the seat and only a marginal amount of fuel would get to the bowl area. I tried to tap the brass tubes back into the underside of the top cover which worked, and I put a new hangar for the needle and adjusted the float level. The car fired up nice idled fine so I decided to hit the gas station 2 miles away to top off. It drove fine on light throttle but medium gas would cause a stumble. I did fill up and once I left the gas station, the car died within a half a mile. Pissed, I pulled the carb right there on the side of the road and took it apart. Bowl was completely empty. My in-line filter was full so I know the pump works. Everything looked right inside. I tried pulling the fuel cap on crank, no dice. I removed my clear in line filter and ran direct to the pump thinking it was a clogged filter-no start. I swear gents, I'm about done with this qjet. Please, can someone reply with troubleshooting techniques, proper replacement ideas (mechanical vs vacuum secondaries), and brands to consider(holler, edelbrock, demon, etc). Hell, fuel injection is even a consideration. Seems pricey but worth it. Bottom line, I'm 95% sure this qjet will be my son's BB gun target.
As weird as it sounds, it almost like the venturi effect has left this carburetor and it won't draw the fuel through it. I doubt I'm explaining it properly but that's what I feel.
Where did you get the Q-jet? Sounds like it needs an overhaul. Send it to Mark or Ken. You can also just go to an 850 Holley double pumper. Your gas mileage will take a hit, but it should run good at WOT
I had mark overhaul this thing already and set it up for my 455. He had originally tuned it for my 350 prior to the new engine. This this thing is toast for sure. Question, I'm running out of hood clearance and have a spread bore SP1 intake. How do I mount a double pumper to it? I'm tracking the holley is a square bore type
View attachment 356048 View attachment 356048 I have the SP1 as well, with the spread bore opening. I run the Q-jet on the street, and my 1000 DP at the track. I can switch carburetors in 15 minutes or less. Very easy. First you get this thin plate, https://shop.advanceautoparts.com/p...ingcampaigns&gclid=CJrzha2zzNMCFZCKswodjn8Cyw The SP1 is drilled for both bolt patterns. At the rear, all you need is to move the carburetor studs to the square bore holes. In the front, you need two more studs in the outer holes. The carburetor bolts right on. I use a throttle bracket like this, http://www.ebay.com/itm/Throttle-Ca...ash=item211e252434:g:phoAAOSw241Yc9AG&vxp=mtr It is fully adjustable, and accepts the stock GM throttle cable. The last connection is the fuel line. I use a -6AN fuel line. I have a male connection on both carburetors, so connections are easy. This is what the Q-jet connection looks like, http://www.russellperformance.com/mc/adapter-fittings/sb/640340.jpg Same fuel line for the Holley. Female 6AN hooks right to the male 6AN.
Excellent advice. No, you don't know that the pump works. If the pump QUIT working, but the check-valve(s) in the pump still held fuel, the in-line filter would be full, yet no fuel would be moving to the carb. You are very likely to be shooting at a perfectly-fine carburetor, (well, I have some concerns about the brass tubes!) when the problem is the fuel pump, engine eccentric, or perhaps the plumbing somewhere between pump and the tank--including the strainer and tank venting system. Venturi effect doesn't pull fuel from the tank. Venturi effect is pretty good at draining the float bowl when the pump can't keep up--which is what you seem to be having problems with. WHAT IS YOUR FUEL PRESSURE? WHAT IS THE FUEL PUMP VOLUME? WHAT IS THE FUEL PUMP VACUUM? No. The float is held in place by the steel "D" spring that the float pivots on. The plastic piece is a "stuffer block" that takes up space in the float bowl area, helping to reduce fuel slosh. Not having a wire clip holding the needle to the float won't cause the carb to starve for fuel. Fuel pressure will push the needle open as far as the float will allow. If the needle were varnished (glued) to the seat, the car probably wouldn't have run at all.
Bottom line, I haven't hooked a fuel pressure gauge up and can't due to the fact that the car won't start. The online fuel filter was emptI'd when I took the carb off. Once I reinstalled it, I watched fuel pump into it as I attempted to start the engine. Survey says....the fuel pump works...the sending unit is fairly new (10 months or so), the fuel pump is an ac Delco stage 1 style purchased from rockauto and installed late February. As far as the tank venting system, I cracked the fuel tank cap and attempted to start in order to rule that out. No change. At the end of the day, all I know is 3 of the 6 brass tunes tapped into the underside of the top cover are damaged or missing and the car won't draw fuel into the bowl. Any other ideas?
The engine doesn't NEED to run to do rudimentary pressure, volume, and vacuum tests. The starter motor should be fine. However, you could always FILL THE FLOAT BOWL with gasoline from a small bottle, and the engine should run on the idle/fast idle circuit along with the accelerator pump, until the float bowl is empty again. How fast did it fill? Did the pump provide appropriate pressure? Is it liquid fuel, or aerated? That's bad. I thought you fixed that. Note that NONE of those tubes are used at idle, although two of them probably supply extra fuel when the choke cracks open; (and again at heavy throttle. Those are the two "farthest forward".) Two more supply a blast of fuel when the secondary air valve first opens. The other two are air bleeds that emulsify the fuel spraying out of the secondary "main fuel tubes" which take the place of a round 'n' pretty venturi in other carbs. These tubes don't prevent the float bowl from filling, or interfere with the idle circuit. Fuel is pumped into the bowl. I'm trying to get you to VERIFY that the pump and plumbing is in acceptable condition. Once we know that, we can move on to carb metering at heavy throttle, and potentially ignition/compression/exhaust.
I'm taking your advice and going with the new holley 850 double pumper. They have a new model that even has electric choke as well. I'll let you know how it goes in a few weeks
Larry, had a guy at work tell me I was crazy today for sacrificing the driveability that a 750 gives over the minor cfm increase of the 850 on the top end. I told him he didn't know "the wizard" like I do. Prove me right. What makes the 850DP the better choice?
Probably a Chevy guy, right? Buick engines like bigger carburetors. They go faster on the track with bigger carburetors. Most race oriented guys would go for the 950 or 1000. I figured the 850 would be better for the street. The bigger Q-jet was 800. See what others think.
Yep, chebby guy. I figured you would see through the smoke. After all, you are the wizard. Thanks for the advice
I'm just jumping in here, i've had the situation where the pump was sucking in air (pre-pump) from a rubber hose connection near the tank. i found this when by accident i block the carb vent tube and the fuel level rose and flooded the carb. Because the seat was bouncing at idle. at high RPM it caused a lean condition due to air in the fuel. FIX- replaced hose clamp TEST- block carb vent tube
