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I have a question about what is happening when I hit the throttle at idle. I am trying to run through some test to figure out a low vacuum situation and one is to snap the throttle and release it quick. But, when I do this I can hear a strong suction sound from the carb, but instead of the engine reving up, it almost stalls. It returns back to normal and doesn't actually stall, but doesn't do what it should.
I also noticed something similar when checking the timing. It says to check it at 1100 RPM so I was just easing on the throttle slowly and the RPM started to climb but then went back down to the point of if I continued to hold it that slightest bit open past idle it would have stalled. Similar to above, as soon as it is let go it returns to normal.
I am still running points. It looks to be in good shape and the dwell checks out at 30 degrees.
I came across something that mentioned the rubber hoses that connect to the gas tank. Apparently they get old and can let unwanted air into the fuel mixture and lean it out. I was under there today and they did look to be in bad shape. Would these possibly be contributing to the problem? I am going to change them either way, just wondering if this could be causing the issue
The hoses could be a problem just not this problem. Did you set the timing with the vacuum advance plugged? Did you adjust the air/fuel screws on the carb?
Timing set with vacuum advance plugged, and fuel mixture screws adjusted for max vacuum, which isn't much. Stuck at 15.75". It is a new restored carb from Ken at Everyday performance. All vacuum hoses have been replaced too.
I realise it varies from one engine to the next, but approximately how many turns out should the screws be?
I would check for vacuum leaks, open ports, old tubing, base gasket, etc... I don't know how many turns I just adjust by highest vacuum or rpm. They do need to be turned out the same right and left.
That was my thoughts too. That is why I replaced all the tubing in case there was a cut or crack somewhere. I plugged anything I could find. There is that piece at the front of the manifold with a port on top to the carb, and the three down the side. Nothing was connected when we got the car but nothing was plugged either. They are all plugged now. The hose from the carb to the canister was also disconnected and plugged. It seemed to get another 1/4" of vacuum when I connected that so I changed the filter and reconnected it. That is what got me wondering if there was something leaking downstream of that near the tank. Would that even cause a vacuum leak?
I also did notice a few weeks back when doing an oil change that the bottom of the fuel pump appeared to be wet or dripping, but there was a coolant leak right above it so I assumed that was it. I will check again, but would a bad fuel pump gasket or fuel pump itself cause some issues like this?
That is what got me wondering if there was something leaking downstream of that near the tank. Would that even cause a vacuum leak?
No, there is no vacuum connected to the fuel lines. If there were a leak in one of the fuel lines, the suction created by the fuel pump would draw air into the line instead of drawing fuel from the tank.
I see, so it could cause a lean issue but no vacuum leak.
One other thing is from a cold start, I pump the gas a few times and it fires right up, runs in high idle for about 3-5 seconds then struggles and dies. Another pump and it fires right up again and runs fine. Not sure if this is related to the other issue above or maybe something else, but probably worth mentioning. After the initial start I can prevent the stall by reving the engine a couple times. It just seems like there is something fuel related going on. Maybe of there is something causing it to not get the right fuel mixture, or at least a consistent mixture it is making it hard to dial the fuel mixture in and causing the low vacuum issue....
Replace the fuel pump to start with. The cold start issue maybe either the choke tension or the choke pull off opening a little too much. The only issue my Everyday Performance Qjet has had is the choke run bending then binding the plate. Ken replaced the parts free of charge, years later I might add, it worked great for a month, did it again, WTF? I have never had this issue in nearly 30 years of running Qjets. Make sure the fuel delivery is up to par with a new pump and filter before contacting Ken.
Ok, sounds like a plan. I will get a pump on its way over here. Next weekend I will get that put on and those rubber hoses at the tank changed just to rule anything out there. Hopefully it either isn't getting enough fuel or air is getting in somewhere. If I can get that problem fixed and then re-adjust the fuel mixture maybe the engine will smooth out and get some more vacuum pressure....
One more thing I just noticed on rockauto - there are 2 line and 3 line models. Mine has a 2 line (which kinda sucks because the AC Delco only comes in a 3 line version). This would for sure be the correct one right? I just want to be sure that there wasn't a 3 line that was supposed to be on these and someone at some point changed that and capped a line somewhere for some reason....
Buy the Carter replacement pump with two connection pumps unless you are planning changing the sender and adding the vent line. The AC Delco name means squat these days. The A/C equipped cars got the 3 connection pumps, non A/C cars had two.
Last edited by olds 307 and 403; September 2nd, 2018 at 09:09 AM.
Ok, two lines it is. Sad to hear AC Delco has gone down the crapper. Seems to be a common problem with brands that were once good lately. I have had a bad experience with Fram oil filters and then found out they are now made in Mexico. Have also heard similar things about Interstate batteries.
Anyway, I will place the order. A new distributor cap and ignition coil ships from the same place so I have those coming too. Speaking of which, for the coil I have an option of a Standard Motor Products UC12 and UC12X. There doesn't seem to be a difference in the description. Is the X just a heavy duty version? I couldn't find anything about the difference online. I was just going to go with the UC12 since the car is basically stock.
So the new fuel pump will be here tomorrow. I just had a couple of questions ahead of that. I was reading that I have to make sure that lever goes in either above or below what it rides on depending on vehicle or it could result in damage. Is that something to worry about with these cars or will it either fit or not? I just want to be sure I don't cause a new problem trying to fix an old one.
I was also wondering if having a gasket leak where it connects to the engine could cause a vacuum leak? It would be nice if this fixed a couple of things at once...
No, a leak where it connects to the engine causes an oil leak. Never had an issue installing a fuel pump on an Olds V8. I put sealer on the gasket and get the nut started on the top stud.
By sealer do you mean like that black RVT? Would you put that on the engine side or fuel pump side? Probably doesn't matter too much, I assume it is to help hold the gasket in place rather than seal?
You said you're using a "restored" carburetor from Ken. Has the carburetor been tuned and restored or just restored? I have seen quite a few posts like this where there is a hesitation off idle. Tuning these old carburetors is crucial for them to operate correctly on today's gasoline. From what you have said I would assume the carburetor was not tuned. I had similar issues (i.e. hesitation off idle, rough idle...) until I had my q-jet tuned and rebuilt. The fuel circuits in the carburetor have to be drilled out, so the engine runs right on today's alcohol gasoline. Hope this helps!
Hi, it was my understanding that it was tuned and restored. He knew that my car was basically stock and had it tested and setup on a similar engine before sending it out. He said it performed well and that all I should have to do was adjust the fuel mixture screws to my engines liking. I have contacted him and explained what was going on. He gave me some tips but I think if there was a misunderstanding about what I received from him it would have been exposed there.
I have the new pump installed, new rubber line to the pump and am going to replace the rubber line from the sending unit tomorrow before I start it. Hopefully it will be a big difference.... Thanks to everyone for their help with this, that picture was very helpful for me to understand what that lever is contacting and how it all works.
I have emailed Ken just to be sure about the carb.
I started it this morning, and it didn't seem to do that thing where it stalled and had to have a couple more pumps of the gas before firing up and running on its own, so it seemed promising. But, after warming up and getting to low idle it wasn't much different, actually ran worse if anything. I thought maybe with more fuel pressure the fuel mixtures screws might just need adjusting. I wound them in and started that process over again but that didn't seem to help much. I didn't have much time so I figured I would just post my findings here and see if anyone had any other ideas. After it cools down and I have more time this evening I will go try again.
Playing around with it this morning I have a bit more info about that "dead spot" at low idle around the 750 RPM mark. Before the fuel pump change, I think the low idle in park was around 800ish, but after it was around 630. I tried raising that up to around 800 but when adjusting the low idle screw it really doesn't increase around there and actually bogs down. If I go far past that the engine roars to life and anything above about 950 RPM sounds ok. Similarly, if it is idling around that 700 or so, and I snap the throttle it almost stalls instead of revving up. I know that basically just sums up the above information, but I think it is a little more detailed in case that helps at all.
Thanks for then help guys. I am actually going to go get a compression tester. I don't think bad piston rings or valves not seating right would cause this, but in terms of low vacuum those are the only other things I know of that I haven't checked yet. Of course the low vacuum could just be because of the poorly running engine... As far s I knew, bad rings and depending how bad, the valves would be noticeable through the exhaust. I have driven behind the car and there is now smoke at cold start, accelerating off a light, of cruising. If anything piston or valve was worn enough to be causing these issues I would have thought there would be smoke at some point.
September 1st, 2018, 03:38 PM
