Carburetor question

tyr_shadowblade

tyr_shadowblade

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I have an odd question I'm unable to find the answer to online, hoping someone with more experience might have some idea what's going on.

So I've been running an Olds 307 with a Rochester Quadrajet off and on for the past decade or so.

Original owner detuned the carb "to save fuel" by removing the choke and locking the secondaries shut. It always ran well, but if it'd been sitting for a week I usually needed to prime the carb and pump the throttle a buncha times to get it started.

Had carb issues this year, so limped it to a shop and they rebuilt the carb, opened up the secondaries, and installed an electric choke. Drove it home and it ran perfectly.

First time I tried starting it after that, I pumped the throttle a few too many times and flooded the hell outta it... but a coupla days later it started fine. I learned I need to be careful with the throttle now that it sucks a lot more fuel. It will usually start with only one or two pumps, no priming required. I learned to go very light on the throttle now, whereas before running only 2 barrels I had a leadfoot.

Now, my question is, at high speed (70+) with the throttle wide open, it seems to be bogging down a bit like it's getting too much fuel. Can't really get it over 80, sounds almost like it is starting to flood when wide open. Partial throttle around town runs great. Step on the throttle hard and it bogs down a little, but at sustained high speed it sounds and feels like it's drowning in fuel. Sometimes flames shoot out the exhaust when wide open, but I've never heard it backfire.

Idles steady and smooth... but when I put it in gear and lift my foot off the brake it idles at 10 mph.

Haven't been able to check the plugs or timing yet.

Anyone got any idea why it seems to be flooding at top speed? I ain't never heard of nothing like that before, and apparently neither has Google.

Thanks.
 
Might need a better air intake setup, like a K&N aftermarket job. Gas needs air to burn. Gets enough air at lower speeds, floor it and it's gasping.
 
Never mind- I went back and re-read the original post where you had it set back to stock functionality. (I can't believe anyone would ever do that!)

It could be flooding. Did they rebuild it to stock spec?
was someone messing around with rods/venturis?
Did you check to make sure the secondaries will open for you?
Do the secondaries have the same stock spring for the valve?
I assume the tech knew what he was doing, but if it's not acting right I'd start questioning everything about the system that's not stock.

My guess is you're getting enough air, assuming you're running a stock outfit. a 5 liter shouldn't have issues with airflow.
How many RPMs are you running at 70+?

Edited to add:
Have you replaced the fuel pump ever, if so, is it high volume?
Do you have a 'return to tank' line installed after your fuel pump?
 
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Honestly, I do not have a tachometer and have no idea about the fuel pump... likely the original one from the 1980s.
 
Have not worked on my cars in decades, so my thinking may be off target.

You need multiple things working in tandem for combustion. Air, compression, exhaust, fuel, and spark. When it bogs down, do you get black smoke from the tail pipe (unburnt fuel)? The person behind you would smell the raw fuel in your exhaust. šŸ˜„ You may be hitting a peak volume of air coming in, but are adding additional fuel over 70 miles per hour. They have machines to measure the performance from the exhaust, so it may be time for another trip to the mechanic for a diagnostic report.
 
EngrSorenson said:
I assume the tech knew what he was doing, but if it's not acting right I'd start questioning everything about the system that's not stock.
Click to expand...
This is one of Rachel's laws- "don't put it past them to not know what they are doing".

The quadrajet is fairly simple but that doesn't mean it is perfect when compared with modern FI engines. The primaries are relatively small, the secondaries are very large. If the secondaries open at a low rpm then it will sound like it is bogging down, there isn't enough airflow through the secondaries to pull in fuel through the venturis. So it might be opening too early. This would be something to check especially if someone at some point in time had set them up so they wouldn't open.

Another thing is there are large metering rods that the secondaries pull up when they open. These rods are tapered and go down into the secondary jets. There could be a problem with the rods or the jets.

If you have backfiring in the exhaust then that implies that it is running too rich. There could be several ways this would happen- metering rods, jets, choke.
 
Sounds like the regular idle is either too high, or the fast idle is getting stuck somehow. At lower speed if you step on it and it bogs, could be an accelerator pump issue.

I wonder if the original owner increased the primary jets to somewhat compensate for shutting off the secondary, and now that both are active again, running too rich?
 
jlauffer said:
Sounds like the regular idle is either too high, or the fast idle is getting stuck somehow.
Click to expand...
Fast idle would be connected to the choke, since the choke was originally disabled there could be a problem with the fast idle linkage.
 
I went back and re-read your first post. I don't recall seeing a quadrajet with electric choke so I'm not sure about that. The heat-operated chokes could be adjusted to stay choked longer or to release the choke earlier. And the fast idle is connected to the choke so if the choke is still engaged the engine will idle faster. Once the choke is completely open then it should idle at its lowest speed and you can adjust the idle speed with a screwdriver. From your description it sounds like the choke is too tight and doesn't open up soon enough. If it never opens up completely that would be another reason that the engine is running too rich.
As for running wide open, that's a whole different situation. If you aren't familiar with working on the quadrajet yourself then you might need to find another enthusiast in your area to help you with it. There aren't many mechanics around that have experience with the quadrajet. If the engine is limited in power there could also be a problem with the ignition timing being too slow, and worst case there could be a timing chain/gear problem that is retarding the camshaft. Those engines had an alloy timing gear with plastic outer ring that would wear and could fragment slowing down the timing or slipping to the point where the engine wouldn't run at all. It is pretty easy to check the ignition timing with a timing light.
 
I'm hardly an expert on the Quadrajet, but I do know that a misadjusted choke can cause some problems. If the choke does not open (for whatever reason), it will lock-out the secondaries, and prevent them from opening (I think there are 2 or 3 different secondary lockout systems on the Quadrajet, depending on what year/model it is). That could be the reason you are not getting full power, and for flooding. I'm not saying that is the problem, but it is a thought. Oh, and Quadrajets did come with both mechanical, and electric chokes, over the years.

There are a bunch of videos on Youtube about how to adjust the choke on a Quadrajet. And checking to see if it is operating properly, and making those adjustments is not too difficult. And one other video that I find fascinating, is this 1960's film from the manufacturer. It's worth watching, to learn the proper starting procedure for the Quadrajet.


Good luck!!
 
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