Lagonia

My 79 L82 is a matching numbers engine and manual transmission. It has an Edelbrock intake - inscribed on it is says Edelbrock performer - no other identifying marks. Most likely a 2101 but not at all sure. It has the original QJet carburetor which was "supposedly" rebuilt. All smog equipment has been removed, it has headers and true, dual exhaust setup - no catalytic converters or resonators - just a pair of mufflers. I believe the heads are original but do not know. The other thing that I do know is that the cam has been replaced with an Enginetech ES1014R with

• duration @ .050: 204/214
• lift: .420/.443
• lobe separation: 107

The lifters have been replaced at the same time.
The idle is loud and lumpy giving the impression that this car will fly into the stratosphere once the gas pedal is pressed. That could not be further from the truth. It is a dog with horrible gas mileage on the highway: 7 - 9mpg. I figured, ok, it's driveable, I am still the learning about the car and what I could do to it and eventually I'll learn enough to where I can get it where I want it - a decent cruising machine, that's it, nothing fancy, no racing, no nothing - a comfortable highway cruiser.

All this work was done by the previous owner.

Just the other day, a problem developed to where the car is not driveable any longer. It starts and idles just like it always has. Once I press on the gas, the rpms go up and if I hold the gas pedal at the same position, the rpms go down and the engine dies. If I flutter the gas pedal I can get it to stay alive and idle but that's it. Once I try to lock it at a certain rpm, it will get there but will gradually die within seconds. To me it smells like a carburetor problem. I did install a fuel pressure gauge but I put a cheap one that is not liquid dampened and it is totally useless - the needle just goes crazy.

I have a fuel regulator, a liquid dampened fuel pressure gauge and an Edelbrock 1906 carburetor on order to start troubleshooting this. Even before this problem developed, there was always a bog on acceleration which I loathed. I am thinking on going to a stock cam to regain a better idle and low end torque especially since I am planning on replacing the 4-speed tranny to the 5-speed TKO Tremec from SST in the spring. I do have to get the engine to behave first....

Any thoughts are welcome.

cagotzmann

What kind of vacuum do you get at idle ?. I would connect a vacuum gauge to see if the engine is healthy or shows signs of leaks in the intake system.

REELAV8R

That cam has a very narrow LSA for a 350, combined with low lift, relatively low compression (9.0CR advertised likely more in the neighborhood of 8.3ish CR) It probably has no bottom end and then the 882 heads are junk and the cam duration is low limiting any kind of top end pretty severely.
So I can see it being a dog with bad gas mileage.
Rear diff 3.55 maybe? 3.73 would make the gas mileage even worse but the bottom end response better.
Probably has some pretty poor vacuum as well.

I believe you may be on the right track as your symptoms sound like a failing fuel pump to me.

vince vette 2

Just a thought on one piece of this - the bog when you put it to the floor. That was always a problem with the later Q-jets. There are many issues driving this, all due to these being set up for mileage and emissions. I have an 80 L82 so know what they are like in that vintage. When they rebuilt the carb did they drill out the idle mixture screw plugs so the idle mixture can be adjusted? The carbs were set up to idle extremely lean. Basically the process was to turn the screws all the way in, then turn them out 2 turns. Then with the car running and warmed up and the idle set to around 700 RPM propane would be sent into the carb with the amount being increased until the RPM peaked and then started dropping. If the peak RPM was within a specified range, it was considered properly set for idle mixture. If it was too high the idle mixture screws were turned into lean it some more. If it was too low, they were turned out a little to enrich it. Then the plugs went in and idle mixture was sealed off so Joe Public couldn't mess with it. What this means is that the idle was purposefully set up lean since it took another combustible substance added to the fuel vapor to get the air/fuel ratio correct. Just how lean was it?

Having just had my Q-jet rebuilt and jetted specifically for the L82 compression and cam, I then went about setting it up including the idle mixture. What I found was that the screws needed to be turned out about 4.5 turns to get peak RPM. So essentially at idle an engine set up with the idle screws only two turns open per the GM book is running very lean. Even with the added boost from the accelerator pump it takes time for the fuel to get vaporized and become useful. Getting the mixture set up properly, along with the proper jetting for the CR and cam specs did wonders in getting rid of most of the bog on a hard acceleration on my '80.

A simple question concerning the carb rebuild would be did the person who did it ask what the CR and cam specs were. If not, then the carb was not rebuilt with any concern for what the engine actually needs. Consider that the L82 specs are 450/.460 lifts, 222/222 duration, 114 LSA (or there abouts) which is a long way from the cam you have. So if this was not considered, it would be another issue with overall performance.

Concerning the lack of drivability that has developed I could see vacuum as an issue, fuel pump, clogged filter, improperly set up carb float, etc. Good luck.

DaveL82

Bog or misfire when pushing the pedal can be a sign of the HEI module failing. I chased a few of these in my day as it first seems to be a fuel issue.

Look under rotor to see if there are signs of rust like material on top of advance weights. If so, the rotor is bad and voltage is leaking to distributor and module causing it to fail over time.

dave

Dynra Rockets

As REELAV8R said, the issue with the lack of low end and poor mileage is the 107. You could change the cam out to something the 350 displacement and ~8.9 CR wants or you can change heads to 58cc chamber units to get about 10.75:1 CR (@ .028" head gasket, ~11:1 with .015") which would work much better with that cam.

Fix your carb and/or ignition issue first though.

HeadsU.P.

Any idea how many miles are on the cam swap? Most street cams come with 4* of advance built into the cam. This advance valve timing gives the new owner of the cam a happy face because he or she now has more torque than ever before. As time goes by, the timing chain begins to stretch. When that happens the 4* becomes 3* advance. Then 2* and so on. If the cam timing becomes zero degrees or actually retarded, it will be a dog with no grunt.
Besides the fuel issues, I bet the timing chain is stretched or could have been installed incorrectly. Just about all crank sprockets have a choice of three cam timing settings. Who knows where yours was installed?

wilcar

If you read the specs for this cam it will show the intake centerline at 107 and the exhaust at 117(107/117) Add the two together and divide by 2 and it will tell you the LSA is 112.
​​​​​​
Very mild cam......not the cause of your problem.

Lagonia

Thanks for all your responses! As I work in the shop taking measurements, I will be answering some questions that you guys had:

- Engine was built August of 2017 - this is a fresh build - hardly any miles to it
- My guess is that owner #1 did not like what he got and sold it to owner #2
- Owner #2 did not like it (he told me it did not have enough power for his liking) and I bought it from him first week of October - I since then I put may be 300 miles.

- The QJet DOES HAVE idle mixture screws
- At idle (700RPM) the intake vacuum (taken at the base of the carburetor) is steady at 12 in Hg.
- Initial distributor timing with the vacuum connected to the distributor is 14BTDC. Same reading with vacuum disconnected and plugged. It turns out there is no ported vacuum at 700RPM
- Rear end is 3.7
- Fuel pressure fluctuates between 4 and 8 psi but I do have a cheap gauge connected - no dampening - waiting for the good one to come in.
- The alternator regulator may be off - voltage goes from 14.5 to 15.5 - dancing - causing flickering of the interior lights

I will check the distributor next and replace the alternator - got a freshly rebuilt one on hand.

mongoose87

I went through a similar issue with my 1972 vette over the summer.
I thought it was the carb, so I totally rebuilt it, which helped a little, but didn't solve the problem.
You should take a look at the distributor. Mine had the original, and the weights were all gummed up, causing it not to advance the way it should. 14BTDC is not a bad setting for a base mechanical advance, but if you are getting 14BTDC, with or without the vacuum connected, there is a problem with the vacuum advance.

One way to tell if it is the distributor is to get a timing light. If the timing doesn't increase with higher RPMs, or only increases slightly, you know your distributor is part of the problem.
With this new cam you're talking about, the engine doesn't produce as much vacuum. So if the timing only increases slightly by 2700 RPM and the distributor looks ok (without corrosion), you could get lighter weights to make it advance the way it should.

Changing the timing to a more aggressive advance setting REALLY helps with the power of the engine.

Lagonia

Distributor is brand new - no issues there. The black you see in the pic below is grease. Timing does advance with higher rpms. I do not have a tape on the harmonic balancer so I do not know what the total timing is. Plus, I cannot get it to stay at any RPM other than idle (700rpm)

vince vette 2

So the screws are accessible, the next question is did you adjust them after putting the carb on? If not, then you should with the car fully warmed up and at idle. Before starting the engine, turn both screws fully in - they don't need to be tight and shouldn't. Then turn them both out 4 turns. Then start the car and have it fully warm up. Then turn one out a half turn. If this ups the vacuum and RPM, then do the same to the other. If the RPM and Vacuum drop then trying turning them in (leaner). Keep them within a half turn or less of each other. Shoot for a setting with peak RPM/Vacuum. You may have to tweak the curb idle as you go as you want to keep the RPM in a typical idle range. I apologize if you know all this already. Note that the vacuum you listed is lower than I'd expect. Should be at least pushing 15 at idle. You might try a different carb base port. They're not all the same. On mine the port in the rear of the carb worked best.

On the issue of lights flickering, does your carb have an electric choke and is it wired up to work? If so, is the choke light flickering even when the idle is steady. If so then you could have an alternator issue. I had this on mine. Got the carb back, put it on, went to set it up and the choke was light was flickering. Spent some time on the choke circuit to see if there was some bad connection somewhere, but ultimate had to replace the 37 year old alternator to fix it. An easy starting point is to just watch the choke plate right after starting the car. It should slowly open over 30 to 60 seconds.

calwldlife

12 inches seems low to me for a mild build.
i never checked a stock l82 but i can't believe it would be less than 18

Dynra Rockets

If the LSA is actually 112 and not 107 as originally posted then you are absolutely right. Thanks Wilcar for the research!

REELAV8R

Wilcar is right it is only a 112 LSA. Didn't see the advertised duration but did see that it has a claimed 51* of overlap which would mean long slow ramps on the lobes prior to .050 lift. More overlap likes more timing.

I would try 16* or more of initial timing. Get the vac advance on manifold vacuum not ported and insure that it's actually working. You should have 30* some degrees of advance at idle with the vac advance pulling and 16* of initial.

If you have no timing advance at all then that's a big problem for normal driving.

Get yourself a digital timing light so you can see the advance without any timing tape. It's a great tool to have when trying to figure out timing issues and what is going to work best.

Then work on the bog if it still exists.

Lagonia

The video below clearly shows the problem described in this thread.

I got new carburetor, fuel pressure regulator, gauge but first I will play with the existing carburetor - set idle mixture, install fuel pressure regulator and see how far I get.

REELAV8R

Fuel pressure is running high for a q-jet. fluctuates between 5 and 9 psi. Try to get it down to 3 to 5 psi. Could be it's forcing fuel past the needle valve and flooding it. Have you checked the float level? Does it smell rich.

The engine seemed to start stumbling soon as it came off idle. Does the throttle shaft seem loose in the hole, like it could be pulling air in around it?

Also make sure accelerator pump squirt is present although with that slow of a accelerator application the pump should not play much of a part and would serve to make it richer.
Seems like once it gets into the transition circuit is when it dies. A carb expert like Lars may know exactly what causes this.

What is the timing running at? Like I mentioned before it should be in the 30's at idle with vac advance.

Lagonia

I got a fuel pressure regulator and an Aeromotive gauge. The pressure is around 5PSI




Correct, as soon as it got out of idle it stumbled. Throttle shaft seems to be fine.

Pump squirting is fine in both chambers.

I connected the distributor vacuum line to the intake (not parted) vacuum and the advance was 27BTDC. Idle was a little higher and vacuum lower. Maximum advance was about 42BTDC at a high RPM. The bog is still there albeit at a higher RPM range - between 1400 and 1600RPM. That is weird... Distributor issue??

I have another issue that I have had since I bought the car - a small coolant leak at the front of the intake manifold as shown at the pic below. Probably not related but once I am done with the current set of measurements, I will button-up the weatherstrip job I left half finished, replace alternator and take it for a drive - after that is removing the intake manifold and making sure I have the correct gasket for that mystery intake and then try the new Edelbrock carburetor.

REELAV8R

Have you checked the float level. This could be a lean stumble.

If the float is too low it will be lean off idle.

Doesn't sound like it stumbles if you throttle it suddenly activating the accelerator pump squirt in the video. Correct?

timing is still too low IMO. Should be 52* at cruise.

This doesn't make sense to me. higher idle should give you higher vacuum.

Get the timing set up with more advance which should give you a higher idle.

What is your initial with that reading of 27* of idle advance with vacuum?
It sounds like you could add 6* to 8* more initial.

Once the initial is adjusted up then adjust the idle down via idle screw and re-adjust the idle mixture for highest vacuum or idle, then adjust the idle down again repeat with mixture and idle screw if necessary until it stabilizes.
This should give you the best idle mixture and allow for the throttle plate to be closed or nearly so.

Lagonia

I took the intake manifold out, resealed it with new gaskets and bolts and installed a brand new Edelbrock AVS-2 (1906). I adjusted the idle and fast idle speeds and idle mixture. I am feeding the distributor manifold vacuum which happens to be 15 in Hg with initial advance of 36* @750rpm. The original problem described in this thread disappeared - starts great, idles great and no bog off idle whatsoever.

*HOWEVER* a new problem appeared:

When driving and accelerating, anything from 3500 RPM onwards, when I step on the gas, bogs the engine. If I baby it, it will go beyond that to 4500+ with no problems - on a hard acceleration, this issue comes up. If I have the car idling and simulate this hard acceleration I have absolutely no issue. Since this happens only under load my thoughts are that it is either the fuel pump (pressure is good when I am watching it in the engine bay) or the float adjustment on the brand new carburetor - could the HEI be the issue where it manifests itself under load?