Technical Autolite 4100 4 barrel assistance please and thank you!

Hi Tommy and thanks for your response. I believe the pump is working alright and was going to double-check it today but our weather turned bad and the car is outside. Will do hopefully tomorrow and pull it apart to check the spring. Regards, Dave.

 

Hey 57Custom300. Thanks for your input! Mine has the rubber check valves which I will check. The choke tube and spring are in good shape and mine also has the bracket that runs the heater hose against the outside of the plastic choke cap so there should be a good source of heat to unwind the bimetallic spring. No, there is no PVC system. Thanks for the "three grand purge" tip - I will definitely give it a try! Regards, Dave.

 

Thanks for your observations ebbspeed - more fuel for my diagnostic fire and yes, the "three grand purge" does sound like an excellent idea! Regards, Dave.

 

Damn! There's a good idea I never thought of! Thanks man! Will do! Regards, Dave.

 

Thanks for your additional input Bob! The old fuel pump had a large filter on the bottom which the new one doesn't have but I did put a filter just off the tank when I redid it.

 

The filter between the tank and the pump might be causing a bit of restriction on the vacuum side of the pump. A strainer in the tank should be sufficient if it's not plugged up or damaged. Try to find a place for your filter between the pump and carburetor.

It's easier for the pump to push fuel thru the filter than it is to try to draw fuel thru the filter from the tank.

 

The accelerator pump should pump enough fuel to start the engine if you push the pedal to the floor once or twice before cranking. If it will idle with the choke long enough to get the engine up to operating temperature of 180 or higher, you should be able to open the choke and the engine should run. Try holding the throttle open more to get off the idle circuit before opening the choke. If it won't run without the choke closed, it is running lean. If the carb is the one that came on the engine I ***ume it had the correct jets for the engine and you have them in the correct position and have blown out all of the p***ages. It comes back to a vacuum leak.

These engines are notorious for intake gasket leaks. When the engine pops back through the carburetor, it can blow an intake gasket. They can leak at the bottom from the lifter valley or at the top from under the valve cover. Since the intake to head connection is under the valve covers they are more difficult to find. Since the engine isn't run daily, the gaskets could have dried up. Another possible vacuum leak is from rust on valves and seats so they don't seal tightly.

Finding intake leaks on these usually requires removing the valve covers and spraying some flammable substance in the gasket areas.

 

ClayMart: The strainer in the tank is fairly recent as it was replaced along with the tank sender when I had an issue of the fuel gauge not registering. It would be easy to swap locations for the inline filter. Many thanks for your help! Regards, Dave.

 

Thank you for your response Engine man! As far as I know, the carb is the original factory-supplied one with the correct jetting (even after I rebuilt it as I think I am pretty **** in grouping removed parts and placing them in Ziploc bags as carbs are not always one of my strongest suits!). The intake gasket would have been replaced when the engine received a full shortblock rebuild back in '91 at a local shop. Thanks for sharing this intake knowledge which I was not aware of and I will follow up with it for sure. Regards, Dave.

 

UPDATE #3: OK, got a nice sunny day so back out with my list of things to try. First, fuel delivery at carb: Yup - good strong stream! Next, fuel squirt down primary throat......Aaah........no.........OK......Dammit! Just blew it all out! ****! Alright, to hell with it! Took carb off and completely apart and blew out every last orfice and p***age I could find. In the process, I found some I had missed in the last "*******" p!us the secondary throttle shaft was badly gummed up. Back together except for the top cover. Filled the float bowls and pumped the primary throttle. YES! Two good sprays! Carb back on engine. Two pumps on the throttle and it fired right up! Sounded decent. Turned idle up to 1500 and let it warm up. Choke plate opened as it should and engine didn't die - YES!! Got up to standard operating temp. and choke plate just a hair off vertical. Backed curb idle screw off and it died around 800 rpm. Couldn't restart it. Screw it! At least I made some progress! Miller time!
Am I correct in ***uming I still have a vacuum leak to find? Will try the other tips tomorrow (weather permitting!). Thanks in advance for any further observations! Regards, Dave.

 

power valve. if rupchurd (diaphram) it will leak all the fuel out of the bowl into the intake manifold. so when you try to start the engine the next day, it has no fuel inthe float bowl. after it sterts it runs very rich. if it has to have the choke closed to run, maybe a intake gasket . put a vacuum guage on it if you have not yet. all else fails try a carb off another running engine. process of elimination or something like that

 

Thanks birdman! I pulled the power valve today and it looked fine. The vacuum gauge is on my list of things to try (hopefully tomorrow) plus checking for an intake leak. Thanks again for your reply! Regards, Dave.

 

Sound like your making progress!Cheers!


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Thanks Tommy! Yes, progress, however so small, rocks!

 

Sounds like your making progress. Still sounds lean/vacuum leak to me. I would check for vacuum leaks like engine man suggested. Pull the valve covers and spray carb cleaner at the intake runners especially near the bottom of the intake. Just because it had new gaskets at an earlier time doesn't mean it hasn't ****ed in at some point. One other thing. Does the car have power brakes? If it does you might try clamping off the hose to the brake booster. Shouldn't really cause the problem your having but its just one more thing you can eliminate.

 

Thanks for your additional help 57Custom300! Yes, it has power brakes and I will try plugging off the hose as you suggested plus spraying the intake runners (and other suspect areas). Thanks again! Regards, Dave.

 

Is there a chance of weak compression or ignition failure causing it not to restart?

 

Shouldn't be, wfo guy. Gave it a compression test not too long ago and all cylinders were good. Checked the ignition system out a few days ago and other than a cleanup of the distributor and a new set of points didn't find anything wrong. Thanks for your reply! Regards, Dave.

 

The general rule of thumb on mixture screws is: turn them in until they bottom out, gently. Then back out 1.5 turns. This should allow the car to run and you can fine tune it once it warms up completely.

 

Thanks Bob! That's exactly what I did today. Think I got it a red one better after the initial 1 1\2 but nothing earth-shattering. Will now post an update:

 

UPDATE #4: Fired right up like yesterday with proper choke operation as well. This time got it to idle down to what to me sounded like curb idle spec of 500 (think my tach/dwell meter is having issues - was reading 1,000 but engine speed sounded like 500). Not a real smooth idle. Played with the distributor, but didn't improve things. Tried the idle mixture screws and may have got it just a red one better, but still not good. Shut it off and tried a restart and it took a bit of gas to get it going again. WTF! Gave it a few good "idle to wide open" cracks on the throttle. No hesitation and sounded great! Noticed when trying to restart it that it was pushing pretty good out the breather and dipstick tube (yeah, with the dipstick IN!) "That seems like a lot of base pressure......hmm.......maybe should pull a valve cover"......Did and wished I hadn't! PILES of crud!!! I don't know how the oil is draining back to the sump (or even if it is as I didn't pull the dipstick). Guess the other side is just as bad and I can just imagine what the valley and the pan look like!..........Lovely, just ****ing lovely!! Guess this is what happens when old non-PVC systemed cars are off the road for eleven years and only started and run once a week! So I guess off with the rockers and pushrods and clean it up best I can. Big ShopVac maybe??? Stay tuned for further developments and as before, all comments and observations gratefully accepted! Regards, Dave.

 

Clean up what you can with the covers off. Change oil and filter using 2 quarts of automatic transmission fluid. Run it at just over 1000 rpm for an hour. Change oil and filter again using a quality oil. Run it for a couple of hours and change oil and filter again.

 

Rule out a vacuum leak with this easy test. Air cleaner off, any open vacuum lines should be plugged off. Let it idle, place your hand over the top of the carb like you're trying to smother my step mother (too late, she's gone since 2011...). If the idle picks up and smooth out, you have a vacuum leak. If it tends to want to die, you have no vacuum leak.

 

How did you check the power valve? It is hard to tell if the diaphragm is ruptured unless you check it with a vacuum source. If it is ruptured it will create a vacuum leak as well as draining the fuel bowl and causing a hard start condition.
Also check the power valve cover for warpage. Do not over-tighten the screws on these carbs!!!!!!

 

This is a good diagnostic "tool" for helping to correct idle problems. It appears frequently on the forums here. But I often feel the urge to make a few additions to this testing technique.

As stated, make sure any open vacuum lines are plugged. But also make sure the engine is warmed up and that the choke is fully opened. Then gradually move your hand over the top of the airhorn (just the primary side if it's a 4 bbl) to restrict the incoming air flow which should temporarily richen the idle mixture. Just make sure that your hand isn't moving any choke linkage or moving the the choke valve from the fully open position.

If the idle drops it's because you've made the mixture too rich by restricting the air flow with your hand. But if the idle increases and the engine run smoother, that means the carb is running lean and the engine "likes" the additional fuel at idle. The thing to remember though, is that a vacuum leak isn't the only thing that can cause a lean idle condition. The idle mixture screws may need adjusting. The carb may have a plugged idle circuit. The fuel pump may be weak or a fuel filter may be plugged. On a 4 bbl carb the secondary throttle plates may not be closing completely at idle (which is technically a vacuum leak, I guess).

It can also indicate a vacuum leak, of course. But if you don't find an obvious vacuum leak, you need to remember that it's not the only thing that can cause a lean idle condition.

 

Thanks for this Engine man!! Two questions: 1: Using this procedure, do I need to pull the intake and oil pan and check them for crud? 2: So it would be two quarts ****** fluid and two or three quarts of oil for the change and do I need to mix the two together before pouring them in the engine? Thanks again! Regards, Dave.

 

Great stuff Bob! Thanks again! Will try it after I deal with the crud removal! Regards, Dave.

 

Hi Rick's Garage! Thanks for your reply! I just gave the power valve a good visual and a few light pokes with a small round-ended tool. I will try the vacuum test. And yes, I learned a long time ago to be nice to carb screws! Thanks again for your input! Regards, Dave.

 

Thanks for expanding on this procedure ClayMart. Will put it to the test once all the "crud" has been routed. Really appreciate your additional input! Regards, Dave.

 

If it's mucky it will clean up a lot of it without pulling the intake. Transmission fluid is high in detergent so it helps clean things up. It depends how badly it's gummed up. I have seen engines that the dipstick shows full but only a couple of quarts come out when they're drained. That indicates that the oil pan is full of ****. I've seen that in engines that had been run with Amzoil.

You don't need to mix the transmission fluid.