what are the symptoms of perculating

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trudysduster

trudysduster

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You guys mentioned the reason to use the thick gasket over the thin carb gasket when I asked which is better. Said it was to keep it from perculating. could you tell me what the symptoms of this is. I think I had that problem yesterday. Was coming back from the car show and the Duster ran like ****. I was going kinda slow to allow junior to keep up. I kept the throttle at a constant point, about 45MPH and I noticed it surging a little. I came up on a stop sign and I had to set the line lock and keep my foot on the gas a little to keep it running. later down the road, I pulled into a parking lot and it died on me. started it up and took off and put my foot in it and it seemed to clear up a little but have not had time to play with it yet. It seems to do this a little when hot, not cold. I also question whether it would be better to put a 650 Thunder series on this instead of the 750 I have on it now. I have a 440 .030 over with Kieth Black flat tops in it and a purple cam in it. 509/292cam. what do you guys think. I am leaning towards a thicker gasket. AM I PERCULATING. thanks,Bill
 
Usually percolating happens when you shut the car off, not when driving normally.
After the engine shuts off and the heat from the engine heats the fuel in the carb to the boiling point, then the fuel is aerated causes surging, a flooded feeling and hard starts.
Sounds like you have a different problem, like fuel level or supply.
Varying timing might be a possibility also.

If it was percolating while you are driving, it would be REALLY bad after you stopped.

I could be wrong, and it sure couldn't hurt to add more insulation for the carb but I don't think that is causing what you described.
 
Your running lean.
When you shut the car down, lift the hood and run your ear over to the car and listen. If it sounds like a old style on the fire coffee pot, your percolating.

Try adjusting your floats to raise the fuel level.
If this fails, your fuel pump may not be pumping enough.
 
ok, you mean when you shut off the car and it still wants to run,is that perculation. I know what you mean if that is it. Mine isn't doint that. This is the first time this has done this and it only did it that once. Do you think I would be better off going to a 650 Thunder series instead of the 750 I have now. I know you all mentioned that the Roadrunners and some of the big block cars came factory with 650. I am not sure I have the right carb. on here. I know that some times when I get in it hard I hear the valves rattle a little. I am running 93 octane in it. I think the timing is off a very little.
 
its sounds like you have "run-on" or dieseling. that is timing . timing situated first then go after the carb. I have ran 600's up to 750's on stock small blocks and they have all ran good
 
Think about it... once you shut off the key, there is no timing/spark.. run-on isn't caused by timing..

Ping can be caused by timing, among other things..
 
trudysduster said:
ok, you mean when you shut off the car and it still wants to run,is that perculation. I know what you mean if that is it. Mine isn't doint that. This is the first time this has done this and it only did it that once. Do you think I would be better off going to a 650 Thunder series instead of the 750 I have now. I know you all mentioned that the Roadrunners and some of the big block cars came factory with 650. I am not sure I have the right carb. on here. I know that some times when I get in it hard I hear the valves rattle a little. I am running 93 octane in it. I think the timing is off a very little.
Click to expand...

Sounds like timing to me, if you are hearing that rattle I would guess detonation not valves, you will want to address that pronto.

Percolation is as described above by TB and RF. It makes for hard hot starts.
 
Run on us not percolating. Percolation is the fuel In your carb bowls boiling off when it sits after running. This causes hard starts. It sounds like you are suffering from a lean condition that could be caused by fuel starvation. Could also be a timing issue. I always check the easiest fix and work my way from there. Check your plugs, they can tell you the health of your engine. Check fuel filter while at it.

Just read the part about rattle, check your timing. You may need to back it off a couple degrees.
 
Have you adjust your New carb for that big 509 cam....

how much initial timing ?

might new lighter step up spring with the low vacuum.
 
well, I am gonna put a thicker gasket on it. I am going to go over to a friends and have him check the timing. I have no light or gauges for that. I have always done it by ear. maybe I don't hear so good anymore. hehe. I am going to check the plugs and play with the float. gotta get ready for a road trip show this next weekend. It just seems funny to me that it only done this once. after I ran it out a little hard, it stopped acting up and ran fine back to the house. brought it back in the garage and it idled ok.
 
73AbodEE said:
ok , then explain run-on to us
Click to expand...

http://en.wikipedia.org/wiki/Dieseling

Dieseling or engine run-on is a condition that can occur in spark plug, gasoline powered internal combustion engines, whereby the engine keeps running for a short period after being turned off, due to fuel igniting without a spark.
Dieseling is so-named because it is similar in appearance to how diesel engines operate: by firing without a spark. The ignition source in a diesel is the compression of the fuel in the cylinder, rather than a spark as in gasoline engines. The dieseling phenomenon occurs not because the compression ratio is sufficient to cause auto-ignition of the fuel, but a hot spot inside the cylinder starts combustion. An automobile engine that is dieseling will typically sputter, then gradually stop.

Usually, the car is idling too fast or has vac leak, or both..

Often it'll actually do that last cough, and rotate backwards,, occasionally walking an old stiff timing chain back a tooth, causing a timing chain prob..

Correction: Crackedback has reminded me that extremely late timing can cause an engine to run hot enuff to cause run-on..

I was addressing the misconception that too much timing can cause run-on..
thnx Crackedback
 
trudysduster said:
Lance, this is a big block. would a 650 be better.
Click to expand...
I had a 4160 600 cfm holley on my 440 , it ran very well. I just put a brand new competition series 750 AFB on the same 440. it runs very good, but it was really rich out of the box, in other words , I could run the mixture screws all the way in with no change. through the advice of another member, I switched the primary and secondary jets , and now it runs much better and I have adjustment at the mixture screws. I think it would run very good with either the 650 or the 750, as long as its jetted decent.
 
I ran a Eddie 600 on my NYer's 440 for 2 yrs. stock low comp. ran fine. But I wasn't trying to spin it to 5grand either. I think a 750 is just right for a street stalker 440. Might leave a little on the table above 6grand.
 
trudysduster said:
ok, you mean when you shut off the car and it still wants to run,is that perculation.
Click to expand...
I never said that. I do not "Mean" that. Re-read what I wrote.


Do you think I would be better off going to a 650 Thunder series instead of the 750 I have now. I know you all mentioned that the Roadrunners and some of the big block cars came factory with 650. I am not sure I have the right carb. on here. I know that some times when I get in it hard I hear the valves rattle a little. I am running 93 octane in it. I think the timing is off a very little.
Click to expand...

Carb size is irrelevant at this point in time.

Your "Rattleing" valves are nothing of the sort. It is most likely 1 of 2 things and you ruled out one of them by stating your running 93 octane. That leaves timing, your running to much. This makes your rattling sound which is actually detonation. Take 2*'s of timing out of it as a min. to start.

If you don't, have fun destroying your engine.
 
inertia said:
Think about it... once you shut off the key, there is no timing/spark.. run-on isn't caused by timing..
Click to expand...

100% false statement. I've fixed a lot of run on issues that were rooted in poor initial timing settings.

The issue is that these cars are a series of systems. If one system has a compromised setting, say not enough initial advance, that requires the throttle blades on the carb to be open more to maintain same idle speed. That allows fuel which should not be available to be introduced into the intake tract. A issue causes B result.

If the car is running on, it likely doesn't have enough initial timing.

Guess what happens to exhaust temps when there is insufficient timing... they go UP... Let see, it idles and seems like it's boiling fuel in the carb.. hmmmm what may be the cause here?

There's the lazy way (Total method) and right way to set timing, been covered ad nauseum in this forum. Choose your path and live with the results.
 
The OP needs to start the car and look in the carb to see if fuel is dripping from the boosters. If it is, he has a pressure, float level issue.

Make sure it has at least 20* initial on it and tune the carb. Tony hit on another point regarding step up[ springs.

Timing first then do the rest.
 
I do not have run on. it does not run after the engine is shut off. I just said I know what that sounds like. the only thing this car did was kinda surge when it was at a constant speed, about 45MPH. it was not bad but enough that I could tell it had a little surge in it. I came up on a stop sign and it tried to die on me. Later down the road I pulled in a parking lot waiting on my son and it died. I pulled out of the lot and got in it hard because some kids was yelling " light em up" and I did. after that it ran fine on the way back home. I may have the idle set a little too low. I don't have all the tools some of you guys have to set the idle and check vacuum and timing and stuff like that. I have always done it by ear and never had any problem. The only thing I can say right now is that sometimes when I get in it, I can hear what sounds like the valves rattle a little. I guess I need to adjust the timing a little. I just thought that the surge I felt was perculating but I guess it isn't. I have never heard what you described as perculating be called that. I have always heard it called dieseling. My car has never done that. When I got this carb and put it on, it was running rich. I did change the jets in it and the springs also. It has done fine till this happened. I am going to keep a close eye on it and see if it acts up this weekend. Thanks for the info guys.
 
crackedback said:
100% false statement. I've fixed a lot of run on issues that were rooted in poor initial timing settings.

The issue is that these cars are a series of systems. If one system has a compromised setting, say not enough initial advance, that requires the throttle blades on the carb to be open more to maintain same idle speed. That allows fuel which should not be available to be introduced into the intake tract. A issue causes B result.

Thank-you Crackedback, apologies 73AbodEE, I had forgotten an extremely late engine could get hot enuff to run-on..

Totally agree, and I find it curious that his mixture screws don't work, indicating a coupla other problems, which likely means idle screw is beyond idle circuit.. ( would idle too fast when probs solved) = run on.. lol..
still no spark with key off..

I lived through lean-burn, lol,.. lotsa experience with run-on.. lol
Click to expand...
 
If you don't have a timing light, there's no telling what is going on. You don't need a vacuum gauge.

Get the initial set where the engine wants it or the starter can handle and then get it dialed in. No way that thing should have less than 20* initial IMO. Any less and you are not doing the engine any favors.

If the mixture screws don't alter the way the engine runs, that's another hint at insufficient initial timing and something is wrong.

Hey I like lean burn... at least the distributors for a cheap locked out piece!
 
don't recall saying mixture screws don't alter the way the engine runs. I have the initial where the engine and starter can handle it. it does not hesitate starting.
 
So where is it set?

As I wrote, if it's not at least 20*, you're pissing in the wind, IMO.
 
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