The Rodding Roundtable
Motorhead Message Central => Rodder's Roundtable => Topic started by: docchevy on May 08, 2006, 08:37:23 PM
Well, everything seems to be working well until I really get on it. I have plenty of power on the primaries. She's running smooth as glass. But everytime the secondaries open the beast backfires through the exhaust AND intake! :oops: I did have problems with the carb filling with junk out of the new aluminum tank, through a filter! (?) That has all been cleaned out. :evil:
It's an Edelbrock 650, brand new. I'm running a Holley Blue with 6.5 pounds of pressure, thorough a regulator.
Any ideas?
Quote from: "docchevy . But everytime the secondaries open the beast backfires through the exhaust AND intake! :oops: [/quote
Dang Johnny :!: :shock:
I beginning to believe you have a rain cloud hovering over you :(
I may be waaay off base, but it sounds like you still may have timing issues. :? a back fire thru the carb usually indicates a cylinder firing while the intake valve is open.
where's that JackStands feller when ya need him. :roll:
Good luck buddy, keep us informed.
Vance
Dial your pressure down to 5 lbs. and see if that helps. Edelbrocks don't like as much pressure as Holleys do, and 6.5 is too much. It may be a combination of timing and too much fuel pressure. I agree with Vance that it sounds like a timing issue is involved as well.
Good point Lynn, I forgot about the fuel pressure.
I run a Holley on my coupe, with a mechanical fuel pump.
I believe in the K.I.S.S. principal..........Keep It Simple Stupid :shock:
Vance
You really need to check your timing with a light.
While we are talking about carbs and pressure regulators have been mentioned. When my car was under construction, I was told to go buy a pressure regulator for it, so I did. I am running an Edelbrock 600 carb on a small block Chevy 350. Everything was put together and when we fired the motor for the first time, it would run just long enough until all of the gas was out of the carb. So we thought it must be the manual fuel pump that came with the crate motor, so I bought a stock fuel pump and it was put on. Same problem. So the next step was to blow out the fuel lines since they had been on the car for a couple of weeks prior and a dirt dobber's nest might be in there. Well I took the ends aloose and something came out so it was all put back together. I drove the car around the block and it ran good. A few more times around the block after that, no problems. Finished bolting on the front fenders and hood, put lights on the car. Drove it a little farther, no problems, then a little farther, but still close to the house. No problems. So, now it's time for a real road test, I'm going to drive it to work. My normal trip to work one way is 20 minutes, on that day, it took me an hour because I would drive down the road a little ways and then have to go to the shoulder; a little farther and then do the same. Each time I did not turn it off, but it seamed to catch up so I would go again. Came home from work with it doing the same thing. (It's July 2003 and in a couple of weeks, I'm supposd to drive this street rod to Louisville, KY to the Nats for the first time.) I limped over to a friend's house one Saturday and we tried everything we could think of and still had the same problem. Finally, the pressure regulator was taken off. End of the problem!
My friend took the pressure regulator and it would spin all the way around, it was a dud. We did not put another one on it. Got over 18,000 miles on it since then.
Quote from: "Mikej"You really need to check your timing with a light.
I did use the light and had no power. We vaccum set it and it runs great until you kick in the secondaries. The reason I doubt the timing is the issue is that it fires through BOTH the exhaust and intake. I'm thinking maybe one side is clogged and the combination of lean on one side and rich on the other may be causing the backfires. Can you blow air back through the orifices on the outside?
If you check the timing now, that will give you a reference for the future. Also timing with the vaccum would depend on the vaccum canister. You still don't know what the total timing is.
couple things come to mind.
secondaries are really lean or possibly a coil output problem(not enough spark)
what kind of ignition system is on it?
Quote from: "40chevy"While we are talking about carbs and pressure regulators have been mentioned. When my car was under construction, I was told to go buy a pressure regulator for it, so I did. I am running an Edelbrock 600 carb on a small block Chevy 350. Everything was put together and when we fired the motor for the first time, it would run just long enough until all of the gas was out of the carb. So we thought it must be the manual fuel pump that came with the crate motor, so I bought a stock fuel pump and it was put on. Same problem. So the next step was to blow out the fuel lines since they had been on the car for a couple of weeks prior and a dirt dobber's nest might be in there. Well I took the ends aloose and something came out so it was all put back together. I drove the car around the block and it ran good. A few more times around the block after that, no problems. Finished bolting on the front fenders and hood, put lights on the car. Drove it a little farther, no problems, then a little farther, but still close to the house. No problems. So, now it's time for a real road test, I'm going to drive it to work. My normal trip to work one way is 20 minutes, on that day, it took me an hour because I would drive down the road a little ways and then have to go to the shoulder; a little farther and then do the same. Each time I did not turn it off, but it seamed to catch up so I would go again. Came home from work with it doing the same thing. (It's July 2003 and in a couple of weeks, I'm supposd to drive this street rod to Louisville, KY to the Nats for the first time.) I limped over to a friend's house one Saturday and we tried everything we could think of and still had the same problem. Finally, the pressure regulator was taken off. End of the problem!
My friend took the pressure regulator and it would spin all the way around, it was a dud. We did not put another one on it. Got over 18,000 miles on it since then.
Let guess it was a Mr Gasket fuel pressure regulator! A real piece of junk! johnny
More pieces to the puzzle.
As I said in a prvious topic, the timing tab or the cam must be off because setting the initial timing with the light at 12 degrees sucked. We disconnected the vac. adv. and advanced the dist. till we got a tad under 20 inches of vaccum. That turns out to be about 24 degrees by the bolt on timing tab, so it's obviously wrong. She runs smooth and gobs of power until the secondaries open .. then the problems. I am running an HEI, good plugs and they turn brown. I had to lean out the primary rods (Edelbrock) because the 650 came too rich to begin with. I guess I'll go out and pull the carb apart again to see if anything is plugged. Tape at 11!
Quote from: "speedracer"Quote from: "40chevy"While we are talking about carbs and pressure regulators have been mentioned. When my car was under construction, I was told to go buy a pressure regulator for it, so I did. I am running an Edelbrock 600 carb on a small block Chevy 350. Everything was put together and when we fired the motor for the first time, it would run just long enough until all of the gas was out of the carb. So we thought it must be the manual fuel pump that came with the crate motor, so I bought a stock fuel pump and it was put on. Same problem. So the next step was to blow out the fuel lines since they had been on the car for a couple of weeks prior and a dirt dobber's nest might be in there. Well I took the ends aloose and something came out so it was all put back together. I drove the car around the block and it ran good. A few more times around the block after that, no problems. Finished bolting on the front fenders and hood, put lights on the car. Drove it a little farther, no problems, then a little farther, but still close to the house. No problems. So, now it's time for a real road test, I'm going to drive it to work. My normal trip to work one way is 20 minutes, on that day, it took me an hour because I would drive down the road a little ways and then have to go to the shoulder; a little farther and then do the same. Each time I did not turn it off, but it seamed to catch up so I would go again. Came home from work with it doing the same thing. (It's July 2003 and in a couple of weeks, I'm supposd to drive this street rod to Louisville, KY to the Nats for the first time.) I limped over to a friend's house one Saturday and we tried everything we could think of and still had the same problem. Finally, the pressure regulator was taken off. End of the problem!
My friend took the pressure regulator and it would spin all the way around, it was a dud. We did not put another one on it. Got over 18,000 miles on it since then.
Let guess it was a Mr Gasket fuel pressure regulator! A real piece of junk! johnny
Yeah, I'll bet. I bought one at napa, and it regulated the pressure fine, but started dumping gas from behind the dial. I returned it, and he asked me if I wanted another. I refused, and took a refund.
Nope! I pulled the carb apart and there are no blockages in the secondary circuit. The coil is an Edelbrock HEI super coil with 1300 miles on it. There don't seem to be any vaccum leaks, but I'll give it the old carb cleaner routine and see what happens. Thanks, guys!
Quote from: "docchevy"Nope! I pulled the carb apart and there are no blockages in the secondary circuit. The coil is an Edelbrock HEI super coil with 1300 miles on it. There don't seem to be any vaccum leaks, but I'll give it the old carb cleaner routine and see what happens. Thanks, guys!
Timing.Ignition.The outer rings on balancers have been known to slip.Keyways have gotten so chewed up..or the crank..that they slop around and get stuck at one end or the other of the play.Timing tabs can be different.Crank/cam timing can be off.Yes there are factory retarded crank timing gears.Cam timing through the gears..marks off..chain stretch.Even blocks that have had the mains bored wrong or..off..can affect the crank/cam/chain relationship.
You may need a degree wheel.
I would establish tdc.Mark the balancer.Make sure the dist. has no slop in it.Springs ok.Weights not stuck.Weights,plate pins not worn out.Disconnect the vacum advance..and leave it alone until this is fixed.Plug any vaccum leaks.
Set the initial at about 10-12 deg.at idle.
Watch the advance.Get this all dialed in first.That way you don't need to go back and forth.
I went through the above before.By the time I figured out it was a bad cam..soft cam lobe..there were bad exhaust and intake lobes.
Weak valve springs can also allow them to be yanked off their seats by engine vacuum.
Borderline adjusted valves..too tight can bring weird symptoms.
Hook up a vaccum gauge to engine vaccum and watch what it does during wot/secondaty opening..both at idle and loaded..different rpms.
A carb full of gas will operate properly for a split second or so before fuel pressure/volume problems show up.
When you say you found aluminum after the filter..in the carb.I had a piece of casting flash break off in a carb once.Now and again would plug it up.
If the carb is the problem it could be the air valve opening to quickly in the secondaries( the new ones are supposed to be adjustable) or you need bigger jets in the secondary. Does it run ok at WOT from a standing start or does it act up from cruise to WOT?
Quote from: "Mikej"If the carb is the problem it could be the air valve opening to quickly in the secondaries( the new ones are supposed to be adjustable) or you need bigger jets in the secondary. Does it run ok at WOT from a standing start or does it act up from cruise to WOT?
Everytime the secondaries open up it backfires, even sitting at the curb! Does an Edelbrock have an air valve?
The 750 I had, had a valve that opens with air flow on the secondaries so it doesn't bog. It was weighted so it only open at a certain airflow. The newer carb are suppose to have a valve that is adjustable. But if you are backfiring thru the carb just by reving it up, my guess is its not the secondaries. You usually can't them to open with a blast of the throttle. Check wiring order?
Yes the Edelbrock has an air valve. Normally what is happening to you is caused by leaning out. I suppose there is a possibility the air valve was left out. My car will do that if you roll into the throttle with a cold engine, but never once it warms up.
Quote from: "enjenjo"Yes the Edelbrock has an air valve. Normally what is happening to you is caused by leaning out. I suppose there is a possibility the air valve was left out. My car will do that if you roll into the throttle with a cold engine, but never once it warms up.
Thanks for the advise guys. Wires are correct. I'm sorry, I was thinking power valve like a Q-jet. That huge butterfly on top is what you are talking about, right? How can it be adjusted? It does this hot or cold, sneaking into the secondaries or WOT, sitting or driving. I originally had larger jets, and rods, in the primaries but went one step leaner because the plugs read rich. (that was when the mixture was way too far retarded because of the timing tab being off) I could easily go back to the original jetting, although the plugs still show a bit rich on the mixture.
Jetting by the plugs is difficult at best any more because of the crap they put in the fuel now. best way to do it is with an Air/fuel meter.
Quote from: "enjenjo"Jetting by the plugs is difficult at best any more because of the crap they put in the fuel now. best way to do it is with an Air/fuel meter.
I never thought of that! Maybe I can wrangle some time at one of the work stations. Thanks.
Until I can get to the shop, I changed to the pink springs! It stopped the backfire and improved power 80%. I may even need stronger springs as it bogs on WOT.