I have a sbc 350 with edelbrock intake and carb i believe the carb is 550 or 600 cfm the problem is that it idles realy high and i know i can adjust that but when give it full throttle it backfires pretty hard and doesnt seem to have that much power. It has a one inch spacer in it and i know that it can effect vaccum but i dont know much more. Just looking for a little guidance.
It's possible it has a vacuum leak in between the spacer. check the gaskets. First check the bolts on carb to see if they are tight. make sure they are snug and not over tightened. do you have a vacuum line goin to the distributor? make sure it'sa snug fit. check any other vacuum lines. Take a can of WD 40 and spray it at the spacer gaskets all around the base of carb while its running. If the idle changes you probably have a gasket leak.. mike
Plug wires are good and the timing shouldnt be advanced to face i took it to our mechanic that does most of our work but he did it for free cause were good freinds but he said he didnt have time to work on the carb them. I put my brand spanking new 650 on and i still couldnt seem to get the idle down so maybe it is spark.
What cam is in the motor? stock or ? Is this a stock carb or has it been modified at all? backfiring out of the carb could be a timing issue or even a burnt intake valve, or it could be that the distributor advance is not working. I would recommend checking the timing first, initial timing around 10 degrees btc is good, check to make sure you have your vacuum line connected to port vacuum for the advance line to the dist. check by hooking up a vacuum gauge. when you give it throttle you should see vacuum at the gauge, then make sure you have no vacuum leaks. i probably missed somethings, but there are some things to check. Post back with what you find
Sounds like a vacuum leak. May not be at the carburetor. Backfiring is caused by a lean fuel mixture. May be the vacuum advance at the distributor or the vacuum modulator at the transmission. If the manifold was just installed it could be leak around that somewhere. Check you lines for leakage. Don't us WD40 to search for a leak, use a Propane torch. Acts the same when you locate the leak without the mess. NO, you don't light the Propane, just turn the gas on.
Those carbs are super sensitive about fuel pressure. I'd make sure thats correct first and then start hunting for vacuum issues. Are you running power brakes?
You said you put the new carb on it.does it run better now or do you just have the idling problem.If its just the idling down problem you said you used an adaptor,You may have to adjust the throttle linkage or cable whichever you have.It may not be letting the idle come down do to location.
I tried it with the new carb but then put the old one back on. The motor is a crate 350 with power breaks and electronic ignition. The carburetor and motor are stock. I am going to take the spacer out and replace the gaskets and leave the spacer out to see if there was any leak there. The tranny is a power glide the motor, tranny, and carb have less than 1000 miles
Did you put a vacuum gauge on it? I think that would tell you a lot. Have you gone to the Edelbrock site and followed through on their information? If it back fires in idle try capping the hose to the trans, see if it still back fires. Be sure you have the proper vac line going to the distributor. Also a good point above, make sure you are clearing the spacer plate.
Just had the same thing pop up on mine. Blamed the old junk carb and swapped on a new edelbrock. Plugs are reading good and everything else seemed fine so far. Just seemed to lose acceleration and started acting up on hard acceleration with some popping. Same with new carb. Never had these symptoms come out of nowhere like this before, so I'm checking the same as you and will let you know what I find out. Just too cold out right now to fool with it and it's not a daily driver. But I'll let you know when I find the solution in case it helps.
I'm betting on a vacuum leak. Sure shows all the right symptoms of a vacuum leak. I'd pull the carb and check the gasket fit from carb to spacer, then check spacer to intake with a gasket on each to see how it mates. You could also spray some starting fluid around the spacer and see if the engine goes even higher on the idle.
You didn't elaborate on the backfire...out the exhaust is rich or unburned fuel ...through the carb is a lean condition and/or timing in both cases. A large spacer added will some times right off idle have a lag/lean condition if the accelerator pump is out of sync or adjustment, but I wouldn't think 1" would have that much of an effect if everything was or is good. I would lean towards finding a vacuum leak though, ...just things to check
Possible that the 2 mixture screws on the front of the carb are leaned out too much. With the car off, turn them both all the way in and count how many turns or partial turns they are out, then put them back to where they are. This will give you an idea of where it is set. With the car running, adjust the idle to around 700rpm. Then start turning one of the idle mixture screws on the front of the carb all the way in as far as they'll go until the idle stops picking up then back off 1/2 turn. ADJUST YOUR IDLE AGAIN, THEN DO THE OTHER SCREW. Both screws (CIRCUITS) should have about the same adjustment.
It is electric choke but it's never been hooked up. Which means that the choke is not operating properly, which is affecting your fuel mixture and causing rich lean fluctuations and improper air fuel ratios and thus a back fire when your engine loads up. You will also notice that you may have to adjust the choke setting when the weather warms to compensate for the temperature increase. Try hooking her up and set her at mid range to start out, adjust as necessary. Let her cool and try again if she is hard starting adjust till she is happy. Edit: There is a procedure for adjusting the idle mixture screws from Edelbrock, it should be detailed in your carb owners manual, it involves a tach reading in conjunction with a vac gauge, If I recall. A just about setting should be in all the way and out 11/2 turns, should also be in manual. I think the manual is in PDF on their site.
If you can't hook up the electric choke, you shouldn't attempt to work on old cars. You need a role model.
Yea, 1 and 1/2 turns out is usually the sweet spot. That is where I have mine also. You use your tach to keep an eye on the idle rpm and when you make adjustments to the air/fuel mixture your tach will raise/fall and you use the idle adjustment on the carb to compensate for this. If you hook up a vacuum gauge the sweet spot (1 and 1/2 turns out) will give you max vacuum also. Your cam will have a big effect on what that max vacuum reading is though. You don't have to use a vacuum gauge though, just lets you verify what you're ear is hearing.
The Jalopy Journal
