hey hope some one can help my 340 is poppin thur the carb could it be my timming is not advanceing far enough thats what some people have told me what do you think ????????o No:
Popping back through the carb is usually an indication of a lean condition. Check for a vacuum leak. The most common point is a disconnected or cracked vacuum line or a bad carb to manifold gasket. Spray some carb cleaner around the gasket and watch for idle changes, when you hit the leak point with the spray, it will temporarily seal the leak. Please post your name.
this is whats confusing engine was just completely rebuilt i haven't even had it on road yet it was burnin rich the fumes would fry your eyes out. real strong gas smell i thought that was it then i leaned it out some but still pops, one time then takes off. it seems like it hesitates then pops this just boggles me
Josh, Start with the simple stuff. You wouldn't believe how many guys on this BB have reversed plug wires and such. Take a good look at the firing order and make sure it is correct. Very common to switch #5 and #7 up. 1-8-4-3-6-5-7-2, clockwise around the cap.
You don't want to spray it on a freshly painted engine, it might dull it. You can put a vacuum gauge on the engine instead, and check your idle vacuum.
THANKS BUT STILL GOT SOME ????? SHOULD I HOOK GAGE UP TO CARB OR INTAKE? WHAT SHOULD IT READ IT HAS A LITTLE BIT BIGGER CAM. WILL THAT DROP MY VACUM, THE LIFT IS INTAKE .488, EXHAUST .490 ADV. DUR, IN 276, EX 281, GRIND LOBE IS, 112 I GUESS I REALLY DONT KNOW THE EFFECTS OF A CAM THIS SIZE OR IF IT EVEN CHANGES THE VACUM. I WANT TO GET IT GOING SO I CAN CRUISE AGAIN, CANT WAIT, JOSH
Hook it up to the carb. If it is a Q-jet hook it up to one of the bottom ports. With the engine warm and the trans in gear you should se a steady 12-15" of vacumn. As Larry said check firing order. I have done that myself.
Check sparkplug wires/firing order one more time! Is there any gasoline comming from the accelerator pump outlet/nossles? Carb type? What did you do to lean it out? Do you hawe any (the suspected) power before popping starts?
its an edelbrock 600 cfm it has power before it pops then is slugish i will check the fire order but need time been workin 14 - 16 hour days if i cant work on it at least ill talk about it he he p i hope its just somthing small i love these tips thanks guys . MY BEAST WILL ROAR AGAIN :blast: Josh
Man Josh were are going through similar problems. I have a little over 500 miles on my newly rebuilt 340 and my engine is running too rich. I have changed the plugs 3 times since I rebuilt it. Today I put my third set of wires, I used to accel super stock sets, now am back to the autozone 1 year stock wires. It runs better but it still is not burning the gas and has a rough idle. I am also running the elderbrock 600cfm manual choke carb with an 1inch adapter plate, which I recently replace both gaskets just to make sure it was sucking air,making car not idle. But one thing I notice even though it running rich the fuel pressure is weak on my engine, I will be putting a new fuel pump on today. I am going to go with a hotter plug, most likely Autolite AP26. My dad thinks I need a msd box to make burn the gas better. I currently have the pertronix conversion with stock coil, the accel coil died in a month. I will tell you one thing josh I put a distributor out of a 73GS350 with curving kit in my 340 and it woke it up until the engine temp goes up then the engine runs crappy. I broke the motor mount the same night I put the new distributor in. I could barly move the throttle the engine was wanting to comeout. I now this is a long thread,but just hang in there, here is a firing order picture that someone may can help us both out with as far as the timing and firing order. The Blue number represent the way my cap is hooked up if you lay this diagram on top the engine with the top of the page facing the distributor. I tried just moving all the plugs forward one place and car just would not crank, I did not reposition the distributor. Tommorrow I am going to sears and buying a dail back timing lite to see what my timing is. I will check this thread ASAP for any suggestions also Josh. Thanks Julian
advanced Back the timing off once to see if that helps. Advanced timing - pop thru carb. Thru Exhuast - Too retarded
pop...pop...pop.... I've got a real similar problem. At highway speed there's a point where the engine begins to pop back through the carb. The frequency is totally related to engine speed. Too much advance makes sense, so I'll alter the advance springs, but if it were excessive timing, shouldn't pinging be evident? o No:
Josh, Ive read your post and I think your problem is in the carb. the cam specs you gave is going to affect your carb set up. the cam is going to have less vacum at idle than a stock one. your carb is to rich ( burning eyes). the meter rods need a lighter spring under them.edlebrock makes a calabration kit with differant springs and metering rods.They will be color coded for differant sping tensions. your dist may also need recurved once you get the carb. on track. but one thing at a time.Hope this helps Tim.:TU:
i had this problem on a 650 edelbrock. it was a new carb and backfiring right up through it every time i put it to the floor. turns out the timing and dwell was way off. took it to a mechanic and 70 dollars later it was running fine :spank: pete
