[71nova1]

I have a 71 nova with a 388 stroker, it has vortec 906 heads, and 467 lift crane cam, and hypertonic flat top pistons, 750 edelbrock cam, dual plane air gap crosswind 1500-6500rpm intake. When ever I push the gas past half throttle and let go, the engine backfires out of the drivers side header. And also when i go to take off fast the engine hesitates sounds like its choking out, and then it wil go but seems like maybe not all the power is there. The timing is set to 12 degress and a total of 36 degrees, which i need to get a new distributor with a timing curve. The total i belive is suppose to be 34 degrees. I checked the top dead cent to the crank timing marker and it is dead on. Any ideas please help.. Thanks

 

[chevyIIheavy]

timing may still be off a lil bit is this a flat tappet cam if so i hate to tell you this you may have wipped out some lobes on the cam :no:

 

[David_D.]

check the easy stuff like a crossed plug wire, etc. You can check for a bad lobe on the cam by removing the valve covers and looking for loose rockers, or rotate the engine by hand and watch each rocker to make sure it's moving the correct amount.

 

[levisnteeshirt]

might be ,,

you might have a plug trying to foul too. I'd scrap the Edelbrock carb and make life easy for yourself and get a Holley , 750 vs or 650-700 dp and live the easy life. If it is coming from the carb accelerator pump being off , a Holley will be alot easier to work with.

 

[6NOVA4]

advance the timing and see if it helps. Also sounds like the accelerator pump linkage needs some adjustment. On those edelbrock carbs you see the linkage on the driver side the rod that attaches to the accelerator pump can be moved for more fuel shot. With 12* at idle and 36*@3,000RPM's you have a broad advance curve of 24*. You can have the distributor curve redone so it comes in quicker. As a start should be around 17*-18* initial and 36*@ 3,000

 

[71nova1]

Ok from set at 12 degrees at idel, i moved the distributor little by little untill the hesitation was gone, and noticed hardly any backfire, so i went down the street it ran awesome, but the new day i ran again and still no hesitation but the backfire had come back. the plugs are a light light brown, and look good, i checked compression on side that was backfiring, and was fine, and checked to make sure the rocker arms werent loose. The only thing i can think of is to get a timing controller or new distributor with 20 or less degrees and see what that does.WHat do you think would be best?

 

[71nova1]

I have performed all the simple stuff i can think of. Is there an easy way to measure the lift of the rocker with it all together?like something that would set on the head and have two dials one where it is and one moves to where it moved to?

 

[71nova1]

Do i put the timing back to where it suppose to be? And what exactly will that do for it? Will the engine be running at max rpm or half throttel?

 

[mdla]

Are you checking your timing with a light so you KNOW what it's doing? Do you have a vacuum guage to eliminate a vacuum leak? How's the idle? I know nothing about tuning an Edelbrock carb so can't help there. Where in Oklahoma are you?

 

[David_D.]

Ok, when checking for loose rockers, you need to rotate the engine over and check each one when the lifter is on the base circle of the cam. Really, if you have a worn lobe, it should be really easy to determine. A fool proof way to tell is to take the oil filter off and cut it apart using a method that does not make any metal shavings (I've used a cheap knife before), and take a look at what's inside. If you see a lot of shiny metal flakes in the filter, that's a sure sign you have a problem. If it's a fresh engine, you will have a minimal amount of metal, but not a bunch.

Adjusting the timing shouldn't affect the idle too much. If your distributor has a vacuum advance, you should disconnect that, and plug the hose to the carb, then adjust the timing. Use a timing light.

All plug wires are on all the way?

 

[71nova1]

I checked all the plug wires, and all the spark plugs, they all look the same, I reajusted the carb idel screws to even amounts and ajusted idel and had the timing set back to 12 degrees with vacume hose to distributor on the carb side pluged off, I made sure all vacume plugs and hose were not leaking and in good shape. I checked the carb to see if the fuel was coming out of both front jets, i checked all the rocker arms and push rods for any play and made sure all the valves were opening and performed another compression test. i have proper fuel pressure and engine is warmed up to running tempurture. The idel is ok each exhaust side sounds a little different from each other, like the drivers side is kind of inconsistent and the passenger sdie sound even flow. I am running heads with turn downs that have circle trace muffler inserts in them. The engine still hesitates at launch and backfires.

 

[David_D.]

It kinda sounds like a timing or ignition issue. I'd go back to TDC #1 and pull the distributor cap and make sure the rotor is pointed to the #1 cylinder.

Does it fire right up, or is it hard starting?

 

[64PRONOVA]

If you advanced the timing and the hesitation and backfiring went away but then came back a few days later, the first thing I would check is to make sure the timing isn't changing. Make sure the distributor hold-down clamp is securing the distributor and it isn't moving over time. Another thing you can check is to make sure the distributor gear isn't worn.

 

[71nova1]

i rechecked the distributor position, and its tight and not moving, with the vac line pluged its running about 12 on timing marker and 22 on the crank, with it set here, it doesnt hestiate much if any at all, but still have back fire, if i were to set timing to 12 degrees on timing marker and at zero on crank, it doesnt run good and hesitates, and i have made sure the zero on the crank is tdc and the distributor is pointing right at the spark plug wire one. How can it be running better so far advanced, cause it would give me a total timing of like 50 to 55????

 

[6NOVA4]

why are you so concerned with the timing being at 12 degrees? with a light and the vacuum advance plugged set the timing at 36 deg at 3,000. Then check the timing with the vacuum advance hooked up and see where its at at 3,000. it should add about 10-20 extra. That's okay cruising unless it pings. Then at idle with the vacuum advance plugged off what is the timing at? If its at 18-20 deg thats fine. As long as it doesnt "grunt" when you start it. Do you have the vacuum advance hooked up to manifold or ported vacuum? Just for grins maybe borrow somebodys holley carb and and see if it changes anything. The edelbrock may need some more jet or smaller metering rods.

FYI if its backfiring thru the pipes something is causing fuel to ignite in the pipe or a crossed plug wire. If its back firing thru the carb its too lean or not enough timing.

Do you have a degreed balancer or tape on it? are you using a timing light with a dial on it? Are you sure the balancer hasn't slipped or the timing pointer moved?

 

[71nova1]

the reason i am concerned about the timing running at idel at 24 degrees that the cylinder is already on the down stroke and that its already pass tdc. and at 3000 rpm, it degrees to around 42 degrees, proracers dont even have that. I just dont want to find i am loseing horsepower and running the engine, wrong, if somebody else has the same problem as me and runs 12's then i will be happy with that, its not nessacarly the timing i am so concerned about its the annoying backfire after letting off the gas.

 

[6NOVA4]

so it sounds like you have 18 deg of advance in the distributor. You're gonna have to recurve it to get what you want. IF you indeed have an 18 deg advance then setting the initial timing at 12* + the 18* should give you 30*@,3000. so setting it at 36* at 3,000 should be 18*. Thats fine. Maybe hook up the vacuum advance to ported vacuum so the initial is low where you want it and when you bring up the RPM's the vacuum advance will kick in whatever it does.


So again with that you shouldn't have any issues with backfiring as far as timing is concerned. Usually backfiring in the pipe is from fuel left in the pipe igniting.

 

[71nova1]

Ok i talked to a pro down at aps and he said if i had even the smallest exhaust leak then thats where the backfire was coming from, and i know that there is a slight one at the head and header, so i can repair that and have no problem, as far as the timing i need to recurve the distributor. So i am just going to get a new distributor with adjustable timing advance and that should make all the difference.

 

[Dan_Lebherz]

I am curious how you are checking the timing at both the timing mark and on the balancer. Are you using a degreed balancer or a timing tape? If you have installed a timing tape on the balancer, is it installed correctly? Don't bother to ask me how I came to know this can cause a very confusing situation.

I was running vortec heads on a 350 and found that 34 degrees total was as much as you really want to run. My stock distributor as well as my aftermarket were set up for 24 degrees of mechanical advance, which meant I needed to run 10 degrees initial. Your car should run OK with the 10 degrees if everything else is OK.

By the way I am running the same heads and distributor now.

With the distributor cap removed, rotate the rotor to see if it returns. If it doesn't, remove the rotor and check the bushings for the weights and also the springs. I had a situation a year or so ago where the car seemed to run fine, but the ET had slowed by seven tenths. I couldn't figure out why. When I put a timing light on it i found that I was oddly getting no mechanical advance. Finially figured out one of the brass bushings had worn allowing the weights to **** and lock preventing the mech advance from coming in. i put new bushings in and immediately re-gained the 7 tenths i had lost.