shr

Well I am having a issue with my 1969 302, here is some info before the problem:

1969 302, new cam (just a bit more mild then stock), new 4 barrell intake, 600 cfm edelbrock, stock heads(took them to a cyl head shop and they told me they have been rebuilt and need nothing other then valves lapped and new oil seals) stock bottom end (before taking apart approx 130 psi in each cy on the compression test) headers, new timing chain, oil pump, and gaskets.

Problem:

I have broke in the cam per manu. specs, put new oil in it, set the timing and took it out for a test drive, when I accel up a hill or just try to get into it, it feels and sounds like it is backfiring through the carb. I had a proform HEI installed so i took that out and put in the stock dist. fired it up set the timing took it out again and same thing. It will run smooth as long as you dont get on the throttle to fast then it pops and misses out and again sounds like it is coming through the carb. My balancer looks like has not slipped as when you pull off the pass valve cover and roll the motor around tdc on the balancer is right on with the valves being closed on #1 cylinder. Spin it again and they are closed again. On the timing when you set it at 6 before top dead center it runs really rough! when advanced to like 40 after it smooths out but will not start out and run. The timing gear installed is a stock straight up unit no retard mark in it.

I am at my wit ends with this!! Any one have a clue what is going on?

JMD

I want to say you are going lean, vac leak or carb issue.

67mustang302

Does it only do that when you open the throttle and then evens out, or does it keep doing it if you stay in the throttle? If it only does it for the few seconds after you open the throttle it's prolly the accel pump.

If not....

You need to rotate the engine over so that cylinder number 1 piston is at TDC and verify that the balancer is at 0 at that point. If it's not then you need to fix it. Base timing should be around 10* idle as a starting point. Do a compression test to see what you have on the cylinders.

Once that's checked, get it running and spray some carb/brake cleaner along the intake manifold where it meets the head, if you have a gasket leak it'll cause the engine idle speed to change.

The carb could be lean, but not likely, typically they're calibrated rich out of the box and your engine is pretty mild. I'm thinking either a vacuum leak, the valve lash is too tight or the timing is off.

jojobanks

get the good ol' vac gauge out and put it on. Reference this chart when reading the gauge:
http://www.classictruckshop.com/club...ts/vac/uum.htm
Your vac reading should be slightly lower than normal due to the different camshaft.

For good measure, go ahead and pull your plugs and look at them while referencing this chart:
http://www.spark-plugs.co.uk/pages/t.../diagnosis.htm

between these two diagnostic measures you should have no problem finding your problem.

shr

It does it until I let out of the gas, then sometimes when I get back into it, it will do it again. I have my accel pump in the middle of the three positions on the linkage. TDC is on the compression stroke correct? Just want to make sure on this as that is how I have it! Now I have the timing set to 6-8* before TDC as that is what the manual states to put it at, you would put it at 10* before TDC? I will spray some cleaner around the intake and see what that gives me but I am pretty sure that I have it sealed off pretty good! Now for the vac. gauge where do you attach that at? I have the vac ports on the carb, the constant vac is plugged off and the Dist is on the variable vac port on the carb (pass side outlet on the edelbrock), then I have one on the back of the manifold that goes to the vac mod on the trans and has one other capped off! Thanks for the help!

jojobanks

I would "t" the vac gauge into the manifold. run your vac gauge into a t-fitting with another vac line coming off of it. pull a vac line from the manifold and attach it to the t-fitting and attach the whole thing back into the manifold.

I'm gonna guess that you just need to advance your timing a little, but the gauge will tell you exactly what you need to do if you read it right. The manual's timing setting is more of a starting point when timing your engine. You'll have to play with it a little to get it right, especially since you have an aftermarket cam.

also, when your camshaft was installed, did whoever install it degree it properly or did they just set it by the marks?

shr

The cam was installed by the marks, I forgot to put on the previous reply that the rocker arms are stud (5/16" shouldered) mounted so i just ran the rocker nuts down and torqued them. By advanced you mean move it to TDC or 2* before tdc? Right now with the timing light on it to get it to smooth out the mark is about 2" above the pointer. I pulled some plugs and they all looked consistant, i checked the accel pump and it is working properly. But here is how I stabbed the dist. I took off the pass valve cover and spun the motor until the intake valve opened and closed, lined up the balancer mark with TDC and put the dist in. Should I run it past the exhaust valve too open and close? The pointer and TDC mark line up on the balancer where the valves are closed. Thanks for the help this is the first motor build i have messed with and so far it is winning!

shr

One thing I did notice on my rocker arms when torqued down that the springs compress approx 1/8" down, is that normal?

JMD

The springs on the valves that are supposed to be open will compress, but not the springs on the valves that should be closed.

If ALL of the valves compressed this much, your engine will not start.

A compression test will largely eliminate this as a possible issue.

kalli

if on all: very abnormal. that means the valves will never close causing them to overheat and engine running **** or not at all.
like JMD said: compression test would be good to see if it's valvetrain issue or carb/ignition issue. only that will tell us for sure what direction to look at