Hi Listers

I am tuning my 68 327/350hp I set the timing at 4 degrees before and when I hook up the vacuum advance the engine speed increases from 750 to 12-1300 it then drops back to idle after about 30 seconds or so -- I changed the vacuum advance but still the same, could it be the springs for the dist weights ? Without the vacuum advance it seems to accelerate and return to idle ok-- any Ideas?? thanks

this is just a wild guess..

ive never heard of this..

are you sure it is hooked up to a ported vacuum outlet on the carb..

and the only thing i can think is that it on a non-ported outlet on the carb..

did you have the dist. rebuilt or no ? and make sure you are hooked up on the carb right ,hope this helps ,if not just let me know and ill scrach my head and figure it out for ya or ask some others on here ,there are some great minds here !!!!

If the vacuum advance is connected correctly, I would monitor it with a vacuum gauge while at the same time monitoring the timming. It sounds like the vacuum advance is sticking, but that would tell you for sure. Good Luck!

Dave

If you are connected to the right vacuum port on the carb, then it could be that you need to adjust the vacuum advance on the distributor. Most of these can be adusted by pulling the vacuum hose off and use a allen wrench to stick into the vacuum hole. By turning the screw you are removing tension from the spring so it requires less vacuum for it to start advancing. Tightening it will cause it to take more vacuum. Be careful how much you adjust this as you can damage the diaphragm or keep it from functioning at all. You really should use a timing gun to set your timing corectly.

The 750 RPM might be a bit high. You may have slightly opened the port to the vacuum advance, allowing some slight vacuum. I drop of as little as 50 RPM could make a difference.

Thanks for all the input - I checked with Edelbrock and I am on the correct port, but I may have the throttle plates open slightly causing vacuum at idle -I'll check it out tonight and update later....

Heres a 1am update:

I put a vacuum gauge on the intake and it is fluctating -

I can get the engine to idle down to about 500 but still a litlle trickle gas coming out of the tubes in the carb - I am told this means that the thottle plates are not closed and it's not operating on the idle circuit.
If I close the thottle plates, the enginwe stalls wherever I put the idle mixture screws at///

Could there be a vacuum leak or would the carb being messed up cause the same symptoms. what is the best way to determine if there is a vacuum leak ?

The engine was completely rebuilt so new intake gaskets, sealer etc..


I am using a 1901 Edelbrock Qjet that was off ebay about 6 months ago looks like new but who knows>>>

thanks for the help, hope we can figure out what to try next....

Do you have the stock cam? This would make a difference in the idle settings. Also if the lifters/rockers are adjusted too tight it would have this effect. The changing vacuum bothers me.
When the throttle is closed enough, is it too rich or lean. It could be the mixtures are WAY off. When you set it lower, try adding fuel with carb cleaner, propane etc. and see if it gets better (it was lean) or worse (it was rich). May need a float adjustment, different jets, etc. Or the timing could also be way off.

Could just be a bad carb. Might be why it was on Ebay. I run into people all the time that buy a used carb at a swap meet, car show, off the internet and 8 out of 10 times if they didn't get it from a reliable and compentent source they have trouble with them. Then again it could be a intake gasket leak. Typically at the valley corners between the block and intake. You may also want to check the base plate on the carb to make sure its not warped causing a leak. You can do that with a straight edge. Another area that can be a problem is on the throttle shafts. You have to under stand that if the carb is used they could be worn and pulling air through the shaft. This may be the culprit. Take the carb off and wiggle the shaft to see how loose they are.

Also if fuel is coming out from above then you are correct that your throttle blades are too far open and its starting to pull fuel from the mains. If the blades are in the correct position you should be able to screw in the idle needles and it will kill the engine.

You can always take the carb off and turn it upside down to inspect where the throttle blades are at in relation ship to the idle feed holes. Don't get them confused with the idle transfer slots. If you screw the needles in you can see where they will stick through the holes. Once seated, screw them out about 1-3/4 turns. The turn the curb idle screw until the throttle blades are resting closed just above these holes. Put the carb back on and if it won't idle then their is either a vacuum leak or their is something else wrong with the carb.

If you is still being pulled over your float adjustment could be high. This will allow fuel to run down the boosters into the carb.

I hope you can make sense of all this information.