Look for a vacuum leak.
6sally6

 

I don't think I have a vacum leak, the only vacum hooked up is the pcv valve and brake booster. I don't even have the advance hooked up. So the only other place would have to be possible intake vacum leak but it has new felpro gaskets installed about 4 months ago.

 

With flat top pistons, I bet you don't have enough compression to support the cam at low speeds. You can cover this by more timing at idle. Your MSD should have some bushings and springs that allow you to limit the total advance to about 38 degrees or so with only about 18 coming from the distrubutor. Then you can set the timing at 20 or so so it will run at off idle and in gear. Some combination of springs will get all the advance in at around 25-2800 rpm. Power time it to make sure of total then see how much you have at idle and if reasonable, let it be. ALSO, aluminum intakes are famous for loosening the bolts. Check them. You can spray a little carb cleaner around the intake/head surface while idling and see if it changes, but be careful. It might surprise you.

 

Ok thank you for your in put, I didn't know as to where to set the advance bracket on the distibutor. So you don't think that it is off a tooth on the timing chain?

 

Hook up the vacuum advance.

 

Make sure 5 and 7 plug wires arn't crossed.

 

I've checked and no crossed plug wires, and the reason the vacuum advance isn't hooked up is when I do hook it up without putting the advance stop bracket in the engine won't idle down. What does that mean?

 

I've checked and no crossed plug wires, and the reason the vacuum advance isn't hooked up is when I do hook it up without putting the advance stop bracket in the engine won't idle down. What does that mean?

Well, you lower the idle speed w/the curb idle screw. Are you saying it won't lower the idle? Is the fast idle cam hanging up?

If nothing else, hook the vac. adv. to a ported source.

 

Yes when you hook up the vacuum advance it takes it from idle of 800 or so up to around 1700 to 2000, when I try to lower the idle it stays high until the carb idle screw is moved enough that it just suddenly drops and becomes so low that it is unable to idle and dies, its like there is no happy medium with it.

 

What type of carb do you have? (just for my knowledge) And the vacuum advance has to be hooked up to correct your timing problem.. I'm not sure what your saying with the carb not idleing down..if your saying once you turn the idle adjustment it still takes the carb awhile to idle down this amout?

 

It is a holley 750 cfm, with dual fuel lines and yes with the advance hooked up it will not idle back down, that's a mystery to me, and everything is new on this thing so everything should be working properly. So is there a different adjustment needed to bring the idle back down other than the curb idle adjustment screw?

 

Have you tuned the carb? And what type of intake gaskets are you using? Like the rubber type all the way around or gaskets and silicone ? I would check for vacuum leaks around intake manifold with carb cleaner as noted and also check for proper intake bolt torque.. I could be wrong but this is what it seems like..also try setting timing at 12 degrees before you hook up the vacuum advance.. in my experiences you will have to have the vacuum advance hooked up to be able to have your timing curve... it could be something simple or something like your cam is out of timing.. what fuel are you running?

 

Also with that cam you may have to run a good amount of advance on the timing! If you don't have to it will surprise me! goodluck keep us updated

 

Yes we set the mixture on the carb, also just running regular unleaded. I have the blue raised felpro intake gaskets and like a fool I went ahead and used the rubber front and back seals. And I just noticed that the front passenger corner of that rubber gasket is sticking out a bit.

 

What kind of intake gaskets would you recommend?

 

What kind of intake gaskets would you recommend?

If it were me and its not so this is basically an opinion...I NEVER use the rubber gaskets on the block (front or rear of the intake) the always leak oil! Always spend the extra money to get good intake gaskets..(from head to intake) and use a good r.v.t./silicone on front and rear with a nice uniform bead..

1) Check for the vacuum leaks around the intake gaskets and replace as needed..
2) Try running something like 92-93 octane fuel to see if this help also...

Again this is only my opinion , Keep us posted!




Joey

 

Thank you for your in put, I will check it out in the next few days. I will keep you guys posted as to wether or not it helped.

 

OK man good luck!

 

Thanks again, and just to double check if none of the previous things work would it sound like it could be at the chain?

 

Thanks again, and just to double check if none of the previous things work would it sound like it could be at the chain?

Yes it could be..anything is possible b ut my bet is gonna be the vacuum advance and/or the vacuum leaks!!

 

Ok thanks for all the advice.

 

Your welcome.. I have a few friends that specialize in the BBC's I'll ask around tommorrow and get their thoughts also!

 

Thank you, I was to the point I didn't know what to try next and on the verge of taking in to a shop, but now I have a few things to try. I would have tried the things mentioned today but instead I spent some time cleaning out the fuel tank and lines on a 28 chevy.

 

If you were off on the cam timing/or a tooth off on the chain....it would NOT want to even crank! I DON'T think the cam timing is your problem...My opinion
6sally6

 

I haven't seen anyone mention this, but have you double checked your valve lash? Make certain that none of them are too tight, or you'll get the backfire and issues you're getting on acceleration.
I always leave mine at zero lash. I know most books say 1/4-1/2 turn past zero, but my big blocks always ran better at zero with a larger hydraulic flat tappet cam.