Ok, so if you saw my thread about my carb issues, you will know that it was idling rough. Well, I am pleased to announce the car is idling great...EXCEPT, now it pops at all RPM speeds. I did the ole dollar bill trick and it nearly ripped in half sucking it in the tail pipe. Sticking valve right? But, I pulled the valve cover, turned it over and all the rockers seem to move like they should. I also checked vacuum leaks with carb cleaner and didn't notice a change in RPM. But I must have a leak somewhere because I am pulling less the 15". Also, I have a buddy help me time it in. Set it at 8* no vac assist. I mean, if it is out of time, I wouldn't be able to see the line right?

 

Is this a hydraulic cam or mechanical? Did you recently adjust the valves? Do you have a stock distributor or has the curve been modified? Did you reconnect the vacuum to the distributor after setting the timing?

 

I believe the cam is mechanical. It did not pop before changing the carb, but this isn't saying much because the car may not have been firing on all cylinders when I got it. The car shook and sounded lobey like it had a bigger cam. The PO even said it had a cam in it from the guy he bought it from, but I suspect it was missing on a cylinder. I changed the plugs and it runs very smooth. Everything is stock except the intake, carb, and headers. I changed the HEI, and connected the advance after the initial timing.

 

so how about details on the carb, what brand, what model#, did you change the jetting or anything else?

 

It is the Edelbrock 1406. I did not change anything other than idle screw settings. They are about 2.5 turns out.

 

'Nuff said.....

 

How is this comment supposed to help me exactly?

 

It likely won't. But the Edelbrock carb is the 'weak link' in your induction system. Quality 'out of the box' is questionable, at best.

 

Try switching the carb vacuum port for your distributor. One on drivers side is full time vacuum and the one on the passengers side is ported vacuum. If the car has an HEI distributor it may run better on the ported side.

Unk

 

I dont know much about edlebrock carbs but if you could find a different carb to test your system ,it would let you know if the carb was indeed the issue, if you believe that it is. Some folks seem to have good luck with edelbrock carbs, while some dont. I dont know the cam size, but id figure youd need atleast 12 degrees initial at idle with out the vaccuum advance hooked up, maybe more depending on cam size. If you suspect a valve being stuck you should run a compression test on each cylinder to trouble shoot and identify any issues, like you if your exhaust sucks in ward while running it dont seem right and is more than likely the issue. You didnt say if the pop was comming from the carb or exhaust, id bet its comming from the exhaust. The 15" or less of vaccuum could be from cam timing events, but the needle should be some what steady if the needle is erratic this would also be a sign of a valve not closing. If you dont know if your lifters are hydraulic or mechanical, now would be the time to determine, maybe you should call the previous owner, if thats not possible. pull the intake and not think, but know what you have. Id guess there hydraulic just because you dont know, if by chance there mechanical and some one has adjusted the valves theres a good chance there misadjusted and leaving a valve or two stuck open

 

Popping on overun? Have you blocked off the other vac ports (brake booster, headlight vac reservoir) to eliminate these systems as having a leak? I had this issue and it was the hose feeding the wiper door valve.

 

Easiest way is to try and adjust the lifters with it running as if it were a hydraulic cam. Hydraulics will recover rpm when tightened slowly, mechanical won't.

If a rough running engine is new to you, then adjusting the lifters properly is one of the first things you should do anyway. Then diagnose further from there.

A fresh change of 5w30 oil and sometimes a little bit of road time can make a world of difference.

 

It's useless to adjust the lifters when your not certain what you have.

 

That's the whole point.

Trying it the way I described, tells you which you have and you can then go from there.

 

What makes an Edelbrock carb questionable at best? there are thousands of them installed on cars and hundreds on this forum alone. The car had a Holley 750 DP originally. It made the car run like crap. I changed to the Edelbrock because it was a 600 cfm. The same cfm that the car came with. Plus I gained the manifold port back. The previous owner installed a bolt in it then installed the Holley, and "T'd" all the vacuum off it. Funny thing is, this all started just to get the lights to work properly. The PO said the lights quite after the carb install. Well, he lied. And about other things as well. I will try and block off all the vacuum and see what happens. I tested everything before i installed them, and the only thing that created a vacuum leak was the booster, which I suspected needed changed. Also, I will change the timing vacuum assist to the driver side port and see how that works. I also bought some Sea Foam, and a new distributor as well. After that it is either valves, wires, or timing? Thanks everyone. I will let you know what i find.

 

If it sucks a dollar bill into the tail pipe doesnt it have to be related to the exhaust valve not closing? I wouldnt think carburetion would be a factor in this issue. I would check timing, and then do a cylinder leak down test to see if an exhaust valve is stuck open.

 

Thanks! I will add that to the list? I was thinking maybe carbon build up on the valve perhaps? All the lifters seem to be working fine. Maybe not seating well though.

 

When I had popping coming from my exhaust back in June, it was due to crack in the spark plug wires. Just my two cents on things to check. I thought it was carb issue and wasted 2 days calibrating the carb until one of the forum member pointed out that issue could be the wires and it sure was. If you have a cam 15iinch vacuum is pretty good. If u want more vacuum at idle advance the base timing. I m pulling 15 inch vacuum on 12 degrees initial and have a big cam

 

Thanks Jack, on my things to do. Gradually narrowing it down.

 

Thats what id think to.

As to adjusting the valves, ive not ever ran a solid lifter, so i dont know if you could adjust them with the engine running or not. Ive only heard of solid lifter fellas adjusting them by setting the lash, i might be ignorant there. But as i stated before if it was my car and I wasnt 100% certain about what type the lifter the camshaft used, that would be my first prority.

As to the carb, there again I've never ran an edelbrock, some guys have great success with them some dont. Id say if it works for you great.

Do you have specs for the camshaft? Intial timing will depend alot on cam specs.