Barfly

My 340 with a Carter 606 AFB carb runs pretty well idling and with slow acceleration but any time the secondary opens up on the road or if I tromp it in the driveway the engine back fires through the carb.

Brief history, I just rebuilt the fuel pressure regulator and have tried the psi set at 6 lbs up to 9 lbs with no change in the backfire. I went through a kinda rule of thumb carb adjustment and believe that the fuel mixture is good.
My timing pointer is missing so I can only set the timing by ear at idle, small adjustments either way make it idle rough or spark knock.

One other thing that is abnormal but I have no idea if it is related, the volt meter increases with engine speed.

Thank you very much for any help.
Joe.

sweeperking

Not sure what kind of ignition your using but if you got a vacuum advance I would check to see if it's working and/or hooked up correctly. Your probably right in that the voltage increase with engine speed is unrelated but at the same time it aint right. Sounds like maybe a bad voltage regulator should at least be checked.

Barfly

The vacuum advance is hooked up with a small hose, 1/8" I would guess to a small port on the front/bottom right of the carb. I don't know if it is working. Is there anyway to test it without a vacuum pump?

1966sportfury

how i test a the vac advance is kinda crude but it works. pull the hose put in your mouth suck on it and put your tongue on the end of the hose and see if leaks off. if it doesnt the hose would be stuck to your tongue.

SCAMP TRAMP

If your vac. advance is working ok then your base timing is wrong, too much and ya get back fire through the carb because the plug is firing while the intake vavle is still open to much & through the exhaust when its late, plug fires too late while the exhaust has already opened ...... just going by what you said with "no tab and set the timing by ear" that don't work too well because you can be 8 deg out and it sound fine .... and dont forget to much timing will increese cyl. temp big time and thats when things start to break

sweeperking

Barfly, you said that the hose to the vacuum advance is connected to the base of the carb right. It should be connected more towards the middle. This is called ported vacuum what you described maybe manifold vacuum. Check it out, with the car running at idle maybe 5-600 rpm pull the vacuum advance hose off distributor and there should be no vacuum. Now go off idle a bit maybe 8-900rpm and you should feel the vacuum. As far as checking the advance goes what 66sportfury says will work but personally I dont like sucking on hoses see if a friend has a vacuum pump or you can get a cheap on at your local napa for less than $20. I also agree with scamp tramp although some of what he says I'm not sure I follow. Good luck, oh and one more thing, worse case scenerio maybe you jumped a tooth on timing chain (that would be a bummer)

Scott-- (your friendly neighborhood sweeperking)

Barfly

Guys you are the greatest!
I love test procedures that are simple and I am already equipped for.

I had already checked the hose itself for a leak, I pulled it off the carb and gave a good suck and felt no resistance, several try's and still no resistance. Then I blew through it and while there was resistance I was able to continue to blow, it's leaking for sure! I took about 20 pictures from all sorts of angles then pulled the distributor and off with the vacuum advance portion.

Being its Wendsday I probably will not have a replacement till next week. But I am really feeling confidant about this

Thanks to all three of you guys, I really appreciate your responses and help!

Joe.

1966sportfury

i know its a far cry from a hooka

sweeperking

You got that right buddy

Barfly

Quick update.

With shipping the vacuum advance unit for my distributor was going to cost me $34 and take 5 days to get here.

The identical distributor ready to drop in is costing me $54 and will be here tomorrow because they had one in stock.

I'm really getting pumped up, I so much want to hear those wheels spin, it's been a long time 15 years since I had anything close to this guy.