SFT

Hello,

I have a 327/300 hp 1968 Corvette with a Carter AFB Carburetor. It has not been driven much in well over a decade. I replaced the distributor cap, wires, rotor, and replaced a blown exhaust manifold gasket and the car was running great for about a week. Then, at speed, I hear a loud clunking sound under the hood which I determined to be backfiring through the carburetor. I checked the points and all the wires to make sure they were secure and set the idle at 700 with a dwell tach and set the timing to 4 degrees BTDC...now it is backfiring and sputtering even worse than before and the idle is not even steady. I am also blowing a lot of white smoke out of the exhaust. I am stumped and do not know what else I should check. Thank you for any advice.

RickyBerg

You may syffer a clogged fyel filter, dirt in carb or maybe water in the tank.

My suggestion is to check filters, tank and carburator for water/dirt.

//Ricky.

scottyp99

Don't you mean "carbyrator"?

Seriously, tho, doesn't white smoke usually mean coolant in the combustion chamber? Look in that direction, blown head gasket, maybe? Hope not,



Scott

RickyBerg

Sorry, writing to fast, never check spelling and on top of all that, -the languageproblem..

But i can always try to write in Swedish.

scottyp99

I just like to tease, that's all, and I guarantee that you speak English better than I speak Swedish!

Scott

RickyBerg

Haha, I can take it.

CAMAROCORE

yep, i think that you should clean the tank, fuel lines , and new filters and also complete carb cleaning.
it`s really mandatory after sitting for ten years.

Vette5.5

How old's the fuel in the tank, because it loses octane rating over the years and could be pre-igniting. Something to check for. If you decide to syphon it out, you can always mix a bit in your daily car to get rid of it.

scottyp99

I am not really sure how, but I have a feeling that the most important clue we have so far is that it ran great for a week, then there was a big, ugly noise, and now, all of a sudden, it runs like crap. have you pulled the spark plugs and inspected them?

Scott

knockbill

have you gotten gas just before it started the problems? could have gotten bad gas then,,,

RickyBerg

Could also have been fragments of rust in the gastank that clogged the filter/carb after a while.

Have you checked the bottom of the gastank?

Just light it up with a flashlight and spot trough the filling hole.

One sholud be able to se if there is any collections of water and/or rust in there.

Be careful not to drop the flashlight in the petrol thogh..

//Ricky.

SFT

thanks for the help so far everyone. I had already used up half a tank of gas before the problems started occurring so I don't think it was bad gasoline. I will look into the other possible problems suggested as soon as possible and let you guys know if I was able to fix it. thanks again

RickyBerg

Hi again.

One can not take for granted that one always get clean fuel when filling up. The petrol has passed several different storage containers and trucks before it gets in your Vettes petrol tank.

The tank on the petrol station may be dug down in the ground and there may be condense water in the fuel due to that.

I have experinsed this a couple of times.

I hope you solve the problem.

//Ricky.

SFT

Ok I will put some new gas in it as well. Thanks again for the help everyone. Hopefully I'll be able to work on it today or tomorrow.

johnmb

Might be good to drain the tank and see what you find... if it's full of rusty crap, you might need to work your way forward to see if any of the fuel passages (line, pump, filter, carb) are clogged or restricted. One of those clear glass fuel filters temporarily installed might give you an indication of what's coming thru the line.

John

SFT

Hi everyone,

thanks again for the input. I just finished doing a compression test to see if the problem was inside the engine. Solely based on the PSI results, it would seem as if this wasn't the case, since all of the cylinders had a strong output of between 160 and 190 PSI (factory specifications for my engine is 160). However, when I was testing one cylinder (so this one particular cylinder is plugged with the compression kit while the rest are open), I heard a popping sound which I identified to be backfiring through the carb - seems too coincidental to be insignificant? This backfiring did not occur when any of the other 7 cylinders were being tested. Does anybody know what this signifies? Does that mean I have a sticky valve or some other internal problem even though the compression in that cylinder was strong?

Also, I checked out the fuel tank...it looks very clean to me with virtually no rust or dirt...found a crack in a rear fuel line and am in the process of replacing that.

Please let me know your thoughts. Thanks again

Aruba1

recheck your timing.

lonzoo

I would bring #1 piston up to top and check rotor for relationship to #1 plug wire on cap. If this is way off , could be timing gear or distributor off a gear or two.

SFT

hello again,

I just removed the valve cover and believe I found the source of my problem. One of the push rods is coming out at the wrong angle and so its rocker arm is not connected in the spot where it should be...I tried to simply move the rocker arm back in place but it won't let me. I believe it is because the push rod is coming out at the wrong angle (maybe it is bent? I'm not sure).

Can anyone tell me how serious of a problem this is and how I can go about fixing it? Is it simply adjusting the rod or pulling it and replacing it or does this signify some other problem deeper inside the engine?

The engine ran perfectly for about a week until I was pulling onto the freeway one day and heard a popping sound which I identified to be backfiring through the carb. This must be the cause of my problem.

I tried to attach pics but I couldn't figure out how to so instead I took a youtube video of the problem so you all can see it firsthand....as they say a picture is worth a thousand words.

http://www.youtube.com/watch?v=QE-oShxiPsA

Thanks for the help.

68sbcoupe

This is an easy one. Get a 5/8" socket, and loosen the gland nut on the rocker 1/4 turn at a time. After each 1/4 turn, grab the rocker and twist until you can get the pushrod back in place, and the tip of the rocker back on the valve.

After you get things back to normal, re-tighten the nut the same number of turns yiu loosened it. Then add another 1/4 turn, becasue the rocker was most likely too loose.