Been driving my '66 for 3 weeks and she's been running and purring like a kitten. Been working on it for 5.5 years and finally tag, titled and driving it! Has a (real) 390/C6 - rebuilt by PO a number of years ago. Has new plugs, wires, dizzy cap and rotor, Pertronix ignition and a new Edelbrock 1406 4bbl carb. Has been running just great until this weekend. On Saturday I noticed some slight surging and when I came to a traffic light and sat idling for > 20 seconds it would act like it was loading up: RPM dropping becoming erratic and when I finally started to go it would hesitate, and mis-fire and no power until it cleared up and then run OK. Checked idle mixture - it is good. On Sunday it acted up even more so it seemed to me to be fuel related - new carb got some junk in it? Or - bad fuel pump?? Pulled the fuel line off the carb, stuck it in a bottle and the wife cranked the engine. The gas seem to sputter and cough it's way into the see-thru fuel filter and minimal coming out the end of the tube.....! Spent ALL day yesterday R&R'g a new fuel pump (no fun there!). Started right up last night (cold - choke on), so packed it up for the night. Started up first hit this morning, and then drove to work, and........same d@mn symptoms! No power, hesitation, surging, wants to die at idle when in gear, crud!

I am sort of at a loss as to what to reasonably do next - and need some advice. Bad dizzy (vacuum mechanism appears to working)? Bad/rusty/crud in gas tank (I did notice a FEW particles of stuff in the fuel filter)? Purring pretty with excellent response last week - now running like a dog..

Help!
daggerNC

 

Over the years of working on cars, my Dad and I both learned to think like my Mom when trouble shooting. In other words, don't think like a mechanic, think simple first. So please don't take offense while I state the simple 'dumb' ideas.

-Pull the fuel line before the filter and see if any large sediment comes out. If you have rust, you might have a large flake that is covering the end of the fuel line limiting the amount you have coming through. (Actually had this happen onboard a boat I used to work on. Took two weeks for the mechanic to figure it out. Basicly rebuilt the entire engine for no reason.)

-Double check that your fuel gauge is working, and that you have plenty of gas in the tank. If you don't have much, any sediment that is in there won't be suspended, and can cause it to build in the fuel line.

-Check your entire fuel line, make sure you don't have any pinches or kinks forming anywhere.

Just a couple thoughts. Feel free to argue in 3... 2... 1... NOW!

Jay

 

Thanks Jay - all suggestions are good ones.
1- Will check this section of fuel line. Large flakes would be bad....
2- My fuel gauge is not working correctly - but I was saving that for another thread (sending unit OK, gauge goes to empty if tank > 3/4 full then comes on once below 3/4!?!?)
3- I've replaced all the soft lines in the fuel line. Main factory metal line has no kinks in it.

Hmmm, I just thought of another test I could do - grab a gas can with fresh gas, insert line from pump into gas can, and see if it runs OK?

Thanks

 

If you use a gas can, before you insert the line, blow it back towards the tank with an air hose just to make sure the line is clear.

 

Question for all - If I disconnect the fuel line at the fuel pump, can I blow air into this fuel line that goes back to the gas tank, or is there a one way valve or restriction going back into the tank? The reason I asked is I tried this yesterday with just barely touching my air gun trigger and it wouldn't blow back into the tank - it just blew the air gun tip off the hose and sprayed gas as if the line was restricted......

 

Remove the cap and you should hear the gas bubling in the tank. it should blow back easy there are no check valves. It is also possible your tank is not venting, usually when it is a vent problem you can hear a vacumn when you remove the cap, and they will usually start and run good for a little while until it pulls a vacumn and then starves it for fuel.

 

starmilt - hmmm... The first time I tried blowing back into the tank stupid me I left the gas cap on. Second time I took it off but same result - lots of resistance to the air flow (what I don't know is if the diameter of the fuel line plus weight of about 7 gallons of fuel in the tank would make it really hard to blow any air into the tank)?

My cap is vented, but the opposite happens - when I remove the gas cap it vents out (I guess that's why they have the warning sticker on the cap). I could try running without the cap to eliminate that as an issue.

 

do you have a power brake booster? Might the diapham spung a (vacuum) leak?

 

carras - interesting question because I do have a PB booster and the original '73 donor unit was actually a bad one and it took me a long time to find it/figure it out. However, this is a new PB booster now.

 

Ok even if the tank is full you should be able to blow back through it and hear the air bubling in the gas, it hardly takes any pressure at all if there is no blockage.

 

Hmm----watched my fuel filter while the truck was idling/stumbling in the garage. Looked good and then the fuel level dropped down to less than 1/4 full???

Just in case I got a bad tank of gas I filled it up with Exxon and a can of Sea Foam (hoping I'd get lucky), but I doubt it

 

Sounds like a partial blockage somewhere...maybe a bug/bee in the gas tank?

 

Sounds like you should try draining and cleaning out the tank. then try and clean the lines again. I would guess that there is something blocking that fuel line and only slowly letting anything past.

 

Anybody do an R&R on their gas tank? Approximately how many hours for the job? If there is some junk including rust scale has anybody had any luck with any tank cleaners and if so what did you use? One step or more steps, etc? (I'm rethinking the costs of a new tank and then would need to paint it first, etc. But if cleaning is a hit or miss process or really painful to do then a new tank it is..)

Thanks all again for your inputs and suggestions!

 

Check out the Por15 site...they have a "kit" that is fairly reasonable in price for refurbishing gas tanks. I had a shop take mine out for cleaning/checking or gunk and they were surprised at how clean it was...I lucked up on the tank, I guess.