What's it sound like when........

[Docmacs'77]

Got a question. When you have bad gas (gasoline that is) - i.e. water in it, what's it sound like? I know I've gotten bad gasoline before, but then again, maybe I just need some reinforcement/consolation. I mean I hate the fast machine gun (although somewhat soft in nature) rat-a-tat-tat-tat-tat-tat-tat-tat sound when you when you put the pedal to it. Here's some background. Me and a buddy of mine built a 383 stroker, pulled the 350 outta my '77, and dropped the stroker in, about a year and a half ago. Immediately after we fired her up, I took her for a drive. Seeing as how I was close to empty, I drove down to the corner gas station and filled 'er up. However, and that's a BIG however, there were some circumstances that prevented me from finishing up the project. This week, I finished several minor modifications like having to replace all four calipers, replacing a U-joint, installing an MSD distributer and box, etc. I fired it up and it sounds real good. EXCEPT for the rat-a-tat-tat-tat when I humped on it a few times. When I'm cruising along it sounds great. Idles great. It couldn't be anything else could it? I mean, more than likely it's YEAR AND HALF OLD GAS! Right? It would definitely make me feel better if you guys told me that that's your opinion too. PLEASE!!!!!!!!!!!!
Thanks, Marc.

 

[wishuwerehere82]

Bad gas... usually is going to give you troubles. It may be water contaminated or just the wrong octane rating. Gasoline does not store well without adding stabilizer to it. If your gas is more than a year old, I would try to get it out of the tank ASAP. You can add Methanol based Drygas to the tank to absorb water from the tank and some Octane booster to keep it from pinging while you drive it off. Maybe find a station that has some 100 octane racing fuel and add a couple gallons to the tank to spike the octane rating a little higher than it is presently.

Water in the gas usually causes idle problems and stalling and will freeze the fuel lines in the winter time, but you aren't worried about that now. The pinging usually happens going up hills and any other time your engine is under load like acceleration, so I think you have it nailed down what the problem is. If all the above remedies don't have any effect getting rid of the ping, then the other solution is to retard your timing until it stops, then get some good high octane gas after you drive it long enough to empty the tank.

 

[Vettehead Mikey]

It couldn't be anything else could it?

Sure it could be something else. Are you sure you have the plug wires installed in the correct sequence? Is it timed correctly? Do you have the correct vacuum advance can?

I don't agree that it's bad gas. A year and a half is not that much time and if it's water it wouldn't start or would keep missing.

Good luck, and check out all the simple things first.

 

[Evolution1980]

...also, if you filled the tank, getting water in the gas from outside temp changes and condensation in the tank is lessened because there's less air (due to a fuller tank). There could certainly be other issues here, but I couldn't say what else. I'm guessing you'll have the typical 'process of elimination' that we all go through...

 

[Docmacs'77]

Yeah Pete, I would tend to agree with you. As a matter of fact, after dropping in the stroker (and actually, I re-figured the time element, and it's been closer to 2 years), I drove it down to the store and filled it up with 87 octane. I was so used to filling my pickup up with 87, I didn't think about it in time. I knew with a compression ratio of 10.5:1, I would probably be pinging. So I went ahead and poured a can of octane booster in. Even though that raised the octane a little, I'm pretty sure 2 years of just sitting would take it's toll on the quality of the gas. I drove the car around quite a bit yesterday evening and today doing errands and managed to get it down to just a little below 1/4 of a tank. Tomorrow I plan on driving it to empty and then fill it up with 93. Hopefully then no more pinging.

 

[Docmacs'77]

Well, I ran it to empty and filled it up with 93, drove it around Sunday and today a little, and I'll be darned if it still pings. Taking off, even with my foot in it from idle, sounds fine, no ping. But when I'm at cruising speed and hump on it, it starts to ping, that is until I let off the acceleration a little, then it runs fine without any pinging. Don't get it. I even went ahead and retarded the timing to about 12 degrees (had to adjust the idle up a bit with the idle curb screw to keep it from dying - have a new Holley 750 vacuum secondary) and it still pings. The only thing different was that when I killed it after driving it around a little (with 12 degrees), I got a couple of seconds of run-on. I drove it around a little again and killed it and no run-on, and the next time, run-on again.:confused (I haven't fooled with the mechanical advance any - have a new MSD Pro Billet [#8361] and a 6AL). Any suggestions?
Marc.

 

[wishuwerehere82]

Marc,

Some things to check:

Timing advance. Make sure you have full advance of 36 degrees BTDC @ 3000 RPM with Vacuum advance disconnected. Should be around 52 degrees full advance with Mech +Vac. The less advance you use, the higher the combustion temps. are going to be, so aim as high as you can at idle and adjust the advance curve to max out at 52.
The MSD has interchangable springs and variable stops to adjust this.
Your timing advance wouldn't in itself make the engine run-on , since the ignition is off. But the combustion chamber temperatures are greatly affected by the timing.

Spark plug temp range could be too hot. Causing the after-run and pinging. After-run or deiseling is usually caused by carbon deposits on the pistons or too hot plugs. Might try a bottle of Techron run through the tank to clean up the carbon.

Carb power jets too lean. If the mixture is too lean, it will cause pinging under load and acceleration and result in higher combustion temps. in the cylinders which could be the run-on problem. See if you can find out what Holley is using for the 750 CFM. You might want to go a number or two larger.

 

[vette-dude]

I agree with the above. I think you are running too lean at hiway speed. Fatten up the jets by 2. Check the plugs first and if they are white it is lean!! Don't want to burn a hole in the piston.

Randy