Got Shell 93 Octane and now barely idles 1973 Dart 340

-
T

TRWRacing

FABO Gold Member
FABO Gold Member
Joined
Nov 3, 2015
Messages
414
Reaction score
113
Location
Chicago
I put in a half of tank of 93 Octane at Shell, which is the same gas station as last the time I filled up at and by the time I got home 4 miles later it will barely idle. If I close the choke or cover the primaries on the carb the idle speed goes up drastically and if I spray carb cleaner into it while running. I tried adjusting the A/F mixture but that does nothing. I checked 2 spark plugs and they look good. Vacuum gauge reading 7-10" when I normally have close to 16"

Whole car is shaking and can barely get into the garage. Carb is a Carter AFB competition series and might have a little cam. I don't know.

It back fire through carb once when I got home. I checked timing and it is at 2.5 Degrees BTDC per factory specs. Champion RN12YC plugs in there from previous owner but look good, no fouling. Checked accelerator pump and spraying fine.

It was running good this morning.

Please help.

Thanks,
Eric
 
Last edited:
Heard some report on the news about bad gas at shell stations resulting in engine damage. You should probably check that out.
 
I have not been heard anything recently. Google not showing anything.
 
this is not a comment on the gas...but you need to up the timing....BTDC 2.5 degrees even though is factory spec....the engine will run alot better with more initial advance.
 
70aarcuda said:
this is not a comment on the gas...but you need to up the timing....BTDC 2.5 degrees even though is factory spec....the engine will run alot better with more initial advance.
Click to expand...
Ok. But I can tell it's not running right. I close the choke and the idle speed shoots up to 1200 rpms. Did something clog a jet? Carb rebuild?
 
If I close the choke or cover the primaries on the carb the idle speed goes up drastically and if I spray carb cleaner into it while running. I tried adjusting the A/F mixture but that does nothing.
Click to expand...

My vote is for an air/vacuum leak
 
my money is on a stuck float. tap on top of the carb while it's running. maybe crap in one of the needles and seat.
 
greg r said:
My vote is for an air/vacuum leak
Click to expand...

I was thinking that as well. The previous owner doubled up 2 gaskets on the stock manifold and then a adapter plate and then a thin gasket. There is even evidence of red RTV. My assumption the reasoning was because of replacing the stock Carter Thermoquad which is a spreadbore? Please see the pics. Is there a way around this without changing the intake?

Thanks,
Eric

IMG_4161.JPG


image1.JPG
 
You can't buy a vac leak at gas stations. :D
That sounds like restricted idle jets or water in the fuel to me.
Those carbs are pretty quick to pull the top off of a take a look in the very lowest spot in the bowls for water, but first I'd pull those idle air screws and blow some air through the holes just for kicks, and a possible fix. :D
 
Would closing the choke and raising of the idle greatly to 1200 rpms be also a symptom of water fuel.

If there is water in the fuel and its a fall tank now, then the gas tank would need to be dropped and I don't have that ability.
 
Last edited:
Would this square bore to spread bore adapter w/gaskets work with the above Carter AFD pics?
 
TRWRacing said:
Would closing the choke and raising of the idle greatly to 1200 rpms be also a symptom of water fuel.

If there is water in the fuel and its a fuel tank now, then the gas tank would need to be dropped and I don't have that ability.
Click to expand...

Well, closing the choke would pull more fuel/water mix and could get enough fuel to run faster, but now I'm kind of second guessing this.
If your idle wasn't set at 1,200 before and it's raising to that when you choke it I have to agree with the leak theory.
If it were my car I'd pull every single vac hose that was over 1/8 inch and plug it so see if anything stands out (Like smoothing out and idle lowering back to under 1,200)
Your brakes work the same?, as you have vac assist power brakes.
Does plugging the PCV change anything.

If everything above check out ok I would have to think there is a vac leak under or around the base of the carb next.
 
TrailBeast said:
Well, closing the choke would pull more fuel/water mix and could get enough fuel to run faster, but now I'm kind of second guessing this.
If your idle wasn't set at 1,200 before and it's raising to that when you choke it I have to agree with the leak theory.
If it were my car I'd pull every single vac hose that was over 1/8 inch and plug it so see if anything stands out (Like smoothing out and idle lowering back to under 1,200)
Your brakes work the same?, as you have vac assist power brakes.
Does plugging the PCV change anything.

If everything above check out ok I would have to think there is a vac leak under or around the base of the carb next.
Click to expand...

When I sprayed carb cleaner around the 2 base gaskets stacked on one another below the carb manifold adapter. I noticed a change in the rpm as well. Is there a reason to raise the carb that high? I know it's a square bore Carter AFB on a spread bore stock Thermaquad intake.

Thanks much!
 
All you need for that carburetor to work on that intake is the thin metal plate from Edelbrock. Throw that thick BS adapter in the ditch. Whether that will help your problem, I don't know, but that thick adapter plate is not needed.
 
TRWRacing said:
Ok Thanks!. Will I have to change any throttle or the kickdown linkage? Why did the previous owner use 2 gaskets that look to be 3/8" thick, plus the thick adapter and RTV?

If I have to have someone drop the gas tank then I won't be too happy.
Click to expand...

No you shouldn't have to change anything. He probably used all that because those adapter plates are junk. I hate them.
 
RustyRatRod said:
No you shouldn't have to change anything. He probably used all that because those adapter plates are junk. I hate them.
Click to expand...
Ok. Not my preferred method, but I would rather not change the manifold. Do you think it's water in the gas? The exhaust is sputtering and I have to enrich the mixture screws close to 3 turns just to keep it idling. Before this problem started they were out 1.5 turns

Thanks,
Eric
 
TrailBeast said:
Well, closing the choke would pull more fuel/water mix and could get enough fuel to run faster, but now I'm kind of second guessing this.
If your idle wasn't set at 1,200 before and it's raising to that when you choke it I have to agree with the leak theory.
If it were my car I'd pull every single vac hose that was over 1/8 inch and plug it so see if anything stands out (Like smoothing out and idle lowering back to under 1,200)
Your brakes work the same?, as you have vac assist power brakes.
Does plugging the PCV change anything.

If everything above check out ok I would have to think there is a vac leak under or around the base of the carb next.
Click to expand...

Since I got the car, the brakes have never been great. Pads and shoe lining look good, but I can be on the brake and give it some gas and the brakes won't hold the car. I press harder and see the pedal goes to the floor and seems to hold the car.

I seem to hear a hissing that will indicate a vacuum leak. I cannot if it is coming from the brake booster or the carb.

Eric
 
I must have missed the post that said there was 17 gaskets , adapters and RTV between the carb and intake
 
No need to drop the tank for water in the fuel, if you suspect that put a bottle of isopropyl alcohol in it. Sounds like a vacuum leak to me, where is it leaking? I would do like mentioned above, disconnect and plug all the vacuum lines, see if it still acts the same. Very likely that adapter is leaking if it has rtv on it.
 
Mufflers sound like loud thumping and the engine. Took a long time to start and wouldn't idle this morning. Only to run is at 1000 RPMs and playing with the throttle. It's almost sounding like if you ever crossed ignition wires. But that was not touched. When I cover the choke with my hand the idle goes up but the exhaust and engine still doesn't sound right. My concern is vacuum leak, water in the gas as this started happening 10 min. after filling up, but the mufflers are a loud thumping.
 
Last edited:
You must log in or register to reply here.
-

Back
Top