Ok chaps, I feel I am getting closer on dad's old 70 duster. Rebuilt heads, new gas tank, pick etc., her's the question. When I crank her up I close the manual choke. She fires up nop problem, but I have to keep my foot on the gas and the rpm's around 1200 or she shuts down. any suggestions?
fuel / vaccum issue?
- Thread starter johnnydop
- Start date
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VonCramp
Well-Known Member
I am going through the exact same thing! It's a Mopar thing I am sure. I am hating my Cuda right now and it's probably something really stupid and easy. If u figure it out before I do would you let me know?! Thanks!
Whats the carb?? Idle rpm?
VonCramp
Well-Known Member
If the charging system was insufficient then wouldn't the battery die after cranking for a little while? I have been cranking mine on and off for 3 days and I still have the idle problem, but the battery is still holding strong.
BillGrissom
Well-Known Member
Definitely not "a Mopar thing". All gasoline engines need spark and a fairly narrow range of O/F to fire. Mopar never made carburetors or fuel pumps. GM & Ford used same suppliers.
Could be a lean idle condition. Most likely from a major vacuum leak. A broken PCV valve could let in a rush of air, as RedFish says. Another is the vacuum hose to the brake booster (plug it). Also the carburetor gasket, in which case you might hear a sucking sound. I agree with you that it should run fine off the battery at any rpm. The alternator's job is to keep the battery charged.
To get an idea. On a newer fuel injected engine, remove the big hose to the brake booster. The engine will greatly speed up. Most will run fine since the fuel controller measures the increased air flow and compensates (perhaps not if it uses a mass flow sensor and the booster connects downstream). However, the carburetor in your classic car will not see this increased air flow from the leak, so will not add the extra fuel needed, thus the engine will misfire and shake, if it runs at all. A classic test is to flow propane around any suspected leak. It the engine smooths out, you found the leak. Don't smoke.
Could be a lean idle condition. Most likely from a major vacuum leak. A broken PCV valve could let in a rush of air, as RedFish says. Another is the vacuum hose to the brake booster (plug it). Also the carburetor gasket, in which case you might hear a sucking sound. I agree with you that it should run fine off the battery at any rpm. The alternator's job is to keep the battery charged.
To get an idea. On a newer fuel injected engine, remove the big hose to the brake booster. The engine will greatly speed up. Most will run fine since the fuel controller measures the increased air flow and compensates (perhaps not if it uses a mass flow sensor and the booster connects downstream). However, the carburetor in your classic car will not see this increased air flow from the leak, so will not add the extra fuel needed, thus the engine will misfire and shake, if it runs at all. A classic test is to flow propane around any suspected leak. It the engine smooths out, you found the leak. Don't smoke.
Snake
Mopar Nut
IS there any chance the rubber hose from tank to fuel line kink have a look.
Time for an update. I crawled back through the hood and discovered the gasket between the carb and the intake had a leak on the pass side. Upon removal I discovered that dad had rtv'd two 3/16" rubber gaskets together and the fuel was seeping out between the two. I replaced that with a 1" spacer and new gaskets. Now the baby will idle on her own but she still sits at about 1100 rpm. I began adjusting the idle screw with the spring on it next to the throttle and the rpm's went up but would not go any lower than 1100 without stalling out. While looking closely at the carb I noticed that I now have fuel seeping out at the passanger side throttle body shaft. Could it be the bushings on the throttle shaft. I have had a couple of the seasoned gentlemen that hang out at NAPA speculate that the secondary may be dumping fuel and causing the leak. Any suggestions?
nm9stheham
Well-Known Member
The bushings themselves do not seal any fuel anywhere. You can check them easily for being loose by just seeing if the shafts wiggle sideways in the carb. The fuel seeping is more likely a sign of an internal carb leak or a float level being high (as suggested at the NAPA store). Have you looked at the plugs to see if they are blackened?
Proto
Well-Known Member
Not sure but I may be running into something similar right now.
Street Demon carb on a 318 in my 74 swinger.
Runs great until warm, then either fast idle or so low it stalls. It was running fine yesterday and no spirited driving. My son drives it back and forth to school.
Street Demon carb on a 318 in my 74 swinger.
Runs great until warm, then either fast idle or so low it stalls. It was running fine yesterday and no spirited driving. My son drives it back and forth to school.
Thanks for the input guys. I plan on getting back under the hood tonight or tommorrow night. The first thing I am going to check is the fuel level in the bowls. There is a lot of opinion that the secondary bowl is more than likely dumping fuel causing the leak. Last night I did go out for just a minute and checked the throttle shaft and it was dry. Could be that it only leaks when running due to the secondary dumping fuel. I will keep you all up to date.
Any suggestions on where I should set the initial timing?
Any suggestions on where I should set the initial timing?
VonCramp
Well-Known Member
My intake was also leaking due to leak at base plate under carb. I used two gaskets to seal the carb against the intake. Seems to be working well. However, I think over time these old alluminum intakes warp, corrode, or something causing them to not seal as well as before.
Woods74
Broke Senior
Carb issue.
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