Slant Six Forum :: Tuning?

What is floating around in the fuel bowl?

Disconnect the vacuum line to the distributer, and plug it. Now do a road test. If that cures the problem, you might have too much advance, or the points not set correctly. Set the points with a dwell meter, and then reset the timing. If that doesn't cure the problem, check the carb.

Does your carb have a dashpot? It's a little vaccuum solenoid for manual trannies that hold the throttle plates open and slowly closes them when you let off the gas... A couple of situations can be occurring here:

1) The plates are closed enough to be in the transition slot and not have the main metering one line...if you have enough rpm and advance going and you let off, you may not have enough gas to cover the advance/load/ and minimal gas the idle/transition circuit gives (retuning, richening the idle/transition circuit... or a hihg rear gear ratio that will put your "cruise" rpm at the speed you are trying to keep up with.

2) Check by driving with a vacc. gauge hooked to a vacc. source under the throttle plates or worst case scenario off the #6 runner.... when you let off the gas if the vacc. is high, and load is high it will starve the engine out of gas... reading the plugs or watching an O2 sensor will allow you to see if you have a "lean out"...which can be a combination of vacc. advance (too much at that moment), and not enough gas (it is lighting the fire early and you might be "shooting ducks", get a rough feel from the engine....)

Either way you need to find out which way it goes and rememdy it before a piston top gets too hot or a plug gets melted.

Good Luck,

-D.Idiot

Sounds like a fuel problem. What is floating around in the fuel bowl? Water? old gas? You may want to take peak and see what is in there. If you have a 1920 Holley on yours you can cut down a red plastic Folger's coffee can to slide under the bowl to catch the old fuel and debris. It is amazing what you find, like chunks of old rubber fuel line......the new fuel really does a number on old rubber.
As you replace the fuel lines, use fuel injection hose 30R9.

Loose base gasket and worn shaft bushings... hmmm. Vacuum leaks wreak havoc on how they drive.

Thanks, but why would I be getting liquid gasoline bubbling out around the shaft for a minute or more after shutting off the engine?

A proportion (most?) of the sediment is likely to be fuel additives that drop out of solution as the car sits for an extended period of time and the fuel ages and evaporates. These can be extremely difficult nigh impossible to resolubalize so they must be cleaned out manually.

Author:	RossKinder [ Sun Nov 22, 2009 2:22 pm ]
Post subject:	Tuning?
My '65 Valiant (standard equipment) sat for a year while I was putting in an A833 OD. I don't remember how it was doing before that, but I put in new points and plugs and set the timing and choke. As long as I'm accelerating (not wildly) it runs smooth as glass. When I reach speed and ease off it starts running rough - random missing. I don't even know where to start. Suggestions? RK

Author:	Aggressive Ted [ Sun Nov 22, 2009 3:25 pm ]
Post subject:
Sounds like a fuel problem. What is floating around in the fuel bowl? Water? old gas? You may want to take peak and see what is in there. If you have a 1920 Holley on yours you can cut down a red plastic Folger's coffee can to slide under the bowl to catch the old fuel and debris. It is amazing what you find, like chunks of old rubber fuel line......the new fuel really does a number on old rubber. As you replace the fuel lines, use fuel injection hose 30R9.

Author:	Charrlie_S [ Sun Nov 22, 2009 4:20 pm ]
Post subject:
Disconnect the vacuum line to the distributer, and plug it. Now do a road test. If that cures the problem, you might have too much advance, or the points not set correctly. Set the points with a dwell meter, and then reset the timing. If that doesn't cure the problem, check the carb.

Author:	DusterIdiot [ Sun Nov 22, 2009 7:16 pm ]
Post subject:	Dashpot...
Does your carb have a dashpot? It's a little vaccuum solenoid for manual trannies that hold the throttle plates open and slowly closes them when you let off the gas... A couple of situations can be occurring here: 1) The plates are closed enough to be in the transition slot and not have the main metering one line...if you have enough rpm and advance going and you let off, you may not have enough gas to cover the advance/load/ and minimal gas the idle/transition circuit gives (retuning, richening the idle/transition circuit... or a hihg rear gear ratio that will put your "cruise" rpm at the speed you are trying to keep up with. 2) Check by driving with a vacc. gauge hooked to a vacc. source under the throttle plates or worst case scenario off the #6 runner.... when you let off the gas if the vacc. is high, and load is high it will starve the engine out of gas... reading the plugs or watching an O2 sensor will allow you to see if you have a "lean out"...which can be a combination of vacc. advance (too much at that moment), and not enough gas (it is lighting the fire early and you might be "shooting ducks", get a rough feel from the engine....) Either way you need to find out which way it goes and rememdy it before a piston top gets too hot or a plug gets melted. Good Luck, -D.Idiot

Author:	RossKinder [ Sun Nov 22, 2009 9:12 pm ]
Post subject:
Quote: What is floating around in the fuel bowl? I'll check it out. Thanks

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Author:	RossKinder [ Sun Nov 22, 2009 9:14 pm ]
Post subject:
Quote: Disconnect the vacuum line to the distributer, and plug it. Now do a road test. If that cures the problem, you might have too much advance, or the points not set correctly. Set the points with a dwell meter, and then reset the timing. If that doesn't cure the problem, check the carb. I love how-to's! Thanks

Author:	RossKinder [ Sun Nov 22, 2009 9:22 pm ]
Post subject:	Re: Dashpot...
Quote: Does your carb have a dashpot? It's a little vaccuum solenoid for manual trannies that hold the throttle plates open and slowly closes them when you let off the gas... A couple of situations can be occurring here: 1) The plates are closed enough to be in the transition slot and not have the main metering one line...if you have enough rpm and advance going and you let off, you may not have enough gas to cover the advance/load/ and minimal gas the idle/transition circuit gives (retuning, richening the idle/transition circuit... or a hihg rear gear ratio that will put your "cruise" rpm at the speed you are trying to keep up with. 2) Check by driving with a vacc. gauge hooked to a vacc. source under the throttle plates or worst case scenario off the #6 runner.... when you let off the gas if the vacc. is high, and load is high it will starve the engine out of gas... reading the plugs or watching an O2 sensor will allow you to see if you have a "lean out"...which can be a combination of vacc. advance (too much at that moment), and not enough gas (it is lighting the fire early and you might be "shooting ducks", get a rough feel from the engine....) Either way you need to find out which way it goes and rememdy it before a piston top gets too hot or a plug gets melted. Good Luck, -D.Idiot Thanks. I'm going to try reading this one after I get some sleep. I _may_ be able to grasp it then. RK

Author:	RossKinder [ Tue Nov 24, 2009 2:30 pm ]
Post subject:
Quote: Sounds like a fuel problem. What is floating around in the fuel bowl? Water? old gas? You may want to take peak and see what is in there. If you have a 1920 Holley on yours you can cut down a red plastic Folger's coffee can to slide under the bowl to catch the old fuel and debris. It is amazing what you find, like chunks of old rubber fuel line......the new fuel really does a number on old rubber. As you replace the fuel lines, use fuel injection hose 30R9. The carb is Carter BBS. I found over an eighth of an inch of extremely fine sediment settled and hardened in the bottoms of the float chamber. I got into it today after having a hard time starting and finding gas all over the top of the manifold. ALL the hold down nolts and screws had worked a little loose. When I stopped at home I checked with a light and gas was bubbling out around the throttle shaft! I tightened the screws and bolts and now no more gas all over. But it was still trying to kill almost as bad as it did on the road today. I thought sinking float. But the float is dry and the gas level stops just below the gas inlet needle. That looks about right at a strong 3/8 inch below the top of the bowl, but is there some setting to use other than what came with the carb kit a couple years ago? It may be a fluke about the loose bolts. It may be that the rest of the problem is electrical. Anybody got further ideas? RK

Author:	'74 Sport [ Wed Nov 25, 2009 12:31 pm ]
Post subject:
Loose base gasket and worn shaft bushings... hmmm. Vacuum leaks wreak havoc on how they drive.

Author:	Aggressive Ted [ Wed Nov 25, 2009 1:22 pm ]
Post subject:
Ross, Under steady acceleration your getting a richer mix, and when you back off it is going lean. Any kind of a vacuum leak will up set the balance of the mixture and make it run rough. If it feels good under acceleration I wouldn't think it is electrical. Another item to check would be to test your vacuum advance on the distributor to see if it is leaking.

Author:	RossKinder [ Wed Nov 25, 2009 9:35 pm ]
Post subject:
Quote: Loose base gasket and worn shaft bushings... hmmm. Vacuum leaks wreak havoc on how they drive. Thanks, but why would I be getting liquid gasoline bubbling out around the shaft for a minute or more after shutting off the engine?

Author:	dakight [ Thu Nov 26, 2009 5:19 am ]
Post subject:
Somehow you're getting raw fuel spilling onto the throttle plate while it's closed; some of it seeps out past the throttle shaft. Perhaps a leaky needle and seat. It sounds like the carb needs to be rebuilt and the throttle shaft bushed. You also need to address the source of the sediment. If the car sat for an extended period with fuel in the tank it could well have a rusty fuel tank.

Author:	Aggressive Ted [ Thu Nov 26, 2009 9:33 am ]
Post subject:
Ross, Quote: Thanks, but why would I be getting liquid gasoline bubbling out around the shaft for a minute or more after shutting off the engine? The needle and seat aren't sealing against the pressure in the fuel line. The metal fuel line gets hot and boils the fuel causing it to expand. If there is some fine muck or rusty particles on the seat, it will not seal off the expanding fuel. After a few minutes the carb starts to percolate like a coffee pot. Dan's fuel line mod helps to keep the fuel from boiling. It may take some pressure of the needle and seat after shut off. You need a really good filter down to the 2 micron level to filter out the debris and a new needle and seat. Your fuel pump and line back to the tank and the tank itself are probably contaminated. On mine the inside of the metal fuel line was rusting. A good filter will help capture the small particles and get you buy until your able to clean or replace your fuel system.

Author:	Kevin Johnson [ Sun Nov 29, 2009 4:54 am ]
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Author:	RossKinder [ Sun Nov 29, 2009 7:30 pm ]
Post subject:
Quote: A proportion (most?) of the sediment is likely to be fuel additives that drop out of solution as the car sits for an extended period of time and the fuel ages and evaporates. These can be extremely difficult nigh impossible to resolubalize so they must be cleaned out manually. Makes sense to me. It was really, really fine and almost chocolate colored. It was pretty hard too and I dug it out with a stick. I could barely dig it with a finger nail.