Distributor curve problem ?

[Ralph]

I have a 73 340 with a performance rebuild and auto.
No matter what I do the car is burning rich - I can smell it.
I have had a couple of distributors and it gets a little better but not there.

The distributor is set at 16 to 18 degrees initial and stops at 34 degrees at 3200 rpm and it runs good. Not using a vacuum it will not take the advance either ported or constant.
Maybe its not a distributor problem, the carb is a 650 AVS2, I tryed leaning it out and it got a little better but with no power. So I put it back.

I crossed over the ballast resister for a higher volts at the coil per FBBO kit.
What am I missing here. The builder wanted 14 degrees at 700, 27 dergrees at 3000 and 29 all in at 4000 rpm - so he wanted a slow curve - is that why I am too rich too much curve ?
Any help would be appreciated.
Thanks Ralph

 

[gzig5]

Interested in what you find out. I have about the same setup and it is stinky cruising down the road but I was thinking it was exhaust leaking into the cabin through all the holes and no carpet at the moment. 340, 650 AVS2, FBO ingnition, 15 initial, 35 total, vacuum advance is disconnected. I would bet that most carbs come out of the box on the rich side. I haven't touched the carb yet, but the last time I looked at the plugs, they didn't look too rich. Really need to look at the plugs to know if it's rich or the timing is right.

 

[Ralph]

Funny that you said that about the plugs - haven't driven it much but they look good and i have a full new exhaust to the rear. The 650 AS2 is not a big carb for the motor with a .504 lift and duration at .05 at 224 and I bet is just timing. Need to get this right soon as I am not enjoying the ride.
Are you using a mechanical distributor or vacuum advance ?
Thanks

 

[gzig5]

Stock 73 electronic distributor with the FBO plate in it. I think I have medium springs or one heavy one light, been a while. Mechanical is all in at around 3000-3200. My vacuum can didn't seem to work right so I plugged the hose. I'm wondering if the extra vacuum timing at cruise would help??

 

[Ralph]

I think you may be right - will try a mechanical distributor next per the engine builder. If not go back to the stock unit.
I will let you know what works eventually.

 

[moparleo]

Hook that vacuum advance back up. Guess what it controls ?? That's right, quicker advance at lower rpm's. Vacuum advance is used on all street applications. Mechanical advance only is for constant high rpm's like foot to the floor driving, like racing where the engine stays at high rpm all the time. Read the complete following article. It is one of many out there.
Bolt-On Hop-Ups
Mechanical Advance Vs. Vacuum Advance

 

[Adam]

I have a 73 340 with a performance rebuild and auto.
No matter what I do the car is burning rich - I can smell it.
I have had a couple of distributors and it gets a little better but not there.

The distributor is set at 16 to 18 degrees initial and stops at 34 degrees at 3200 rpm and it runs good. Not using a vacuum it will not take the advance either ported or constant.
Maybe its not a distributor problem, the carb is a 650 AVS2, I tryed leaning it out and it got a little better but with no power. So I put it back.

I crossed over the ballast resister for a higher volts at the coil per FBBO kit.
What am I missing here. The builder wanted 14 degrees at 700, 27 dergrees at 3000 and 29 all in at 4000 rpm - so he wanted a slow curve - is that why I am too rich too much curve ?
Any help would be appreciated.
Thanks Ralph

Why does your builder recommend such a slow curve and only 29 degrees advance? Unless you have an unusual build I think you should set the timing at 34 degrees all in, by 2500 rpm, with vacuum advance disconnected, then hook it back up after the timing is set.

Also, I have never touched a AVS2 carb, but I have rebuilt and tinkered with the original AVS (Air Venturi Secondary). The secondary opening was adjusted by tightening or loosening a screw that secured a clock type spring. If too loose the secondaries would partially open when cruising around; too tight and you got late or never opening secondaries. So all that to say, check that your secondaries aren’t opening prematurely, which would cause a rich condition while driving, but not at idle.

Too rich at idle also? I would check needle & seat adjustment. Lastly, put a gauge on your fuel line and see how much pressure your fuel pump is putting out. Anything over 7 1/2 can overpower the needle and seat causing a rich idle, even with the screws turned all the way in.

 

[Ralph]

Not sure why the engine builder stated that in writing - could he have advanced the timing when building. Carolina machines engines built it and he likes a mechanical distributor.
I have a fuel guage set at 5 psi.
I tryed adjusting the secondaries and that did not help secondaries opened up to late.
How do you check needle and seat adjustment or is that just the idle screws. About 1/2 turn out now
I have a FBO distributor setup with initial advance now at 18 degrees when i plug in the vacuum advance (12 degrees at 16 ") at constant as he suggested it backfires or runs rough - like 30 degrees at idle then 16 degrees mechanical at 3200. The engine runs great without the vacuum advance but smells of unburnt gas.

 

[Adam]

Ask your engine builder if he installed the cam straight up, advanced, or retarded, and why he recommends the slow timing curve and limited advance.

For others that may read this thread: I have two FBO distributors and I like them very much. Here is how I time mine: Using a timing light with an advance dial on the back I set the dial to 34 degrees and screw in the idle stop screw until the engine is steady about 2500 rpm. I then twist the distributor until the timing mark lines up at TDC (without vac line hooked up). I tighten the distributor down and confirm the timing did not change, and no more mechanical advance occurs above 2500 rpm. Then I screw the idle stop screw out to set my idle at an acceptable rpm. Lastly I hook up the dist vacuum line. That’s all; I am not even concerned with the initial timing at idle. My engines start easily and respond very well to this. If your cam is straight up and your engine does not like this I would check your distributor is not installed one tooth off; and confirm TDC on your balancer is accurate. (This is easy and quick to do).

I do not know how to set the float level on an AVS2, but they are NOT the same as the idle mixture screws, if present (I think that carb uses metering rods). I am sure someone here will help out.

 

[Ralph]

Thanks great approach to timing.

 

[John Rimel]

Ask your engine builder if he installed the cam straight up, advanced, or retarded, and why he recommends the slow timing curve and limited advance.

For others that may read this thread: I have two FBO distributors and I like them very much. Here is how I time mine: Using a timing light with an advance dial on the back I set the dial to 34 degrees and screw in the idle stop screw until the engine is steady about 2500 rpm. I then twist the distributor until the timing mark lines up at TDC (without vac line hooked up). I tighten the distributor down and confirm the timing did not change, and no more mechanical advance occurs above 2500 rpm. Then I screw the idle stop screw out to set my idle at an acceptable rpm. Lastly I hook up the dist vacuum line. That’s all; I am not even concerned with the initial timing at idle. My engines start easily and respond very well to this. If your cam is straight up and your engine does not like this I would check your distributor is not installed one tooth off; and confirm TDC on your balancer is accurate. (This is easy and quick to do).

I do not know how to set the float level on an AVS2, but they are NOT the same as the idle mixture screws, if present (I think that carb uses metering rods). I am sure someone here will help out.

one tooth off?

 

[Ralph]

Yep, will look into this as well and advise.
Thanks much