Edelbrock 650 Thunder AVS Carburetor

tx65coupe · Dec 29, 2010

My 65 is still running a little rich. It has an Edelbrock 650 Thunder AVS carb model number 1806. Its enough so that I get fuel residue on the outside of the exhaust tips and the bumper gaurds. The car runs really well though.

After I go somewhere I can wipe my finger inside the tail pipe and my finger is damp and sooty. There is raw fuel inside the tail pipe. I went on a 20 mile drive to my friends house and after I got there we did this test and got the same results. It was a warm day too.

I've never had a car leave fuel residue on the bumper gaurds before.

The exhaust always smells rich even when its hot outside and the car is warmed up. Alot of people comment that the fumes are too strong. You can't stand anywhere near the rear of the car while its running for more than a minute or your eyes will burn.

I have looked at the plugs and they look fine.

I have also checked the choke multiple times and it is working properly.

Fuel pressure is 6 psi.

Here is a quick question. How long should it take the fuel pressure to bleed down after the engine is turned off?

I got this calibration kit. I think the jets need to be downsized a step. What size comes in it out of the box? Does anyone have any tips or advice for me?

Edelbrock 1840 - Edelbrock Thunder Series AVS Carburetor Calibration Kits - Overview - SummitRacing.com

woodsnake · Dec 29, 2010

Water is a by product of combustion, in a well tuned engine. A 650 should not be too much fuel for your combo listed in your sig below. If you have a performance cam, at idle, you will have unburned fuel due to the cam profile. How do the spark plugs look? Did you tune the engine with a vacuum gauge?

tx65coupe · Dec 29, 2010

I didn't think a 650 would be too big either.

I did not tune it with a vacuum gauge. I'm not even sure how to do that.

The spark plugs look normal. They don't show signs of things being rich or lean.

The exhaust fumes are pretty strong at times. It just seems a little excessive to me. I've been around alot of other friends classic cars and hot rods etc, and they don't seem as bad.

It seems weird to me that there is residue from the unburned fuel on the outside of the exhaust tips and on the bumper gaurds as well as even some on the bottom of the rear bumper and the reverse lights.

How much does one jet size effectively change things?

tx65coupe · Dec 29, 2010

I was thinking about getting this Edelbrock 6593 air fuel ratio tool. I just realized that the instructions want it to be installed in the car. I would rather use it as a temporary diagnostic setup. I wonder if it can be used that way.

Edelbrock 6593 - Edelbrock Air/Fuel Ratio Monitors - Overview - SummitRacing.com

NY-67stang · Dec 29, 2010

tx65coupe said:
I didn't think a 650 would be too big either.

I did not tune it with a vacuum gauge. I'm not even sure how to do that.

The spark plugs look normal. They don't show signs of things being rich or lean.

The exhaust fumes are pretty strong at times. It just seems a little excessive to me. I've been around alot of other friends classic cars and hot rods etc, and they don't seem as bad.

It seems weird to me that there is residue from the unburned fuel on the outside of the exhaust tips and on the bumper gaurds as well as even some on the bottom of the rear bumper and the reverse lights.

How much does one jet size effectively change things?

If your smelling fuel at idle but your plugs look fine then you need to look at the idle circuit first.
What is your vacuum and RPM at idle?

There are step-up springs that are used to hold the metering rods down into the primary jets at idle. You can get different springs for different vacuum levels they are in the kit. Try a weaker spring. They are very easy to change.

At idle, the rods are held down and the fuel rate is primarily controlled by your idle screws. I have a very low vacuum at idle (5" in drive) so I had put in a weaker spring (4"). The stock stronger spring was overcoming my vacuum and lifting the metering rods at idle causing it to be too rich but during cruise and power mode it was fine. Usually you will have little control with the idle screws if this happens.
You could also check your float level adjustment, but you have to remove the top of the carb to do that.

woodsnake · Dec 29, 2010

Unless the plugs are showing signs of running rich, I wouldn't worry about changing the rods in your carb. I'd buy a vacuum guage before the AF tool you linked to. All you do, is connect the hose for the VG somewhere that has intake manifold vacuum, and then adjust the two screws on the front of the carb, so that you get the highest number of inches of vacuum at idle. Proven technique for working on carburetted automobiles.

tx65coupe · Dec 30, 2010

Thanks for the input guys. I'll have to check the vacuum and see what it is. I think we still have a vacuum gauge. It idles at about 800-850 RPM. I did check and slightly adjust the floats a short while back.

dbfarr · Jan 6, 2011

I have that carb, had that problem. Used to foul out plugs like no tomorrow.

Replaced the Duraspark with an MSD 6 box, no more problems. Doesn't hurt that I have a 200 amp alternator.

Not necessarily your problem, still I used to mess with that carb all the time. Ask Woodsnake, he knows.

PoppyMod · Jan 7, 2011

tx65coupe said:
I was thinking about getting this Edelbrock 6593 air fuel ratio tool. I just realized that the instructions want it to be installed in the car. I would rather use it as a temporary diagnostic setup. I wonder if it can be used that way.

Edelbrock 6593 - Edelbrock Air/Fuel Ratio Monitors - Overview - SummitRacing.com

Hi,
In addition to the savvy advice offered by Woodsnake, if you are serious about an AFR gauge, buy a wide-band unit, like an LM-1 (Innovate) or similar. You then need an O2 sensor bung just after the collector about 90 degrees (or slightly less) relative to the ground. This way you can use the gauge for tuning, then remove.
The good AFR gauges are a little expensive, but then the cost can be shared among good friends.
Between the vac and AFR gauges, you don't need much else, to get a good start at carb tuning.
Happy Motoring!

Bullitt · Jan 16, 2011

Did you get the manual with the carb? There are some handy charts in there on jet / rob / spring combos that you might look into.

FYI, I had one of those A/F monitors, next to worthless... Unless you are absolutely steady state on the throttle it's going to jump around. It'll give you an idea if you're rich/lean, but that's really about it.

While I haven't tuned with a wideband before, it's got to be better than 8-10 LEDs...

tx65coupe · Jan 17, 2011

dbfarr said:
I have that carb, had that problem. Used to foul out plugs like no tomorrow.

Replaced the Duraspark with an MSD 6 box, no more problems. Doesn't hurt that I have a 200 amp alternator.

Not necessarily your problem, still I used to mess with that carb all the time. Ask Woodsnake, he knows.

Thats interesting that switching from the Duraspark to the MSD solved your issue. I wouldn't think that it would make that much of a difference.

tx65coupe · Jan 17, 2011

PoppyMod said:
Hi,
In addition to the savvy advice offered by Woodsnake, if you are serious about an AFR gauge, buy a wide-band unit, like an LM-1 (Innovate) or similar. You then need an O2 sensor bung just after the collector about 90 degrees (or slightly less) relative to the ground. This way you can use the gauge for tuning, then remove.
The good AFR gauges are a little expensive, but then the cost can be shared among good friends.
Between the vac and AFR gauges, you don't need much else, to get a good start at carb tuning.
Happy Motoring!

I'm still not sure if I am going to get one. I don't really have the extra cash for that right now.

tx65coupe · Jan 17, 2011

Bullitt said:
Did you get the manual with the carb? There are some handy charts in there on jet / rob / spring combos that you might look into.

FYI, I had one of those A/F monitors, next to worthless... Unless you are absolutely steady state on the throttle it's going to jump around. It'll give you an idea if you're rich/lean, but that's really about it.

While I haven't tuned with a wideband before, it's got to be better than 8-10 LEDs...

I was thinking the same thing about the readout on that tool. I'm not sure how accurate it really is. Now that you have verified that, I doubt I buy that one.

68RCodeConv · Jan 18, 2011

The manual with the carb has nice simple directions for leaning out the carb.

You want to make it REALLY easy then instead of trying different jet/rod combos just look at the rods you have and buy a couple more sets of them that are different sizes. Then all you have to do is change rods.

PoppyMod · Jan 18, 2011

tx65coupe said:
I'm still not sure if I am going to get one. I don't really have the extra cash for that right now.

What you might consider, is have an 02 sensor bung added to your collector and seek the services of a "go fast" shop to have them check your ratios.
In defense of AFR gauges, don't lump all AFR gauges into a single category. AS the good units are wide-band and are much more accurate.
Good Luck!

tx65coupe · Jan 24, 2011

Sorry it took me a while to post back. The vacuum at idle is about 15 psi. Isn't it supposed to be around 20 psi?

PoppyMod · Jan 24, 2011

tx65coupe said:
Sorry it took me a while to post back. The vacuum at idle is about 15 psi. Isn't it supposed to be around 20 psi?

The vac range is about 15-22 HGs. There are a number of things that will influence the reading, such as, cam events (usually lower), valve lash or lifter pre-lod, (too tight), and or manifold leaks. Depending on the severity of the leak, the quality of idle and running will suffer.
So, what is the action of the gauge needle? What do you know about your cam, lash/pre-load settings? As a comparison, I'm running a custom
ground cam, which the grinder stated, I should see 16.9" of vac. at idle. 800-900 RPMs. I'm making 17, or so.
So, are you seeing a steady reading? If not, There is an animated guide for trouble shooting using a Vac gauge on another site, I know of. PM if interested, as the admins here may block the reference link.
keep us posted.

tx65coupe · Jan 24, 2011

The vacuum gauge needle fluctuates a little. I didn't think it was possible to get a steady reading.

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