Carb Rebuild Questions

All,

I've been having intermittent stalling issues and my carb really looked like the ethanol gas was getting the best of it. It looked all black in the inside, so I decided to rebuild my carb, bought this rebuild kit from Summit:

http://www.summitracing.com/parts/HLY-37-485

I hooked up the vacuum gauge that I just bought before I removed the carb. Once the engine was warmed up the needle was pretty steady on 16.

Once I removed the carb and took it apart, I noticed that there was no power valve in the secondary metering block, only in the primary. My jets are 31 in the primary and 28 in the secondary. I also noticed that almost all of the bolts holding my intake were very loose.

Questions:

1) Is 16 a good vacuum reading?

2) Could the loose bolts on the intake cause my stalling issues?

3) Should I replace my jets?

4) Is 31 and 28 jetting a good combo? I never really felt like the car had the power it should have. Could be the 2.91 gearing in the rear end.

5) My old power valve looks like it has a 5 stamped on it. The kit came with two 6.5s and a 10.5. Should I use the 6.5 or the 10.5?

All the metal parts are soaking in carb cleaner overnight. This is my first carb rebuild so any advise would be really appreciated. Thanks to all. Here are a few pictures:

1. 16 in/hg sounds fine but at what RPM?

2. As MotoArts said any leak can cause problems. It would be interesting to see if the idle speed and vacuum drop when the intake is tightened down (vacuum leak).

4. and 5. What I believe you think are jets (pic. #5) are actually accelerator pump discharge nozzles. The jets are shown in pictures 2 and 3. If the timing is set right and the engine has 16 in/hg at a normal idle speed an 8.5 should be about right.

From the Holley site, original calibration for LIST 4777-5; Jets, 67 pri., 73 sec.. .028 nozzles front and rear. 6.5 power valve.

The car may have had a hesitation off idle and someone changed the pri. nozzle trying to increase the initial pump shot.

Given the carbon in the choke and venturi area, the car is back firing through the intake. I'd start looking at the timing and make sure the intake is properly torqued.

Let us know what you find out. Chuck

Click to expand...

I didn't think of that.

Yes, your main jets are in the 2nd and 3rd pics. They are the round things with the small holes in the center at the bottom of the metering blocks. There are 2 per block. Numbers will be stamped on the sides.

Click to expand...

Your jet sizes sound way to small...you're not referring to your accelerator pump squirters are you?

I believe the black soot has nothing to do with ethanol, you have other issues! Reversion, bent or non fully seating intake valves, mis-timed, jumped timing chain, loose intake? Not necessarily in that order. Probably other things could cause it as well..... I believe that somehow or another you are getting combusted gases reverting....straight gas would not leave the soot IMHO.

Click to expand...

I didn't think of that.

Yes, your main jets are in the 2nd and 3rd pics. They are the round things with the small holes in the center at the bottom of the metering blocks. There are 2 per block. Numbers will be stamped on the sides.

Click to expand...

Thanks Moto... yes I'm showing my ignorance. As I said, this is my first go around rebuilding a carb. I thought the squirters were the jets. The 31 and 28 are the number that are stamped on the squirters. I'll pull the main jets tonight and let you know what numbers they are.

My car is a 4 speed top loader.

Your jet sizes sound way to small...you're not referring to your accelerator pump squirters are you?

I believe the black soot has nothing to do with ethanol, you have other issues! Reversion, bent or non fully seating intake valves, mis-timed, jumped timing chain, loose intake? Not necessarily in that order. Probably other things could cause it as well..... I believe that somehow or another you are getting combusted gases reverting....straight gas would not leave the soot IMHO.

Click to expand...

Thanks csgt428,

I'll have to do some research on reversion. Hopefully doing this rebuild will help or fix the problem. I was referring to the numbers stamped on the squirters, not the jets (see the last picture I posted). I'm going to check that tonight. Thanks again.


1. 16 in/hg sounds fine but at what RPM?

2. As MotoArts said any leak can cause problems. It would be interesting to see if the idle speed and vacuum drop when the intake is tightened down (vacuum leak).

4. and 5. What I believe you think are jets (pic. #5) are actually accelerator pump discharge nozzles. The jets are shown in pictures 2 and 3. If the timing is set right and the engine has 16 in/hg at a normal idle speed an 8.5 should be about right.

From the Holley site, original calibration for LIST 4777-5; Jets, 67 pri., 73 sec.. .028 nozzles front and rear. 6.5 power valve.

The car may have had a hesitation off idle and someone changed the pri. nozzle trying to increase the initial pump shot.

Given the carbon in the choke and venturi area, the car is back firing through the intake. I'd start looking at the timing and make sure the intake is properly torqued.

Let us know what you find out. Chuck

Thanks Chuck,

I'll check the jets tonight and report back. I don't have a tach, when I did it used to idle at around 900 rpm. I'm hoping that tighening down the intake will fix the stalling problem. The car did back fire occasionally, but not very often. I took it to a local speed shop prior to driving to Charlotte for the 50th and they "advanced" the timing a bit to make it run better? Actually that is when the "stalling" issue started. Can I find the torque specs for the intake in my shop manuals?

Thanks again... Pete

Click to expand...

I didn't think of that.

Yes, your main jets are in the 2nd and 3rd pics. They are the round things with the small holes in the center at the bottom of the metering blocks. There are 2 per block. Numbers will be stamped on the sides.

Click to expand...

Thanks Moto... yes I'm showing my ignorance. As I said, this is my first go around rebuilding a carb. I thought the squirters were the jets. The 31 and 28 are the number that are stamped on the squirters. I'll pull the main jets tonight and let you know what numbers they are.

My car is a 4 speed top loader.

Your jet sizes sound way to small...you're not referring to your accelerator pump squirters are you?

I believe the black soot has nothing to do with ethanol, you have other issues! Reversion, bent or non fully seating intake valves, mis-timed, jumped timing chain, loose intake? Not necessarily in that order. Probably other things could cause it as well..... I believe that somehow or another you are getting combusted gases reverting....straight gas would not leave the soot IMHO.

Click to expand...

Thanks csgt428,

I'll have to do some research on reversion. Hopefully doing this rebuild will help or fix the problem. I was referring to the numbers stamped on the squirters, not the jets (see the last picture I posted). I'm going to check that tonight. Thanks again.


1. 16 in/hg sounds fine but at what RPM?

2. As MotoArts said any leak can cause problems. It would be interesting to see if the idle speed and vacuum drop when the intake is tightened down (vacuum leak).

4. and 5. What I believe you think are jets (pic. #5) are actually accelerator pump discharge nozzles. The jets are shown in pictures 2 and 3. If the timing is set right and the engine has 16 in/hg at a normal idle speed an 8.5 should be about right.

From the Holley site, original calibration for LIST 4777-5; Jets, 67 pri., 73 sec.. .028 nozzles front and rear. 6.5 power valve.

The car may have had a hesitation off idle and someone changed the pri. nozzle trying to increase the initial pump shot.

Given the carbon in the choke and venturi area, the car is back firing through the intake. I'd start looking at the timing and make sure the intake is properly torqued.

Let us know what you find out. Chuck

Thanks Chuck,

I'll check the jets tonight and report back. I don't have a tach, when I did it used to idle at around 900 rpm. I'm hoping that tighening down the intake will fix the stalling problem. The car did back fire occasionally, but not very often. I took it to a local speed shop prior to driving to Charlotte for the 50th and they "advanced" the timing a bit to make it run better? Actually that is when the "stalling" issue started. Can I find the torque specs for the intake in my shop manuals?

Thanks again... Pete

Click to expand...

Click to expand...

I can't tell which cams they are but they are probably fine. I like DP carbs however, if it really has a 2.91, or anything close, rear gear the DP is not going to like it. That may be causing the backfire through the intake. Going WOT at lowish RPM with that gear and a DP creates a large "hole" if you will. It also sounds like someone jetted the primary side down in an attempt to make it idle. Let us know what you end up doing. Chuck

Click to expand...

I can't tell which cams they are but they are probably fine. I like DP carbs however, if it really has a 2.91, or anything close, rear gear the DP is not going to like it. That may be causing the backfire through the intake. Going WOT at lowish RPM with that gear and a DP creates a large "hole" if you will. It also sounds like someone jetted the primary side down in an attempt to make it idle. Let us know what you end up doing. Chuck

Click to expand...

Hey Chuck,

Sounds like you may be suggesting that this combo of carb and rear gear ratio don't/won't work together. I've always thought that this car with this engine/tranny combo should "feel" like it had a lot more power. I've thought about going upto a 3.25 or 3.50 rear. I'm thinking that could make a big difference in the power delivery. What do you think?

Click to expand...

I can't tell which cams they are but they are probably fine. I like DP carbs however, if it really has a 2.91, or anything close, rear gear the DP is not going to like it. That may be causing the backfire through the intake. Going WOT at lowish RPM with that gear and a DP creates a large "hole" if you will. It also sounds like someone jetted the primary side down in an attempt to make it idle. Let us know what you end up doing. Chuck

Click to expand...

Hey Chuck,

Sounds like you may be suggesting that this combo of carb and rear gear ratio don't/won't work together. I've always thought that this car with this engine/tranny combo should "feel" like it had a lot more power. I've thought about going upto a 3.25 or 3.50 rear. I'm thinking that could make a big difference in the power delivery. What do you think?

Click to expand...

Some more gear would help acceleration. It depends on what you expect from the car. Have you confirmed the gear ratio? Chuck

Click to expand...

It will help if there is something wrong (fouled, worn, wrong gap, wrong heat range) with the ones now installed. I would at least pull a couple to check condition and correctness. Chuck

Click to expand...

Hello,

Here is a chart comparing different plugs in different condition

http://www.mudinmyblood.net/forum/view.php?pg=sprkplgchrt

After a while, you need to tight the two bowls, I noticed after the rebuilt of my carb that I could tight the 4 screws on each bowl. No need to be tight too much to avoid any damage? Just enough.

Click to expand...

Hello,

Here is a chart comparing different plugs in different condition

http://www.mudinmyblood.net/forum/view.php?pg=sprkplgchrt

After a while, you need to tight the two bowls, I noticed after the rebuilt of my carb that I could tight the 4 screws on each bowl. No need to be tight too much to avoid any damage? Just enough.

Click to expand...