Need carb assistance

[jj72]

I have a 72 Bronco that has a Holley 2V mechanical choke carb. I rebuilt the carb using a rebuild kit (gaskets and all the other parts that come with the kit). The problem I have is that when it starts up it idles fine. I pull the choke to start and then open once it starts.

When start driving it and putting it under any kind of load, it wants to stumble some or some times when I come to a stop it will die altogether.

I have replaced the mechanical fuel pump over the last couple of years, but was needing to know the most likely culprit when it came to this issue.

 

[SteveL]

If you want to keep the 2v get a stock 2100 and dump the Holley. Unless you're really into playing with carbs it's hard to keep a Holley running right.

 

[jckkys]

The power valve may not be one with a high enough rating in inches of Hg vacuum. Do you know what power valve you have? 6.5" is the most common for street engines at sea level. The power valve enriches the mixture when the engine is under a load. Do you have a vacuum gauge, so you can see at what vacuum reading the engine stumbles? If your rebuild kit included the current power valve and the stumble only happened after installing it, you may want to reinstall the previous valve to see if the stumble goes away.

 

[ugly74]

A stumble right off of idle, is most likely related to the accelerator pump. Look down into the carb, and at the top of the venturis, there are two little squirters (actually it’s one piece, but it discharges to both sides). The instant you move the throttle, fuel should be coming out of those.
Check that.
Holleys are great! I have one on a dodge 360 that hasn’t been touched since the late 80s, and it’s fine.

 

[ugly74]

That being said, gotta give credit where it’s due... the autolite/motorcraft 2v is tough to beat for driveability

 

[jckkys]

The OP stated the stumble occurs when the engine is under load. That's not the common off idle stumble. A better description of the symptoms would be helpful.

 

[ugly74]

Oh whoops. My reading comprehension has slipped. I blame Coronas

 

[ugly74]

Where is your float level set?
It could very well be a crappy power valve

 

[jj72]

To ugly74's question: I set the float to level when the carb was off the manifold and upside down.

To jckkys's question: are the power valves marked so you know what size you have? Do you measure it?

One other thing I failed to mention was that when the engine was idling but still cold, it wanted to stumble or bog when you gave it throttle, but once it was warmed up it would take some throttle much more easily.

Thanks all for suggestions present and future.

 

[SHX669]

Try setting your float level without taking it off the manifold .

 

[jckkys]

Holleys have a sight plug in the side of the float bowl, to set the fuel level with the engine running. The power valves are stamped in one of the flats. A 6.5" Hg power valve would be stamped 65. That is the most recommended power valve for use at sea level.

 

[1970 Palmer]

I agree with checking the power valve. Make sure the accelerator discharge nozzles are working, and your have the initial timing set correctly.

But, if the Holley has cork gaskets on each side of the metering block don't let them dry out. They shrink up very quickly. Just dump the carb upside down, pour the gas out of the vent into a aluminum pie pan. Then lay the cork gaskets in the fuel filled pan while your working on the power valve. When you put it back together, the original used gaskets will fit just fine if they have stayed wet in the fuel.

As others have already stated, you set the float level with the engine running and view through the side site hole. 5/8" box end and a flat blade screw driver. It takes about 30 seconds.

 

[ugly74]

I usually set my floats so their just a touch under the sight plug.

Ya know, I’ve never had a holley gasket do more than seep a little bit over the years, but Its rare to see one fail. At least for me. The bitch about the stock ones is cleaning them off!

 

[1970 Palmer]

One more thing to check when you have the front metering block off is that the main body is still flat. What happens is the bowel mounting screws get "over tightened" by previous owners and warp the main body. When the Holley main body gets warped the accelerator fuel path squirts back into the carb and not completely out of the discharge nozzle. Just lay a straight across the main body float bowel screw holes and make sure the flat edge touches the small accelerator port in the center of the body. Back in the 60-70's this was a common issue and the fix was to knock the highs off with a nice flat sharp body file.

 

[jckkys]

Dido. Most Holley performance builds include milling the main body/metering body gasket surface.

 

[oldiron]

To ugly74's question: I set the float to level when the carb was off the manifold and upside down.

To jckkys's question: are the power valves marked so you know what size you have? Do you measure it?

One other thing I failed to mention was that when the engine was idling but still cold, it wanted to stumble or bog when you gave it throttle, but once it was warmed up it would take some throttle much more easily.

Thanks all for suggestions present and future.

This ^^^ warm bog versus cold is a CLASSIC example of an incorrect or blown power valve.
Greg

 

[jckkys]

A couple more things. A blown power valve will cause a super rich idle, killing the engine. An engine that dies when the throttle is opened is usually an accelerator circuit problem. This is easily diagnosed by looking down the venturis for fuel squirting from the nozzles with the slightest movement of the throttle. If there is movement with no fuel, start looking for the reason. First check for any play in the linkage. Then look for the check needle under the pump discharge nozzle. These are often misplaced during a rebuild.