[Siggy_Freud]

Howdy all,

I rebuilt the Holley 1850-2 this weekend. Was my first carb rebuild. All pretty straight forward and went smooth except for a few issues.

After we put it on, we noticed the rear bowl was leaking fuel from the brass plug where a second fuel line might go if it was a dual feed setup. Was just a drop at a time, but then I pressed on it a bit and fuel came pouring out. I found a few others online who had this issue. I cleaned up the plug, wire brushed it, and JB Welded over it. No leaks so far.

I also went from #66 Primary Jets to #62. Runs great, except at about 60 mph on an incline, it surges some. It also has a slight bog (no lean pop though) when I punch the gas, but then picks up and pulls (well, pulls as much as the 307 can lol).

My idle vacuum in drive is around 12-13. The power valve that came in the rebuild kit is a 6.5. Should I go up to the 9.5 power vavle? Isn't the idea idle vacuum - 2 to get to the proper power valve size?

I'm thinking that and going to a #64 Primary jet might help a bit.

Thoughts?

[T-bucket23]

Originally Posted by Siggy_Freud

Howdy all,

I rebuilt the Holley 1850-2 this weekend. Was my first carb rebuild. All pretty straight forward and went smooth except for a few issues.

After we put it on, we noticed the rear bowl was leaking fuel from the brass plug where a second fuel line might go if it was a dual feed setup. Was just a drop at a time, but then I pressed on it a bit and fuel came pouring out. I found a few others online who had this issue. I cleaned up the plug, wire brushed it, and JB Welded over it. No leaks so far.

I also went from #66 Primary Jets to #62. Runs great, except at about 60 mph on an incline, it surges some. It also has a slight bog (no lean pop though) when I punch the gas, but then picks up and pulls (well, pulls as much as the 307 can lol).

My idle vacuum in drive is around 12-13. The power valve that came in the rebuild kit is a 6.5. Should I go up to the 9.5 power vavle? Isn't the idea idle vacuum - 2 to get to the proper power valve size?

I'm thinking that and going to a #64 Primary jet might help a bit.

Thoughts?

If this is a relatively mild cam I would check for vacuum leaks. That vacuum at idle is way low for a stock engine. should be 18-20

[Siggy_Freud]

Its 17 at idle in park, and 12-13 at idle in drive.

[Richiehd]

Originally Posted by Siggy_Freud

Its 17 at idle in park, and 12-13 at idle in drive.

You go by idle in Park, or neutral. You didnt say what cam you had. The 6.5 power valve is probably ok but 4 steps down on the jets is a big jump. Why did you go smaller? Did you read the plugs? or was it rich before? I would go at least to the #64 and possibly back to the #66

[engineczar]

The stock jetting on that carb calls for a 66. I would go back to that size. Generally the stock sizes are pretty close. Rarely do they ever need more than one or two sizes from what Holley puts in them from the factory.

[cobalt327]

The power valve rating is about 1/2 of the idle vacuum IN GEAR if it's an automatic, neutral if it's a stick. For your 12-13 in/Hg vacuum in gear, the 6.5 PV is perfect.

Why did you change the jetting 4 numbers? I, too, would go back to the stock jetting. Baseline it, then start playing around w/more or less jetting. You'll need to run it at the track to know whether you're making a change in performance for the better or not. If economy is your main concern instead of performance, you can go by the seat of your pants along w/the color of the plugs. But just dropping 4 numbers for no reason isn't how it's done.

In any event, I suspect the stock jetting will be closer to correct than 4 numbers smaller than stock.

The bog when you punch it could be accelerator pump-related or the secondaries opening too soon.

Is the timing curve sorted out correctly?

[Siggy_Freud]

I jetted down because the plugs were reading rich. I didn't go down 4 holley sizes, just two, as they come only in even numbers.

From what I've read online, Holley recommends that you check your idle vacuum while in gear, and then take two off that number for your power valve size. That way, its activating quickly on part-throttle acceleration.

I realize the stock jetting is 66, but this carb is already "big" for a 307 I figured.

I switched to a 64 and an 8.5 power valve, and so far it's much better.

[cobalt327]

Originally Posted by Siggy_Freud

I jetted down because the plugs were reading rich. I didn't go down 4 holley sizes, just two, as they come only in even numbers.

If the plugs were looking “rich”, are you sure that’s not from oil coming into the combustion chamber from the guides, rings, PVC system, intake gasket leaks, etc.?

Gasoline main JETS are available in even AND odd numbers. The numbers do not necessarily equate to the orifice size in thousandths of an inch, either. You went down 4 numbers and IMO that was too far- that's the MAIN point.

From what I've read online, Holley recommends that you check your idle vacuum while in gear, and then take two off that number for your power valve size. That way, its activating quickly on part-throttle acceleration.

The 6.5 PV is the correct part for your idle vacuum in gear.

While Holley has posted somewhat conflicting info regarding PV sizing, the "couple numbers less than idle vac. in gear" is not usually what is used for a mild street engine such as yours. The reason you wouldn't necessarily want the 8.5 PV in there, is because you're getting enrichment almost every time you accelerate- remember, the PV opens at the vacuum rating, so each time the carb "sees" 8.5 in/Hg or less, it's at full enrichment.

Yet another way to size the PV if you don’t want to use the common “1/2 the idle vacuum in gear”, is to mount a vacuum gauge that can be safely seen while you drive under various conditions and select the PV number by going w/a PV 2 in/Hg below the lowest steady speed engine vacuum observed.

I realize the stock jetting is 66, but this carb is already "big" for a 307 I figured.

I switched to a 64 and an 8.5 power valve, and so far it's much better.

The jetting change is what’s likely making the improvement. If you thought the 600 was "large" for your 307, the 8.5 PV makes it even "larger" from an air/fuel ratio standpoint.

[Siggy_Freud]

Thanks for the info. I'll try the 6.5 PV again and see how that "feels".