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Old 01-13-2018, 09:37 AM   #16
overdrivesteve
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Default Re: New 2300 carb questions

Thank you both.

I intend to replace the power valve. The one in there now could be 40 plus years old. And even if it works ok now, I don't expect it will last long once put back into service.

Which brings me to the question ... what power valve do you recommend?
If original, this power valve was originally intended for a 2300 carb in a light duty 2wd pickup with a 304 and automatic transmission. But the carb is going into a Loadstar 4x4 with a 304 and a manual transmission.

Reliability then fuel economy are my number one and two goals with this carb. Gearing is 5 speed direct, 3 speed aux overdrive and 2 speed transfer case. So the truck should be able to travel at any reasonable speed unless I load it down with something heavy.
.

Last edited by overdrivesteve; 01-13-2018 at 09:48 AM..
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Old 01-14-2018, 07:29 PM   #17
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Default Re: New 2300 carb questions

ok everyone,
here's where I really need some advise from everyone who has had experience with Holley carbs.

I was planning on rebuilding the Holley 2300 carb above, IH part number 443269-C91, list number 4308-1. It seems like a simple carb and I have read some books on Holley carbs so I understand their theory of operation from a performance point of view much better than I did a year or two ago.

However theory is not practical experience. My situation is this: I just came across a NOS Holley 2300 carb for sale, IH part number 442-159-C91. At the moment all I know is that it was made for a 345 with exhaust emissions. This carb is new old stock, not re-manufactured.

Being 40 plus years old I know I will need to replace gaskets and seals. And probably replace jets and power valve to make it work properly on my 304. But my thinking is this - mechanically it should be like new otherwise, correct?

And my question is what other changes are there between an exhaust emission carb and a non-exhaust emission carb? How are they different other than jets or power valve differences? Can this carb be tuned to work as well or better than the other carb and be even more dependable because its not worn out? Is there any problem anyone sees in tuning this carb to work really great on a 304 without exhaust emission considerations?

The only differences I see between the two is the throttle plate assembly is different, the jets, power valve, accelerator cam (and possibly the accelerator discharge valve assembly) is different - all interchangeable if necessary for tuning (except for the throttle plate).

So what are your thoughts on using this carb as opposed to the other carb?
Thank you, everyone for your advice.
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Old 01-15-2018, 07:44 AM   #18
farmall57
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Default Re: New 2300 carb questions

The 442159C91 carb should be a List #6379. The Holley book actually shows it for the 304. It shows that it came with 51 jets and a different power valve. I wish I had a old time Holley cross that would show specs for the old Holley power valves but that I do not have. I suspect it is tuned to run just a bit leaner (51 jets) with the different power valve making up the difference. Without having the detailed specs about air bleed sizes, etc, it's really hard to figure those things out on paper. The vacuum advance control is probably different. For emissions control they needed a lean idle and a delayed vacuum advance. You'll just have to try one out and then tweak it like you want. I don't think either will be better than the other, heck fix both and try them out and keep the other for future projects.
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Old 01-15-2018, 01:54 PM   #19
overdrivesteve
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Default Re: New 2300 carb questions

Quote:
Originally Posted by FDChappie View Post
. . .
While you're in the carb look at the power valve to see at what vacuum level it opens and then try to keep the vacuum above that level when driving.
yes, good advice . . . but I now have a couple other questions about the two-stage power valve in there now. I'll quote from the service manual:
". . . during light load and part-throttle operation where manifold vacuum drops to a pre-determined level , the first stage opens to enrich the mixture slightly ..." - ok, I understand that - ". . . when the throttle plate reaches a 50* or greater opening, a hole through the throttle shaft aligns with passages in the throttle body admitting atmospheric pressure to the power valve permitting the power valve to open regardless of manifold vacuum."

I never heard of this before. Is it common to all 2300 carbs? To me that sounds like this carb is going to get horrible gas mileage. First, Holley no longer sells two-stage power valves. They recommend the single stage 125-65 power valve to replace it. Does practical experience with our engines agree with this recommendation?

Secondly, can this mechanical 50 degree throttle opening of the power valve be defeated so it responds to manifold vacuum only? What would be the ramifications and is that something I would even want to do? Or should I leave it as is? Or put a power valve in it rated such that it will only open at the 50* throttle opening? What are your thoughts?

I'm still waiting to hear on the price of the other NOS carburetor but that IH dealer is probably going to want a couple hundred dollars for it. I'm sure that's why he's never sold it in all these years - but we'll see.

Thank you.
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Old 01-15-2018, 05:11 PM   #20
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Default Re: New 2300 carb questions

The two-stage power valve is common on emissions carbs. The hole in the throttle shaft is a new one. With a 50 deg opening you're pretty far into it already, so the PV would probably already be open. This could be defeated by pressing some soft lead into the hold in the throttle shaft. I'd try it first though. The extra fuel might be to insure the cats light off.
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Old 01-20-2018, 09:24 PM   #21
overdrivesteve
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Default Re: New 2300 carb questions

hi,
As an update, I ordered the two jets as NOS by IH part number. It turns out they are stamped 522 on each jet. I assume that's fractionally larger than a 52 jet.

I also ordered a new NOS power valve by IH part number so I would know what its supposed to really have. It turns out to be a 2-stage power valve but the only number stamped on it is "B-2". So I still really don't know anything about it's operational pressure / vacuum settings.

And the two fuel restriction passages behind the power valve look so tiny that I don't think that power valve will make much, if any difference in fuel mileage. They looked so much bigger in the Holley carb books I've read.

Anyone have any idea how long an old new power valve diaphragm will last with today's ethanol gasoline blends?

And is there anyone rebuilding 2-stage power valves using diaphragms designed for today's gasolines? This power valve looks very rebuildable if I had the right set-up. I used to rebuild 2-stage pressure/vacuum release valves very similar to this many years ago when I worked for Custom Control Sensors in Chatsworth, CA.

And I traced down the throttle shaft - power valve connection. The parts manual calls it a "Power Valve Modulator", not to be confused with a "Throttle Modulator", which is very different. Sorry, no camera yet. And the remainder of this post is just boring info about the Power Valve Modulator - skip it if you want and you won't be missing much. . . but it's all new to me.

There's a hole about a quarter inch from the corner of the air horn through the top of the carb plate on the drivers side. It goes straight down through the corner of the body to a passage on top of the throttle plate. The passage goes through where the throttle shaft is, to a passage on the bottom of the throttle plate, which goes to a passage to the power valve's vacuum cavity. I can see the opening appear when I open the throttle plates. To plug would be easy - just remove the air cleaner and put a plug or self-tapping screw into the carb plate's hole near the air horn. That's the only use for that hole in the carb plate.

Cheers.

Last edited by overdrivesteve; 01-20-2018 at 09:34 PM..
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