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Holley 350 carb (7448) problems
https://slantsix.org/forum/viewtopic.php?t=37563		 Page 1 of 3
Author:  Dart270 [ Sun Oct 18, 2009 4:30 pm ]
Post subject:  Holley 350 carb (7448) problems
Slant sages,

I bought a "new in box" Holley 350 2bbl to try on Slantkota. Thought I might go for a bit better mileage and it was a decent deal. The carb was made around 2001-2002 and was sealed in the original packaging - never opened out of its sealed bag.

Bolted it on and it idles perfectly, revs up crisply in neutral up to around 2000-2500 RPM. However, under any kind of load, it bogs down and acts lean. No smoke out the back, so it must be lean. I tried putting in 64 jets up from the stock 61's and it ran a bit better, but still not functional at all. Accel enrichment circuit is working perfectly, since you can pump the gas going down the road and it will smooth out and accelerate while you are pumping.

I took the metering block and fuel bowl off and blew out all passages and couldn't see any debris or blockage with simple tests. It seems as if the main circuit is plugged or maybe air bleeds are not functioning/plugged?

Any ideas here? Not sure I have any way to return this since it was an Ebay seller and any Holley warranty would be long gone.

I put my 500 2bbl back on and it runs exactly the same as it did before - no running problems at all.

Lou
Author:  coconuteater64 [ Sun Oct 18, 2009 6:14 pm ]
Post subject: 
Interesting; I have the same carb on mine and it acts as you described, but the 61 jets were too rich for mine. Then at part throttle it surged like it was lean. Never did figure it out totally, but I plan on tossing in some 54 jets to see if I can bracket in on the optimum setup.
Author:  SV162 [ Sun Oct 18, 2009 9:53 pm ]
Post subject: 
Could the power valve be stuck shut Lou? therefore no extra fuel when needed under load.
Author:  the_shadow [ Sun Oct 18, 2009 9:57 pm ]
Post subject: 
Quote:
Interesting; I have the same carb on mine and it acts as you described, but the 61 jets were too rich for mine. Then at part throttle it surged like it was lean. Never did figure it out totally, but I plan on tossing in some 54 jets to see if I can bracket in on the optimum setup.
61 jets too rich? Are you sure? Are your plugs getting black fouled? I have the exact same carb and I found the #61 jets too lean, on some occations I would get a lean surge at idle and my plugs were running fairly white. I upped it to #63 or 64, can't remmeber, and it fixed that, but it's still on the ever-so-slightly lean side it seems.

Dart270:
A simple check would be swapping the powervalve if you have one laying around, that sounds like it could be the problem. Stock should be 9.5......

All and all i've found the 7448 to be a so-so carb at best. My first one wouldn't run and after I pulled the metering block, I found metal shavings embedded in the gasket (poor assembly process). My replacement one had only 1 metal chip in the metering block gasket, so I removed that and it runs fine. Like cocoanuteater described, it runs leaner part throttle sometimes it seems, and i've had issues with powervalves sticking in mine (tried 3). Eventually i'm going to spend the money and get a Weber so I don't have to deal with these cheaper-line aftermarket Holleys.
Author:  slantfin [ Mon Oct 19, 2009 5:14 am ]
Post subject: 
I used a bigger jet and power valve, and it made a big difference. Before it was boggy like you describe.
Author:  Dart270 [ Mon Oct 19, 2009 5:27 am ]
Post subject: 
Thanks for the responses. I tried a new powervalve already on my first round, and no difference. It ran better with 64s in it, but still wayyyy off.

Any other ideas?

Lou
Author:  Charrlie_S [ Mon Oct 19, 2009 5:29 am ]
Post subject: 
Lou, remove the air cleaner, and with the engine running, look down the carb. Raise the rpm slowly and see if fuel is being pulled out of the pump shooters, at about 2500 rpm and higher. If it is, that could be your problem. If you figure out how to cure that, let me know.
Author:  the_shadow [ Mon Oct 19, 2009 7:36 am ]
Post subject: 
I know this sounds retarded, but how about trying another powervalve.......

I've found the quality of powervalves these days to be piss-poor at best. I had a problem for over 2 months, even made a post about it on here, and it turned out to be a bad powervalve, and I had to get 3 news ones to find a good one.

Even my current one sticks once in a while after shutoff...sigh...
Author:  Doc [ Mon Oct 19, 2009 8:43 am ]
Post subject: 
Another vote for a power valve / power curcuit enrichment problem.
Be sure to use tha correct PV gasket, there are different styles and in some cases, the wrong gasket can block fuel flow.
Also trace the PV fuel passageways to be sure those are clear.

On the Holley 2300 series, 350 CFM I worked with, it needed a 10.5 PV and I also had to open-up the PV "restriction" point by about .010 (per side) before it would transition cleanly into the power curcuit.
DD
Author:  Dart270 [ Mon Oct 19, 2009 10:37 am ]
Post subject: 
Interesting!

Doc, when you mean the restriction point, do you mean the ~0.040" holes (2) in the metering block just under the PV?

It did seem to run better after going to the 6.5 PV and bigger jets from the stock 8.5 PV and 61 jets, but still pretty horrible.

BTW, there is no transition to the main circuit at all, from what I can tell. I guess if the PV is stuck closed then that is limiting total fuel input, right?

Lou
Author:  coconuteater64 [ Mon Oct 19, 2009 10:44 am ]
Post subject: 
61 jets too rich? Are you sure? Are your plugs getting black fouled? I have the exact same carb and I found the #61 jets too lean, on some occations I would get a lean surge at idle and my plugs were running fairly white. I upped it to #63 or 64, can't remmeber, and it fixed that, but it's still on the ever-so-slightly lean side it seems.


My exhaust is sooty black, and it smells awful (gas smell) when I shut it off. I am beginning to think the problem lies elsewhere, other than the jets. Gonna try the 61s again and check the float level.

I will unhijack this thread now...
Author:  the_shadow [ Mon Oct 19, 2009 11:26 am ]
Post subject: 
Quote:
My exhaust is sooty black, and it smells awful (gas smell) when I shut it off. I am beginning to think the problem lies elsewhere, other than the jets. Gonna try the 61s again and check the float level.
Actually it's really not hijacking, this is probably a notorious problem with these carbs due to their [poor] manufacturing process. It's a good idea for others to hear the common problems with the new 7448 2300 series carbs. Note: Holley made several different types of 2300 series carbs over the years, I can only account for the 7448 as discussed in this post.

I had the exact same problem, for some reason the needle and seat won't restrict the increased gas pressure after shutoff, and will cause flooding problems after it's turned off. I've tried 2 new replacement needles AND set the float level, no difference, the only way I was able to solve this problem was a fuel pressure relief system using the 3-fitting fuel filter that was reccomended on here.
Author:  coconuteater64 [ Mon Oct 19, 2009 11:31 am ]
Post subject: 
Gonna give that 3 prong filter a try. I guess next week I'll grab a few different size jets and see what happens. A leaky fuel situation might have something to do with it acting rich.

Didn't know these carbs had manufacturing problems.
Author:  radarsonwheels [ Mon Oct 19, 2009 12:34 pm ]
Post subject:  Slant 6 Holley Tuners Unite!
I'm psyched to see this thread!

I did my first holley tuning on my slant a few years ago. I have a vacuum gauge and a wideband installed in my dashboard. This gives me the tools to see in real time exactly what is going on with different circuits in the carb etc.

I have a 225 with headers and a stock cam, same holley 2 barrel as you.

Here is the problem I had with my tuning efforts- the power valve always applied way too much gas. A main jet lean enough to run with the power valve open was way lean under high vacuum. I was able to make it workable by running a plugged power valve and jetting up. The a/f now rarely gets to the 14.x:1 and operates mostly at a less than optimal 11-12:1. It does hit the 12.5:1 sweet spot pretty good at 3/4 throttle but goes doggy rich at WOT

The plug was meant to be a temporary solution. The motor runs pretty well but often quite rich. I am just now contemplating another go at it.

Since the PV is like a adjustable switch, and not adjustable for volume as I see it the solution is resizing the Power Valve Channel Restrictions- the two little holes behind the power valve in the metering block. These were probably sized for a chevy 305 or so, not a low rpm 225. I have heard of sticking wire or little Vs of metal in the holes to make them smaller? Then when you screw in the PV they are trapped in the PVCR. I am thinking maybe different guitar or bass strings for adjustable PVCR restrictors? Where can I get some different size wire nips? I am thinking about epoxying the holes then drilling them or drilling and tapping for adjustable air bleeds but I've only ever changed main jets. I don't have an expensive box of dominator air bleeds or whatever I would need to do this for cheap. Did I mention that I'm cheap?

I am set up pretty well to test jetting combos etc. and I would love some support and nudging to get the process going. I'm in Philadelphia so no dramatic thin air or hot/cold climate to skew results.

Lets work together to get a really good baseline tuning for ourselves and maybe we can put together an article for the board.

Kevin
Author:  coconuteater64 [ Mon Oct 19, 2009 2:05 pm ]
Post subject: 
I wonder if I just remove the PV and install a brass plug. Think I could tune around that?
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