Hello all, I'm a new registered user but I'm a long-time lurker. I can typically find all the info I'm looking for from searching the archives, but I for the life of me can't figure this one out. Please help me before I heave this carburetor into my neighbor's yard.

Small backstory: 8 years ago I purchased a brand new holley 670 street avenger for my 350 (.030, victor jr, holley systemax heads, 9:1 cr, 292hr comp cam). With a little bit of tweaking the engine ran great, a little rich but I was still getting 26 mpg on the highway so no complaints. In 2006 I dropped the car off at a bodyshop; 5 years later I pull it out of the bodyshop incomplete because i was tired of their bs excuses and neglect, and I finally had time to mess with the car again.

So for the last few months I've been slowly getting it closer to being on the road again. I picked up a trick kit and used it to rebuild the 670, but it still runs ridiculously rich...like teary-eyed idle rich. If I just drive it doesn the block, it leaves a haze of unburnt fuel. I've torn the carb back apart several times and blew compressed air through every passage, as well as carb cleaner. Everything seems to check out fine, here are my issues of concern:

1) throttle plate bushing has some play in it, enough that when I hook a smoke machine to the carburetor, smoke comes out of it, indicating a small vacuum leak. So I plan on picking up another base plate for the carb, but I doubt that's where my problems are coming from.

2) I have a low vacuum source (5-6") most likely from having too much cam for the engine / compression ratio, but I had the same cam in it before I dropped it off at the bodyshop and like I said, the carb performed just fine with it. I'm wondering if the low vacuum source is causing me to have to open the primary throttle blades too far that it draws in too much fuel. I tried tweaking with the secondary throttle blades but that was a disaster...I just figured I'd try again with the new baseplate.

My low profile air filter was interfering with the choke linkage, so the entire choke assembly / plate is removed...don't really need it in texas anyways. I've installed a 3.5 powervalve to make sure it isn't messing with me on the idle circuit, and just for kicks I installed 64 primaries but it still ran stupid rich.

Also have another problem with a different carb: So a week ago I picked up a holley 750 4160 off craigslist that was supposed to be a "bolt on and go" carburetor. Lol, well it hydrolocked my engine by dumping in waaay too much fuel, gas literally poured out of cylinders 2 and 4 when I removed the spark plugs. Today I got to messing with the carb and found a blown power valve and baseplate gasket that needed to be changed. Only other thing that I can't figure out is the accelerator pump shoots out the bottom of the carb. As in, no fuel comes out of the squirter on top, but instead I'm assuming the check valve isn't seating beneath the squirter screw, and the gas is just blowing passed it. I've attached a picture of where the fuel is squirting out underneath the carb.

Please help with this, I can't tell you how many hours / days I've spent messing with this stupid carburetor to no avail. It's so painful to know my car is just a carburetor adjustment away from being able to drive it on the road again, I just can't figure out what's wrong with it.

 

There are a few things I would look at before throwing the carb over the fence (although, that would probably feel good!):

1) Cam is pretty big, but 5-6 is low vacuum. Check and make sure you don't have an intake gasket leak. It may beon the valley side, and not ont he outside.
2) What is your timing at idle?
3) Take the carb off, turn it over, and set the idle screws so the transition slot looks like a small square (not a rectangle). This should be all you need for a good idle. If you need more, try to adjust both primary and secondary sides equally.
4) Are the floats set correctly and is the fuel pressure correct? It almost sounds like your fuel pressure may be way too high.

Hope this helps. Don't give up yet!

 

1) I connected a smoke machine to one of the vacuum ports on the carburetor, that's how I found the leak at the throttle plate. Anyways, I was also checking around the intake manifold for leaks, but didn't notice any.

2) Base timing is at 21*, I'd prefer it to be about 26*, but my advance is 18* so my total timing would be a bit too much...but I still think 21* should be sufficient.

3) As I mentioned earlier, the secondary throttle plate doesn't want to adjust, so I was hoping I'd have more luck with the new base plate I'll be picking up.

4) Floats are set flush to the bottom of the sight, and fuel pressure is between 3-5 psi.

 

Looks like you already thought of the same things I did! For sure, the 5-6" at idle is killing you. There must be a vacuum leak somewhere (I doubt the throttle shaft bushing is the main source). I would think you should be at 10" and maybe even more at idle.

 

like you said, you need more timing at idle.
Use these bushings to do that http://www.4secondsflat.com/MSD%20Di...r%20Tuning.htm

But the real problem is the cam and single plane intake are to much for the 9:1 compression. So its probably never going to idle right and make any decent vacuum at idle.

Also you can try putting a bleeder valve on a vacuum port and let some air in and see if it idles better. It's basically an alternative to drilling holes in the plates.

 

Just for reference, my 350 has 10.5:1, but the cam is a little bigger and on a 108LSA. It was pulling 12" at a 1000RPM idle (this was with the ring seal going away). I had 52* advance at idle (with the vacuum advance hooked up). Any less than that, and the car was a bear to drive. I also agree that the Victor Jr. is overkill.

I have never tried the bleeder valve idea (but it sounds good). I have drilled holes in throttle plates with little success. My current carb has an idle bypass system, but I don't use it. Once I got enough initial with the vacuum advance, it was pretty good.

 

Yea if you have enough timing at idle with the vacuum advance you usually don't need the extra air leaked in. But unfortunately most people don't have a vacuum advance distributor because they don't really understand how its used and what its for.
An easy way to tell if you need the extra air at idle is to lean the idle screws out as much as possible with out making it idle worse. Then pull off a vacuum line. If the idle goes up and smooths out. You need the extra air.
I usually use the bleeder valve just because I hate drilling the plates. If I ever need the carb for a different setup I would need a new baseplate.

 

I know that I have a few mix-matched parts installed with the setup, but keep in mind that this exact setup still ran fine before it sat for 5 years, and I'm pretty sure I had low idle vacuum at that time too. I'm trying to focus more on what would be going on with the carburetor itself to cause these issues. ALSO keep in mind that it's running rich / leaving a smokey haze everywhere I drive, not just at idle. I understand that my setup could use more initial timing, and I would benefit more with my performer rpm than my victor jr for idle vacuum, but there's still something else going on here that I can't figure out, which is why I'm turning to the gurus here.

Also, does anyone know how to fix the accelerator pump problem with the second carb in question? If I can at least get that circuit fixed, I can install this other carburetor to see if it at least runs better.

Thanks so far for the replies

 

This car sat for 5 years so there's no telling what has happened inside the motor. If the car was PIG rich you should be blowing out black smoke on acceleration. Blue smoke and you have oil burning and that also causes the eye watering like a car running rich. These cars are known for wearing out valve seals and you might be having a problem there as well


I believe the power valve passage is what is right above the vaccum hole in the base. that you have shown

See here:
http://www.holley.com/data/TechServi...wer_valves.pdf

Looking at the main body there is a gasket between the metering block and the body. The acceleration passage goes from the bowl to the metering block. On the bowl side you can see the passage angle across to the center of the metering block. From there it goes to the main body right in the center and the gasket seals this off from the vacuum passage. I would say you have either a bad gasket or the sealing surface on the main body. The gasket has a small hole right above the big opening in the center, item 120 & 149 on this drawing--> http://www.holley.com/data/TechServi...ded%20View.pdf

 

I ran a compression test a couple days ago and all 8 were 155-160 psi with the engine cold, so I would assume a warm engine would be 170-180 psi. It's always dark by the time I'm able to get home and mess with the car, so I can't tell what color the smoke is. Now that you mention it though, it seems to linger around like burning oil does, but it just smells like pure unburnt fuel, so I figured the smoke was from it running rich. The engine is a pretty fresh build (from several years ago), and I don't think it has over 4k miles on it. The heads had been reworked through a machine shop so I wouldn't suspect them as the problem. I'm assuming since my compression is good that the rings are fine, but I guess bad oil rings could allow too much to slip by...I'm not sure how I could test this though.

I'll be hooking up my wideband soon so I can have some actual AFRs to give you guys instead of vague descriptions. Plus I was finally able to get my secondary throttle plate to adjust, so now that I backed the primary plate down a bit, I have a more normal idle transition slot (about .025"), and the driveability has definitely improved...but it's still smokey.

You were also correct with the 2nd carburetor's issue. I feel foolish for not checking this before because I simply checked that the gaskets weren't cracked / torn, but didn't actually pay attention to them . The gasket that the PO installed between the primary metering block and carb body was wrong, and didn't have a seal for the accelerator pump passage (I'm assuming the gasket was for a secondary metering block with vacuum secondaries). Therefore very little gas made it into the shooter nozzle area, and most of it dumped underneath the powervalve. At least some progress has been made, thanks for the help so far. Like I said before, I'll be sure to update this thread with some AFRs.

 

Not saying that this is your problem but IF a motor is running PIG rich you can wash down the cylinder walls and cause abnormal ring wear.

Compression test is only testing the compression rings which they seem okay but a leak down can tell you more. I've seen a motor produce good compression test numbers and still have a bad leak down rate. (>10%). Just throwing the idea out there.