Now that I finally got the 69 and its 468 out with some track time, I've found my carb being the week spot of the car. If you read my earlier post on the engine bogging under hard braking, you already know part of the story. I didn't have enough time before the race to really tear into the carb so i simply added a little bit of rubber hose to the vents to hopefully keep it from dumping too much fuel out of them. How much this helped is uncertain. I would be coming off of a straight with good speed and go into a hard corner and halfway through the corner the engine would start stumbling or on occasion actually die. It did do it consistently on the faster side of the course when I would have to decelerate and turn coming from higher speeds. I talked to another guy there running a 64 with a healthy smallblock with a Holley and he said he would have the same problem, he combated it by idleing the carb up to 2k and run the course like that. I upped my idle to 1500 and ran it like that and it cured my stalling and most of the stumbling, but it did tend to get my engine warm in the pits like that, so I didn't consider this the correct solution but it got me through the rest of my runs. So my question to everyone is how do I set up my 870 SA to run an autocross or track event and still drive it home without having to mess with it between runs.

thanks

Pat Kunz

 

There a number of things that you can get to help with these issues. First would be some little white plastic things called 'whistles' that actually do look like whistles that are fastened to the vent openings on each metering block. They extend forward and aft from these openings and help keep fuel from sloshing up into the vents during hard braking and/or acceleration. Another would be jet extension tubes that fit over the jets to help keep them covered with fuel during acceleration and deceleration. Many road-race types also put a rubber tube completely across the bowl vents and cut a small slot across the top to help keep sloshing fuel from getting into the venturis. You can experiment with float levels as well, but my own experience has shown that Holleys like the fuel level right at the sight plug just like they're designed. Lastly, check your needle-and-seats to see if they're the spring-loaded variety- these help control the float level better than the plain ones. Holley carbs' best feature (large float bowl capacity) can also be their worst enemy (controlling all that sloshing fuel), so anything you can do to keep them from ingesting unmetered fuel spilling out of the bowl vents will help.

 

The vent baffles (aka whistles) and/or the old hose across the bowl vents trick are both good ideas.

On the outside chance that your carb doesn't already have center feed bowls, you absolutely must change them for hard cornering.

BG makes a special float for road racing that helps control fuel movement during cornering, but I don't remember if Holley has such or if BG's will fit.

A word of caution about jet extensions... Being more of a crutch for the strip I've never run them myself, but according to BG under very hard braking the fuel can/will uncover the secondary extensions, which in turn can cause a stall. I suppose one could conjecture the same about the lack of extensions in the front bowl or the use of them up front under hard acceleration... A dilemma, I know, but if you don't have starvation issues under acceleration or deceleration which can be directly traced to uncovering the primary or secondary jets, there's a chance you could actually create a problem by installing them. Hence, I'd proceed with caution on trying extensions.

Best of luck, and post up with your results as you run down a solution.

 

If you have of install float chamber "whistles" you may want to cut the rear one down to 1/2 length, I have found that there can be fuel splash out of the vent with a full length whistle in the secondary flat bowl. You should also make sure your float heigth is not too high, the higher the fuel level, the more likley the chance of fuel "splash" out the bowl vents. I also advocate running a tube between the bowl vent tubes, just make sure you make a large enough opening in it to keep both bowls properly vented. Idle mixture is also very important to have correctly adjusted, maybe a LM-1 wide band is in your future.

 

Thanks everyone, very good info. Unfortunately the tying both vents together with a rubber hose with a hole cut in the middle top isn't an option due to my air cleaner/intake setup (see my braking post), wish it would be becouse it would have been a simple solution. I don't seem to have a problem with going lean at all, no fuel starvation issues that I could tell. More loading up with fuel as the issue. So it looks like the vent whistles are definitly in my future as a modification to the carb. I really don't know a whole lot about Holley carbs, always been more of a quadrajet guy myself, this is my first attempt messing with a Holley (by the way my quadrajet never had these issues on my 73), Maybe someone who knows a little about these Street Avenger carbs can give me some info on how the feed bowls and floats are setup on these. It's specifically a 870 SA, given to me as a gift from Holley's R&D department

Thanks

Pat Kunz

 

What do they have to suggest, or maybe you're their guinea pig.

 

I can't remember when the Street Avenger series carbs came out, I had this one laying around for about 3 years before finally putting it on the 69, becouse it had a little 650 double pumper on it, ran ok down low but ran out of steam on the top end. I still have it though.


Pat Kunz

 

Try setting your float level so the fuel is just at the bottom of the sight glass. This is low enought to not need vent extensions. You need to dial the idle mixture screws with a vacuum gauge at 1000 rpm to get the highest vacuum reading.

You need to have as much advance initial as you can like 16 - 18 with vacuum adv, disconnected while timing. This usually requires recurving the dist.

You might need to adjust the airbleeds

I road race without extensions of any kind