MN80Vette

As I said in another post, I need to buy bigger squirters for a Holley 80457 on a GM HO crate. I just learned that there are 2 kinds of squirters: standard and tubular.

Supposedly tube type squirters are recommended when additional top end fuel enrichment is required. My carb has problems at the low end, so I shouldn't need tubular squirters, but is there any harm in buying tubular squirters anyway?

Should I put on a 50cc pump while I'm at it or will the combination of bigger jets and bigger pump push too much fuel?

I also learned that there is a hi-flow nozzle screw available. Do any of you guys have one in your Holley?

MN80Vette

I found a good article about Holley accelerator pumps:
http://www.stockcarracing.com/techar...ent/index.html

Now I know that I already have a tubular squirter but not a hi-flow screw. The squirter pictured in the article is exactly like mine:


I still don't know what size squirter to buy though.

tonyv123

Heres some info on yer squirter, (a little ways down the page) browse the site for more.

http://holley.com/TechService/FAQ.as...ory=Carburetor

tonyv123

Just read your post below, and here's what I'd do:

First, make sure you don't have a vacuum leak. Disconnect one at a time, your power brake vacuum connection, headlights, pvc, and make sure nothing is leaking vaccum. Alot of off idle stumble is caused by a vacuum leak.

If no vac. leak, go up two squirter sizes and check driveability.

MN80Vette

I stopped by TNT Raceshop (http://www.tntraceshop.com/) near work with my list of parts. (Those guys seem to really know what they're talking about.) They agreed with the diagnosis and my parts list but suggested I try the fixes in order:

1. .035 squirter
2. Biggest, steepest accelerator pump cam
3. 50 cc accelerator pump

I took the car for a test drive after the squirter change: Noticeable improvement but still studdering.

Then I put on the biggest, steepest cam (the brown one that came with the 50 cc conversion kit), adjusted the lever bolt length to get max shot, and took it for another test: BIG difference. The front of the car visibly rose when I stomped on the pedal, BUT then it went back to studdering.

That tells me that the .035 squirter and cam are shooting more gas but I think the 30 cc accelerator pump is running out of gas.

I ran out of time tonight, so the 50 cc conversion will have to wait until tomorrow evening. That will be just in time too, because dyno day is Saturday - 3 pulls with print outs of hp, torque, and A/F.

BTW,
Thanks for the suggestions about vacuum leaks Tony. I'll check those things tomorrow when I continue the project.

SHAKERATTLEROLL

You may not need the 50 cc. If you like you can add an extra gasket on the pump.

MN80Vette

That sounds easy. You've got my attention.
However, I don't think that would increase squirted volume enough. Another gasket would increase volume of the accelerator pump (a little) but the lever and diaphram would limit the output volume.

I already bought a 500 cc conversion kit, so I am going to put that one tonight and tweak everything one more time. That setup is what's going on the dyno tomorrow.

GM rates the 350 HO at 330 horsepower and 380 lb.-ft. of torque. Given my novice amateur rating, I'd be quite pleased if I get 250 to the wheels and quite surprised if I get more. Realistically, I am expecting 220-240.

BTW, the objectives of this carb tuning are 1) wake up my '80 and make it more lively to drive, and 2) get a baseline to compare against after I install the Holley TBI system I have in the garage.

Matt Gruber

where is base timing? it will take a HUGE shot to make up for less than optimum timing.

KJL

I have used an LM-1 wide band O2 sensor for years on several types of carbs and have found uniformly that a lean spike occurs upon rapid acceleration with the smaller pumps. The larger pumps gives you more flexibility to control it. You will most likely need a spacer for clearance.

MN80Vette

Yikes! I don't have room for a spacer under the carb to make room for a 50 cc pump, and I am already using a drop-base air cleaner to fit under the stock hood.

I will check the timing again before I convert to 50cc. Base timing is at 14 deg. I have 2 medium springs on the weights (Moroso). I had 2 light springs on, but the weights weren't returning all the way.

Matt,
How do you recommend I set the timing to require a smaller shot to stop the studdering? Re-timing is easier than converting to 50 cc.

gordie1465

think about a longer intake run or spacer

Matt Gruber

14 isn't bad. if it likes 16-17 that could help. a trick kit, comes with lots of squirters and cams. really helpes tune.
some guys let the carb drive; others drive the carb. (there is no reason to nail it from a stop; best acceleration is a skill) no doubt it could work better, but without driving the car i have no idea if is a big problem or not. if it bothers u enough, buy the trick kit. another drivability idea is to make the power valve kick in early
http://community.webtv.net/MATTGRU/pv the pv won't help at launch, however.

Vette-4-Life

i am going thru this with my new engine/holley right now. i had a stumble at wot and have eliminated it.
i went to a bigger pump nozzle, .035 tubular, that helped but didn't fully resolve. I then bought the pump cam kit and thought the same that the most aggressive would work. That didn't resolve either.
Thru experimenting i am now using the red cam which is not as aggressive but provides a longer duration shot. You may need to try a longer duration pump cam.

morganjd

red or orange are the 2 to use

bozzman3

Please keep us posted and dont forget to post the dyno run!!!

MN80Vette

Check out my "Dyno Day results" post on C3 General.

bozzman3

Matt this is a intresting statement some guys let the carb drive; others drive the carb. Are you saying that the carb cant deliver perfect preformance in all areas?Do some of you have perfectly tunned carbs that have no bogs,hesition,etc in all areas of driving?

KJL

My setup provides a consistent fuel curve throughout the rpm band. But again, I use an LM-1 wideband O2 sensor for tuning. Unless you are an experienced tuner, ball park is the best you may be able to expect. You should be able to at the very least, get the hesitation and bogs out of it but perfect performance in all areas is a tall order without being able to "see" how small adjustments impact the combustion process.

MN80Vette

I use a narrow band butt-o-meter for tuning.
I am going to switch to a NOS Holley 4-bbl TBI conversion I got for cheap, but not until the end of the season. I will probably weld in a bunge and attach an A/F meter so I can "see" what's going on now and tweak it a little. That will establish a baseline to compare to when I convert.