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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
Just pulled my car out of storage from this past fall. Carb issues just continuing from when I put it away.
Issues:
-Car runs for a few seconds after I turn it off, I assume from being run to rich for a few months creating build up.
-idle cold is a rough 750-800 in park, and 1000-1100 warm in park. When put into drive it lowers idle speed by 200 (while warm) and 50-100 (while cold). Not sure how much of an "issue" this is or not.
-does not like IMMEDIATE full throttle. If I push full throttle QUICKLY while parked, from a stop, or even while cruising, it will pop and the engine dies or sputters, usually it will correct itself after sputtering a moment.
-Only runs rich?
Otherwise it runs great, cruising is good and I notice maybe the slightest possible bog running at low rpm's. Runs nice and drives smooth. All issues from acceleration and cold-warm issues
I have size 70 jets, I've tried adjusting the accelerator pump on the side, it seems to be ok.
I have a .474 lift comp cam, 69 Corvette heads, headers and 3-2.5 exhaust. I'm about as quick as v6 Camaros/mustangs of not faster. So assuming around 350 hp or so but I've never Dyno.
Re: 650 Holley. Runs rich and won't run otherwise.
Start with the basics:
1) All of the vacuum lines hooked up? No vacuum leaks?
2) Next, move on to the timing. What is your base, total mechanical and vacuum advance?
3) Once this is all sorted out, I think most of your issues will be solved. It does sound like you may have an accelerator pump issue. Look into that.
There is a great Holley tuning sticky at the top of this forum. I would encourage you to read it and then follow it.
Re: 650 Holley. Runs rich and won't run otherwise.
Originally Posted by pancherj
Start with the basics:
1) All of the vacuum lines hooked up? No vacuum leaks?
2) Next, move on to the timing. What is your base, total mechanical and vacuum advance?
3) Once this is all sorted out, I think most of your issues will be solved. It does sound like you may have an accelerator pump issue. Look into that.
There is a great Holley tuning sticky at the top of this forum. I would encourage you to read it and then follow it.
Yes all of the vacuum lines are hooked up. I don't think I have any leaks. I've been told you can spray carb cleaner around the base of the carb to check for leaks, any other good ways to check those?
Timing is good, it's advanced a little bit, my engine has 10:1 compression or so
And yes my accelerator pump has been looked at, but I've seen it squirt just fine so I don't know... Is there a possibility it sprays to much fuel?
I've read the Holly thread a few times and that's got me here.
Re: 650 Holley. Runs rich and won't run otherwise.
What is your timing set at and are you using a vacuum advance distributor? With 10:1 compression and those old iron heads, you may be forced to run less than optimal advance.
It is probably possibly to inject too much fuel with the pump shot, but that would not be a common issue. The intake manifold plays a big part. 99% of my experience is with small block chevy motors. Usually, a mild motor only needs a #28 shooter. I messed with one small block Buick and I worked up to a #36 and it still had a stumble!
Re: 650 Holley. Runs rich and won't run otherwise.
Originally Posted by pancherj
What is your timing set at and are you using a vacuum advance distributor? With 10:1 compression and those old iron heads, you may be forced to run less than optimal advance.
It is probably possibly to inject too much fuel with the pump shot, but that would not be a common issue. The intake manifold plays a big part. 99% of my experience is with small block chevy motors. Usually, a mild motor only needs a #28 shooter. I messed with one small block Buick and I worked up to a #36 and it still had a stumble!
I'll have to check my advance again.
I have a Edelbrock performer rpm air gap manifold.
Re: 650 Holley. Runs rich and won't run otherwise.
The shooter should have a number stamped right on it. You may have to remove it from the carb to see the numbers. The higher the number, the more volume of fuel it can flow. You also want to make sure that even the slightest movement of the throttle causes fuel to come out of the shooter.
What carb and is it new? I had an older, used Holley once that had a worn out spring on the pump arm. It would squirt fuel, but not in a steady stream. Replacing the spring fixed the issue. If it is a new carb, it is doubtful that the spring is the issue.
Re: 650 Holley. Runs rich and won't run otherwise.
Originally Posted by pancherj
The shooter should have a number stamped right on it. You may have to remove it from the carb to see the numbers. The higher the number, the more volume of fuel it can flow. You also want to make sure that even the slightest movement of the throttle causes fuel to come out of the shooter.
What carb and is it new? I had an older, used Holley once that had a worn out spring on the pump arm. It would squirt fuel, but not in a steady stream. Replacing the spring fixed the issue. If it is a new carb, it is doubtful that the spring is the issue.
Re: 650 Holley. Runs rich and won't run otherwise.
Ok I just drove the car after getting back from the tires shop. Turned it off, parked. I checked all of the vaccum lines, I have a red/turning white cam (I can mess with that).
Turned it on and I sprayed carb cleaner around the base and noticed the rpms took a nose dive. Particularly right below the accelerator pump. So I can safely assume I need a new gasket even though it's not but a year old. I'm wondering since it's a more universal gasket if it's leaking through one of the other available bolt holes that's not being used?
You can see in the picture if you look closely, the available bolt hole for a different carb.
Re: 650 Holley. Runs rich and won't run otherwise.
Update:
Vacuum leak got fixed with a new carb gasket.
Timing was at well... Uhh... 3. So moved it to 14.
Minor tweaks to the idle speed half a turn or so.
The cam is also not correct. There is a little bit of play between throttle being pulled and when the cam actually starts to push on the accelerator pump, so I'll be buying a good handful of those to test some afternoon.
There is no more backfire, the engine shuts off fully, it runs so much smoother, waaay faster. I appreciate all the help, I'll update once I replace some cams!
Re: 650 Holley. Runs rich and won't run otherwise.
Persistence pays off! Glad to see you are making some progress. Start with the blue pump cam in position #1 (the cam will have 2 and sometimes three holes...the hole labeled "1" will start the pump shot earlier than "2"). If I remember correctly, the Blue cam is the most aggressive early on and then tapers off quickly.
Re: 650 Holley. Runs rich and won't run otherwise.
My suggestion would be, leave the acccel pump alone!!! Fix what ails the thing. Messing with the pump won't cure the effects of a vacuum leak or other BROKEN stuff.
Fix whatever is wrong with it FIRST. Then set the timing to where it runs the best, without worrying AT ALL about the "number". Just keep tweeeeking it until whichever way you tweeek it further makes it not run as good. "Runs good" might be any combination of best power, best gas mileage, coolest running, no hard starting when hot, no "pinging", and perhaps other factors that may come to light during the TUNING, according to your personal taste. IGNORE your timing light, IGNORE "book" and "spec", just make run good. Start out by advancing it until it pings, and back it off until it quits, then dial it in toward perfection (or as close as you can get, given whatever your distributor's curve is) from there.
Then see the "Holley Tuning" sticky at the top of this forum. Follow it from start to finish, starting at the start and continuing through to the finish, skipping nothing, following it IN ORDER. If any word of that sentence is unclear I'll be happy to explain further; especially "start", "skip", "in order", "finish". Remember, start at the start, skip no steps, do it IN ORDER not skipping around or doing a later step before an earlier one. Odds are, by the time you get through, it almost won't even need an accel pump at all.
Last edited by sofakingdom; 06-15-2018 at 11:09 AM.
Re: 650 Holley. Runs rich and won't run otherwise.
on my rpm air gap the accelerator pump arm hits manifold were it touches pump under carb when you bolt it on it depress the pump a little bit so it runs rich and diesels when shut off you can grind a runner a bit but i just got a mr gasket gasket that is 1/4 in thick then readjust arm again with no gap on spring that salved my problem give a look i hope it helps
Last edited by davoss2012; 06-15-2018 at 11:34 AM.
Reason: make more detailed
06-13-2018, 08:32 AM
