i'm going back oldschool th289 - blending in a lot of tech videos. hope ya'll enjoy. this is a channel for teaching and sharing knowledge - I miss doing stuff like this for you guys.
I've been a chump these past couple months trying to figure out this off idle stumble, but after watching this video I went out and checked the lever and it had so much play you could almost put a pencil in it. Immediately closed the hood and took a walk to ponder my existence. When I finally came back, I adjusted the lever and the ole 460 runs like a champ now. Thanks Luke.
John, you’ll get it man. The truck in my profile pic was my dads also, and he couldn’t get it running. Do your research and keep faith. It’s been 7 years since my dad passed, and the truck is 100%. Best of luck man
I learned a lot of this stuff from my dad a long time ago, and forgot most of it. He is gone now, and I have a carb engine to work on, so it is great having your channel to relearn from. It is great to know that old school mechanics all seem to have had the same real world applications! Thanks, and keep it up.!
Your video was MUCH better than any Holley tech vids explaining how the pump is supposed to work, I “all of a sudden “ have a hesitation when I stab the throttle, even on the highway, if I backed off the throttle then back onto it, a split second hesitation, NEVER would I have considered the fact I lowered my idle and that directly affects the pump operation. THANK YOU👍
Same here! I guess it only affects it if you lower it, not raise your idle speed. Raise idle too much, you'll get over problems with the accelerater pump circuit. Gona varify mine tomorrow!
Thanks just fixed my holly on a 67 mustang. Was stumbling off idle after vacuum tune. Didnt realize I needed to readjust the accel pump! Solid gold my man!
i think that might be the problem we're having with my daughter's 65 mustang. never knew that we were supposed to adjust the accelerator pump whenever we change the curb idle. gonna try that out tomorrow. glad to hear it fixed your problem.
I have been chasing a stumble for about 2 weeks on this truck I put together. I have messed with the accelerator pump adjustment until I went insane, replaced the pump discharge nozzle to a larger size, timing, on and on and on. This was the fix. Thank you so much!!!
Great video Luke as always. It’s funny how the way different people absorb and interpret information, well differently, and I think that’s one reason I gravitated towards your vids, in that you generally deliver what I consider to be vital with instruction videos, and that is concept. The concept here is the dynamic relationship between off idle adjustment and the accelerator pump are joined at the hip with seemingly everything like AFR, initial mechanical advance, jet sizes, the throttle linkage, etc. it’s quite a bit but slowly I’m beginning to understand how necessary it is to comprehend the myriad of relationships between components, their adjustments, and not a single complements adjustment can stand alone. That would make one hell of a video, a video that explains the woven interconnected dynamic mess of displacement, bore, stroke, fuel delivery, variables in fuel delivery, eliminating variables in fuel delivery, timing, compression, valve events, engine under load, low load, heavy load, elevation, temperature, gearing, vehicle use, and the endless compromises one must understand in order to tune all of it to meet a very specific goal, which for everyone is different. Oh boy, there’s no end to the learning. Thanks for your sharing
I FINALLY broke down and bought my best first dedicated RU-vid recording piece - a Bluetooth mic. That plugs into a phone still 😂 Defiantly low tech! Thanks so much 👌
I really enjoy your videos. Catching up as I put the finishing touches on my 63 Merc Comet S-22 engine bay. Your carb and engine/distributor videos have been very helpful.
Man, I got behind in your videos, so I've got 6 more to watch. Which means I get to binge! Anyway, thanks, Luke, for the great tutorials. You're my favorite teacher by far.
Not just Holley, Edlebrock too... Hey man thank you for pointing out the obvious, because t was not registering. I just finished a nightmare build that went from a Ford 400 to a 351M to an actual 302HO crank in a 351M block, by the casting codes, with 400 heads. Don't ask it's a long story. and on top of that, new cam, intake, card, valve springs, lifters, etc.and with all the changes getting the timing right was a battle and so I was thinking timing and hadn't even checked closely the accelerator pump. Sure enough it was loose as hell. tightened it up and what a difference... Thank you!
This video explains why having the pump misadjusted causes problems in both cases of it being too much or too little. Excellent info if you want to understand 'why' the adjustment is important.
Good explanation. My Holley book for a street dominator I had years ago said I should have a little gap (I think .015") between the accelerator pump arm and the throttle linkage. From what I've read, you may want a split second of air before spraying fuel into the boosters. I feel like this will vary between engine combo's so maybe no gap or maybe a little gap.
I have had some stumbling problems before and did all the same ol fixes, plugs, wires, carburators, edelbrock, holley, demon, timing adjustments, fuel filters, fuel pumps, coils, distributor cap, roter, etc, still the same dead dog stumble from dead stop..... What could it be??? It's kinda rare and something you may never see or even guess that could shut down a high hp engine. Are you ready? AIR CLEANER....It has happened to me twice, a small air cleaner caused me to buy two new carburators, Holley 750, elderbrock 750. Finally exhausted one day and out of patience and money I inadvertantly closed the hood for another test drive. I had forgotten to put the air cleaner on as I was in a hurry and not just a little aggrivated. A 460 ford engine setting in a 1985 mustang should scream, and in this test drive it did. I couldn't believe such a simple thing a a undersized air cleaner could shut a engine down like that. One of the reasons I brought this up is I just built a 1971 plymouth Duster with a big block 400 with 10.5 to 1 pistons, 750 edelbrock and all the goodies. Changed the gear to 373 and ready for that test drive, flat on it's face, barley squeaked the 9'' wide tires. Oh what a disappointment. Had to be the carb, no the timing, what could it be? Then I remembered a long time aga a 460 ford engine. I ripped the small breather off and lined up on the road for what I belived would likely be another failure as this could never happen twice in a lifetime. It burnt the tires so bad that it climbed into third gear still smoking them dudes. Crazy right, Strange but true. Thanks for listening...
I have one for you Luke. I had an off idle stumble in my 72 Lemans. The car just has an Edelbrock carb and intake on it. The rest is stock. I did all the things you said here and scratched my head. Then I started over and checked the timing. I had it on manifold vacuum, so much for double checking, and was running 21 degrees at idle. LOL. I put it back to ported. I am back to 12 degrees mechanical at idle and 28 degrees maximum mechanical, with around 38 or 40 on vacuum. I reset the carb and it runs awesome. I wondered why it wasn't starting so easy. LOL Great video.
@@ThunderHead289 Thanks. It only has 88,000 miles on it right now. You saw it in Norwalk, Ohio when I worked with you on the 67 GTO. I grabbed my torque wrench out of it.. LOL
The pump lever would stick every time after adjustments over and over. It made the throttle too stiff, but I rigged a return spring for just the accelerator pump lever to stop that stumble. It ssems a bad design. No matter what pump or lever or adjustment, the thing will only return halfway, so next time you gst no fuel until it takes up the slack. Nobody talks about this but I saw it on every Hoĺley.
I looked everywhere for a mechanic that was comfortable working on my old carbureted car, and when he did, he ruined my engine timing, couldn't figure out the carb settings and I'm afraid to find out how he managed to disassemble and clean my spare carb without using any of the provided replacement gaskets.
Could never get a Edelbrock carb tuned right. Tried everything to get rid of my off idle bog. Bought a summit carb and the rest is history. Holleys are so much better but you need more carb knowledge to adjust a Holley. Thanks for the video.
Hi I am running 600cfm carb on a mild 351 clevo, has been hard to tune so I did what you said on you last video in regards to a fuel pump reg on a mechanical fuel pump an BAM! I works really well it was running nearly 8 psi on an old carb, the tune is more stable had to re adjust float heights it starts easier An tunes better so Thank you! Gene, Australia
Thank you so much, and it's time to get a new carburetor for mine. Because I go to blast it to get out of that rough idol. And it still keeps idling very low...I have headers and all new fuel lines and wires. Only thing left is the Holly carb. And air intake.
I got a stumble at low rpms when initially giving it gas other then that it blast thru but it also backfires on deceleration. U think the stumble/hesitation is because that accelerator screw needs tighting? And is the backfire because the idle mixture screws are too rich?
Thanks, I have a boat with more engine than the drive should be pushing. I never paid much attention to my accelerator pumps cause I always take off easy. I'll still set things correctly though so it all works together properly. I bet there's a little gap in the linkage setup.
This helped a lot. So I made adjustments so there is no play between the accelerator pump arm and pump diaphragm lever. But this adjustment made the idle way too fast. So should I move the screw on the throttle to the 1st position to obtain a slower idle?
If you read the adjustment portion of the instructions that come with the rebuild kit you'll find the proper procedure for setting the accelerator pump arm preload. In a nutshell you work the throttle arm so it's at W.O.T. with the pump arm fully depressed, then you use a flat feeler gauge to set the distance between the arm and the pump hex bolt by turning the lock nut. It's as easy as that with no guess work involved.
No, with it fully depressed there will be no clearance - that’s just a test to verify you aren’t bottoming out the pump arm which with the stock pump cam is pretty impossible to do. You make the clearance adjustment to your pump lever which should be zero lash with no load with the throttle closed. Thunderhead289
Your explanation is close, but it's simpler than that. Liquid fuel has more inertia than air. So it takes longer for fuel changes to happen than air changes. The accelerator pump preempts the lag in fuel delivery.
It takes longer to draw the fuel than the air, so mechanically it is applied to bridge the gap. I’m not sure what I said that wasn’t correct, but I like the technicality of your explanation
@@ThunderHead289 I've thought about it too. But there's that, plus, a lot of people have different (even strange) ways of understanding (and misunderstanding!) a lot of these things and don't want to see a different point of view. I think all the time about building my own carburettor design in stages just to demonstrate how simple the concepts are. But I doubt I'll ever take the time. I really enjoy your videos, and I'm sure there are others who also don't complain so you never hear from them. When I understand something, I do enjoy relearning it. If there was one big book on carburettor theory that explained everything in detail, I'd read it over and over.
I got a built 355 sbc duel plain intake, headers, big cam, holly 600 cfm carburetor, its having a hard time accelerating and it makes a pop out of the carburetor somtimes if you really get on it quick but it runs great on the top end, it idles fine and revs up fine in neutral but sometimes itll do that pop even in neutral, i upgraded the acclerator pump nozzle from a 31 to a 35 and it seemed to help almost taking the stumble away but now its stalling when i roll around a turn or give it alot of gas and lay off it barely wants to run, any help would be appreciated, i think the nozzle needs to go even bigger or a jet might be plugged up, the idle is fluctuating now also, it will idle down low off the cam then the rpms will jump up to about 1500 rpms, then it drops back down to barely idling on a big cam
Great videos Luke keep em coming I have a boat 351 Windsor 650 Holley marine all insides r new got it set too ur videos of course but they is a spot here we go at the lake that I have too idle in (no wake) which is a long way into the spot it will stall out sometimes it starts right back up n sometimes it takes a few times too get it too start back any advice would b greatly appreciated...... Joshua
I have an AMX with a crossram. I'm running 2 1850s and before jumping to Quickfuels I would like to see what I can do with the 1850s. Good learning. How about a lesson on two carb tuning.
TH289, I have a stock 83 mustang Gt, the 4180c bowls are leaking and just WONT seal, so I bought a 4160. Long thing short Leaking down into cylinders. Okay I got screwed whatever. Switched to another 4160, this one worked amazing on a 454, it runs great, won’t start back and grunts like it’s high in time, but it runs smooth and good. Would it be a adjustment or a Fuel pressure issue? As it’s the second 4160 having similar issues. But not flooding cylinders(hydro lock). But the stock 4180c fires up every hit of key no grunts or anything. No gas nothing, just key and it starts. The 4180c was stock 7-9lbs of fuel pressure, the 4160 is a max of 7 lbs, should I Check and Lower fuel pressure or any ideas? I’ve been pulling hairs
Wouldn't the number 2 hole be best on the primary side for a foot brake racer that has to come up on the converter to 2000 rpm so your not already using like 20% of the pump cam?
Good video..I Love the vw I got one too .what have you done to it? What size motor is in it..I am having problems with my holley street wayyor carb on my 303 f150 I'm not getting any vacuum to it the edelbrock has it I don't know what to do it also has a edelbrock intake on it
Can you explain an Edelbrock carburetor? I have a 360FE and I have an off-idle stumble, I have tried all the different accelerator pump settings and changed the springs in the carburetor. I'm tuning with a wideband o2 gauge and the air/fuel mix is perfect at idle and cruise speed.
Remember that carbs and ignition are a balance. Where is your initial timing at? If you advance your initial mechanical to 10-18 (transfer slot vs idle rpm will determine what exact initial) and then put your vacuum advance on ported.
@@ThunderHead289 I'm using ported vacuum advance, also currently using the factory advance of 7 degrees of initial timing. I will try to set my initial mechanical advance to 10-18 and see what it does right now.
Hey Luke, got a question. I had a 1976 Dodge Aspen with the slant 6. From the time I bought it new, if I made to sharp of a right hand turn the car would stall. I took it to the dealership a number of times under warranty, but they never fixed it. After warranty a buddy with more mechanical knowledge than I changed carburetors. It helped, but still occasionally stalled. We moved from Illinois to south Florida and a friend with more mechanical knowledge adjusted the carb and I never had the issue again. Sorry I don't know the brand of carb it had, but have you ever come across this and what caused this issue? To you and yours, stay healthy and I enjoy your videos.👍
Hey, Luke. Hope you can answer a question. I have got a 77 f100 302 c6 Has GT 40p heads New lunati cam Edelbrock, torque 2 and a 600 quick fuel brawler. Truck runs great idol's perfect and sounds good. But as I keep tuning on this thing, I am stumped, cannot give the truck a quick throttle input, or it backfires through the carb You got any ideas
didn't know I had a problem with my accel pump until I watched this video and jiggled my idle lever. I'll start adjusting and see what happens, may fix the temporary lag at hard acceleration.
You are super awesome guy you know what is going on with stuff like that. I hope and pray 🙏 that you and your family are doing well and safe from the coronavirus going around. I like your pooch..I have two they are in my profile picture. Ol bigfoot on the left side and Arnold on the right.. bigfoot is a pit bull mixed and 13 year's old and not doing good these days.arnold is a beagle and he is 9 years old and is doing pretty good right now he is my right hand man .lol. Be safe Luke.
Thunderhead...I have the AVS2 650 brand new. I've been having a stumble or bogging at take of or it seems like it's flooding can you give me pointer to adjust my f.a.r on a sb 350 with a rv cam. Thank you
Hi im Bob i really some advice im stumped. Been around this stuff for years so im not new to it. I have a Rochester 2bb carb on a 305 new rebuild it starts nice runs nice. But with choke fully open at idle it wont sit on cam to idle properly little on high side. But if i goose the throttle it idles down and sits on cam. then if i give it gas again does the same thing return springs are strong. Its like engine vacuum holds open a bit.,. Again if i goose throttle she idles down like it should. If i turn off car its fine drops down on cam.. Im stupped here any suggestions? Thanks i would appreiate it.
No play at 0 throttle. .030 of clearance with throttle fully open. Which to achieve this, you have to be just barely BARELY on the accelerator pump with your idle throttle position. Does that make sense?
You don't know my friend Dave. Back when I met him 15 years ago. Im telling you. He could set a Holly carb. And distributer. And it would fly.. If he could stand long enough. I would have him set my carb. But he is 73 years old. Has 2 different times. Broke his back. His stepson and I changed the gears in his 79 F150. 400 2barrle. Helped that 400 a little more peppy.275 replaced by 3 56.
I’m sure you’ve fixed it by now, I’m curious if the park idle needs to be dropped, and accelerator pump clearance tightened. Let me know. I have same issue
I put a reman 600 Cfm holly 4 b on my old GMC snow truck at the end of summer, I didn't have time to play with it, I got it started, but at low idle, it ran ok after it got warm, I put fresh gas in no methonal, , And now its -7 outside, a blizzard, and it wont start, I have to pump the hell out of it to get it to even try to start, but it wont, I did have it started 3 days before and adjusted the curb idle down a bit, , So how do I get it to start in real cold weather?
Umm Im in Australia and I got a f100 truck and the pump gear on the carb is none existent and the rod that I think controls the secondary is also not there, but it still idles but backfires on acceleration and runs rich. Could this be Becuase the motor was predominantly set up for LPG?
How can i richen my low speed circuit. When i try to lug down my truck lets say down to 1000rpm it will start leaning out on my AFR gauge and stumble. I can recover the stumble with a light hit on the throttle. I suspect it is because the accelerator pump sends a shot of fuel in.
Hey Luke, great channel, I watch it all the time, junkyarddigs too. I have a Holley Street Demon 1901, 625 CFM with electric choke, and I can't get it tuned to save my life. It seems the throttle plates won't close enough to make the transfer slots square, even with the idle screw backed all the way off. Any ideas?
my 4160 Cab on my 390 engine, i had to spray gas into the Carb for the car to start it wasn't spraying when you press gas, , i rebuilded the carb now it's spraying but now i have to press the gas to start the car once i stop pressing gas car turns off, any suggestions please?
