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.

Thank you for this my dad passed away and I'm trying my best to get his car running

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.!

Great video! the only way people will stop being afraid of carburetors is by learning about them. Can’t wait for the edelbrock video!

I just bought a 77 F150 with a 351M... Ran like crap. After viewing numerous vids, I have it dialed in perfectly. Thanks Luke!

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.

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 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!!!

Always look forward to your tech videos. Thanks for great information. You have really helped me out. Not afraid to tackle my carb now.

THANK YOU!!!!! 87 El Camino has been killing me. Exactly what I needed

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.

Good stuff! I'm getting ready to deal with a marine carburetor and appreciate the lessons!

This video is way better then the one from Holley thanks man

Thanks, Luke. Good, precise information explained so that even I "a self-proclaimed non carb guy" can understand. Good stuff !!

Just like in Vespa Lx 125 with Walbro carb, fantastic, thank you!

Great as always Luke, best part? The mic level is perfect volume and clear, love it! Don't want to miss a word of this gold!

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👍

This makes a lot of sense. Thanks for explaining things!

Always love to learn from a guy with a bottle opener ring :) Great video

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.

Thanks Buddy.. simple and to the point!

Thanks Thunderhead, I learned something today.

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!

Verry helpful! especially given i just got done rebuilding my Holley off my '74 F350

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.

great tip,something I knew , but many people dont.

Such a smart bloke love this guy

Thanks Luke, Please make a video on the Edelbrock.Your tutorials are most helpful.

Thank you so very much for a concise easy to understand tutorial- much appreciated.

Another great video, information that Holley should supply with there carbs when you buy them.

I can't wait to see the Edelbrock . Because I having problem with it . And how you explained things I might have a chance to fix it 😁

I've been learned! Another good class to give me more clarity on my 650 DP! Thanks Luke!

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.

Dude your info is spot on

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 helped fix my problem, thanks!

this is so ridiculously helpful - thanks !

Great job explaining. Thanks

Love ya vids about carbys learned heaps from em thanks from aus

Great info. Thanks for posting.

Thanks for the video, very informative.

Releases subscription to the channel, big fan

Falled in love with Holley Carburetors first time I met one !!!

Thanks for sharing your knowledge Luke and in a way that's easy to understand

THANK YOU!! Very helpful man you’re the man!

Great video brother very informative

Neve knew the idle adjustment altered the accelerator pump setting, cool

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.

Very informative video, thank you sir

Thanks for this video man as a 16 year old I needed some help with this

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.

WOW thanks for the amazing sound quality upgrade!!

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...

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

Excellent, and thank you!

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.

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.

Great explanation thanks

👏🏻👏🏻👏🏻👏🏻👏🏻 Bravo Zulu!

The mic volume was queit, but perfect for me! I didn't have to turn the volume up all the way either. Thanks for the ThunderHead Tech Tip.. Lol. 👍

That made me smile

I like to use a feeler gauge of 0.015 for the gap setting on a Holley. I think Holley video says that. Check their video though for sure. Thanks

Learned a ton from your channel! This is sadly a lost art. Most mechanics I know lift their eyebrows when you even say the word carb....

Legit didn’t even think of the accelerator pump adjustment after changing idle speed Give it a shot tommorow reckon it’ll be perfect

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

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.

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?

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.

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

Thank you

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?

Man I wish you could tune my 73 Chevy stepside

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

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.

Thanks for the information TH289! Where r u located at ?

Another fine vidya Luke. Keep them coming. Talk to me about a letter CAM brother. I'm about to buy one. E303? Street Driver

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?

Hello bro. Kindly tell about 1982 toyota corolla dx distributor vacuum hoses connection to carburator hoses.Thanx

Hell yea

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.

Good to know

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.

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

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.

Do you ever work on 2 barrel ford carberators?

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.👍

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

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 would you decide on which cam would work best?

I know you dont like edelbrock but you should make a few vids on them

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.

I think I owe you a nickel! 1961 mercury comet with a 302

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?

Actually,, you forgot to mention the transition slots which are the accelerator pump, so to speak, which allows fuel to reach the manifold before the acc. Pump shot, because they are at the bottom of the carb. Which is closer to the manifold.

Good video as always. Is that ring a bottle opener?

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.

Thank you. Holley recommends .010 adjustment at closed throttle. You sound like there should be no gap? What adjustment gap will you use?

Do you work in a speed shop or something? I'm wondering where you are seeing all these misadjusted Holley carbs.

Installed a 600cfm 4 barrel holly carb on my 81 Ford f100 302, seems like it idles a little high and when put in any gear it dies.