4150 Carburetor Accelerator Pump Tuning 

What Keith said is very important and needs to be corrected in the video, .015 clearance to the accelerator pump arm is a WOT adjustment, if you are trying to select which color cam to use while you already have .015 clearance in the pump arm you will choose the wrong cam every time! (and the cam that you already have might already be the correct cam if adjusted correctly)

Awesome video mate. I've been learning a lot over the last 12 months but this video really takes the cake. I keep having take off hesitation in my ski boat.

Excellent demonstration. I'm all ears and learned more about my 4150 that I did not know. I honestly did not think that it was a long demonstration very informative. Thank you for your time. Keep the videos coming😊

With the accelerator pump arm adjustment, what I’ve read and done is to rotate the accelerator to WOT, then measure the .015 clearance to make sure the arm still travels and doesn’t bottom out. David Vizard’s book also says to preload the arm by 2 flats while still having the .015 clearance at WOT for instant throttle response. I haven’t tried that as as I got pretty good results by just taking up all the slack, better than the Q-jet accelerator pump adjustments results I’ve gotten in the past.

Thank You for Sharing this !!! I am rusty and this dust off my love of tuning the Holley carb back in the 70-80s... Yep old guy but running a 520 bbc on the street including delivering auto parts was a hoot !!! Yes old guys still say hoot...😊 Now last hotrod 540 bbc nitrous blower street car to drive to Kroger...my last hoot...lol !!!

Thanks for the cam information!! Definitely something that is not talked about at all Nicely done sir!!👍👍👍🏁🏁🤘

I will watch this a few more times. This is exactly what I needed

that still gets me on the nozzles being a measurement of time and not volume. i always just assumed it was a bigger shot of fuel. makes perfect sense your the only one who has talked about this

Definitely like the videos. I'm still learning carbs, and videos like this are incredibly helpful.

Great video as always. You make me miss tuning carbs.

Best information I've seen yet on carb adjustment..thanks for the video. Now I can get my carb tuned.

Man I know a fair amount about basic carb tuning but did not know about that screw. My new carb runs great but if I just slightly touch the gas off idle, it bogs. If I hit the peddle faster, it's fine. THANK YOU SO MUCH DUDE!

Thank you so much. This was so helpful. I'm starting to get a clue on how to build and tune my carb. I will have some questions when I start my project. Until then thank you again

I'm pretty sure you knew I would be visiting this video, lol. Anyhow, I got everything set just about to factory setting. The secondaries were way to far opened. So the car runs pretty well. I have a slight bog/hesitate just off idle. I was hoping to have more time this weekend on the car, but my old dog needed my attention. Dog trumps car every time. She's looking a lot better so hopefully, the long weekend I'll be able to get some more tuning time!

Great video. Another piece of the puzzle acquired.

Great video, tuning a 870 cfm Holley vacuum secondary on a bbc 540 right now in my c10. Baby stepping through the circuits. You confirmed something in the sequence of tuning I’ve never heard verbally really well. Great information. The secret is combination together! Loved the video.

Excellent tuning reference video. I always watch this before I jump into a tuning scenario with my 4150 style carburetor.

Thanks for the info you always share. 👍

Great info. Thanks.

Thank you Sir.

Greetings from Australia, many thanks for the info 👍

Awesome. Great info as always!!

Great video, but accelerator adjustment needs to be touching at idle. The .015 clearance is for all the way open clearance, otherwise you delay the shot for a few degrees throttle which could give a slight hesitation off idle hit. On the 30 cc pumps, I've never used a larger 50 cc even with E85 and had a great throttle response. At the same time I've tuned the idle air bleeds and mab's along with jetting to get the right mix. The best tool for carbs are a good o2 sensor, but realize unless you video the gauge and tach while driving or just hitting the throttle wot then you won't see exactly what's going on. At the same time a vacuum gauge in video is needed to determine the power valve. Wrong power valve is hard to solve with pump corrections!

Awesome video very instructive and precise. What would be the typical symptom of an accelerator pump found to be slightly pre loaded ?

As others have said, you are incorrect with the .015. There should be no slack in the pump AT ALL, and the .015 is measured as Additional pump arm travel at WOT.

Great video. I am currently running the pink cam, which came with the carburetor. It appears that the duration of my 1st shot is not long enough, and the stumble occurs between the 1st and 2nd shots. Which color cam would give me a longer shot duration?

Thanks for the information on the pump size. I will change back my pump from a 50 to a 30. My 750 vacuum secondary is for the street. My friend has a problem with his 750 vacuum secondary carburetor. When he does wot and let's go of the gas. The engine would die, but would start up after this happen.

Awesome video! I needed this! I have the 650 double pumper. I put hollow screws in the squirters. The solid screws barely let out the gas? Its better but a slight bog into the secondarys. I also have 31 squirters. 340 Chrysler, x heads.

Carbs are amazing, what a freakn rabbit hole. Learn to tune....!!!!!! A/F gauges and carbs should be sold together as a package... Mandatory..!!

I BUILT A 292 INLINE CHEVY 6, 12.1. 525/505 SOLID SCHEIDER CAM 108 OVERLAP, no budget !!! all machine work doe by professionals that know these inline chevys !! But its gonna be street driven to shows and some drag racing. HEI dist. M-21 close box 430 Dana 60 9 years to build it !!!! First pull on the dyno with a MAN A FRE 3X2 It shot almost to 370HP . AND CRISP !!! The rear carn took a crap and we slapped on a brand new 2x4 complete set up. It Made 383HP. 418 TORQUE. We had some time left and changed jets ,1 maybe 2 sizes bigger.and it lost power. we drilled and tapped the rear plate for a jet and it worked best stock jet size. But this 2X4 will tear ass, but it bogs, has flat spots Im stumped !!! Look on you tube for " 2 DR Checker Marathon Hot Rod,Thanks

thanks for explaining but the one thing you left out is wich way to install the pump cam. from the pictures I can see that the flat side faces the throttle lever. nobody ever starts the video with this is how to install the cam...... Great video.

Does the rules for the cams apply to the secondary side? Only put on the second position if your idle is over 850

In foot brake racing and I'm at 1800 roms for 5 sec waiting for the green. Am I using my squirters or still on the idle circuit?

I’m not sure, but I’ve read, from a bunch of articles in magazines, and from books I’ve bought about Holleys. They pretty much say that you should open the throttle all the way, then make sure that you have at least .015 clearance, so the pump doesn’t bottom out at full throttle. What’s your thoughts on that? I’ve been setting my pump arm like that for years. I still check to see that there’s no play in the linkage, and the pump reacts as soon as any movement is made with the throttle. Could I be limiting any shot from fully being used?

In regards to the secondary side...hole #2 if idle is above 850rpm or just leave it in #1??? Im thinking its more so just the primary side for that initial take off???

Still waiting for Billy Godbold , concerning tappet fails. Some have whispered bud lighting and targeting comp cams on the internet webs .

A small question. for a mercruiser boat caburator. because I barely start the engine. uncontrollably begins to supply gasoline to the cylinders. And when I turn off the engine, it is still supplying gasoline. It does not have an electric fuel pump.... greetings from rome..thanks

If anybody can help, im having that dead spot coming off from idle and i put brand new accel pump, jetting is two up from stock, 35's, timing is ok and no vac leaks, its a holley4150, single meter block, vac secondries, on 289 sbf, any pointers would help, thanks

So does the accelerator pump cam have anything to do with idling problems?

Its weird that I've never had an issue with a right-out-of-the-box 4150. There's formulas to use to find the right cfm for your application. Other than the float level and air bleeds...out of the box was perfect. I'm talking about 90's "gold" holleys, not the silver/polished versions that came out in the late 90's and after. Always had problems with those. I guess people think "bigger is better", and in certain situations, that's true. But MOST of the time, for all-around trouble-free operation, compromises have to be made. But before that silver/polished era of holleys, those gold carbs were trouble free. Even today I look for older used carbs and grab those 4779, 3310, or 1850 carbs from back then.

I put a 50cc accelerator pump with brown cams and #45 nozzles now my pedal is hard to press in when i try to go full throttle, there’s a definite hard spot going into secondary’s….whats the fix for the hard pedal?

So when your tuning the secondaries on a double pumper, they could be set very differently than primaries? Like I could have a 28 squirter in front and a 35 in back? Same with cams?

I love your videos but you do need to correct the part about adjusting the pump arm. it should touch at idle, the .015 or more is the play at WOT. We also start with squirters and use cams only for fine tuning. Not trying to be a hater, keep up the good work!

I see you have the new Edlebrock Double Pumper on the bench! I have one in my 78 bronco and am in the middle of tuning it. I love it so far. I have an new MSD box and AFR gauge and have swapped jets a couple of times(before the MSD box fixed a LOT of issues). Right now I'm working on getting a vaccuum gauge in cab to help tune the power valves. It seems good in the primaries but WOT is a bit wet. A question for you - Since the new VRS 1450 has thicker throttle shaft, can I swap out the cams on it with a holley unit? I've not gotten to the cams or air bleeds or PV restriction channels just yet but I do like digging into the details. I may even get another set of metering plates to make the hot swaps even hotter/faster. Dig the channel! Keep WOT!

7:26... You'd NEVER want to have be using position 2 on ANY "street car". If the idle screw has had to be cranked in THAT far to get the engine to idle, that would mean that your T-slot setting IS going to be totally out of whack, and that NEEDS to be corrected before you move any further. Whether it's drilling holes in the primary butterflies, or adjusting the secondary butterflies open a little more, the T-slot setting HAS to be adjusted properly, or else your idle, tip-in, and light throttle cruise performance WILL suffer big time. The #2 pump cam setting would ONLY be used for a radical race style engine where idle, part throttle, and tip-in performance is not needed and is non-existant. What I have found throughout my many years of tuning Holley style carburetors is that the pump shot squirter size is way more important than the pump cam profile is. 99% of the time, I can get the accelerator pump circuit operating flawlessly on any vehicle by adjusting the squirter sizes, and using the box stock pump cam. There have been very few instances where I have gained any noticeable improvement by changing the pump cams. In the few cases where I have had to play with the pump cams to get the throttle response 100% crisp and instant, it has been on a large cubic inch engine with a radical camshaft, and a somewhat tight torque converter.

So if I'm interpreting the pump cam chart correctly, most cams will not deliver 1/10th of 30cc with a full sweep. They will deliver less. The colors tune how much is delivered to the squirters and by when and I guess it's up to the spring to hold the tension on the diaphragm in the chamber as the squirters flow out what they can in the time they are pressurized. The cam's action on the arm can't outrun the squirters rate of flow.

Any way I can email you a afr video of mine? I've been stuck with this proform 650 I have. My afr is all over

So if u have a brown on the primary would you need brown on secondary?

Hi my friend. Great video. I am almost there with the tune of my 4150 edelbrock 750 cfm carb. I got all the right afr’s in all the right rpm ranges. But now i have the following problem. When i go quickly to wot it gets way lean. When i gradually press the throttle it stays on point. So I figured the accelerator pump needs some tuning. I dont think the pump cams for these carburetors are available yet, and i think i need a longer and maybe faster shot of fuel. Do you think enlarging the nozzles could help my issue?

I hope you can help I have this type of carb (actually a summit carb 650) -I rebuilt it and now I don't remember seeing a check valve ball and I don't see it on an exploded view chart.

I live in Sydney, and I have a full Bronco 1986 with a 351 Cleveland with (15' Rim, tyre size - 31-10-15 . Diff ratio 3.5), Engine bean rebuild no so long ago, but it was up to now dedicated LPG, with 18 Degrees static advanced because of the type of fuel. Now back to Petrol, ( what you guys call it "GAS"), I mounted a 600 Vacuum secondary manual choke Holley carburetor with external adjustable needle valves. The Bronco is mainly use for occasional trips going camping, and fully loaded. I was wandering if you could please give me an initiation setting of the carburetor , jets , power valve. I know that longer fuel delivery for a heavy vehicle and a slow curve of a distributer advance, is ideal. I had it all worked out for LPG over the years, I actually learned a lot. in my younger days, I experimented a lot also with petrol system, but just as an inexperience young man with no disasters results , otherwise I would had contacted the specialist. Would it be possible to have some help with carburation and distributer timing general idea to start with?. I know I'll have to experiment to finally pin point the best possible result, but it would be hard to tune and tray with an empty truck, with very different result once loaded. I fallow you tutorial videos and I enjoy your detailed explanations. Knowing stuff is one thing , but having the ability to transmit knowledge is another, and in my opinion you have both. Your reply would be very much appreciated, and very important to me as I will be start tuning soon. At the moment the carburetor is very stock ( as far as I know), with probably a 6.5 power valve. Thanks again for your splendid work. I am sure many of us have beneficiated from your videos. Kid Regards... Cos.

I have a holley 650 double pumper I bought off someone. It has a major stumble when I take off. I changed the nozzles from 28 to 33 and adjusted the accelerator pump. Still no change. I see it has a red cam should I change it and to what color?

Nozzle size is about the duration of the squirt, not the 'time' of the squirt, right?

What would cause a slight leak from the accelerator gasket area? I don't want to over torque the four p2s, but there is the slightest leak even after sitting? Are the blue gaskets not good for oil? Mines on a rotary application so I have to premix with 2stroke

When adjusting accelerator pump the choke needs to be open or closed I assume open?

Mines cut off when I try to do a burn out

What are those bright colored plastic looking things?

Hole #1 and hole #2 has to do with throttle position at idle, not engine rpm.

I just picked up my stock 82 bronco 351w I added a jegs 4bbl intake and bought a Holley 4bbl carburator I just pick it up from the shop the guy told me its running to rich when in park it will rev fine but when I put it in drive it starts to bogg after little presses on the peddle its fine but still running to rich. So my shop guy told me its a bat carburator and it has a flat spot so I need to send it back. But is was new or rebult when I bought it. Cost me 500 bucks for the dam thing. What whould u suggest I do