Holley 750vs lean spike

[cstmwgn]

Squirrel is probably right that you are chasing windmills in trying to fix this small spike.
At idle the throttle plates should be all the way at the bottom of the slot. If you do not want to drill the throttle plates another method is to raise the secondary plates by adjusting the secondary idle screw. You have to take the carb off to adjust it so it can be a pain but it will allow you to see if the transfer slot helps without permanently modifying the carb.

On the idle screws, you may find that reducing the idle restrictor will help with adjustment and might allow you to lean the idle mixture better.

[Scott Liggett]

Most of these Holley's have the tiny Red accel pump cam. Get Holley's pump cam kit and go to the green one. Use it in the top hole with the screw in the top hole as well. You should not need more than a 31 squirter. Also, make sure to adjust the linkage so that when you move the throttle anything at all, it starts moving fuel. Typically, I adjust the linkage by tightening the screw with the spring on it until there is slop and it rocks between the throttle linkage and accel pump arm on the fuel bowl. The start adjusting until all the free play is gone, then 1/2 to 1 full turn farther.

[Lit549]

Most of these Holley's have the tiny Red accel pump cam. Get Holley's pump cam kit and go to the green one. Use it in the top hole with the screw in the top hole as well. You should not need more than a 31 squirter. Also, make sure to adjust the linkage so that when you move the throttle anything at all, it starts moving fuel. Typically, I adjust the linkage by tightening the screw with the spring on it until there is slop and it rocks between the throttle linkage and accel pump arm on the fuel bowl. The start adjusting until all the free play is gone, then 1/2 to 1 full turn farther.

Well,i tinkered with it yesterday.I Took out the 37 squirter that i had installed and went back to the 31,it got ALOT better,now it only spikes to about 16:1.I went back to a 72 jet,the lean spike came back ,so i went to a 73 jet,(cause the 74 is too rich),and the lean spike is still about 15- 16:1.Every once in a while when im cruising,let off to coast a second,if i get back into it a little to fast(part throttle),itll spike and hesitate.It ONLY does it now when i do that,if i accelorate quickly(full throttle) it wont do it.What drives me nuts is,why is it better with a smaller squirter now when a few weeks ago that same adjustment made it better??Only thing i can think is i didnt have the linkage adjusted right in the first place??Im going to do a littke city driving here in a minute,just to see what it does..Hopefully its closer.Oh,and i did try the green cam awhile back and it dumped way to much fuel,maybe i should try it again??

[Huskinhano]

try a smaller carb

I was going to say that too. A 650 will be or should be more then enough. on the vintage Mustang forum I hang out on a guy had a pretty hot 347. Big cam and high compression. He had a 750 Holley. At his buddies shop chassis dyno his buddy suggested putting the shop's 650 on in place of the 750. He made more power.

When you crack open the throttle, the vacuum drops off, the carb goes lean because there's no signal to pull the fuel through. The accelerator pump covers this up. Maybe try stiffer secondary spring so the secondary won't open up right away. This may help I'm thinking.

[Lit549]

Tuned on it some more yesterday,i did notice the carb throttle lever was loose on the shaft,when i would pull the yhrottle back it would move a little,then move the shaft (butterfly).I also removed the acc pump arm and it looked bent a little.Seems to be alot better but ive noticed that the lean spot is real bad when the engine is cold.Im guessing the ports on intakr being blocked can contribute to that.Once its warm it gets better,im gonna do some testing today and see if its better.I had a quickfuel 680 on it which is basically a 650,it ran really good but no matter what i did i could never get it to idle.I had absolute hell with that carb,straight from the box it had passages clogged,broken pieces,and would not hold a tune.I sold it and called several carb builders to get advice on best carb,i also wanted them to build it for the fact i could call them..Well every guy i talked to recommended the 750 vs..Idk,it feels like its making more power but man it sux of mpg!

[Lit549]

went and drove it,it was doing it bad,BUT i had the air/fuel screws to lean..Backed em back out and richened the idle cicuit and its fixed..It still spikes but the pump now you can tell the acc pump shot is doing its job,it spikes to about 16 then stops and drops to 14:1..So im thinking yhe acc pump arm and the throttle arm being loose has been my problem,i created more problems trying to remedy it,BUTi always go back to original if changes dont work.SO FAR i think i fixed it!Idles about 13.6:1 ,primary circuit is 13:1,wot is 12.0 :1..

[oj]

If the throttleplate is loose on the shaft it'll never get rid of the stumble, the throttle plate & shaft have to be precisely timed. I do a lot of circletrack carbs and thye never think to put a throttlestop at WOT so they are very hard on the throttleplate. If you catch one early enough you can weld it but if there is slop at that attachment point you might as well replace the throttleshaft. I've got dozens of woreout shafts in my collection and the complaint is always the same, 'I've got this stumble coming out of the corner', throw a new throttleshaft in it an dthey're good to go.

[Lit549]

If the throttleplate is loose on the shaft it'll never get rid of the stumble, the throttle plate & shaft have to be precisely timed. I do a lot of circletrack carbs and thye never think to put a throttlestop at WOT so they are very hard on the throttleplate. If you catch one early enough you can weld it but if there is slop at that attachment point you might as well replace the throttleshaft. I've got dozens of woreout shafts in my collection and the complaint is always the same, 'I've got this stumble coming out of the corner', throw a new throttleshaft in it an dthey're good to go.

The shaft is good,it was where the throttle arm is attached to the throttle plate shaft..It was loose,i took a socket extension and hammered on the corner of the shaft ,just enoigh to tighten it up,now its tight and the stumble is GONE..Finally!This has been driving me nuts..

[Scott Liggett]

A different pump cam, like the green one I suggested, will hit the fuel more right off of idle. That should get rid of that lean spike at the beginning.

[Lit549]

A different pump cam, like the green one I suggested, will hit the fuel more right off of idle. That should get rid of that lean spike at the beginning.

Thats my next move,i messed with it before but nothing helped,im assuming because the throttke shaft deal..Anyhow,im gonna go buy another cam kit and see,thanks..Ill post an update

[Lit549]

i havent tries the green pump cam yet but tbh ,im pretty much done with this carb I need a 650..So its for sale!

[Lit549]

I tried a few things today.I looked at the timing in my ignition as every carb ive had on this engine has had the flat spot.So,i was at 14 initial and 36 total..I installed a mechanical advance limit screw so i could raise the initial but leave the total..I ended up with 21 initial,36 total ,it had a little kick back on starter so i backed it down to 18 initial and 33 total..That seems to be the sweet spot.I also adjusted on the pump arm a little,hesitation is WAY better,i almost have it totally gone!It still does it for a split second but not bad at all.🙄

[Lit549]

also,bought me a holley 670 for 100$ today,just to see what the differance is..

[anotheridiot]

I tried a few things today.I looked at the timing in my ignition as every carb ive had on this engine has had the flat spot.So,i was at 14 initial and 36 total..I installed a mechanical advance limit screw so i could raise the initial but leave the total..I ended up with 21 initial,36 total ,it had a little kick back on starter so i backed it down to 18 initial and 33 total..That seems to be the sweet spot.I also adjusted on the pump arm a little,hesitation is WAY better,i almost have it totally gone!It still does it for a split second but not bad at all.🙄

The only way we got off of the lean spike with either the smaller holley 1850 style or the 750 quick fuel 4410 style was to put heavy springs on the counter weights.

Bottom line, we should have just locked the distributor out at 36, but I cant get past that not being a chevy thing to do. We will probably lock it this winter if we can find the timing contoller we can use with the 6AL and injection, but so far, this edelbrock e street is a pig that is getting worse mileage than either carb.

[Lit549]

bought a 670 avenger for 100$,39 for a kit,dippednit in clr for about 3hrs,let set in dawn soap and water over night.Blewnit all out,assembled,went and drove it,and it runs better than it ever has.Ive had a 600 edelbrock (to small),a 430$ quickfuel 680 (never could get it to idle right),a 350$ 3310 750 (too rich,shitty mileage,lean spot) and a 140$ avenger off craigslist runs the best ,lol..Go figure..Herea a few before and after pics,Clr is some good stuff.