I have been trying to get my SBC dialed in and every time I get it close the timing seems to be too far before TDC (about 16 degrees) when checked with the vac adv. plugged off. When I stab the throttle it stumbles. It also seems to have a small sputter at cruising speeds maybe around 1100 RPM but its very faint. So I decided to focus on the carb and getting it adjusted first. So I started by setting the idle mixture screws back to factory setting per the holley instructions. I got my vacume gage home today and I was going to use it to set the air idle mixture. The fuel regulator is set to 6.5 psi. My cousin was over and he offered to help me adjust the float level which I was planning on doing after checking out the Holley instructions. When we took the sight window out no fuel trickled out, so when I tried to adjust the float level it spewed gas out the float adjustment screw at every adjustment I tried! I tried it all over the place and could never get it to put fuel up to the sight level. I tried the rear adjustment with the same adjustment and got the same results. What am I missing. I also noticed that when the engine was running I could put my hands over the carb and the engine would not choke out, I attributed this to the air idle mixture? The car ran pretty good with the exception of when you first stabbed the throttle. From what I understand it was acting like it was a little lean? If I applied the throttle smoothly the car would run out like a scalded dog. Some of my issues could still be related to the timing, but I'm still looking for some advice! I plan on using the vacume gauge tomorrow so we'll see what I find tomorrow. What else should I be looking for here!
I'm not sure about the float adjustment, but stumbling at acceleration is usually caused by the accelerator pump not pumping enough as you punch the throttle. Although I believe timing can contribute also.
I'd be looking for a HUGE vacuum leak first of all. If the engine doesn't stall when you put your jacket over the carb air horn something strange is going on... Look at the secondary butterflies which often stick open on these things and cause the engine to continue to run even when the idle speed adjustment screw is screwed all the way out. A leaky or blown power valve is a very common issue as well. Once you've got that figured out pull the bowls and set the floats the old fashioned way by turning the bowls upside down and leveling the floats by eyeball. This is a good time to check the needles/seats as well. Stumble could be a lot of things but check your accelerator pump diaphragm and adjustment first. Good luck!
There are 2 places you need to check, first your fuel sqwerters are replaceable with bigger sqwerters, not saying you need um but you may later... On you accelerator is a colored peice of plastic, (cam) they are also replaceable, and they adjust when the accelerator pumps starts to squert... Last you should be able to slightly loosen the screw and turn the nut to adjust float level, keep in mind loosening it just to the point of being able to turn the 5/8 nut but it will bind, Normal !!!! if you loosen the screw, it will leak... I alsways put the biggest accelerator pumps on the primaries and secondareys, as well as large squerters, but that depends on how much engine you got.... A rich hit builds torque, and will get things movin If your power valve is blown, your air mixture screws will do nothing. I plug the valve and bump up the jets to compensate, however its over kill and if your not runnin rich at an idle, then forget the PV its fine. If its blown it will act like a stuck choke...
Shut the engine off. Remove the float nut screw. You can move that nut far enough to disengage the flats on the needle seat and than you can't adjust it at all. catch a couple of threads on the nut and than put the screw back in and try adjusting the float again.
Thanks I watched some of the other videos on that channel but couldn't find that one! Sounds like the gas past the adjustment screw is normal then! I just went out and looked the carb over a few minutes ago and noticed that the choke "flap" was stuck on the fuel squirters so it was def. not working! I'm thinking I got hosed on this carb!
That is strange, I clicked on the link and it went directly to the video, pretty informative, you might want to try again.
When I clicked on the link it went straight there, I was reffering to the night before when I was searching youtube. I'm going to try to adjust the floats again tonight, and maybe take it to a buddy to look it over! If worst comes to worst I can take it to the carb shop, but I'd like to try to fix it my self first!
Holleys are easy... I would think if you have the sightest mechanical ability, you can rebuild the Holley your self.
I like Holleys, agree with them being easy to rebuild and tune. Jet changes are straightforward too. I used to tear them down at the track when I had to... under pressure to make the consi or main more than once. Bob
Going back to the "hands over carb" part.....Definitely very lean... Holley carbs usually have several vacuum ports on the base,...they come with rubber caps over them....I had a similar issue with a customer car....turned out, one of those caps had come off.... One backfire would do that..... No, I did not find the damn thing right away....... 4TTRUK
I'll look at the vacume ports, thought I had them all plugged but can't be too safe! As far as total advance how can I check that without a digital timming light? Or can I? I'm sure I can perform a re-build on the carb, I more or less meant to take it to the carb shop and see what he recomends, before I tear it apart?
FortyFordGuy found my biggest problem! Going back to the "hands over carb" part.....Definitely very lean... Holley carbs usually have several vacuum ports on the base I did have all the extra ports plugged but I found the rubber hose that goes from the carb to the hard line that runs to the tranny vacume was way too large and it was letting lots of vacume escape! I re-set the idle mixture based on highest vacume (it wound up at the factory setting of backed out 1 and a half turns) then I adjusted the float level per the video that slammed linked to! Most of the stumble at idle is gone but there is still some hesitation when I go way wide open way fast. I think its in the timing at this point. The car idles at around 700 RPM very nicely and it runs out pretty well It isn't very happy at around 1400-1500 RPM while cruising. Its kind of spitting and sputtering a little but if I drop down or up a little from there its just fine. I checked the timing again and with the vacume plugged it behaves best around 16 degrees before TDC.
After talking with my dad he thinks I should Re-time the engine and get it back to around 10-12 degrees and try to re-set the idle speed and air idle mixture to try to get it to run closer to the book. Does this make sense? When I back out the idle speed screw I am all the way out and its not dropping below 700. I don't think 700 is too high (6-700 is actually what my motors guide manual says) but I feel like I should be able to adjust the idle till it gets too low so I can find the sweet spot.
a couple of thoughts if I may.... You have a couple vacuum ports, 1 is constant vacuum, and one should be vacuum only while opening the throttle. When you time the car obviously do it with vacuum ports plugged and hose to dist disconnected, get it dead nuts on, then hook the vacuum line to the constant vacuum port, and go for a spin, if it bogs switch it to the other port that only has vacuum while excelerating... It has been my experience that some engines like one or the other best... Make sure your vacuum adv in dist is good also... When adjusting fuel mixture ou should start about 1/2 to 1 turn off seated, and unscrew both 1/4 at a time (evenly) till max vac is obtained, then screw it back in 1/8 turn. If you can turn the screw all the way in, the car should stahl, if not the PV is either to big or blown...
If the fuel mixture in it stalled the car as it should, I started it off at about 1 and a half turns out. When I re-set the timing to about 12-14 before TDC I was able to crank it out and get it to not sputter when I cracked the throttle after about 3 turns of the air fuel mixture on each side. I'll try to test drive it tomorrow and see what happens. I also noticed the electric choke adjustment is rotated about 180 degrees from where it should be. I'll have to look into that tomorrow! So far I've thought that I had it adjusted about 3 or 4 times, and after a few minutes I find something I did wrong. Good news is I'm learning, and its starting to make a little more sense. That is untill I try to drive it tomorrow and a new problem pops up!
Make sure that something isn't binding the linkage, keeping it from being able to idle down too. Does it have an anti run on pot holding the throttle off the idle screw? Sounds like you are getting it dialed in, just takes patience.
A whole lot of Holley stumbles are due to this...... The primary blade has a sweet spot - where the idle transfer slot looks like a square from below. If you have the primary too far open at idle - it won't transfer to the cruise circuit without a stumble. If it idles too fast with the blade set there - check to make sure the secondary is fully closed - and look for vacuum leaks.
Thanks guys I will try to look into all of these things tonight! I actually took my throttle linkage off for a while last night to make sure it wasn't in a bind. However If I force the throttle back hard with or with out the linkage the idle will go down a little so I'm wondering if something else isn't binding?
After you've got the primary blade in the right spot - the next trouble is how do I set the idle speed up without moving the primary?.....its usually too slow. I'm speaking of an engine with no vacuum leaks (holes all plugged) and only initial spark advance. Cars with auto trans won't stay running in gear.....that sort of thing. Hidden under the passenger side of the carb right under the secondary vacuum pot -there is this screw in the base plate - it sets the secondary blade position. I've found them with (1) no screw and had to get one (2) slotted like this picture (3) with a hex socket set screw. Most manifolds and gaskets leave this space clear - so it is possible to get a longer screw in there and be able to get at it with the carb bolted on the engine. There are two fuel delivery ports in the secondary bores that bleed fuel out of the rear bowl - and opening the blade a bit uses that fuel to raise the idle speed. otherwise they feed the air coming in through a PCV hose. The trouble you had with the float setting nut and screw bleeding fuel like crazy - I have been hunting down something besides the worthless "paper thin" gaskets to use on there. Only thing that has worked so far is making my own.
Glad that helped.....What about the tranny end of that vacuum line ? A bad modulator would give you still another vacuum leak. Ditto, Willie 301... Disconnect throttle linkage from the carb, and see what it does. 4TTRUK
I checked that Trans end of the vacuum line as soon as I fixed the carb end. I took it for a drive today and it ran great! No stumble at launch and no miss at 1500 RPM. I still think I have an issue with my linkage or my secondaries. I really don't feel like I'm getting all 4 barrels. When I have the air cleaner off and the engine running I can crank it wide open for a second or 2 and i never see the back 2 butterflys open up? and the choke is way out of adjustment! So I've still got some work to do but for now its running like a raped ape, and I've got a shit eating grin on my face that can't be wiped off!
Be sure that choke is adjusted correctly....If it's the least bit toward the "closed" position, it will lock out the secondaries. That's to keep you from dumping a load of fuel into a "cold" engine. 4TTRUK
I know my electric choke is out of adjustment but its way out! The adjustment pointer is way around at the bottom, and I can't figure out which direction to move it!
If it where me, I would take the choke off, of back it all the way off.... If you look behind the choke round adjuster, you will see the mechanism that locks out or locks the secondaries closed. Back the choke all the way off till that little arm drops out of the way... Keep in mind, secondarys, that are vacuum, have a spring in there, and the spring is designed for the engine it is tuned for. So that may not be good for your application, then again it might be fine. Refrain from the old small bolt in the linkage trick to manualy open them, cuz the vacuum design will not add power but rob power. Double pumpers have the secondary fuel pump... hence the name... Also make sure the diaphram isnt cracked. When you crack the throttle, the secondaries wont open until the vacuum is high enough to pull them open..... SO on a punch, vacuum is low, secondaries will be closed. enough of my babbling
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