Vintage Mustang Forums banner

1 - 20 of 55 Posts

·
Registered
Joined
·
49 Posts
Discussion Starter #1 (Edited)
I have been trying to tune my Holley carb for a while now. My dad had passed away and had given his 1967 Fastback with a 302 bored over to a 347 to me. He always said that the carb was "too big" for the engine so it ran rich? As I am trying to tweak the fuel levels in the float bowl assemblies as well as the 4 corner idle screws and STILL get an RPM of around 600 to 700, online, there are 2 different opinions on fuel levels for this carb. Some say, while running, it needs to barely be visible at the bottom of the site holes. Others are saying it needs to be at the middle of the site holes where there are two "marks" so to speak. I figured, the first step to tuning this carb to the best of its ability with this motor, I need to make sure the fuel level and bowls are set correctly, then adjust the 4 corner idle screws, THEN adjust the RPM's while car is in D and brake is applied. (3 speed Auto). Is this the best way to do so? Also, what are your thoughts on the fuel level and float bowl adjustment in these carbs? Down the road, I will be wanting to replace the gaskets on both metering blocks as well as MAYBE jetting it down. If I do that, where would I start on getting the correct gaskets and/or floats for that carb? Like I said, I BELIEVE its a 4150 Double Pumper Super Street series. Cant find any numbers on it but have looked on Holleys website for pictures that look like the one I have. Any information would be GREATLY appriciated!!! Thanks!

-James
 

·
Registered
Joined
·
2,548 Posts
Every Holley I've had I've adjusted the fuel level to the bottom of the sight hole but that was with the small plugs that you remove with a flathead screwdriver to check. If you have those large clear round window style float bowls it should be midway in that or slightly less. Somewhere on the carb will be a number that starts with List- or R- with that you will be able to look up the specs and see what you have. I always adjust them in neutral or park . Most of the time with the 4 corner idle carbs I seem to end up with the primary idle screws 1-1/4 turns out and the secondary 1 turn out. Without knowing more I'd start there. It would be easier to recommend settings if we knew the carb number/size and more about the engine, cam, etc, as well as the rest of the combo. Did your father keep a build sheet or notes as to what went in the engine as well as the trans and rear gears? There's more to idle adjustment than just the carb, you will want to verify and use the ignition timing to fine tune the setup. Also, post your location, might be a member close by willing to lend a hand.
 

·
Registered
Joined
·
49 Posts
Discussion Starter #3
Ok thanks. I will start with adjusting the float levels, then the 4 corner idle mixture screws. No, unfortunately he did not keep any records. The only numbers I can find is the us patent number. Here are a couple pictures. And I'm south side of Indianapolis.
745071
745072
745073
 

·
Registered
Joined
·
1,178 Posts
Time to purchase a Holly Carb and manifold book and read up! Now I see you have a Quick Fuel carb, I wonder what CFM size? The float should be adjusted for the fuel level to be at the bottom of the sight hole. Turn the idle screws in until the rpm drops and then back out 1/8 turn. Do this operation on one side, then the other side than repeat. Main jet tuning is probably required. Have fun!
 

·
Registered
Joined
·
4,393 Posts
That's a vacuum secondary carb, not a double pumper.It may be too big but all that would do is make the engine a little lazy at low RPM.
 

·
Registered
Joined
·
383 Posts
We had a fleet of F600 ats work and I have rebuilt probably Holleys in 30 years. You always adjust the float level to the bottom of the plug. Just slightly lower. I raise the level until if I shake the car a little fuel slosh out of the hole but it it not running out the hole,

To adjust the a A/F mixture all four screws ned to b set the same. Gently run them in counting the turns. Do not bottom out the screws very hard or it will distort the needle and seat. Just until they touch. Back them out all the same amount. maybe starting with one turn. Take one of those little propane bottles opened just a little and pas it over the carb. if the idle goes up the engine is lean. Turn the four screws out evenly,a 1/4 turn at a time until the propane does not raise the idle. Your really close at this point, If the idle drops with the propane its to rich and you need to turn the screws in. When the propane makes no difference open the screws another 1/8 to 1/4 turn just to make it a little on the rich side. That is because a carb never works the same two days in a row because of the parametric pressure changes. For better drivabliitu you adjust the mixture "slightly ". You can do the same thing with misting starting fluid or carb spray into the carb instead of the propane. I use the propaned because here in CA it was a required shop tool for adjusting carburetors for passing the smog test.

The old way was to turn the screws in until the rpm drops and them back them out to the highest idle rpm plus 1/4 turn more. On an over-sized carb maybe an 1/8 turn would be better. The propane bottle is really the way to go. Its also real good for locating vacuum leaks along the intake gaskets, carb bases and vacuum hoses.

Make sure all four screws are turns the same amount. Last thing is to adjust the idle speed screw. Everything you change effects the A/R at idle so dwell on the point is adjusted first, followed by the timing, then the idle A/F mixture and lastly the idle speed. It must be doine in this order. if you change the timing then you need to go back and adjust the A/F ratio.

If you turn the A/F mixtures screws all the way in and you cannot get the engine rpm to go down then you have a leak in the carb. Fuel is getting into the engine from another source like a leaking power valve. The only fuel going into the engine at idle should be going through those idle passages controlled by the A/F mixture screws.
 

·
Registered
Joined
·
1,178 Posts
Holley Instructions, wet float adjustment. This is with brass sight plugs, but level is applicable to sight window holes. A “wet” level float adjustment can be performed on either the side or center hung floats, if the fuel bowls have provision for the externally adjustable needle and seats. This adjustment is made as follows. Start the vehicle up and move it out of the garage and into an open area where plenty of fresh ventilation is available. Allow the idle to stabilize. Turn the engine off and remove the sight plug from the primary fuel bowl to inspect the fuel level. If it’s been determined that adjustment is required use a large screw driver to crack loose the lock screw. With a 5/8" open-end wrench turn the adjusting nut clockwise to lower the float level. Conversely, turn the adjusting nut counter-clockwise to raise the float level. Tighten the lock screw. Restart the vehicle and let the engine idle stabilize. Shut the engine off. Remove the sight plug to reinspect the fuel level. The fuel level should stabilize at just below the level of the fuel bowl sight plug hole. This same adjustment procedure is performed on the secondary bowl.
 

·
Registered
Joined
·
9,286 Posts
With the sight window carbs it's supposed to be midway or slightly less in the window. IIRC.......
100% correct - center of the sight glass

You appear to have the Super Street 4150 carb. Don't know the CFM and cannot help identify a Quick Fuel carb. You might want to call or email their tech line for help with that.

 

·
Registered
Joined
·
4,830 Posts
It sure is purrdy!
That's an advanced level carb, might have the infinitely adjustable metering blocks that really takes some science and luck to get it perfect. Before you start changing too much on it you might swap it for a dumber one thats just as nice looking. I'm sure you could come out money ahead from that fancy baby.

For most driving err with the floats to be on the low side.
On a new unit like that I would set everything to mfgrs specs and then change the jets downward 1st. Does it have the plugs on the bowls for quick jet change? That $10 driver tool is worth it.
Try and get it to idle in park with the throttle completely off 1st, then add idle if needed in drive.

Buy the blue re-usable gaskets and spray with wd-40 before install. The paper ones are sometimes reusable if soaked with the WD. Diapers or cheap puppy pee pads are great to catch the mess..
 

·
Registered
Joined
·
1,178 Posts
QF is owned by Holley. Your QF carb is based off the 4150 Holley. There are some very good pointers in this Holley utube video for adjusting a 4150 float level is here.
Personally, I wouldn't trade out the carb unless the CFM is incorrect for the engine. If you have a caliper you could measure the throttle plate venturi and the main body venturi size and call QF to determine the CFM. Call Holley, they are always glad to help out. If the carb is the correct size, spend time learning how to tune it and you will be happy Its not hard to do.
 

·
Registered
Joined
·
23 Posts
How long did the car sit for before you acquired it? With ethanol fuel, if it sits too long without running it will destroy the seals. On the flip side, you could run for 20 years without a rebuild if you drive it every day. My 347 powered falcon sat for 2 + years before I bought it and ran terrible. Had a performance carb shop in the area rebuild it and now it runs great. Mine has a Holley HP 750 cfm 4150 mech secondary carb and runs very well with my 347, but probably wastes more gas than I need to.
 

·
Registered
Joined
·
49 Posts
Discussion Starter #14
All great info! Thanks a bunch! I will email Holley and see what they have to say. I just got done adjusting the float levels...the fuel, while running, is in the middle of the sight windows. Then, I attached a vaccume guage and adjusted all af screws to get the highest rpms, and had no bad smoke from tailpipes and no burning in the eyes! I assume it was all good and gravy! Then, adjusted rpm to run at around 650 to 750 at idle. Then, adjusted vaccume secondary so no bog when I hit gas. I know it's always ran rich before because every now and again, my spark plugs would be REALLY fouled and black. So I would clean them and start it up and it would be fine. I may want to look into jetting it down. Would that decrease performance? Or would I just have to do some more adjustments afterwards? And I don't want to replace the carb...love this one and my dad always said he loved the way it sounded!
 

·
Registered
Joined
·
4,199 Posts
Go to the Holley web site, there are a ton of videos and information available, I do mine to the bottom of the hole and have for 20 years. Not quite sure how you do it to the middle of the hole if you don't have sight glasses and these cars do not come with them except as an option. Also, if you drive the car hard and the float is too high, when you brake really hard e.g. Autocross, fuel will dump out the air vent into the carb and flood it, ask me how I know, so I dropped mine to the bottom of the glass and it helped. I finally had to add an extension (rubber hose) to the vent to completely stop it.

Make absolutely sure your choke is wide open when the car is hot! If you are still burning rich, you can downsize the jets one size at a time even if the carb is too big and you should be able to get the mixture correct. Its very easy to do, google is your friend. IF you don't hit the secondaries often, just downsize the mains till your burning nicely. Then take it to the drag strip or track and get the secondaries right. Remember, big carbs are in their element when the RPMs are high where the flow is better matched to the size. You can get them to work fine by matching the jets correctly they just have a little less throttle response in the mid range. If you never had amazing throttle response, you'll never miss it.

Make sure you light the motor off occasionally, runn it in a lower gear once in an while to blow it out. Looks like dad liked a little pepper in his life, you may be babying a race horse that needs to be blown out occasionally...
 

·
Registered
Joined
·
49 Posts
Discussion Starter #17
Ok great info! Yeah, I usually start it up and will put it in 1st and 2nd gear and let it run at least once every week or every other week. Like I said, right now, the fuel level at idle and in P is at the middle of the glass sight plugs. I have tried to tweak the idle screws to where it wont smoke bad out the tailpipes nor smell really bad. I had an RPM gauge hooked up to it so I could adjust all the screws to where it got the highest RPM at idle in P. Then, adjusted the curb idle screw so RPMs were roughly 600 to 750. Im sure I can do a few more things to get the most out of this carb but just unsure of where to go first. Thinking of buying the Holly rebuild kit for gaskets and the jet kit. So by the looks of it, what type of carb is it? And, if ANYONE is in the Indianapolis, IN area, I would GREATLY appreciate a good "looking over" and some helpful tips....

Also, forgot to mention, when looking at the back of the car, the left tailpipe always seems to be putting out more white/thin smoke than the left. Also, when looking under the hood, the right side of the engine always seems to be fouling the spark plugs more than the other side and noticed a small amount of oil coming from a few of the holes where the plugs sit. Could this be from one side of the carb too rich?
 

·
Registered
Joined
·
49 Posts
Discussion Starter #19
Also, there is a vaccume line that goes from the transmission up. It is not hooked up to anything and didn't know if this was just a breather hose for the transmission? Here are a couple more photos. Black line is going to tranny. Also, didn't know if I needed to plug up the port that's circled as well. How would I adjust fuel pressure? Had a mechanical fuel pump...
745635
745636
745637
745638
745639
 
1 - 20 of 55 Posts
Top