Currently, even though the carb was used, nothing's been touched or modified, so all the jet settings are stock. I'll be re-curving the distributor this weekend, so I'm not sure how much that'll change things, but here is how things are going so far:
Idle: It seems to idle nice and smooth. It's a tiny bit rough because I don't have a short or small enough screw driver to reach the secondary idle screw that is underneath the balance out the main idle screw. I'll eventually get to it. I have it pulling about 18 vacuum right now.
Acceleration: The truck bogs off of idle, occasionally to the point of almost dying if I really step on it off the line. For normal acceleration, it seems to accelerate "ok" but sounds like it's straining.
After around 2000 RPMs, I'm assuming the powervalve and secondaries open up because it really picks up and has plenty of power. I generally have to pay attention so it doesn't fly up to 4500 RPMs.
So, from what I've read, the off idle bog is caused by my accelerator pump being too small (stock 0.025). A general consensus seems to be that the 300 needs around a 0.031 or even a 0.035. Does this sound about right? They're about $15 each, so I'd rather make a jump to a good recommended starting point instead of increase slowly. (I'd be another $45 - $75 before I worked up to .035 and then I'd have useless jets sitting around.)
Also, the main jet is a 0.051 if I heard right. I'm at around 2500 feet elevation and have heard a 0.002 drop for every 2000 feet is good. Should I assume a 0.049 is about right?
Currently, my Bronco sits on 30" tires with a 3.00 rear end so it definitely is by no means a "quick" gear setup, so I'm looking for a lower speed increase. I'd eventually like to tune it with a rich/lean meter, but for now I was curious of recommendations of just a good starting point.
Thanks for any help!
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4bbl Holley 390 w/ Offenhauser DP intake. 4 speed Manual w/OD. K&N air filter, EFI manifolds, 2.5" exhaust.
3.00 rear end and 2000 RPMs @ 80mph!
Be sure the pump arm is adjusted properly. Look down the carb and move the throttle open...you should see an immediate shot of gas from the squirter. Technically, whenever the idle speed is adjusted or a pump cam is changed, the pump arm should be readjusted. Instructions for that are in the Holly Tech stuff. But, there is an easier way. Adjust the screw just back off the arm, turn it back down to where it just touches + a little more to preload the arm. Drive and try.
Next is squirter size. The squirter controls the amount of fuel the acc pump delivers. If it has a 25 squirter, try a 31. If that doesn't work, try a 35 or 37. What pump cam does it have? The pump cam determines the timing and duration of the pump shot. If you don't eliminate the off-idle, slow speed bog with the squirter changes, you might have to go to something like the blue pump cam but do just one part at a time...first the squirter size.
Then if you think you need a jet change IIRC it is one size down for every 1000 ft of elevation.
Go through the Holly Tech stuff for instructions...sometimes their search function is not friendly and I use Google and come up with what I want.
Welcome to the world of Holly carb tuning
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1983 F150 300 I6, Comp Cam 260h and lifter kit, Port/Polished head, Offy DP Manifold, Holley 4160/1848-1 465 cfm, EFI Exhaust manifolds, Walker Y Pipe to 3-Way Cat, generic Turbo Muffler, Recurved DSII, Mallory HyFire 6a & ACCEL Super Stock Coil, Taylor Spiro Pro Wires, EFI plugs.
Thanks for the info. And yes, from what I've read, Holley tuning is a big, big world. But there's plenty of information and lots to read, so so far I've had plenty to look over. It's a game I'm willing to play, and should be a lot of fun in the end when I get it sitting where I want it.
The carb shoots gas immediately when I turn the throttle and look in. I'll have to pay more attention to the duration. By watching the speed of the shot, can I tell how the pump cam is working? Or is that something that can only be felt during driving? I haven't adjusted the pump arm, so I will have to look into that to see if that makes a difference. I don't know what pump cam it has, I'm assuming the stock one. IIRC, it is black.
I was going to reduce the jet size down a little bit as per Holley's tuning instructions. No point in using extra fuel if it's not needed. 0.051 stock, 2000 feet, two sizes, 0.049.
After that, I'll start toying with when the secondaries come on, hook up a vac gauge, and pay attention to power valves.
Would it be a good idea to disconnect my secondaries for initial tuning so I can tune how the primaries are working?
Right now, I'll check out putting in a bigger pump squirter. If I remember the sound, it's making the same straining sound my 1bbl made when the main jet was too small.
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4bbl Holley 390 w/ Offenhauser DP intake. 4 speed Manual w/OD. K&N air filter, EFI manifolds, 2.5" exhaust.
3.00 rear end and 2000 RPMs @ 80mph!
The secondaries won't affect the primaries. They basically will not be functional until the vac secondary spring activates them. BTW, sometimes the secondaries cause a bog when going WOT at low speeds because they are opening too soon due to too light a spring. You will find them in the link to the catalog posted and also in the Tech Section on how to adjust with the different spring tensions. The quick-change kit is worth the investment...makes changing the springs easy and fast.
I went and got a 0.031 and it really helped with the off idle bog I had. It still has a little bit, so I might grab the 0.033 or the 0.035. However, the performance change was really noticeable.
I am curious how well most can "hear" the secondaries opening on their carb. I know from other vehicles I've been in, the sound is generally rather apparent. Although it drives nice, I haven't been able to really hear them kick in, even on the interstate at 65 - 75. The guy I got the carb from had the spring kit, and he sent me all the springs he didn't use. Looks like the lightest one is in there, so they must be kicking in. Maybe too early?
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4bbl Holley 390 w/ Offenhauser DP intake. 4 speed Manual w/OD. K&N air filter, EFI manifolds, 2.5" exhaust.
3.00 rear end and 2000 RPMs @ 80mph!
Actually, if you feel and hear them "kick" they are coming on line too soon causing a momentary lean situation and when the fuel catches up to the air flow one gets the kick. Technically, there should be a smooth transition from primary to secondary operation. But some people like the kick. It's adjustable enough to have it either way. You said it starts pulling hard about 2000 rpm. That's about right...it takes some speed to get the air and fuel flowing enough for the hard pull.
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1983 F150 300 I6, Comp Cam 260h and lifter kit, Port/Polished head, Offy DP Manifold, Holley 4160/1848-1 465 cfm, EFI Exhaust manifolds, Walker Y Pipe to 3-Way Cat, generic Turbo Muffler, Recurved DSII, Mallory HyFire 6a & ACCEL Super Stock Coil, Taylor Spiro Pro Wires, EFI plugs.
Alright, so it sounds like the secondaries are kicking in about when they should. It's a nice smooth transition.
I finished recurving the distributor last night. And, despite the warnings on the writeup, I did manage to lose the tiny pin that held the reluctor on. I had to make one out of an similarly sized hex wrench...
The recurve sure made an amazing difference off-idle and the engine pulls really hard. The only things I'm noticing are it makes a funky dieseling sound when I first accelerate off idle, almost clacking. Is this my timing?
The second is that at WOT, when I get up to around 4000 RPMs and then shift, there's a very strange smell I've never smelled in an engine before. I could almost describe it as smelling more chemical based. Kinda like someone sprayed cleaner on the engine and it's burning off. *shrugs* My guess would be it's really lean? I wouldn't know what that condition smells like as I've never had it in an engine before. Ideas?
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4bbl Holley 390 w/ Offenhauser DP intake. 4 speed Manual w/OD. K&N air filter, EFI manifolds, 2.5" exhaust.
3.00 rear end and 2000 RPMs @ 80mph!
I tried timing with the vac gauge and the highest vac I got was 18 1/2. 17 vacuum was around 6 - 8 degrees advance, and 18 1/2 was around 25 - 30 degrees advance and the engine really shuttered. I left it at around 8 (this was before the symptoms described above.) With the recurve, it idle's a bit rougher than it did before.
If I was out driving near my parents house, the dairy scenario would probably be it. But I haven't seen too many in the local neighborhoods in the city here.
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4bbl Holley 390 w/ Offenhauser DP intake. 4 speed Manual w/OD. K&N air filter, EFI manifolds, 2.5" exhaust.
3.00 rear end and 2000 RPMs @ 80mph!
I'm going to be running the same spacer/heater plate. What length studs did you use?
Are you talking about the four studs that hold the carb to the intake manifold? For those, I used 3" studs, but they were a little long. 2 3/4" would be a better fit.
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4bbl Holley 390 w/ Offenhauser DP intake. 4 speed Manual w/OD. K&N air filter, EFI manifolds, 2.5" exhaust.
3.00 rear end and 2000 RPMs @ 80mph!
Is this normal? Yesterday when I was out tuning the idle on the carb (got it to go from 17 vacuum to 19), I noticed that when ever I revved the throttle, it would stumble and then quickly race in RPM. If I just kept blipping the throttle (a quick tap to race it from only 700 to 1200 RPMs), it would continually stumble, stumble, stumble, and then die. I think it was just getting flooded with fuel and wasn't using it.
I notice this when I rev the engine at idle and while I'm driving around. I don't think the squirter is too big, it's only a .031 (and it really struggled off idle with the 0.025 that came in it), but maybe the pump cam isn't the right one? I was wrong on the color earlier, it's a light orange cam. Too much fuel too soon?
What do you think?
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4bbl Holley 390 w/ Offenhauser DP intake. 4 speed Manual w/OD. K&N air filter, EFI manifolds, 2.5" exhaust.
3.00 rear end and 2000 RPMs @ 80mph!
A stumble when blipping the throttle is usually an indication of inadequate and/or late pump shot. IIRC, FTF recommends a 37 squirter. I have a 31 and the blue pump cam installed in position #2 which I'll be changing to position #1 when I get off the road this fall...still have a slight hesitation in mine. Which pump cam is installed on your carb?
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1983 F150 300 I6, Comp Cam 260h and lifter kit, Port/Polished head, Offy DP Manifold, Holley 4160/1848-1 465 cfm, EFI Exhaust manifolds, Walker Y Pipe to 3-Way Cat, generic Turbo Muffler, Recurved DSII, Mallory HyFire 6a & ACCEL Super Stock Coil, Taylor Spiro Pro Wires, EFI plugs.
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And yes, from what I've read, Holley tuning is a big, big world. But there's plenty of information and lots to read, so so far I've had plenty to look over. It's a game I'm willing to play, and should be a lot of fun in the end when I get it sitting where I want it.
