I'm definitely not going for over-powered. I want something that is quick from light to light but will tow a car occasionally and haul lumber, appliances, etc. I did buy this truck intending on rebuilding the engine but for now, if I can get it running and driving, it will probably not be rebuilt until winter unless something feels "wrong" before then. I would be satisfied with 8.9:1 compression. The only reason I was thinking 9:1 over 8.9:1 originally was to brag. It's like a 427 vs a 428, not enough difference to really matter (that I'm aware of) just something more satisfying about that extra .1:1 or 1 cubic inch. Besides, it has the stock '74 heads. I'm likely going to keep them in the interest of saving money so building a powerful engine only to be limited by the heads would be something I'd like to avoid. I think finding the balance between fun, usable, and cheap will be more fun than throwing endless amounts of cash at building a drag truck. Thanks!

 

All engines are basically the same till you bolt the heads on and all engines are limited by the heads they sport.

For the open chamber heads (the ones you have) the best thing you can do is zero-deck the engine and run-flat top pistons this will significantly minimize preignition. With standard 0.040" head gaskets flat top pistons and a zero decked block with a 0.30 overbore you will be about 9.3:1. This combination will have less chance of preignition than a lower compression ratio with the piston sunk in the block or running a zero deck dished piston. Ask me how l know... In short, been there done that. ( If you have to lower compression due to a tight set of open heads used dished pistons and zero deck them.)

This is quite a livable combination on the street for a truck. Pick a cam with a little longer duration, lower valve overlap, and thanks to the large vales in the Cleveland heads you can run a wider lobe separation for good idle. Depending on cam choice this combination will make 300HP and way more (depending on cam) and will be quite happy with no issues on 87 pump gas.
This combination can still all factory lower end it would be advisable to upgrade the valve springs but the cam you choose will have a recommended seat pressure and coil clearance. And really you should replace valve springs during a rebuild just as a matter of fact.

I have built a few 335 series engines in a similar combination and all have lived quite happily on 87 pump gas. I won't have anything built that will not live on 87 octane.
This is a simple low cost and easy-to-do combination that will give you a solid balance between fun low cost and reliability and the ability to tow/haul. Do not get too hung up on the Compression ratio there is no set number between being able to use 87 or not, it is entirely dependent on the engine and the combination of parts and tuning. There are engines that will hammer at 8.0:1 CR and others that will never detonate with a CR of over 10.0:1 on 87 octane

So you should not focus on the compression ratio and focus more on what combination is going to achieve your goal. And your goal is fun while still being able to tow/haul in a lower cost build that will provide long-term reliability and able to live on 87 pump gas.

 

Thanks for the tips! I'll keep reading up on this stuff. Even if I do run into some problems with 87, I'm fine with the extra couple of cents for 89. Id just like to avoid going above 89 for the principle of it (all in my head). I will also keep an eye on gas prices and the oil industry while I get the truck road worthy over the next couple months. Here in central Illinois, we went from $2 per gallon of 87 in January to $3 in less than two months. If they stabilize and things aren't looking too volatile, I won't worry so much about using strictly 87 octane.

I've also heard gas prices will likely go down as electric car sales go up to convince people to continue purchasing gasoline powered vehicles. Hopefully it's not the other way around. We had a family jeep grand cherokee in '09 when gas was $4+ per gallon and had to sell it. I don't want to end up only driving this truck once or twice a week.

 

Here is a link to the truck running after installing the new carb and working out some issues. Let me know if everything sounds okay.

If you plan on buying one of these reman carbs or anything cheaper than $100, buy a matching rebuild kit for it just in case. After installing it, gas leaked from the accelerator pump almost immediately. Thankfully I had a spare from the old carb that was brand new. I was able to swap it in while it was still in the truck and so far, it has worked great. The idle screws were both out 3 turns. I set them at 1 1/2 turns which is where they are in the video. The gaskets were also low quality but seem to be working. I may replace them at some point. Maybe when I get rid of the egr (it's plugged off right now).

The only problem I seem to be having is the ported vacuum. I have the idle set at 700 rpm right now. I had the timing set at 12 degrees advance. I had the vac advance plugged off but when I attached it, the timing when to 15 degrees which means some vacuum is getting to the port at idle. I've tried to drop the idle with no change. I went as low as 550 rpm. Is this normal? It's only 3 extra degrees. I've got the timing backed down to 9 degrees (12 with the vac advance).

Let me know if everything sounds okay. I appreciate it! Thanks again!

Edit: I should also add that I sprayed EVERYWHERE with carb cleaner and didn't find any leaks! If I sprayed it into the top of the carb while running, it kind of bogged a bit. Is that a sign of running rich or normal? Thanks!

 

I started it today with good results! The vacuum advance still has a bit of vacuum at 600-700 rpm (about 3 degrees) is this normal?

Does anyone know of a recurve kit with an adjustable vacuum canister for a motorcraft points distributor? Thanks!

 

Im currently having the same problem with my ported vacuum. I havent been with the truck for about 3 weeks and havent been able to try anything on it.

The cause is the idle is so poor that the throttle blades must be open for it to idle well. So try to improve the idle in anyway.
Tune carb, new distribuitor cap, spark plugs, spark wires, ignition coil, etc. those might help

 

I'll keep working on it. The idle seems very smooth though. I had it down to 550 when warm and it still had a little vacuum.

Does leaning the idle mixture screws raise the idle speed? I could possibly lean the screws a but more (1 1/2 turns out right now) wouldn't the throttle blades needing to be more open indicate it needs more air?

 

You want it as lean as you can with max vac/rpm.
Im sure you know how to tune carbs, but heres how I do them
Once the engine is fully warm, turn one of the mixture screws rich until vac or rpm starts to drop. Then turn it like 1/4 turn rich again. Do this with the other mixture screws. Then start on one screw and turn it in until max vac/rpm. If it gets to a point where it stays the same keep leaning it in until vac/rpm drops. Do the same with the other screw/screws. Turn one of the screws 1/2 turn out and keep going in again until vac/rpm drops (in case it changed the engine dynamic when you did the other). Do the same with the others. Finally turn them rich 1/4-1/2 turns.
Again, Im sure you know how to do it, but I always find other peoples insight and methods helpful if not interesting at the least.

*edit* When I say out that means rich, and when I say in I mean lean

 

Screw out the idle mix screws richens up the idle mix and raises RPM. Screwing in the idle mix screw leans it out and lowers idle rpm. If the idle mix is too lean you will need the throttle blades open more to reach base idle.

So if you have the ported vacuum port showing vacuum at idle you can fix this by adjusting the idle mix correctly for max manifold vacuum or engine idle and advancing the timing a bit if needed. If none of this works then you likely have a carb that is not really calibrated for your engine.

 

Thanks! I will hook the vacuum gauge back up and check it again. Are there any other tips to check lean vs rich other than looking at the plugs (like running quality etc...)

 

Thanks! I'll try backing the mixture screws out to 2 1/2 and see if the idle goes up enough where I can back the idle speed screw down

 

NO, adjust the screws out till reach max idle RPM, that is the correct way to adjust idle air mix if you do not have a vacuum gauge. if you have a vacuum gauge you adjust for max manifold vacuum.
The number of turns out is NOT a way to adjust the idle air mix, the number of turns out of the idle air mix screws is completely irrelevant, the only thing that counts is adjusting for max manifold vacuum or max engine rpm.
Get off this number of turns thing that is only used for a base setting after the carb is rebuilt, before it is dialed in on the engine.

 

I am not on a "number of turns thing". As you can see in the video, I am using a vacuum gauge. I have it set 1/8th turn out from max vacuum (about 1 1/2 turns). At the time, I did not have my tach setup as I was only focusing on the vacuum. I was merely going to set it at 2 1/2 turns out as a base for myself to start from again and check idle speed this time instead of focusing entirely on max vacuum.I will get to it tomorrow because it's too dark now.

 

Well for not being on a number of turns.... that is exactly how you are describing your settings.

Since you have a vacuum gauge set it to just achieve maximum manifold vac and do not run the mix screws out any further than that. That or max RPM if you do no have a vacuum gauge is the ONLY way you should be setting the idle mix.
Once the idle mix is set, adjust idle down to spec and go back and check the idle mix, you may have to go back and forth a few times to get the settings dialed in.

 

Everything I have read has told me to go as lean as possible before the vacuum becomes unstable, then richen it 1/8 turn to be safe. That is EXACTLY what I've done from the beginning. I am only stating that it ends up right at 1 1/2 turns so that people know I'm not at some crazy number like 1/2 turn or 4 turns. If you read earlier posts, you'll see that I was dealing with a vacuum leak from a worn throttle shaft. This required that I run the screws 4 turns out just to get it to idle (trial and error). I am thrilled to be down as low as 1 1/2 turns (SET WITH A VACUUM GAUGE) simply because it means my vacuum leak is likely fixed with this new carburetor, NOT BECAUSE I'M RELYING ON A NUMBER OF TURNS THING! Which by the way, has its own merit. If you have to go extreme one way or the other, like I did, it can help diagnose what's wrong. PLEASE stop insinuating without fully reading through the previous posts and understanding how I got it to this point.

Regardless, I don't think you're understanding the question/problem. I'm NOT asking about how to set the mixture screws and idle speed, I have done that MANY times now. I was simply saying that when I had everything set properly, the idle was down as low as 550 rpm and running smooth, however there was a slight vacuum on the ported "nipple". (I currently have the idle set just shy of 700).

That means the throttle is open just enough to create a vacuum on that port which shouldn't be happening at 550 rpm. That's where I'm trying to direct things, NOT the mixture screws. They only came up because I'm trying to find an alternate way increase the idle speed so I can shut the throttle plates more to close off the ported vacuum. I have tried adjusting the timing and will re-do the mixture screws again to find peak idle. If I can't get it to idle without a little vacuum getting to the vac port, I'm fine with that. It's only advancing the timing about 3 degrees at 700 rpm which is less than what it would be if I were using manifold vacuum for the vac advance.

For reference, this is one of the videos that I watched to help me with the mixture screws.
Please get off this mindset that I'm on a "number of turns thing" so we can actually accomplish something.