Is my 340 Overcarbed? Avg 5-6 MPG

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That plug is way beyond a couple jet sizes rich. The power valve tipping in early combined with jetting maybe, but it even looks richer than that and so does your mileage. AFs in the 12s generally look black but not sooted

Moper is right, your power output on the dyno sheets are way down for that kind of setup. Overcarbed and overcammed would have shown signs of waking up 5500-6600.

Back to the OP your carb is not the MPG problem. Not on its own anyway. Your cam and its installed centerline and overlap are making the engine wheeze at cruise. Dynamic compression determined by valve timing at these part throttle power settings influences the engines economy. The initial timing, advance curve, and lack of vacuum advance is also an economy issue.

Get a vacuum gauge rigged and work your timing at idle and then monitor your cruise vacuum. Hope you can get it 15 or better or the cam is fighting you the whole way. After you have the timing worked out drop in the main jet change and power valve at .5 your new idle vacuum.

I have a real time AF on my carbed engines too. My dual quad hemi with shaker took over an hour for every jet or metering rod change (2xEdelbrock AVS) but after 6 or 7 rounds of hassling with changes and measurement, the payoff is it runs like an EFI setup.
 
Of course this is not what I want to hear right now, but I value everyone's opinion here so that is why I am leaning on you all. The reason I took this engine to a professional builder was to have it done right so I am going to take a trip to go and see him tomorrow. He recommended this for my setup so I thought I was in good shape. If I have to re-cam or re-carb this thing, I am gonna be pretty pissed off, but I will do what is right to make it right and put out the horsepower. I thought the dyno HP was on the low side as well, but I am not smart in that department. I wanted a built, healthy small block. Frustrated...but still receptive...
 
It's ALL in the tune up. It will need more than a jet change is my guess.

Get the initial cranked up and start from there, which bushing on the distributor? Black? You'll need a different one to get it right at idle. I sell them and they work well. If it was tuned on a engine dyno, the in car requirements can and sometimes are VERY different.

I wouldn't worry about changing a bunch of parts, I have stuff with a much larger camshaft that runs well on the street. It's sorting it out that will take some time.
 
Thanks crackedback. Yeah, one and two jet sizes is not helping. It is still yellow at 12afr at cruise. Idle was in in the red at 18afr so I richened up the air mixture screws and that was resolved. Idle is sitting at 14.5-14.9afr.

Here are some pics of the current dizzy setup. Both bushings look to be silver not black. I also took a pic of the spare bushings and springs. I may end up selling this carb and going with a 600cfm or 650. Not pulling that plug yet until I talk to my builder and get all of your thoughts. I am not trying to go through this again so if I have to change carbs I am going to get the correct one!

Appreciate the help as always!

Ken

crackedback said:
It's ALL in the tune up. It will need more than a jet change is my guess.

Get the initial cranked up and start from there, which bushing on the distributor? Black? You'll need a different one to get it right at idle. I sell them and they work well. If it was tuned on a engine dyno, the in car requirements can and sometimes are VERY different.

I wouldn't worry about changing a bunch of parts, I have stuff with a much larger camshaft that runs well on the street. It's sorting it out that will take some time.
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Not enough initial, PERIOD.

You can't see the stop bushing in your picture. It's on the bottom side of all that stuff. Based on the two bushings you have in the "parts" pic, I'm guessing the black 18* is installed.

I wouldn't get rid of any parts just yet. Replacing the carb may not solve any issues.
 
OK I am a little confused on the bushings. Is it under the springs or somewhere else? So you think 30 degrees initial? Does that seem a little high considering total is at 32?
 
You have to look from the underside to see the bushing, use a mirror. If you have instructions for the distributor, it shows bushing location. The springs installed look like a good combo, blue/lt silver.

I'd turn it up to 22-24 and reset the idle mixture and see if it's snappier. I bet it is. DO NOT drive it or hammer on it if you turn initial up without limiting the mechanical/total number. If it will handle 32 total, you could run it there as long as it starts ok when hot.

Find the point where it kicks back on the starter when hot, that's your top side initial timing limit. If that point is greater than the total number, just lock it out (see instructions) at 32* and drive it.
 
OK I see what you are talking about now. I just got out the instructions. It looks like I have either a blue or black one installed. I cannot tell from the underside cause its a tight fit and dark, but looking at the left over bushings I cant tell if the spare is black or blue! LOL! My neighbors are mad at me right now for running this so late so I am calling it a night. I will mess with it some more tomorrow. I am learning here. OK I will set timing up at 23 and do as you suggested. Thanks again for all the help.
 

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Looks like the black on on your table.

The blue is 21* so you should have around 35 total.
 
crackedback said:
Looks like the black on on your table.

The blue is 21* so you should have around 35 total.
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OK thanks Rob. You said you sold different bushings. Is there an in between from what I have here? I will play around with the timing setting that you mentioned tomorrow and post the results and I guess that we will go from there.

As far as jetting, what jet should I pick up? I have a 71 in there right now(down from a 73) and she is still rich. I am going to see my builder on my lunch break so I will trade him out. I am pulling the bowl here shortly once she cools down to remove the old jet.
 
OK here is the update for tonight. I pulled the primary bowl and jetted down to 70's since that was all that my builder had. I also dropped the float levels on the pri and sec bowls since they where half way up the sight glass. I lowered them both to the bottom of the sight glasses. I fired it up and adjusted everything for idle. I went for a test drive and holy **** there is a in the seat difference in power. Putting around the wideband was seeing 13.2. I took her out on the freeway and went to town. I nailed it WOT and AF was at 13.7 the entire range. I backed it off to cruising speed and at 65 mph/2600rpm the wideband was fluctuating between 13.2 and 13.5. Everything is now in the green throughout the entire range. I reset timing back to 14 as it was not liking to be advanced. My only new issue now is my 1st gear has a huge hesitation and stumble. It did not have this before. Is that a accel pump adjustment? Why would that all of a sudden come out? As far as the plugs go, my builder said that all the soot is from the engine idling too long from when he tuned it on the dyno. He said it saw a lot of idle time and with that cam it makes sense. I put new plugs in it just to make sure so I will keep an eye on that. So this has been a good evening so far. Just need to fix that low speed hesitation/stumble and I will run a tank through it to see how it does. Thank you all very much!
 
It's still fat on cruise and I hope you didn't hammer it with the initial timing at 20*+ and no changes to the distributor.
 
13.2 is still pretty rich for cruise even if it runs good. The fact that it ran worse with more timing just means you have good total advance you still need way more than 14* initial. Hate to say it but you still have a ways to go if you want the best mileage and performance.

Others have mentioned you need cruise to be LEANER than wide-open. Cruise should be at least 14.7 and WOT should be in the mid-high 12's that might have something to do with the hesitation.
 
crackedback said:
It's still fat on cruise and I hope you didn't hammer it with the initial timing at 20*+ and no changes to the distributor.
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No I didnt, timing was back to original during that run. I will pick up some 68 jets from an auto parts store today and jet down again. That seems to be working the lower I go. The engine is not liking to be advanced at all. Not sure on that one. Plus the more I advanced it the more total timing increased. Seems like jetting is heading in the right direction and power is coming up. Should I be messing with secondary jetting at all while dropping the primaries to richen up WOT or a spring since its vacuum secondary?
 
OK I just got back from Pep Boys and picked up some 69 and 68 jets as well as some 81 and 82 jets for the secondaries. Do I need to plus up on the secondary to richen WOT out? I will try and mess with timing again, but the more I would advance it, it would start pinging badly. The most I could get was 18 degrees. I checked the bushing in the dizzy and it is a black one so I am as big as I can go there. If I keep my timing at 18 degrees initial that would bump my total up to 36. Does that sound right?
 
What do you think is going to happen to your total number if you up the initial setting?

Why do you think I mentioned to NOT romp on it if you up the initial!

YOU NEED TO INSTALL A DIFFERENT ADVANCE STOP BUSHING IF YOU WANT TO BUMP THE INITIAL TIMING.

Very simple, there are two basic parts to timing with your set up. Initial is the first part, mechanical advance is the second.

Initial + mechanical = total

What you are currently doing may turn out to be a HUGE waste of time until you get the initial/idle settings sorted out.
 
Did you change the power valve? As soon as you hit the gas that thing is opening.

Once you figure the initial/total out, you need to get the correct power valve in there. You're leaning out the primaries and you may not need to. You're already too lean under power and too rich under cruise. Going to smaller jets will exacerbate your problem.

Once the timing's set, put the car in gear and check vacuum. If it idles at 8 in. of vacuum, you should have a 3.5 or 4.5 power valve in there. At the very least, check your cruise vacuum. If you are cruising at 6.5 inches of vacuum or less, your power valve is opening.
 
smartken22 said:
OK I just got back from Pep Boys and picked up some 69 and 68 jets as well as some 81 and 82 jets for the secondaries. Do I need to plus up on the secondary to richen WOT out? I will try and mess with timing again, but the more I would advance it, it would start pinging badly. The most I could get was 18 degrees. I checked the bushing in the dizzy and it is a black one so I am as big as I can go there. If I keep my timing at 18 degrees initial that would bump my total up to 36. Does that sound right?
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IMO you're going in the wrong direction you need to be looking more at your power valve... Read these steps carefully and your car WILL run better:

1) STOP jetting down! In fact go back to where your WOT was closer to 13:1 or less
2) Change the mechanical advance bushing for less advance; I think the next one down is 18* see if you can go even more than that. You want like 12* ideally so that...
3) You can set the initial advance to 20* or so where it should be 14* is way too little and end up with not more than 32-34* total advance.

You're getting ahead of yourself here tuning Holleys isn't only about swapping jets so take a step back and carefully re-read what everyone has been telling you in this thread regarding timing and target A/F ratios.
 
Aaron65 said:
Did you change the power valve? As soon as you hit the gas that thing is opening. Once you figure the initial/total out, you need to get the correct power valve in there. You're leaning out the primaries and you may not need to. You're already too lean under power and too rich under cruise. Going to smaller jets will exacerbate your problem. Once the timing's set, put the car in gear and check vacuum. If it idles at 8 in. of vacuum, you should have a 3.5 or 4.5 power valve in there. At the very least, check your cruise vacuum. If you are cruising at 6.5 inches of vacuum or less, your power valve is opening.
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+1000 too much gas at cruise, not enough at WOT! Timing and power valves trust us smartken22 O:)

In fact I think once the initial is bumped up to where it should be you may have enough vacuum that your current PV will start to work properly
 
MOPEkidD-3 said:
+1000 too much gas at cruise, not enough at WOT! Timing and power valves trust us smartken22 O:)

In fact I think once the initial is bumped up to where it should be you may have enough vacuum that your current PV will start to work properly
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Bingo, listen to this advice.
 
Really great to see you solved your problem...all with the help of the FABO Brothers! So, I am assuming it was the fuel pickup height. ---- Recommendation: DO NOT BUY your fuel pickup off Ebay, use Year One or a reputable dealer. I purchased a 3/8 pickup that would not reach the bottom of my tank and had to repurchase one from Year One. ---- Frustrating problem, GLAD U FIXED IT. :cheers:
 
I think you are mis understanding what is being said about advancing you INITIAL timing.

You are advancing you Initial timing by turning your distributor! You need to replace the bushing in you distributor to get more initial timing.

Example 18 Initial the bushing in the distributor advanced timing up to 36* AKA you bushing is allowing 18* advance.

If you change the 18 degree bushing with 14* bushing, now you set you Idle or Initial timing to 22 degrees and your total timing is still at 36'

I know you are resisting taking the distributor apart to replace the advance bushing but it MUST be you next step.

Trust me your seat of the pants will tell you you did the right thing.

You can't decide what PV you need, YOU can't decide what jet you need UNTIL YOU CHANGE THE ADVANCE LIMITING BUSHING IN THE DISTRIBUTOR.
 
As you go down in jet sizes, you have to open up powervalve restrictions. You need to
determine best size jet for cruise, then open pvcr(power valve channel restriction) for wot. Your motor wasn't responding to more timing because your wot fuel ratio is too lean. Also, secondary jet size a couple sizes bigger. Timing 36-38° total.
 
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