Running rich....To big of a carb or?

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You say the plugs are correct for the engine. I assume then you got them based on application and year model. Your engine isn't stock anymore, so take that into account. When you get the timing and carb dialed in, you should make some full throttle runs and read the plugs. You should run plugs based on how the engine is now.
 
I thank everyone for the help and for pointing out things it could be. But like most any thread people toss out all sorts of opinions and it's hard to stay focused on the issue. I just don't want to run around chasing things that won't solve the original issue.

I've got good spark, plugs should be fine.... I se guys with a lot more modifications running the same plugs. Don't get me wrong... A hotter plug may aid in burning off more fuel. But I think my issues is a too much fuel issue. Not a not enough fire issue.

I don't mind doing the work, but after building the car for 4 years I'm ready to drive lol so I'm trying to figure out the best path to take that's going to require the least amount of headache. I would consider tuning the 750 but I'd hate to find out that after buying and installing a bunch of tuning parts that it still isn't enough to cure the issue. So I'm trying to figure out if it makes more sense to downsize carbs.

Sorry if I don't have all the answers you guys want.... Working with what information I have available to me and what skills I have.

I'm great at body work, paint and interior and am mechanically inclined but the technical specs of carbs always get me lol. So bare with me and try not to make me feel to bad/dumb haha. Thanks again guys
 
Drill the both front outer air bleeds one size bigger at a time. You will fix your issue. The bigger you drill them the less fuel it will flow. This controls idle to mid. Leave the mains alone.

Check that power valve first. if it is wrong or blown it will run real rich. If the car ever backfired it is probably blown. most of the vacuum carbs don't have anti backfire valves in the power valve circuit. This is also easy to install.
 
Carb only has a few hours of run time on it since I bought it new a year ago. Never been back fired. So I doubt it's got a blown PV. I'm not sure what your talking about drilling or to what size or if additional parts are required or if your just talking about larger holes or?. Not sure I'm to comfortable with drilling anything out at this point ( maybe a last resort). Because there's no undoing that if it were to cause an issue.

Sorry for not picking up what your putting down lol
 
I agree with oldmanmopar on the air bleeds there not exspensive and will lean your car right out and you will be happy. You asked for advice now take it. Also any new carb will need tuning also.
 
I would keep drill bits back in the tool box for a while. First, go buy a vacuum gauge! They're cheap and just about mandatory for carb tuning. As said above, both PV's should be well below idle vacuum (and the secondary should be 2 numbers below the primary). Because you need to nearly seat the idle mix screws, I would concur that the primary jets are too large. Try going down 2 numbers at a time on the primaries until the car slows down, then go back up one number. Best to disable the secondaries, until you have the primaries set right.

If I was a betting man, I'd bet you'll end up with #74 jets, 8.5 PV primary, #77 jets 6.5 PV secondary. Make sure the float levels are right before you monkey with anything else.
 
C130 Chief said:
I would keep drill bits back in the tool box for a while. First, go buy a vacuum gauge! They're cheap and just about mandatory for carb tuning. As said above, both PV's should be well below idle vacuum (and the secondary should be 2 numbers below the primary). Because you need to nearly seat the idle mix screws, I would concur that the primary jets are too large. Try going down 2 numbers at a time on the primaries until the car slows down, then go back up one number. Best to disable the secondaries, until you have the primaries set right.

If I was a betting man, I'd bet you'll end up with #74 jets, 8.5 PV primary, #77 jets 6.5 PV secondary. Make sure the float levels are right before you monkey with anything else.
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Vacuum carbs don't have secondary power valves. And you may need those fat jets when the rpm's come up. You would not believe the difference the idle air bleeds make in the transition from the idle circuit to High speed. and then the High speed air bleeds from mid to high.

They have metering blocks with replaceable emulsion jets also to really fine tune. But usually if the carb is 750 cfm it calls for a specific size main jet for that carb. The last thing I would change is the mains. Unless you have a wide band rich lean gauge hooked to a o2 sensor .

Changing the idle circuit will not cause Damage to the motor but will lean it up on the bottom.

The only time you need to drill holes in the venturies is when they need to be opened up past the idle transfer slots for it to idle.

The rule of thumb is as much of the slot should be uncovered at idle as the slot is wide. square it up.

on a 4 corner carb you set the primaries at that and then idle off the secondaries. If you take time and do that with a standard Holley you can make a big difference in performance.

If you really don't want the hassel of fine tuning your carb get a Carter style carb. they sort of adjust them selfves better then a holley. They have metering rods. And adjustable spring controlled secondaries
 
I'm not sure if I'm understanding what your saying exactly...... Did you look at the carb?...... It sounds like most of the info you mention is related to a typical holly carb and this summit carb is like the old style holley and autolite carbs (4110 series I think they were called). It has a one piece housing with a removable top plate.

Just wanted to make sure you were aware of the style of carb I have incase you were pointing out tips for a different style carb.
 
Carb tuning isnt that hard. Jets are cheap. I have ran 750 eddys and holleys and carter competition series carbs on 318s and 360s. Dont be scared. Google what you dont know. This is what I did and i,m very happy with my carb now.Damon has a very good white page on carb tuning at diamondback engines. Read up over there. Lots of good tech. If you dont want to rejet it yes its too big. Get a 600.
 
Way to much jet in the primary.
71's in the front and a 3.5 power valve will clean it up.
I run a 4.5 or 3.5 in everything because i like to be able to control my accelerator pump shot with out the power valve being in the way with a rich condition.
The pump shot is first then the power valves operation.
That power valve 9.5-----is dumping raw fuel at idle and it only gets worse when you put it in gear.
71's jets.........3.5pv................trust me.

Half out on the screws is fine.

750 cfm is not to big....I run a 750 race proform on my 318.(race fuel curve)
These carbs if not adjusted right will run way rich because of the race fuel curve.
They are the complete opposite to a street carb and much harder to tune.
I have mine running really good.
It's the cheapest advice $$$$$$----good luck.
 
Not "scared" to tune it, I've dabbled in tuning edelbrocks a bit before. Biggest issue is right now I have a list on a note pad of things I still need to finish on the car and I'm trying scratch things off the list not add things to it lol.

But you guys are right..... If I get a 600 and still have to dink around with tuning it than I'm looking at even more work than of I was to just tune this carb. The biggest thing was I wasn't sure if it would be a waste of time because I didn't know if it was to large of a carb an if tuning it down would cure the issue or not. But from what a few of you have said.... It's not to big and should be able to tune it down without issue.

So I'm thinking I'll probably get a jet kit and power valve for it here pretty soon.

I'll get my hands on a vac gauge and measure the vac and divide by 2 like was mentioned and see what kind of PV it shows I need.

Should I get a PV based off my vac reading or is everyone in agreement that a 3.5 PV would be a good one to go with regardless of what vac reading I come up with?.

Just so I'm clear on all of this and on the same page as all of the opinions given. I should get a jet kit and power valve?. Or is there anything else I should be looking at getting?.

Sorry not a carb expert and Holley and this summit/ Holley carb is mostly new territory to me.

Sorry to sound so nooby on a lot of this guys but nothing ventured nothing gained. Got to ask the questions so I can soak up the info lol
 
T67POWER said:
That power valve 9.5-----is dumping raw fuel at idle and it only gets worse when you put it in gear.
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I've heard this before but is this true?.....I was thinking that the power valve can only have an effect on the mixture of the main circuit, not the idle circuit at all.
 
cudavert said:
I've heard this before but is this true?.....I was thinking that the power valve can only have an effect on the mixture of the main circuit, not the idle circuit at all.
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only if the base tune up miles off.
 
The power valve adds more gas to the metering plate it's installed in -- front or back metering plate.
I operates on the engine vacuum signal.....
This is why holley suggest to check your vacuum reading at idle and also in drive, with someone holding their foot on the brake pedal.
What ever the vacuum reading is---will be divider by two--- and if the reading is a even number you would round it off to the next lowest power valve.
Example.........10 on vacuum gauge 1/2 reading on gauge is 5---then install a 4.5 power valve.
Go to you tube,,,,,,,,,,,,,holley double pumper tuning.
 
was doing a little bit of reading and ran across this [ame]http://static.summitracing.com/global/images/instructions/sum-m08040-41.pdf[/ame]

Will changing the jets out effect the rich condition at idle or will it only effect it under acceleration?.....same question applies to the power valve?.

if the answer is no.......then are the idle feed restrictors to blame for the rich condition?.

it runs rich under throttle also....no just at idle . which makes me think the jets/PV are to blame if in fact they effect both idle aswell as acceleration?
 
Your problems are what i said they are.
The power valve will open at idle if it go's below 9.5 on a vacuum gauge.
Your 77 primary jets will turn into about a 85 jets under acceleration when the power valve fully opens.

Just change your jets to a 71 and get a 3.5 power valve,

Look up holley video on u tube.

You want the main primary jets to match the rear secondary jets when under acceleration.
 
I just noticed you have a power valve in the back of the carb.
Thats ok but in install a 71 jet in the rear also
If you remove the power valve and put a block off power valve (blank with no hole) then you would run a 78 to 79 jet.

Holley carbs are very easy to work on once you understand how they work.
 
How can you explain my car with 8.5 vacuum at idle running a 10.5 PV and no rich condition?

If the base tune up is off, i.e. throttle plates too far open, then the PV can introduce fuel to the main well if that circuit is active when it shouldn't be. Otherwise, the carb should be running ONLY on the idle circuit at idle.

Float level, ignition timing, fuel pressure can all throw a monkey wrench into the soup.

Good luck with it.
 
There is lots of good information here, read it all, soak it in and do some tuning. Most important, timing HAS to be set properly before playing with the carb.

Even MORE important, and pay attention here - given any engine - if you put a bigger carb on it with stock jetting it will run LEANER. Yes, that is right. Put a bigger carb on your engine, it will have less velocity of airflow through the carb due to bigger venturis, and therefore pull less fuel through the main jets and boosters for a given amount of air.This is a fact. Smaller carbs run richer, but are generally snappier and more responsive. Bigger carbs run leaner, but are more prone to bogging.

The fuel mixture is all in the jetting.

Just my 2 cents, based on fact
 
If the fuel level is in the middle of the sight glass, floats are too high. It should be that when you rock the car, fuel just splashes above the bottom of the hole. This may be your only problem. I'm surprised that it doesn't sputter when you hit second unles your car shifts soft.
 
A blown power valve works the same way a power valve works when it opens at the lower then rated vacuum on the valve itself.

Extra fuel is introduced to the carbs main circuit increasing the fuel the engine sees at idle.
When properly working it opens when it should -- under a load --ie low manifold vacuum signal--at a lower vacuum rating then the valve is rated at.
BUT....
A blown power valve will make a engine very rich at idle.
That's why they suggest to turn your idle screws in all the way to check the power valves operation as being good or blown out.

If the engine does not stall, with the idle screws all the way in then you have a blown power valve giving the engine fuel at idle or the vacuum that is at the manifold is below the rating on the power valve making the idle rich.

holley info.

Troubleshooting Your Power Valve

The --incorrectly sized power valve--, or a blown-out power valve can cause problems like poor fuel economy, black smoke emanating from your exhaust, dark or fouling spark plugs, ------and a poor idle-------. If you suspect that your carburetor has a blown-out power valve, you can perform this simple test.

  1. Check the manufacture date of your Holley carb.
    Performance Holley carburetors come with a power valve blow-out check valve built in. It prevents damage to the power valve in case of backfire. Holley carbs older than 1992, however, may not have this check valve built in.
  2. Test it using the idle mixture screws.
    If you still suspect the power valve is blown out, start your engine and allow it to idle and get to normal operating temperature. Then, turn the idle mixture screws all the way in. If the engine dies, the power valve is not blown.
 
ted carlson said:
if the fuel level is in the middle of the sight glass, floats are too high. It should be that when you rock the car, fuel just splashes above the bottom of the hole. This may be your only problem. I'm surprised that it doesn't sputter when you hit second unles your car shifts soft.
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