Hey guys, first time posting here, and just bought my first muscle car. 73 scamp with 318. It has a mild cam, duel exhaust, 4 barrel intake, msd plugs, wires and distributor, and a Holley 600 cfm carb. The motor is running way too rich and I can't figure out why. Any help would be greatly appreciated.
73 scamp
- Thread starter Moparjosh
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First, congrats on your Scamp and welcome to the forum. What a great looking machine!
So the rich condition could just be a carb tuning issue. How can you tell that it's rich? Are you seeing black smoke from the exhaust?
Just as some unsolicited advice: check the date of manufacture on those tires. They might be totally fine but the make/model doesn't ring a bell and my first thought is that they might be old...and therefore a safety issue once you get the 318 pulling a bit better.
So the rich condition could just be a carb tuning issue. How can you tell that it's rich? Are you seeing black smoke from the exhaust?
Just as some unsolicited advice: check the date of manufacture on those tires. They might be totally fine but the make/model doesn't ring a bell and my first thought is that they might be old...and therefore a safety issue once you get the 318 pulling a bit better.
The carb has been set to about 12 lbs of pressure which is about 1 1/4 turns. It does have black smoke and the plugs are black. I just replaced all the plugs and reduced the jet size. The carb only has 500 miles on it so I don't think it's a bad carb. My theory is maybe a bad fuel pump that is increasing pressure?? Also, the tires are suppose to be brand new put on a month ago.
Welcome to the site!
I haven't heard of a carb that has no tuning adjustments. I'm not a Holley expert but it's got to have similar adjustment screws (idle mixture screws and idle speed screw) and jets that a Eddy/carter carb has? Just because it's brand new doesn't mean it doesn't need tuning. If I buy a brand new TV and just take it out of the box, I won't see a picture on the screen until I also plug it in for power and then provide it with a signal. In the old days, just plugging in the rabbit ears for the TV wouldn't be enough either. You'd have to move the antenna to then get the clearest picture. You need to do the same with the Holley carb. I agree with you in that it's not a bad carb as it can be tuned to run well!
Also, just because the tires were bought new from a store and installed last month doesn't mean they are brand new. Yes, they may never have been sold and installed on rims before but when were they manufactured? Some tires sit on store and warehouse shelves for years before they are purchased. Check the DOT code on each tire as it will tell you what week and year they were made.
Determining the Age of a Tire
While it's hard to tell for sure from the angle of the picture you post and it also could depend on the tire size you're running, your Scamp appears to be sitting pretty low; is the car resting on the lower control arm rubber/bump stop?
I haven't heard of a carb that has no tuning adjustments. I'm not a Holley expert but it's got to have similar adjustment screws (idle mixture screws and idle speed screw) and jets that a Eddy/carter carb has? Just because it's brand new doesn't mean it doesn't need tuning. If I buy a brand new TV and just take it out of the box, I won't see a picture on the screen until I also plug it in for power and then provide it with a signal. In the old days, just plugging in the rabbit ears for the TV wouldn't be enough either. You'd have to move the antenna to then get the clearest picture. You need to do the same with the Holley carb. I agree with you in that it's not a bad carb as it can be tuned to run well!
Also, just because the tires were bought new from a store and installed last month doesn't mean they are brand new. Yes, they may never have been sold and installed on rims before but when were they manufactured? Some tires sit on store and warehouse shelves for years before they are purchased. Check the DOT code on each tire as it will tell you what week and year they were made.
Determining the Age of a Tire
While it's hard to tell for sure from the angle of the picture you post and it also could depend on the tire size you're running, your Scamp appears to be sitting pretty low; is the car resting on the lower control arm rubber/bump stop?
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90% of carb problems are rooted in a crappy base initial timing setting.
Set the timing and square away the total number and then start on the carb. Timing ALWAYS effects carb...
Make sure there is no fuel dripping into the engine from the carb boosters.
Set the timing and square away the total number and then start on the carb. Timing ALWAYS effects carb...
Make sure there is no fuel dripping into the engine from the carb boosters.
It does have adjustment screws on the carb and we have tuned it. I've also adjusted the jets size to 64 from 66 and retuned again. Is there any other thing that can cause it to run rich other than a carb issue?
I haven't checked the timing yet but will definitely check that out. Thanks
swingingdart
Well-Known Member
Nice Scamp! Welcome to the site!
swingingdart
Well-Known Member
Edelbrock 625 cfm electric choke.
Wave good by to carb problems! unless it's something else, then it'll fix nothing
Wave good by to carb problems! unless it's something else, then it'll fix nothing
Thanks man
If it has an aftermarket camshaft in it, DO NOT use any numbers the factory suggest for initial timing. It will probably want anywhere from 14-20 initial. As long as it start OK without dragging the starter, try there. You could also do the vacuum gauge approach.
If you need a bushing for the distributor to limit advance, I have 10 and 14 degree pieces. MSD only goes to 18*.
if I understand you correctly your running 12lbs of fuel pressure ? do you think this may possibly a problem ? or do you mean 12 inches of vacuum ?
Actually running 17lbs of vacuum
It's inches of vacuum
AJ/FormS
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Your carb will not be able to deal with 12psi fuel pressure. And if it's running 17 inches of idle vacuum at 650/700 then it must be a really small bit of a cam. The carb needs the pressure to be around 4.5psi at idle, but most Holleys can deal with 6 or maybe 7psi. So please clarify. Are you really trying to run 12psi?
The jets you changed, are only engaged from about 3/8 open on the primaries. At idle and low throttle settings you can take 'em right out and it will change nothing.
Get your fuel pressure reduced, reset your wet float level,get the timing sorted, and your T-port synced up, like others have said, and in that order;and then the tuning can begin.
The jets you changed, are only engaged from about 3/8 open on the primaries. At idle and low throttle settings you can take 'em right out and it will change nothing.
Get your fuel pressure reduced, reset your wet float level,get the timing sorted, and your T-port synced up, like others have said, and in that order;and then the tuning can begin.
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Ok, thank you
Ok, thank you. I’m new to this and learning as I go. I replaced the fuel pump and that fixed my increased pressure issue. I will advance the timing a touch next and then retune. Thanks for all your help guys. I wish I would have learned this as a kid but everyone starts somewhere.
AJ/FormS
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Oh, a newbe,lol; well then easy on the timing until you learn how to limit the power timing.Most SBMs with oem heads and compression don't like more than 36* at WOT, and after about 3200rpm at the earliest. Any more than 36 or any earlier than 3200 will usually cause detonation, which must be avoided at all costs, on account of detonation can destroy your engine. So learn to recognize detonation when it occurs,and learn how to limit the power-timing,and stay out of the secondaries until you do.
Otherwise; nice ride,enjoy
Otherwise; nice ride,enjoy
Yeah man, I’m a newbie, but have a mechanical mind. I was going to use a timing light to check myself and plan to advance the timing to about 16°
Carb size is fine, IMHO
AJ/FormS
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Ok I'm not sure you understand how the D works. The factory D was set up for the teener with maybe 5* initial and about 35 maxed out. That means there's 35 less 5 = 30 in the D. And that ran just fine with the stock set-up.
Now if you advance the initial to 16 then the maxed out power timing will be 16 + 30 = 46* and that is guaranteed to cause detonation. And if the detonation continues for too long, the engine will be damaged.
What I'm saying is that you cannot just pick a number out of a hat and crank it in.
Well you can for idle tuning purposes, and it might be fine at up to some unknown throttle setting. Bit it will cause problems somewhere over about 1/2 throttle, so stay sharp!
As I stated earlier, the D has to be modified to limit the power-timing to about 35 degrees total, and not maxed out until about 3200.That's a best guess. Some engines will accept max timing about 500 rpm sooner and some not until 500 later, and it depends on the grade of gas being burned.
The easiest way to mod the D is with the FBO timing plate, just use the search feature.
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Might try reading the first post...
AJ/FormS
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Oh MSD distributor . Thanks crackedback
You know I had to read that post about three times and then finally caught it,lol.
Thanks again.
You know I had to read that post about three times and then finally caught it,lol.
Thanks again.
I found another issue today.... my intake is sucking air all over the place. I’m sure that’s not helping. Between my manual fuel pump sending to much fuel pressure and the intake gasket being bad I’m sure that’s a lot of the problem. We will see how she runs after I replace the intake and gaskets
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