When running my car on the highway at 55-75 car acts like it starving for fuel but hit the gas a little and no problem, I am running holly 650 on 351 c 1974 standard fuel pump . Do I need to adjust carb
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Try slightly richer primary main jets.
If it is below 3000 RPM while cruising, you are probably not engaging the main jets. Thus changing them will not help.
When cruising under light load, the low speed air jets are metering your fuel. Frankly, you are out of luck adjusting these bad boys, unless you have a carb modified for adjustable screw in air bleeds. ie, QF, Demon, DaVinchi, etc. These are smaller jets accessible from the top of the carb on each side of the shooters. As the jets meter air, reduce their size, to enrich your cruise mixture.
Of course, it is helpful to have an A/f gauge to actually know what is going on.
When cruising under light load, the low speed air jets are metering your fuel. Frankly, you are out of luck adjusting these bad boys, unless you have a carb modified for adjustable screw in air bleeds. ie, QF, Demon, DaVinchi, etc. These are smaller jets accessible from the top of the carb on each side of the shooters. As the jets meter air, reduce their size, to enrich your cruise mixture.
Of course, it is helpful to have an A/f gauge to actually know what is going on.
PRESUMING that the car was running fine and this is a recent occurrence, you need to check both the idle air bleeds, the idle fuel transfer slots and the main air bleeds.
In order to do this you will need a numbered set of drill bits and a pin vise. Holleys are particularly susceptible to any of these clogging with foreign matter.
It is a 50/50 situation of which it is. IF you had ANY kind of a backfire then it is probably the idle transfer slots located in the throttle body near the the throttle plate intersection at the idle or near idle position. That is where the engine is feed atomized fuel from at least up into the 2,000 rpm range.
I don't have a diagram to show you a picture but you can probably access one on the internet of the Holley instruction sheet on what these things look like and where they are located.
You are going to need to remove the carb, drain it of fuel, turn it upside down and remove the bottom throttle plate on the carb to service it. It isn't difficult and you do not need to be even a German Rocket Scientist to do it.
It is also possible that you have foreign debris in the idle air metering bleeds (air metering jets) located in the top of the main body on the primary side. That could also be from a backfire since it is under the choke plate OR could have happened if you had the engine running with the air cleaner off.
You want to match up the drill bit size as closely as possible to the existing orifices without enlarging them.
The well on the idle air bleeds is fairly deep and you need to run the bit completely into it to make sure something that was liquid -ish didn't drip down into the well and solidify in there. It isn't very likely but you just won't know exactly what happened here. Like I said, it's a 50/50 proposition whether it is the air bleed or the fuel transfer slot. Sometimes it is both.
A backfire tends to create an oily black carbon that the engine has liquefied in an instant then it cools almost as fast into a Crazy glue type of material and plugs one of the orifices.
This is very common on Holleys, particularly the smaller capacity ones like an 1850 that has smaller orafices for smaller and more economical running. I've clogged up a few myself and can tell you that using a cab spray cleaner and compressed air alone will not get the job done. You have to physically remove the obstruction with the drill bit. Then you can use compressed air to blow it away.
Soaking the carb generally won't do it either. Don't even bother with that.
In order to do this you will need a numbered set of drill bits and a pin vise. Holleys are particularly susceptible to any of these clogging with foreign matter.
It is a 50/50 situation of which it is. IF you had ANY kind of a backfire then it is probably the idle transfer slots located in the throttle body near the the throttle plate intersection at the idle or near idle position. That is where the engine is feed atomized fuel from at least up into the 2,000 rpm range.
I don't have a diagram to show you a picture but you can probably access one on the internet of the Holley instruction sheet on what these things look like and where they are located.
You are going to need to remove the carb, drain it of fuel, turn it upside down and remove the bottom throttle plate on the carb to service it. It isn't difficult and you do not need to be even a German Rocket Scientist to do it.
It is also possible that you have foreign debris in the idle air metering bleeds (air metering jets) located in the top of the main body on the primary side. That could also be from a backfire since it is under the choke plate OR could have happened if you had the engine running with the air cleaner off.
You want to match up the drill bit size as closely as possible to the existing orifices without enlarging them.
The well on the idle air bleeds is fairly deep and you need to run the bit completely into it to make sure something that was liquid -ish didn't drip down into the well and solidify in there. It isn't very likely but you just won't know exactly what happened here. Like I said, it's a 50/50 proposition whether it is the air bleed or the fuel transfer slot. Sometimes it is both.
A backfire tends to create an oily black carbon that the engine has liquefied in an instant then it cools almost as fast into a Crazy glue type of material and plugs one of the orifices.
This is very common on Holleys, particularly the smaller capacity ones like an 1850 that has smaller orafices for smaller and more economical running. I've clogged up a few myself and can tell you that using a cab spray cleaner and compressed air alone will not get the job done. You have to physically remove the obstruction with the drill bit. Then you can use compressed air to blow it away.
Soaking the carb generally won't do it either. Don't even bother with that.
No no no guys. Sorry, but don't bring too big a hammer. If you have a symptom like described, don't take a drill right away. And if it's a lean situation, drilling bleeds will lean out further. Or changing them, I've never had a carb I couldn't get to run fine, even without ever changing/drilling any bleeds
pantera74Bills6976, first make sure your idle circuits are properly adjusted. Then check your power valve, on cars that don't drive much they easily harden, and then they can be both too lean and rich. If all those are OK, try richening the main jets.
Or buy my book...
pantera74Bills6976, first make sure your idle circuits are properly adjusted. Then check your power valve, on cars that don't drive much they easily harden, and then they can be both too lean and rich. If all those are OK, try richening the main jets.
Or buy my book...
Oh man. If this isn't a language issue I don't know what is. Why don't you confuse him some more Mikael?
NO ONE ever said DRILL THEM OUT OR CHANGE THEM. I said that the channels beneath the bleeds OFTEN will get debris in them and need to be cleaned out. The two that are the biggest offenders I see are the 1848 and the 1850, simply because the bleeds and passages are the smallest in the Holley carb line.
The smallest debris will clog it.
You need to get into them and the simplest way is to use a numbered drill bit of the appropriate size of the orafice in the bleed.
Probably something in the #70 to #65 size.
The fuel transfer slot in the throttle body is simpler if removing the throttle body.
You might be able to not disassemble it and use a dental pick but that could definitely damage the precision of the slot.
IF that carb WAS RUNNING PERFECTLY FINE and this just suddenly occurred, there is NO WAY IN HEAVEN AND HELL that the adjustment screws turned themselves. Next you well be telling us that it was Hamlets ghost on the marshes in Denmark. Simply put. No way.
Gee-ze!
NO ONE ever said DRILL THEM OUT OR CHANGE THEM. I said that the channels beneath the bleeds OFTEN will get debris in them and need to be cleaned out. The two that are the biggest offenders I see are the 1848 and the 1850, simply because the bleeds and passages are the smallest in the Holley carb line.
The smallest debris will clog it.
You need to get into them and the simplest way is to use a numbered drill bit of the appropriate size of the orafice in the bleed.
Probably something in the #70 to #65 size.
The fuel transfer slot in the throttle body is simpler if removing the throttle body.
You might be able to not disassemble it and use a dental pick but that could definitely damage the precision of the slot.
IF that carb WAS RUNNING PERFECTLY FINE and this just suddenly occurred, there is NO WAY IN HEAVEN AND HELL that the adjustment screws turned themselves. Next you well be telling us that it was Hamlets ghost on the marshes in Denmark. Simply put. No way.
Gee-ze!
PanteraDoug, please agree that a clogged bleed will richen the carb, and his symptoms are for a lean carb...
Yes, but a clogged fuel transfer slot in the throttle body will lean the car out since it has to run on the main circuit which will lean it out at low rpm.
The idle circuit in a Holley is richer than the mains.
He has to read the plugs first to see if they are white or black.
He is only presuming that the engine is lean. He hasn't said it is backfiring. Running out of fuel, lean, even at part throttle will generally backfire through the exhausts at some point of throttle opening.
I say this thinking that the car was running well with that carb on it. IF he just installed the carb, then you are likely correct, that it needs to be set up. Agreed on that also.
He's closer to you than me. Have him bring the car around. I'm sure you will get it straightened out for him?
You know sometimes there isn't anything wrong with the carb at all, it's just a bit of a mismatch out of the box.
Holley on an aluminum intake in the cold weather really are lousy running setups. They just freeze up to easily.
I was just running my 68 GT350. It's 30 degrees and the automatic choke is still being a bear. Warmed it up. Than it sat for 30 minutes and the engine cooled off so fast had to do it all over again. GRRRRR!
They just don't like anything much under 35 F.
The idle circuit in a Holley is richer than the mains.
He has to read the plugs first to see if they are white or black.
He is only presuming that the engine is lean. He hasn't said it is backfiring. Running out of fuel, lean, even at part throttle will generally backfire through the exhausts at some point of throttle opening.
I say this thinking that the car was running well with that carb on it. IF he just installed the carb, then you are likely correct, that it needs to be set up. Agreed on that also.
He's closer to you than me. Have him bring the car around. I'm sure you will get it straightened out for him?
You know sometimes there isn't anything wrong with the carb at all, it's just a bit of a mismatch out of the box.
Holley on an aluminum intake in the cold weather really are lousy running setups. They just freeze up to easily.
I was just running my 68 GT350. It's 30 degrees and the automatic choke is still being a bear. Warmed it up. Than it sat for 30 minutes and the engine cooled off so fast had to do it all over again. GRRRRR!
They just don't like anything much under 35 F.
quote:Originally posted by pantera74Bills6976:
When running my car on the highway at 55-75 car acts like it starving for fuel but hit the gas a little and no problem, I am running holly 650 on 351 c 1974 standard fuel pump . Do I need to adjust carb
In pantera74Bills6976 original quote he does not say it was running fine then went bad or lean or whatever, he states it feels lean crusing between 55mph and 75mph but when he opens the throttle it seems fine.
1. by 55 to 75 mph he should be on the beginning of the primary main jets at least.
Unless he has a diff ratio of 2.55 : 1, but i'm sure Pantera's are higher than that.
2. If it is lean on the primary mains, opening the throttle a bit will seem to fix things, because as you do this the manifold vacuum will drop and the primary power valve will open and allow greater fuel flow to the primary main system.
3. on a holley the primary jet also feeds the primary idle circuit. Even though there are independent idle jet restrictions (not replaceable jets) and idle air correction jets, the main jet does still effect the idle circuit.
4. From the picture of the engine supplied (if it is current) it does not look like it would be a 150,000 mile junker with a carb full of crud. That may be wrong and it is always worthwhile to clean the carb and check things out but i agree you should not go at it with a big hammer straight away.
5. Stay away from interfering with air bleeds unless you know "EXACTLY" what you are doing. They not only effect the richness of the circuit (idle or main) they also effect the "timing" of the circuit. You can wind up with one great big flat spot.
A blocked air bleed with make it richer, Very much richer..
6. if it is true that the car just seems to be a little lean and has always been this way as far as you know, just try slightly richer primary jets
Ps: always worthwhile to check the float level too !
Agree with Aus Ford...
Here's what I would do:
Or get back to us
Here's what I would do:
Check float level
Deliberately richen the idle circuit as a test, maybe 1/4 turn. If it helps, you have a lean condition
Chck that power valve is functioning right, moves freely and not with resistance that vary
Then try main jets 2 bigger
If fixed, good, if partly fixed go 2 jets richer. If you need even more jet, you have another problem, maybe a vacuum leak
Or get back to us
Sorry ..Yes that picture was from a month ago ,yes car has back fired a couple of times in the past years. . Engine was done in 2007. I have about 10,000 into it. Carb was purchased from Pantera performance. Larry he said it was especially tuned for the Pantera. The engine shop that built it told me it did have some nice work done to it. I think this started about 3 years ago. Another Pantera owner said he had the same problem. May be problem is with the jets. Car runs great other wise, tons of HP and stupid fast