Ifitaintbroke Posted March 19 Author Share Posted March 19 what does "idle right" mean ? what is it doing ? 18" is not bad at all depending on the cam installed' It's just not smooth. The lobe separation on the cam is 114 so should be able to idle close to stock. Link to comment Share on other sites More sharing options...
mat in tn Posted March 19 Share Posted March 19 It's just not smooth. The lobe separation on the cam is 114 so should be able to idle close to stock. how responsive are the idle mixture screws? one tip might be to pull off the smallest of manifold vacuum lines or cap while running. as close to operating temp as possible. if the engine slows in rpm then its lean. you are trying to feed a lot of engine. a 3310 should be enough if the adjustments are correct. if the engine speeds up with a cap removed then it is getting the fuel and is responding well to the added air. Link to comment Share on other sites More sharing options...
Ifitaintbroke Posted March 19 Author Share Posted March 19 how responsive are the idle mixture screws? one tip might be to pull off the smallest of manifold vacuum lines or cap while running. as close to operating temp as possible. if the engine slows in rpm then its lean. you are trying to feed a lot of engine. a 3310 should be enough if the adjustments are correct. if the engine speeds up with a cap removed then it is getting the fuel and is responding well to the added air. That's a good method. I'll try that. Scotty did recommend a 600, which is small, but this is a low rpm build. Link to comment Share on other sites More sharing options...
viven44 Posted March 19 Share Posted March 19 That's a good method. I'll try that. Scotty did recommend a 600, which is small, but this is a low rpm build. If you don't suspect vacuum leaks (i'm sure you've already tried spraying some carb cleaner to double check), then something else to maybe look into.. How does the alternator output voltage look ? Steady at ~14.5 V ? I don't know much about "MSD analog 6al triggered by Pertronix module" but the one time I did run a GM HEI on a truck, it idled horribly because the alternator output was all over the place because the battery voltage feedback to voltage regulator was disconnected. Duraspark 2 is much forgiving when it comes to that kind of things but some of the fancier coil systems probably need stable voltage. Oh and one more gotcha/lesson learned... I had a vacuum leak once on a running truck that I bought.. couldn't figure out where it was.. and I had assumed the rear PCV inlet on the carb was sealed. Nope it was wide open!! Link to comment Share on other sites More sharing options...
mat in tn Posted March 19 Share Posted March 19 That's a good method. I'll try that. Scotty did recommend a 600, which is small, but this is a low rpm build. 460s came from the factory with 600 cfm 4180 carbs. in a very general way, carbs are sized per their cfm demand per the ci at rpm. yet the intended (expected) use will have a certain average rpm peak efficiency point. and that is the point at which each is primarily tuned. universal does not "fit" a damn thing yet is more of an acceptable compromise. take the Holley 1850 universal carb. close enough to work well on many different engines but not be the best for any. this is the reason for buying a carb replacement or rebuild kit by the id tag not just the model number. putting a small carb on a big engine was seen as a means of being a rev limiter too. the efficiency would fade off before over revving the engine. was your carb fresh going onto the engine or had it been used then sat for an extended time? this could lead to cracks in the internal diaphragms and also could cause clogged or corroded fuel/air orifices in and around the emulsion tubes. if one side is cleaner than the other it could easily cause an unstable idle. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 19 Share Posted March 19 460s came from the factory with 600 cfm 4180 carbs. in a very general way, carbs are sized per their cfm demand per the ci at rpm. yet the intended (expected) use will have a certain average rpm peak efficiency point. and that is the point at which each is primarily tuned. universal does not "fit" a damn thing yet is more of an acceptable compromise. take the Holley 1850 universal carb. close enough to work well on many different engines but not be the best for any. this is the reason for buying a carb replacement or rebuild kit by the id tag not just the model number. putting a small carb on a big engine was seen as a means of being a rev limiter too. the efficiency would fade off before over revving the engine. was your carb fresh going onto the engine or had it been used then sat for an extended time? this could lead to cracks in the internal diaphragms and also could cause clogged or corroded fuel/air orifices in and around the emulsion tubes. if one side is cleaner than the other it could easily cause an unstable idle. The 4180c is actually 630 CFM. I've also run a Holley 080457-s, an Edelbrock AVS 650 and currently a 750 CFM 4160 w/ Motorcraft electric choke and quick change secondary spring housing. With the original 4180 and a stock cam, set straight up it would pull straight through the 5,800 redline and somewhere north of 6k. The truck definitely wasn't out of breath at redline (4.10's & a T-19) Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 19 Share Posted March 19 The 4180c is actually 630 CFM. I've also run a Holley 080457-s, an Edelbrock AVS 650 and currently a 750 CFM 4160 w/ Motorcraft electric choke and quick change secondary spring housing. With the original 4180 and a stock cam, set straight up it would pull straight through the 5,800 redline and somewhere north of 6k. The truck definitely wasn't out of breath at redline (4.10's & a T-19) One of the best carbs I found for a lot of applications was a Holley 4609 Ford PN C9AF-9510-U. It is a 735 CFM carburetor, essentially a 3310 (780 CFM) with umbrella primary boosters. Originally for the 1969 428 CJ engines. We had scored a batch of them as in 1970 they were only on Mustangs and were a new number hand choke version. I put them on a number of different cars, including my dad's 1971 Lincoln Mark III in place of the Autolite 4300. Better throttle response and fuel economy. Link to comment Share on other sites More sharing options...
Ifitaintbroke Posted March 19 Author Share Posted March 19 460s came from the factory with 600 cfm 4180 carbs. in a very general way, carbs are sized per their cfm demand per the ci at rpm. yet the intended (expected) use will have a certain average rpm peak efficiency point. and that is the point at which each is primarily tuned. universal does not "fit" a damn thing yet is more of an acceptable compromise. take the Holley 1850 universal carb. close enough to work well on many different engines but not be the best for any. this is the reason for buying a carb replacement or rebuild kit by the id tag not just the model number. putting a small carb on a big engine was seen as a means of being a rev limiter too. the efficiency would fade off before over revving the engine. was your carb fresh going onto the engine or had it been used then sat for an extended time? this could lead to cracks in the internal diaphragms and also could cause clogged or corroded fuel/air orifices in and around the emulsion tubes. if one side is cleaner than the other it could easily cause an unstable idle. I had a very nice 4180 that I did my most extensive rebuild on. For some reason I gave it to somebody before the engine was done. Link to comment Share on other sites More sharing options...
Ifitaintbroke Posted March 19 Author Share Posted March 19 If you don't suspect vacuum leaks (i'm sure you've already tried spraying some carb cleaner to double check), then something else to maybe look into.. How does the alternator output voltage look ? Steady at ~14.5 V ? I don't know much about "MSD analog 6al triggered by Pertronix module" but the one time I did run a GM HEI on a truck, it idled horribly because the alternator output was all over the place because the battery voltage feedback to voltage regulator was disconnected. Duraspark 2 is much forgiving when it comes to that kind of things but some of the fancier coil systems probably need stable voltage. Oh and one more gotcha/lesson learned... I had a vacuum leak once on a running truck that I bought.. couldn't figure out where it was.. and I had assumed the rear PCV inlet on the carb was sealed. Nope it was wide open!! Alternator output is around 14 last I looked, but I didn't pay much attention to that. The MSD I don't believe is very voltage sensitive as it can run on as low as 10 volts IIRC. Link to comment Share on other sites More sharing options...
Ifitaintbroke Posted March 19 Author Share Posted March 19 460s came from the factory with 600 cfm 4180 carbs. in a very general way, carbs are sized per their cfm demand per the ci at rpm. yet the intended (expected) use will have a certain average rpm peak efficiency point. and that is the point at which each is primarily tuned. universal does not "fit" a damn thing yet is more of an acceptable compromise. take the Holley 1850 universal carb. close enough to work well on many different engines but not be the best for any. this is the reason for buying a carb replacement or rebuild kit by the id tag not just the model number. putting a small carb on a big engine was seen as a means of being a rev limiter too. the efficiency would fade off before over revving the engine. was your carb fresh going onto the engine or had it been used then sat for an extended time? this could lead to cracks in the internal diaphragms and also could cause clogged or corroded fuel/air orifices in and around the emulsion tubes. if one side is cleaner than the other it could easily cause an unstable idle. Those kind of reasons are why I'm starting to shy away from used/rebuilt carbs. The eddy I have on it now sat in the rain for like 3 years WITH ethanol gas in it and spray paint down the venturis. I soaked it in pine-sol before I rebuilt it, and it came out looking brand new. That does not mean that all of the internal orifices were cleaned. Link to comment Share on other sites More sharing options...
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