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bear with me as this is long and from other posts. i want to keep this current so i can get this resolved and have expressed all the info that i can. if i get requests i will post a video of it running to show whats going on.
so i have a pretty soluid 289. runs about 15 inches of vacuum on the nastalgia 271 whatever solid lifter cam. it also has some 54cc chamber large valved heads (i beleive 2.5 intake?) but for the life of me i cant get the carb sized up right. i have two carbs one being a 570 holley and on being a 670 holley. anyway 570 was way too small so i moved to 670. i have fiddled with everything on this carb and the engine seems to be happy with about size 68 primary jets. happy as in it runs well enough to drive. anything lower and it is extreemely lean. is it possible that my heads flow so well that it takes simply more gas to kkep the fuel ratio happy or whats the story here. it should pull much better than it does. do i need to move to a 750? (yes i know holley recomends a 670 or less carb for the 289/302 but that is a stock engine. i would know i have one in my 74f100 and it loves its 600.) so please any bit of enlightenment to my delemma would be much appreciated. also i have a good handle on my timing as well as my valve timing. so i beleive there are no problems there. long tube headers going into flowmaster 40s(had these off with open headers as i thought i had too much back pressure and them being off made no difference) msd ignition has the biggest stop bushing and heaviest springs as of now( running about 18 degrees of advance) when i ran less advance initial i used ported vac and faster springs. both set ups made no difference. plugs are gapped to what msd had told me to. intake is a weiand street worrior and heads are 54cc 65 heads but with some big ported intake and exhaust. i can tell that it is lean since when i pull the plugs they appear white nothing indicating rich. engine is slow to rev. there is NO smell of gas (very suspicous). when i get out on the road and floor it the rpms climb slow. cruises just fine but with a t5 4.11 gears it aint meant to cruise. if i give it a rev shot it doesnt go over 2ooo rpm and sounds lean cant hear the cam very well. yes all the lobes are there and no it is not a valve timing issue. it runs 7 lbs of fuel pressure. (need to check throttle linkage to see if it has play) engine has an eccentric pump on it. the engine sat for a year after break in so who knows maybe the diaphram is in question. it just seems odd how such a little engine can be so lean with 68 jets. o and it runs 15 to 16 inches of manifold vacuum but another thing that seems damned wierd is that when the throttle is mashed the vacuum will drop to almost literally zero right on tip in. thats not natural i dont think. what does this mean? sorry for the long post but i have faught this all year and am ready to gain some power here. after thinking about it ig the vacuum reading is correct as my 302 responds the same way. i dont mean to question anyones knowledge but i have just listened to many people and met many dead ends. things do work because at one point i ran a quick fuel 680 on it. i was 16 and stupid. plugged the gas tank breather so carb started rich and ended lean but boy was that engine hell on wheels then. so there is an answer to this problem as it did work once. it still has tramendouse compression. i do have a mechanical dissy i could try since im going through every part. anywho i pt the engine in an old mustang with the previously stated set up with 3/8 fuel line and an unplugged gas breathered tank. after that she might as well have been a 4 cylinder. thought this info might be of use as well. shes a tough case to crack.
 

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Your post leaves me dizzy from turning in circles. First, either the 570 or 670 carb would have been fine, but it sounds like you have "tinkered" them to death. Second, it is really doubtful that you have 2.25" intakes in early 54 c.c. heads. You may be running somewhere in the 1.9-2.05" range, but I don't think you can fit up anything larger. Third, I am not the expert, here, but it sounds like the distributor's advance setup is all wrong. If you are running manifold vacuum advance, you should be running ported, not full, manifold vacuum. The advance springs sound way too heavy for quick throttle response, but someone smarter than me should weigh in on that. Forth, if you are running the solid lift cam that the 271 horse engines used, maybe you should check valve lash. If too tight, the engine runs poorly and will not last long. If you are running a hydraulic camshaft, it would be helpful to know the specs.
Best,
Al
 

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ok luke, another thread about the same thing will help nothing. just like i posted in the other thread and as al stated, something is going on with your timing.
 

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sorry fellas. agreed iv messed with the timing too far most likely. valves were a typo. i lost my cool there. im just going to let her sit awhile as it has caused much more irritation than it is worth.
 
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