If I give it more than half throttle, it really coughs good a few times and then catches up and throws you in the seat. Its a 5 spd and it will do this in any gear if I hit the gas hard. If I just daily drive around it doesnt skip a beat. I know "it could be many things", here is some info. Notgetting enough fuel? I am running a high performance summit mechanical fuel pump, when idling the pressure is 6-7. Fuel hard line to tank is 3/8. Several people said it should work just fine, others have said you need an electric pump with that horse under there. I have a holley blue, just wasnt planning to put on right now, but can if thats it. No haters, money was tight, I am running a HEI distributor, could that be a potential vs. using a MSD or something else? Could this be timing related? Cranks and runs good otherwise. Running a 650 speed demon vac secondaries. 6.5 power valve, size 31 squirter, 1 1/4 turns front....3/4 on the rear bowls. 75/83 jets Just Found this on BG website Stumbles under hard acceleration A) Readjust butterfly position B) Increase squirter size (already increased from 28 to 31) Thanks!
Will have to check tonight, I might actually get to work on it. Havent touched it in a few weeks. Did a test drive last night and really noticed it.
fuel starvation? does it happen all the time at the same RPM?..no matter the gear? pulling hard and it noses over or just blips and back into it after the hiccup? or does it keep hicupping as you plant your foot?
sounds like pump shot- from what i understand a bigger nozzle will allow the same shot to come out easier/earlier, whereas a smaller nozzle makes the accel pump slower to be forced out (because it's a fixed size shot 30 or 50cc's and its pushed by a spring not your foot). pump cam probably needs to be stepped up to give more initial hit. I've got a stroke mopar small block running an 850 mechanical double pumper with twin 50cc pumps and it took a couple pump cam selections to get it dialed in. get a pump cam kit and play around with it. also, did you say vacuum secondary? get a quick change vacuum cover and try different springs.... your dizzy and fuel pump arent involved since your talking about the initial WHACK of the throttle- that is alllllll in the vacuum secondary/pumpsize/pumpshot/pumpcam to eliminate an instant lean/rich condition.
It sounds like a carb problem its not tipping over well. Ok that's some sort of lingo for its not making the transition from low/mid range to WOT. I don't know how good Demon carbs are. I do know that a few years ago (2003) one of the catalog speed shops that I use stopped carrying them because of problems. But they may have sorted that out by now. Anyway the power valve is where I would start. What is your vacumm at idle? Not ported vacumm find an open vacumm port (like the one you run your tranny off of or that goes to your PCV valve). Your power valve should be half that number but that is just a starting place. You may have to move your number .5 in either direction. Something else that may be a problem is the way your distributer is advanceing. An advance curve kit for the dizzy is under 15 bucks you should be able to get one at auto zone. Its just a matter of changing the springs and weights. On the HEI they are right under the rotor. Don't know that it will help but its a cheap fix if it does. If its a stock HEI one thing that you should bear in mind is that it starts dropping voltage @ 4500 RPM. Stock they are not a high rev dizzy. I don't think that is your problem but when considering a distributer and performance is your goal you should bear that in mind. I hope that something that I have suggested helps.
Good suggestions, to follow up... I have the quick change cap on the carb and also have different springs to play with. Never used a pump cam kit, I will check it out. I dont know that its exactly the same RPM, only driven a few miles. If I am easing along in first gear and get up to say 4000rpm, shift to second gear and nail it, its cough, cough, shit hold on. Same thing if I just take off in first gear slowly, then punch it, cough cough cough, ok hold on. best I can tell it happens at any rpm, its just a matter of how much pedal I give it to cause the problem. I am going to recheck the vacuum tonight. The engine specs are for vacuum at idle to be 15.6
sounds like a lean condition..when you open the butterflies all the way up and theres not enough fuel for the air ratio the butterflies are allowing, its like a short time of ..not enough fuel to the amount of air your letting in. float level accel pump.. jet size from idle to main..and powervalve, like porkandbeaner said.(to use his term)."tipping over" I used the term clocking thru the circuits..idle to mid to WFO...(Wide Fuckin Open)
Ok, i am going to check the vacuum again tonight and see where that aligns with the power valve. The jets I have in there now were said to be optimum by several engine builders I talked to that use these demons on similar builds. Not to say they arent right for mine though.
Did you actually use the vacuum guage to set the idle mixture screws?? Always shoot for the highest reading on the primaries. Then adjust the idle RPM to lets say... 800 rpm.. Then adjust the secondary mixture screws by screwing those in till they bottom out. Bring those out 1 full turn and adjust from there.. at the same time eye balling the vac guage to see if the vacuum raises or lowers... If the idle rpm is more than 800, re-adjust it to bring it back down. On other thing... Check your float level on the secondary fuel bowl.... If it's to low, that just might be the problem of your hiccups.. Hope this helps.. If you need calibration kits for Holley and Demon carbs, Check out your latest Summit catalog They have those for the vacuum secondary carbs and double pumpers.. I got both kits and they include everything!
X3 Sounds like it's starving. It's not RPM related, right...? Just a delay at WOT? Check the spark plugs first and go from there. A spark plug can tell you a lot.
Does it spit back through the carb or pop in the exhaust? The jetting you have listed is considerably larger then our baseline for that carb and you really can't rely on what others think the jetting should be. As some of the others have said it may be lean when you tip in but this would be accompanied by popping through the carb. If it is popping in the exhaust then it could be too rich. Base timing and how the ignition curve is set up can also play a factor in this. That carburetor requires a min of 14-16 degrees of timing in the motor at idle.
what is the timing? initial and total? Are the weights free in the distibutor? have you installed a curve kit?
Sounds like pump shot to me!! When you nail it you are giving it more air than fuel Which means when you go WOT the carb did not get enough gas from the shot to cover the change in air to fuel. Check your throttle and pump shot. Make sure that ANY movement of the throttle will produce a squirt of fuel. Also make sure the pump is at the begining of the shot and not in the middle thus not giving a full shot when needed.
Ok, so if it is indeed lean, what would be the best thing to do first? I am pretty sure I have the floats set about half way in the sight glass IIRC... I am learning carbs as I go here. I would like to adjust everything before I buy anything, just to eliminate buying un-neededs. If it were acc pump, what size to get? It "should" be factory in there now, which is 30cc. Stock pump cam shows pink #330. Stock jets were 70/78 (now 75/83).
Ok, to answer those above as well, Tech, my initial timing is at 14 and total at 34 if i remember, been a few months. I dont disagree at all about the jetting and what others say, so if you have recommendations, please say. I frequent the ford muscle site and talked to big joe (joe sherman racing) and he personally recommend those jets as did many others there that run these strokers and demons for years, and I just went with what they all said. I dont know enough about them yet to know whats best, so I am all ears! I havent heard any popping, but I am also running open headers and cant hear myself think at WOT. I only hear any kind of popping when decelerating with the open headers, which is coming through the headers. In case this helps Victor Jr intake
It's possible that you have too much slop on the accelerater(spelling) cam lever and pump arm....... If that's the case, use a .015"-.020" feeler gage to set that clearance.. I do that each time I remove the fuel bowls to change jet sizes and or bowl gaskets...
was in your shoes with my 331 about 2 years ago. (also running a 5speed) i was running a holley 650 mech secondaries. i tried the different power valves, jets, changed the eccentric on the accel pump many times, installed larger accel pump, installed electric fuel pump, none of it changed anything for the better. i determined i needed more carb. i went and got an edelbrock 750 (street series) and havent had a problem since. actually the car runs better than ever, idles great, starts easier and even picked up a little in the 1/4. i went with an edelbrock because my father in law swears by them on his hot rods, and drives the crap out of his cars. im not saying to buy an edelbrock, im sayin you may need more carb. i am always concerned about over carbing my cars so i stayed conservitive on my initial choice of the 650. i was wrong. the 331 with the edelbrock heads and long tube headers needs to breath well and that means a bigger carb. if you read the info about the ford motorsport 347 crate motor, they say in the specs they dyno'd it with a 720 cfm carb. hope this helps, maybe you can borrow a carb from someone for a tesst run.
Well, its running, just not any different I havent had time to mess with it much yet, I did just go check the initial timing again, its right about 14. Talking to some other 347 owners they are running 16-18 and said I should try moving it up a tad as well. Some of these suggestions are a little new to me so I will be reading up on how to adjust this thing. I know a lot of people run a 650 demon on these motors, saying the demons flow more then holley etc...Supposedly a 650 demon is close to a 750 holley, but who knows.
It's all in the contour of the venturie area... That's why they flow better. I milled the choke horn from a 600 dp carb once and blended everything in. That's still one of my favorite carbs to mess with.
Get that initial (and the rest of the timing) set before ya do anything to the carb. Just chasing your tail if ya don't!
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