Well the carb on my Fiat is acting funny ,but it was this way when i got it last week.It has a small dead spot at about 2700 rpm on the highway when you lightly accelerate and then its fine.If you give it hell it drives right through it no problem .Its only pulling 7 lbs of vacume at an idle (after readjusting the mixture screws) due to the cam.I figured it was a power valve deal so i put in a 35 and its no different .It seems to run a bit rich ,and the plugs look a little rich (but doesnt load up),but its hard to read them because i drive it on short trips mostly.It has 68 jets in the primaries .What should i try next ?I tried adjusting the accelerator pump shot both ways as well and i checked the float level to and its fine.Its a 4160 "750" vac. secondaries ...
How about more info what motor is this How is compression,fuel pressure ,dist,base timing and timing curve,sounds like lack of timing and or no vacuum advance try more base timing and make sure all timing is in by 2500 rpm,also is vacuum advance hooked up to manifold
I use a 55-65 in my 4160 even with a healthy cam. I had poor luckwith 35's. Like already said though need more info. As I recall the PV has nothing to do with the idle and everything to do with fuel enrichment at the upper end. I had a dead spot down low and needed to adjust the accelerator pump by tightening or loosening the bolt on the lever where the throttle engages it. Different cams are available to adjust the time when the accelerater pump engages.
lots miles on holley ....ck is the accel pump circuit losing its prime...either thru pull overor....make sure all ck balls are seating....try litly appling throttle just enough to re prime circuit ...see if flatspot gone>>>>>>try someones carb that works to help isolate yours
Sorry guys, i was on my way out the door when i typed the thread .Its a 327 Chevy with about 10to1 ,5-6 lbs fuel pressure ,torker intake ,headers /baffles,HEI ,and im guessing about a 220 duration solid cam(based on the sound of it) .The car weighs 2k lbs and has a 350T with 3500 convertor and 4.11's...
Im gunna check the advance on dist., as well as the timing (like some of you pointed out) when i get home.Im begining to think thats whats causing it.Dont get me wong its a tiny flatspot ,but i dont like it .Considering the car sat in a shed for 3 years with dirt dobbers all over the car before i got it ,its doing very well.The guy only drove it 100 miles in the 3 years he owned it and i drove further than that home in the rain .It hadnt even been started in 4 months till he drove it on his trailer to haul it up here .I have put about 350 miles on it in a week ...
I've had good luck watching a vacuum gauge while driving the car in order to determine vacuum level when the engine stumbles. If it stumbles with vacuum higher than the opening of the power valve, try changing to a power valve that will open at a vacuum level just a bit higher than when the stumble happens. If you are carrying 7 in hg. at idle you can move up to a 6.5 opening but the vacuum gauge may tell you something about what's happening during the stumble.
Thats what im starting to think as well .I checked the dist and it is advancing completly at about 2000 -2300 rpm ,according to the timing light.I cant tell for sure how much initial advance is there (since i have an old fashioned light and there is no tape with timing marks on the balancer),but there is a shitload ,because of the cam im sure.Its firing #1 with the notch in the blancer straight up and under the waterpump.The car starts great hot or cold and there is never any ping and runs cool as ice ,so im sure the timing is good and im not gunna mess with it if its not broke.I doubled checked for vac leaks ,cleaned the air bleeds ,float level is perfect and i reset the acc. pump shot to .020 play from bottoming out the lever in the pump housing .I may try to use a bigger shooter and see what happens .Im begining to think its so much carb that its leaning when you first hit it (what i mean is its getting more air than fuel for a second).It also runs kinda weak down low as compared to up high and im thinking it has alot to do with cam ,torker single plain ,and big carb plus it has a 1 inch spacer under the carb (thats proly making it worse).I went to leave work yesterday and it would start then die instantly .I messed with it for 30 minutes before i figured it out.The old Mallory tach/shift/rev limiter ,took a shit .I disconnected it and it started right up .Sometimes when i would get on it last week it would pop like the fire went out for a second at 4500 rpm .Even though i had it set at 6500 on the limiter.I dont need it anyway ,if you cant race without a limiter with an Auto trans ,you are in bad shape...
a few years back we built a wicked 331 for a customers 67 vette. TRW 11.1s, Chet Herbert solid roller cam, flowed the 461's, etc, etc, all the best shit. We had Kim dyno this thing to give the cust "real" number for his money. We started with a Holley 670 that was purchased for this build at the begining.... then get a phone call "not enough carb" so I took him a spare 750 and hung out to see it make a pull...it was in the 390's on the torque and about 410 on the hp sounded wicked and reponsive...then I get "do you have anything bigger???"...I'm thinking WTF?? So the next day I purchased a 850 and we make some more pulls. We picked up a little more hp and lost some torque on the bottom of the curve. We got a printout and loaded it up. After this motor was installed in and beat on a little the car started fouling plugs, we had not changed a thing since the dyno pulls. Car had a MSD 6AL, MSD dist w/tach drive all the best shit..The little car hauled ass but the plugs were almost black, car stank like raw fuel. I finally said screw it and re installed the 670 and whoa!! The plug problem cleared, it didn't stink like raw gas and the car just plained screamed it would pull to 7000 and sounded like a buzzsaw..it proved to me that setting a motor up to run dyno numbers and setting one to run in a street car isn't exactly the same...
oh yea and dump the 3.5 and go back with the 6.5 and don't mess with shooter either. Just blueprint the carb to factory specs and start over.
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