popping and giving out at high rpm

Graydon5oh · Apr 27, 2008

ok i have a 302 block bored 30, trickflow cam about the same stats as a e303, hurricane mid rise intake a holley 750, procomp billet hei distr, in between 5500 and 5800 my motor starts popping and cuts out not able to do anymore almost like a rev limiter. but it does not have any type of one. everybody at first told me it was most likely the fuel system so i ran 3/8 line from the tank into a new nice fuel filter from there into a new holley blue into a regulator and then into a gauge saying i got about 7 pounds of pressure. and it continued so now eerybody is saying valve springs.... what do you guys think

85hatchgt · Apr 27, 2008

could be not enough timing and also sounds like its not getting enough air if it has an air breather or filter or what not take it off and taker for a spin and see if there is any difference. before u do that though have a buddy hold ure car on reved at about 2500 rpm and turn the distributer either way until the engine goes smooth as itll get and that will be the best timing you can put in it, if none of that works let us know and we'll see what we can fig. out

Graydon5oh · Apr 27, 2008

tried the filter and have messed with the timing a ton

347HO · Apr 27, 2008

It IS your valve train.
What springs are you running?
Did you accomplish pushrod length checks? If so, what did you witness marks look like and how wide?

Graydon5oh · Apr 27, 2008

as far as i know stock springs and bb and t racing did the install said clearance was fine... so do you guys think this could be a possibillity

347HO · Apr 28, 2008

droptopfpm said:
as far as i know stock springs and bb and t racing did the install said clearance was fine... so do you guys think this could be a possibillity

Clearance from what? You have three issues with that;
1. compressed spring clearance.
2. piston to valve clearance.
3. lash

If number one was not correct, you'd hear and break the rockers, bend some pushrods, toast the lifters.
if number two was not correct, you be tap dancing the valves on the pistons.
If number three is too tight, you take out the lobes and lifters, if too loose you'd hear it.

To get back to your problem... it is your springs. Not a possibility... it IS.
You may have other issues, but I am positive you're exceeding the abilities of those springs, and you will have the symptons you described.

If you want to chase ignition and fuel tuning... it is your decision after all.

Graydon5oh · Apr 28, 2008

ok thanks man i just wanted some others opinions befor i just started chasing dead ends....

82CapriRS · Apr 28, 2008

if it was your valvetrain it would sound more like a can of marbles when it starts losing power. also a 750 carb with 7 pounds of pressue is wy to much fuel for your setup. i have stock motor with edelbrock intake an 600cfm carb with the same fuel pump an reg that your running, and im only running about 3.5 pounds of pressure. its gotta be running wayyy to rich.

5.0ina66 · Apr 28, 2008

82CapriRS said:
and im only running about 3.5 pounds of pressure. its gotta be running wayyy to rich.

:Word: hell, at 7psi, I wouldn't be surprised if it's overpowering the needle valve and pouring fuel straight down the intake

82CapriRS · Apr 28, 2008

^ yup. thats what i was thinkin. thats a ton of fuel for a lil 302. i read in this book i have for ford small blocks an it tells you how to pick the right carb an exactly how much carb you need. and even for the 347 im plannin on buildin with moster heads it would only need 605cfms or somethin around there. hense why a 750 on a 302 is like dumping gas/ money away

82CapriRS · Apr 28, 2008

oh an my car is actually runnin a tiny bit on the rish side to keep things safe

joel5.0 · Apr 28, 2008

Fuel pressure only deals with the ability to "fill" the carburetor, not A/F. Those CFM formulas are obsolete and outdated. I've been running a 302, single plane intake, 700 CFM DP for 15 yrs, and had to increase the jet sizes so the plugs could get a little tan. Fuel pressure is set to 6-7 psi BTW.

If you're using stock valve springs with an anything else other than the stock cam, upgrade that valve train..... as 347HO said, that IS the problem. LUK

82CapriRS · Apr 28, 2008

some carbs are rated differently i understand that much. but theres no way that it would take 700cfm to fuel a stock 302. way to much fuel. if 700 was indeed a good size for a stock 302 then how is my friends car runnin a 327 stroker with a 650 holley dp jetted down an runnin lil rich? fuel pressure has everything to do with runnin lean or rich. its how much fuel your pumpin to your carb. hook up a a/f on his car ill bet its rich as hell...mine is an im sure yours is too. as for those formulas its an idea not something i would use to give me an exact size. uncles have mine have been drag racing for the past 20 years an also agree that 650 is more then plenty for a stock 302 or modified 302.

joel5.0 · Apr 28, 2008

82CapriRS said:
some carbs are rated differently i understand that much. but theres no way that it would take 700cfm to fuel a stock 302. way to much fuel. if 700 was indeed a good size for a stock 302 then how is my friends car runnin a 327 stroker with a 650 holley dp jetted down an runnin lil rich? fuel pressure has everything to do with runnin lean or rich. its how much fuel your pumpin to your carb. hook up a a/f on his car ill bet its rich as hell...mine is an im sure yours is too. as for those formulas its an idea not something i would use to give me an exact size. uncles have mine have been drag racing for the past 20 years an also agree that 650 is more then plenty for a stock 302 or modified 302.

Then I guess the 289 I had with a 850 DP (way back) was way over carbed...... even though it ran the best with it.

Fuel pressure has nothing to do with A/F control in a carburetor (unless it's way overboard), that's the metering plates job...... mine rich?...... didn't you read the part where I said I had to increase the jets?..... spark plugs last for years, and they come out as clean as the day they were installed. Again, fuel pressure is set to keep the carburetor full as required.

82CapriRS · Apr 28, 2008

then what explains why my car is runnin rich with a edelbrock 600 at 3.5psi of fuel pressure? plugs are good. runs good an gets decent gas milage expecially for being carbed. on the way to mustang week its averaged 21mpg which isnt to bad imo. if i tried to push 7psi through my setup it would deff push past certain parts of the carb becuz where else is it gonna go? 850 on a 289?? stock motor?

joel5.0 · Apr 28, 2008

82CapriRS said:
then what explains why my car is runnin rich with a edelbrock 600 at 3.5psi of fuel pressure? plugs are good. runs good an gets decent gas milage expecially for being carbed. on the way to mustang week its averaged 21mpg which isnt to bad imo. if i tried to push 7psi through my setup it would deff push past certain parts of the carb becuz where else is it gonna go? 850 on a 289?? stock motor?

It either has a problem with the fuel needle and seat assemblies, floats....... anything below 6.5 psi should be OK with an Edelbrock, which is its pressure threshold. Other brands could/do work with more pressure. Anything below 6.5 psi in your case, is OK, but you don't change pressure trying to affect A/F control in a carburetor.

The 289 was a .040 overbore (stock block and internals), Hi-Po heads, HFT smallish cam, single plane intake, 4-spd and 4.11 gears.

347HO · Apr 28, 2008

In droptopfpm's case, the A/F very well could go either way at 5500rpm... the signal to the carburetor is now all FUBAR.
I'm about 99% sure it is not his fuel pressure.

82CapriRS · Apr 28, 2008

was just talkin to my uncle bout 289s. he says if built right they can hit 10k rpms in which case it would need a hefty carb. im not sayin your an idiot, just tryin to make sense out of it thats all

Graydon5oh · Apr 29, 2008

ok deff in the valve train i broke a rocker arm off to night it is actually the 2nd time this has happened i believed the firtst time to be from faulty equipment but it has to be with the springs or needing of larger size stud.... and as far as the carb issue goes i am running a stock 750 with a adjust secondary vacuum cant remember what tention but on a wideband i run right in the green all the way up to this point..... and fuel pressure isnt going to matter running 6.5 to 7 is ideal because anything in that level the floats will hold..... and when i actually drove my car i got about 19 a gallon on the interstate so your arguements dont have any value to me

82CapriRS · Apr 29, 2008

wasnt an argument. it was an opinion which is why you come on forums. just becuz it might have been wrong doesnt mean you have to get all offensive. ill stay away from your posts. kinda rediculous.

popping and giving out at high rpm

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