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Discussion Starter · #1 ·
my engine starts cutting out at about 5000 rpm, as soon as I shift it clears, then when it reaches 5000 again, its starts to break up again. Its not valvetrain related, it doesn't sound like it anyway. Pretty sure its either fuel or ignition related. Engine is a 308 w/ 11:1 comp, should be around 370hp, duraspark ignition, stock style fuel pump and 5/16 line. I'm really thinking its the fuel system, but it clears up as soon as I shift, whereas if it were out of fuel, it seems like it would still be stumbling.

timing is set at 14 base, 36 total. I also jetted up 3 size in the rear in case it was just lean, seemed to have no effect.



<font size=-1>[ This Message was edited by: indigo66 on 9/18/06 6:51pm ]</font>
 

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i had the same sort of problem with a 5/16 fuel line from the tank,used to fall on its face at about 5k,sounds like its time to run larger lines,worked for me.
 

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Larger lines or higher volume pump maybe... If that fails get a better engine builder...



FE
 

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On 2006-09-17 09:41, GregP wrote:
Why do you say it is not valve related? That sounds like the textbook description of valve float to me.

Greg
Sounds like valve springs to me, if it were fuel i would think it would surge.

need more info
 

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Discussion Starter · #6 ·
I've been through through valve float problems on another engine, you could hear the valves rattling like all the rocker arms were loose, along with a slight misfire. The current problem is a much more pronounced misfire with no rocker/valve noise. Plus, the heads have nice double springs and I'm only running a fairly mild hydraulic cam. I would have expected a fuel issue to be a problem before and after the shifts myself, I mean the bowls aren't gonna refill instantly just because the rpms drop.

I should probably upgrade the fuel system anyway, maybe that will handle it. If it doesn't, I really don't know where else to look.

The engine pulls very clean to 5k, then starts misfiring, so I shft, then it instantly clears up and pulls clean to 5k again. I don't know the specs of the valvesprings, but the old heads had springs that matched the cam, they were 130 on the seat, and right at 300 open. I never revved it over 5600 before because it had press in studs and stock rail rockers, but it did rev cleanly. I would imagine the double springs would be at least as stiff. Cam is 228 at .050, 284 adv, .512 lift, flat hydraulic. Heads are PTL 180's with springs rated to .580 lift.

<font size=-1>[ This Message was edited by: indigo66 on 9/18/06 2:20am ]</font>
 

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Not sure what spring you have but were they installed at the proper hiegth....I bought some double springs from Comp that match the e303 cam and the install heigth on those were 1.6.....vs. the common 1.8

I have the 270s cam and it's only [email protected] I think and it pulls way past 6300 rpm with some double spring I got from Comp that matched thier XE274 cam I was runing.

before my spring upgrade it would almost die at 5000 rpm or so ,almost like a switch.....grab another gear and hang on until 5000..just like you said.

Hope you get her straightend out....................
 

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Discussion Starter · #8 ·
I've still got the old springs that go with the cam, so I might end up swapping them. It won't cost me anything but time. I will check the installed height of the springs currently on the heads, just to make sure I won't have to use .200 worht of shim on the old springs. Old springs needed a 1.81 intalled height I think. If its 1.81 on both (or thereabouts) I'll swap 'em out and shim things up to get it perfect. The more I think about the fuel system, the more I doubt its a problem( at this point at least), it just clears up too quickly.

I should be shifting at 6200 or so, I was having to shift way too early. Made for some disappointing time slips yesterday,lol.
 

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What ignition are you running?
 

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Fuel system, I will bet money on it.

Stock fuel tank sender? They can neck down to 1/4 inch or smaller inside the gas tank.

3/8ths line, and a 3/8 sender, and you will be good to 450HP. The stock line is marginal at best over 250HP
 

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I'm thinking fuel sender pickup screen too. Mine was clogged up so bad it fell flat at 4000 and I almost went through the windshield
 

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Discussion Starter · #15 ·
it has a newer fuel tank (5 or 6 years old maybe) and a 3/8 sender. Tank is clean inside, the filter before the pump always looks clean. It will be gettign 3/8 line all the way, regardless if its my problem right now or not. If it were a fuel problem right now, the engine would not recover the instant that I shift.
 

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Nice Looking Car..... I want mine to look the same as soon as I can afford the paint job.

Dress up your engine? Do you have braided sleves over your spark plug wires? If so, I would look at that. Or your spark system... you might have a cracked rotor cap, or broken spark plug....

If you used MSD on a stock points dizzy, did you remove the capacitor? Disconnect your vacuum advance till you figure things out....
 

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Discussion Starter · #18 ·
I'm gonna borrow a MSD coil from my brother and see if it helps. Its the easiest and will at least eliminate a possibility. If that doesn't work, I'll start swapping valvesprings. The old ones will drop right in, same diameter and installed height as the current springs. I'll update the thread once I get it fixed.
 

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On 2006-09-18 03:50, indigo66 wrote:
it has a newer fuel tank (5 or 6 years old maybe) and a 3/8 sender. Tank is clean inside, the filter before the pump always looks clean. It will be gettign 3/8 line all the way, regardless if its my problem right now or not. If it were a fuel problem right now, the engine would not recover the instant that I shift.
Yes, it will. Leave your valve springs alone until you upgrade the fuel system.
 

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Discussion Starter · #20 ·
really? I'm not arguing, I just don't understand how the bowls would refill so quickly if its out of fuel. I mean, it instantly clears up when I shift to the next gear. Then again, I don't see why any set of performance double springs wouldn't handle my little cam.....
 
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