Kinda an odd problem. Whenever I get my engine wound up tight above 5k and let it back down. Sometimes it starts missing and idling rough. But after a minute of driving it's fine.

Any ideas?

 

. You're overrevving it and the hydraulic lifters are pumping up and holding the valves open until they bleed back down again... actually, a common problem with weak valve springs... do it very often and as the lifters come off the cam and slam back down again they will hammer off the cam lobes and bottoms of the lifters...


. Engine(351C 2bbl.?)? What's your cam(still 204/214?)? Valve springs?


. Did you ever regulate the fuel pressure down for that Eddy carb.?
.

 

Yes same cam. 204/214 with 486/510 lift. Supposed to be idle-5500.

Valve springs are COMP springs. 125 seat pressure. Not extreme but just a little heavier than stock.

I've never had it past 5,200. And no I don't do it often.

 

. Maybe it's an electrical or fuel supply problem... those springs sound like plenty from the seat pressure... depending on the spring rate... especially with 1.73 rocker ratio helping the springs keep the rockers on the cam... more seat pressure than I would prolly use with 1.73 rockers and a flat tappet cam...


. Actually, lifter pump up should also be noticeable at the high RPM end first... power suddenly stops and the engine won't rev any higher...

. My 351W with 1.6 rockers and 80 lbs. seat pressure (Crane springs) on 216/228 cam revs to 6,500 with no problems... I don't know the open pressure off hand...

. Is it a factory tach, they can get inaccurate with old age...

. Did you put a regulator on to adjust fuel pressure down for that Eddy carb.? Some of the cheap regulators don't flow enough fuel... when you put your foot into it, you may be nearly emptying the float bowls... then back off to idle and fuel level is too low for the idle circuit until they catch back up again...


. Floor it for 10 miles and see if the float bowls go dry... LOL!
.

 

No regulator on the fuel side.

I'm thinking it could be electrical.

I've never seen how high it will go, and I don't want to find out lol. 5,100 was factory redline, and the edelbrock stuff is good to 5500. So I'm gonna stay at 5200 max. If I ever get it screamin higher than that, I'll let you know HAHA

I hit 5-5100 last night and it didn't do it.

 

Good aftermarket tach. Comp 972 springs. 124 seat. 293 open. Good springs...

 

. Springs sound like they should be sufficient to prevent pump up till 6,500 revs... assuming installed at correct height... when I made first comment, thought maybe you still had high mileage stock springs...


. Looks like fuel and ignition need to be ruled out... maybe add a fuel pressure gauge to see what's happening at high RPMs...

 

Thinking it might be the ignition side of things

I don't know what, but fuel doesn't make sense. running at high rpm, it's fine, it's just when it comes back down the idle that it runs funny for a minute.

 

Might be fuel supply problems, i.e. running out of gas.

 

Comp does have periodic valve spring quality issues......

 

I tested all of them when I put them in and they were at spec.

 

What is a safe redline for a basically stock cleveland? I've been following factory at 5100, but how far is too far? Like I said, basically stock with a cam. Rebuilt not long ago, everything was in good runnable condition.

 

. Not that familiar with Clevelands... don't know if 2 bbl. and 4 bbl. engines had different cranks and rods... the 4 bbl. ones were routinely twisted over 6,000:

Muscle Car Engine Shootout - Ford Vs. Chevy Hot Small-Block Dyno Showdown - Hot Rod Magazine

. My 2 bbl. 351W with stock rods, bolts, and crank built to 425 HP by 5750 RPMs I blip the throttle to 6,500 occasionally and work it to 6,000 or so... it's in a boat, so it may be WOT for a few minutes at a time...


. A stock bottom end 400 though with it's 1/2" longer 4" stroke I would try to keep under 6,000 RPMs... with good heads, good engine quench, and 10-11:1 compression ratio, they'll make 500 HP by 5,000 - 5750 RPMs... so not that much need to twist them higher...

 

Something you might try is a slightly thinner oil. If your lifters are pumping up a thinner oil may prevent that. I have heard some hydraulic lifters are more succeptible to pumping up than others.

 

Hmm, I am running 10-30 oil now. Lifter pump up does seem to be most logical in this case....