Thread: Newly built motor, complete lack of power and out of ideas

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I'm posting this for a friend so I don't have all the details, but we just spent 3 hours trying to figure it out and we're out of ideas, any help would be greatly appreciated! It is a "simple" build of a 350 vortec around 1998 with lightly more radical cam than stock, about 300hp was expected of the build and he copied the specs/parts from some legitimate source. It currently starts better than most new cars, idles without any issues and revs perfectly fine past 4500, headers dont glow, it runs at normal heat etc... what it doesn't have is any guts and I mean any at all... past 3500 you could almost pretend it's normal, but it should be spinning tires in 1st gear as well and it's got nothing to offer, in lower rpm acceleration it also has a slight odd shake but it's not very noticeable.

He pulled out his old tired 350 with questionable internals which before had no problem burning rubber, nothing else was changed, same transmission/gears etc...

so far we have timing at idle set at 10* with vacuum advance disconnected/plugged. If then we rev the engine to about 3000-3500 the timing goes to approximately 28-32* or so (STILL with the vacuum adv disconnected, more on that below..), we are guessing on the actual number because his balancer only has the line, but we're confident it's around that figure. Timing stops increasing at that point as expected. He has an edelbrock 1406 and we messed with the idle mixture screws per the manual, both screws are about 3 full turns out or so right now where they find the higher rpm at idle, we don't hear any pinging , exhaust smells normal, doesn't seem to be too rich or too lean. Otherwise the carb is stock and brand new as is the distributor which is this one https://www.summitracing.com/parts/sum-850001r

Here are some odd things that maybe will make sense to you?
1) we had two backfires in 3 hours of messing with it, nothing crazy but something isn't quite right (plus again, no real power)
2) plugs were more white than I would expect, I'll post a pic tomorrow, we pulled two and both were somewhat white-ish (so lean?) , they are the iridium kind gapped properly (we checked).
3) we tried using both vacuum ports on his carb for the vacuum advance
on the MANIFOLD vacuum port (dr. side) the idle speed increases vastly from 800 to like 1500 and we actually can't lower it.
On the timed vacuum port (pass. side) the idle does not change at all, but AS SOON as we rev it the timing is off the charts like 50*+ (I'm guessing but it goes waaaay off the scale)
is that normal for both? we ended up testing most without any vacuum advance and everything plugged.
4) We were so out of ideas that we ended up pulling a spark plug cable just to see how badly the motor would run, to my shock it wasn't noticeable AT ALL, we then put the #1 wire back, pulled #2 on other side and same thing, couldn't even tell, fired right up and idled and revved the same... that really confused me, I expected a bucking horse type of result.
5) since this is '98 he had to install an electric fuel pump setup, it's all new, gauge shows 5psi at most times, when revved at idle we can see it drop to about 4psi but mostly 5ish, I assume that's fine and since the issue is with no power at lower rpms we ruled fuel pressure out

Unfortunately at that point we blew the oil sensor line and made a mess so the night ended, but what say you oh-wise-carbed-350 experts?

as far as the motor build itself, the only thing we question that he did himself was lap the valves, he had some concerns that maybe there's issues with those but it seems odd that it would idle so nicely with such a major physical issue as valves not seating.. we can't rule it out, it just seems unlikely. He assembled the rest as well with crank/cam, but there isn't a whole lot I can think of that he could get wrong that would still allow it to run nicely as-is.

I'm no expert, but my first guess would be timing and vacuum. I have the same engine with a 1403 edelbrock. My vacuum is hooked up on drivers side.
My high idol timing advance is 32 an low idle is 12. Just some idea's, good luck...

Originally Posted by zracTA

It is a "simple" build of a 350 vortec around 1998 with lightly more radical cam than stock, about 300hp was expected of the build and he copied the specs/parts from some legitimate source. It currently starts better than most new cars, idles without any issues and revs perfectly fine past 4500, headers dont glow, it runs at normal heat etc... what it doesn't have is any guts and I mean any at all... past 3500 you could almost pretend it's normal, but it should be spinning tires in 1st gear as well and it's got nothing to offer, in lower rpm acceleration it also has a slight odd shake but it's not very noticeable..

JMHO, I would check cam timing.