Thread: HELP 350 sbc runs like crap and has no power

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Okay so I have an 86 firebird that I swapped a 350 into, this 350 has a stock cam and hydraulic lifters and stock internals, it’s got aluminum heads with 75cc chamber 68cc exhaust and 180cc intake runner, aluminum 4 barrel intake with a Holley 750 double pumper, this motor is all bolted up to a manual 5 speed (not sure if that matters but oh well) so what’s happening is it currently runs like crap at idle and has next to no power under any kind of throttle, I’ll start it up and it’ll fire right up but it idles VERY badly coughing and hiccuping (no backfiring through carb or exhaust) and then when I get on the throttle it won’t rev high at all it won’t even pass 3000 rpm, if I let it sit there and idle it’ll slowly start running worse and worse and dropping in rpm slowly after about 15 seconds of idling it would be almost idling at 2-300 rpm (which doesn’t even make sense to me) and then it would eventually die. it has a brand new MSD distributor and all the wiring is new, keep in mind I had a 350 in this car before running and driving but then that 350 blew up so I replaced it with the current one, I did not change a single thing about the wiring or fuel system when putting this new engine in, so here’s all the things I’ve checked, the timing is about where it needs to be (I don’t have a timing light so it’s just rednecked lol) I advanced it as far as I could until it died and then retarded it until it died and no where in that spectrum would it run anything close to right, I have all new plugs and wires too, it also has a nice healthy spark, so eventually I ruled out timing and spark, I have a brand new mechanical fuel pump on it that was on the other motor and working perfectly in the car, it’s getting fuel for sure, I checked all the wiring for the alternator and it’s all correct and new and neet, this alternator is also brand new and was working on the car before (it’s also got fresh gas in it too so it’s not an old gas issue) I then moved to the carb I tried tuning it and no matter where any of the adjustment screws are or where the idle screw is adjusted to it makes no difference whatsoever, I checked to see if the floats where stuck open or close and they where moving freely and no gunk was in there either very clean float bowls, I checked for vacuum leaks and there where none, the only vacuum hoses that are in use is the vacuum advance for the distributor and the brake booster hose, I made sure my valves where lashed correctly (tightening the lock nut until there was no rocker arm wiggle or pushrod movement and then went half another full turn) at this point I am stumped and can not figure out what is going on someone please help because I’ve been trying to figure this out for about 2 weeks straight now and can not figure out what’s wrong here

Welcome to the site, good to have you here. First let me say that when searching and diagnosing a problem "rednecking" to a solution just won't get it done. You can pickup a "in-expensive" timing light - even at most pawn shops or used tool shops, while there get a vacuum gauge as well, these 2 can tell you so many things with your engine. And while I'm thinking about it - grab a compression gauge too.. you can live without it for now.. but it could be helpful later!

There are probably 40 or 50 ways to adjust a chevy rocker. I can't say I've ever heard of the process you used. I'll let Glenn or TechInspector pass on their knowledge/experience on that topic.

So - welcome aboard, with some basic tooling I'm sure "we'll" get to the bottom of what ails your motor.

Thank you! Glad to be here and I also should’ve put in that I’m still in high school and don’t have a lot of access to money at the moment so I’m working with no cash right now but I’ll see what I can do about the tools, I’ve obtained a decent amount of knowlage about cars over the years being in the car guy family, but this is still a learning experience for me big time

Too much carb, no bigger than 650. What size jets are in this carb? No bigger than 62's in the primary

I have no idea what size jets are in the carb, and I had this exact same top end on an identical 350 before this one and it ran and drove great for a while till I had a cam lobe go flat and spun a rod bearing and wasted the crank, I do have a quadrajet and the stock intake to match it laying in the garage that was on this motor when I got it would you suggest putting that back on and seeing what it’ll do from there?

Okay cool thank you, I’m borrowing a compression tester from my friend tomorrow so I’ll check that and see where it goes and then I’ll try to get my hands on a vacuum gauge, I’m pretty sure it’s not compression tho because I heard the engine run before I bought it and it ran perfectly fine how it should (keep in mind I swapped the whole top end to my parts vs the ones that where on it when I heard it run before I bought it and that’s minus the cam)

Okay so I had an idea last night, the engine that was in the car before had a .520 (intake) .540 (exhaust) solid lifter flat tappet cam in it, the engine that’s in the car now has a .450 hydraulic flat tappet cam, could my issue possibly be that the valve springs on my heads are too strong for this smaller hydraulic lifter cam?

Not trying to insult or disrespect, but before thinking carburetor size is a problem.
1). Are you sure you installed the cam in the correct position?
2). Did you install the correct lifters for the cam (did not recycle the old solid lifters)?
3). Did you set valve lash with the cam in its correct position for each cylinder?
4). Am I reading you correctly?, one full plus a half turn is to much lifter pre-load?
5). Have you tested for vacuum leaks coming from under the intake manifold?
6). Have you checked fuel pressure?

I never uninstalled the cam for this engine and same with the lifters, it currently has in it the stock cam and stock hydraulic lifters (the old engine I had is the one that had solid lifters) and I set the valve lash like so, I tightened the lock nut right until I could not spin the push rod with my fingers and then went only half a turn. I have not tested under the manifold yet I’ll have to do that tonight, and I have not checked fuel pressure, I wouldn’t imagine that fuel pressure is the problem it has a brand new mechanical fuel pump that was on my other engine and running perfectly fine but I will check it just to make sure.

Have you checked the firing order first bring it up on #1 on compression strok then clockwise 1 8 4 3 6 5 7 2

Yes I quadruple checked the firing order and I’m certain it’s right

Welcome to CHR!

I’m always encouraged by young people who are learning to wrench and have the mindset to work through things and figure out problems. Sounds like you’re doing a lot of things right and we’ll certainly try to help you figure this out.

There’s only a limited number of things that could cause your issues – bear in mind that it could be a couple of these things. I would recommend the following:
1. Check your fuel pressure – I’ve seen 14PSI from a new mechanical pump and you want 4-5PSI.

2. Check compression – need to know what’s happening inside the cylinders. Do this with all 8 plugs out and with a real good strong battery (or a booster cart). Make sure you get a minimum of three complete revolutions per cylinder and preferably five or six - stay constant with all cylinders. Compression should be 100PSI (minimum) with no more than a 10% variation between lowest and highest. If you have a low cylinder, squirt a couple shots of oil down the hole and retest. If compression jumps, think bad rings. If not, think valves. (I think your ½ turn from zero lash is probably okay. I like 1/4 to 1/2 turn for stock or mild build applications.)

3. Buy (or borrow) a timing light and set initial at 8 degrees (with vacuum plugged).

4. Set idle screws at 1-1/2 turns out (may need adjustment later for fine tuning – but this will work for the initial setup).

5. When running, spray WD-40 around the intake where it meets the heads and at the base of the carb. You will know instantly if you have a vacuum leak.

And now a few questions:
1. What heads – EXACTLY - do you have?

2. If this engine was truly stock, what was it originally from? Get the numbers from front pad (on the block where the head meets) on the passenger side. This may help in determining the stock compression ratio as well as the general cam profile.

3. What head gaskets did you use?

4. Did you use new head bolts?

a. How did you tighten them?
b. What was your final torque value?
c. Did you chase the holes for the head bolts with a blind tap and clean out the hole?
d. Did you lubricate the threads?
e. Did you use sealant on any of the head bolts?

5. What do the spark plugs look like? They should be a nice light brown – not black and not bright white.

Let us know – we’re always wanting to help.

Again, welcome to CHR!
Glenn

There you go 86Bird! You got a bunch of help going now! LOL..
I was just thinking - regarding the tools issue - check with some of the big auto parts houses, many times they have a tool loaner program as long as you buy some parts from them... it could be a way for you to"borrow" a gauge or timing light. And keep an eye on craigslist under tools, around me there are always cheap tools being sold.

Thank you guys so much this is all very helpful information, I’ll definitely do all those tests tonight and get my hands on some tools, I tightened the head bolts first with a normal ratchet till they where all just snug not super tight and then I torqued them (yes I made sure to use the correct pattern) to 65 lbs and then continued to torque check each one in the same order 3 times, I did not use any sort of blind tap on the bolt holes but I did wipe them down clean them etc I did not lubricate the threads and I did not use any sealant, the headgaskets I used where from some full engine gasket kit from summit racing I did not use new head bolts but I don’t think they where torque to yield bolts so I figured they where okay to use again and the heads I have are aluminum AFR eliminator street heads from summit racing, their part number is AFR-0911, and then my plugs looked very black and smelled like gas bad which definitely tells me it’s running very rich so I’ll be doing a lot of carb tuning tonight

Like I said earlier, TOO MUCH CARB, for this application