UGGGG....weak 350. Ideas???

[78Buford]

ok few points noted, the engine calls for 34 degrees of timing, youre only running 12, that would make a big difference.

I assume he's talking about 12* advance at the distributor...with the vacuum port unhooked. The 34* figure is with the vacuum advance hooked up.

When you hooked up the vacuum gauge, you said it was 15" and wandered. I'm not familiar with the edelbrock cam #'s. I assume it is the Performer version...204/214 @ .050, correct? That cam is basically "one size larger" than stock for lack of better terminology. That cam shouldn't have enough overlap to cause the 1-2" wander on the gauge.

Try this: Start the engine & let it idle. Raise the hood, put on a pair of gloves, and pull one wire from the distributor at a time. The engine should "slow down" a bit with each one removed. If you find one (or more) that cause no difference in the idle, you have located the cylinder or cylinders with the problem.

You mentioned the engine feels strong down low. If you have weak valvesprings, this would give you adequate power at low rpm, but power will fall off way too soon. If you have the Edelbrock cam I assume you have, you should have decent power to 5000 rpm. If it has good pwer to say, 3000 rpm, then falls on it's face, I'd look at changing the valvesprings.

With weak (but not broken) valvesprings, you will have a fairly smooth idle. If you do happen to find a weak/dead cylinder with the plug wire test, and the idle is kinda rough, you may have a broken valvespring, bent pushrod (normally you will hear this), or a flat cam lobe. Cam lobe failure/lifer problem is an increasingly common problem due to the newer oils not having the ingrediants (zinc among others) to make flat tappet cams survive and marginal lifter quality.

Do the plug wire check & post your results.

Roy

 

[jtexfisher]

Roy...that's what I was going to say...12* is base..no advance in play.

I'm thinkin' I paid (hired the job out for the 1st and LAST time) to have an intake leak. All the goofyness acts just like it. I've run it with all the carb vacuum ports capped, the brake boost capped and the manifold vacuum port plugged. Vacuum doesn't improve.

C10 motor (very, very similar) pulls 18-20" solid, is crisp.

Maybe I'll buy beer and invite my grease buddy over this weekend. Beer always helps.

 

[K5dreamer]

well if the advance is set right, then like i said, you bought a smog era replacement motor, and got what ya paid for. nothing wrong with the engine, just designed to be anemic. when all else fails, upgrade and modify

 

[78Buford]

A 290 Horsepower engine (even in a heavy vehicle) should feel snappy up to reasonable speeds. My old dying (it was in the dying process for many months) 460 could still easily keep up with traffic & accelerate when needed...in a 7000 lb. vehicle with 42" tires & 4.10 gears. Something is not right, and the relatively low engine vacuum reading & fluctuation is showing that something isn't quite right with his engine. I understand you are likely tired of piddling with it at the moment....but the pulling one plug wire at a time & seeing what happens method is worth your time. It will only take a few minutes.

Roy

 

[76zimmer]

I disagree, I've had this engine in a 1/2ton 4x4, with good results. 3.42 gears, and a 700r4. It pulled up most hills fine in OD, occasionally downshifting to 3rd. Check your ignition system, and carburetor, and fuel pump also.

 

[jtexfisher]

like yeah... mind you I DON'T expect bat out of hell performance. The 'hill' I mentioned early on isn't a big hill by any means. Slope?? 30'-40' elevation gain in 1/2 mile. Gets to 60 pretty well going DOWN.

I have experience with building some 400s (olds 403, 455, chevy 400) with moderate cams & intake, good spark package etc. They sure pull SWEEEEEET. But mine had been bored out too far to be any good. I'll do the plug wire test in the cool of the morning and see if it's any one cyl. in particular.

Thanks to all for the feedback, it's truly appreciated.

 

[1985_K5_Silverado]

I wonder if the secondary metering rods in that Q-jet are just a little too skinny for the 50 cu in less displacement you have now - so that when your secondaries open, the skinny rods allow too much fuel to pass the jets and semi-bog you out.

 

[blazinzuk]

well if the advance is set right, then like i said, you bought a smog era replacement motor, and got what ya paid for. nothing wrong with the engine, just designed to be anemic. when all else fails, upgrade and modify

I disagree I have this motor and last time I took a long road trip 4.56s and 40s with a turbo 350 there were not many hills that I went up I couldn't mantain speed. Without a downshift. BTW my motor is about 14 years old too.

You should be getting more from your motor and the vaceum gauge says so.

 

[rjfguitar]

I will agree that you may have some tuning issues, but I don't think you are that far off either.

I had some of the same issues. I have a built 406 at about 325HP in my K5. It would pull hills for the most part fine in 3rd, but towing anything and it slowed down considerably, and sucked all kinds of gas. Thats a gas engine for you.

I finally got tired of all that and bought a Cummins. 80mph with 7K behind me up a 6% grade. I'm not saying you should do the same, just saying that gas engines sucks in the hills for the most part, I got tired of it.

 

[jtexfisher]

Roy:

All 8 produced the same sound, tach wiggle and vacuum drop.

 

[jtexfisher]

Pulled the distributor today to do intake retorque. Decided to check the advance....what advance??

Mechanical advance was STUCK.

Much happier truck now. Much happier driver too.

 

[broncoman6524]

mechanical? like your mechanical advance on the dist? wth is that?

 

[lifted76k5]

sounds like its a weight vs gearing problem. a 2wd PU probably weighs 1500 lbs less then a burb. and it depends on your factory gearing, for a sub you'll want at least 3.73 for even 31's.