Technical SBC not performing well

I have an Chevrolet small block with a perplexing problem. It idles high out of gear, but drop it into gear and it wants to die. Also, it doesn’t rev up or down crisply, no peaks and valleys, more like rolling hills. Sorry, best analogy I can give. History, engine rebuilt, 350 with 305 heads, 283 4bbl intake, Edelbrock carburetor with spacer, cam is moderate with hydraulic lifters ( a bit of a lope to it), stock distributor with points, ram horn exhaust, turbo 400 transmission. Ideas on what might be going on? Carburetor? Distributor?

 

High idle might indicate a vacuum leak. Spray around the intake area with a little carb cleaner. When you hear a change in RPM, you've found your leak.

 

Has it ever ran well?

Chris

 

Did the intake bolt holes line up ok when the motor was put together? Could have been milled and now it’s leaking vacuum under it. Definitely sounds like a vacuum leak.

 

Mark the distributor and take a photo of it without the cap. Make a note as to where the rotor is, 12 o'clock, 3:00 o'clock. Then remove the distributor.

-Put it in the vise and take it apart. Clean everything with the wire wheel. Make sure you do the bottom of the distributor where it touches the engine block and the steel bracket that holds the distributor to keep it bonded to the engine block. Then very sparingly use distributor lube on the weights and springs or use the lube that came with the Accel points kit. Just a little is all that's needed.

-Replace the points and condenser with this Accel 8404 kit. It comes with their 32 ounce #110128 points, condenser and lube. Set the points to .017 with a feelers gauge. Once started use the dwell meter.

- Make sure you use the factory advance weights and springs. The aftermarket springs and weights are junk.

- Replace the stranded wire between the points and negative terminal of the coil. Use good stranded #14 wire.

-Remove the vacuum advance and screw the points plate to the distributors frame. When setting timing set the initial somewhere between 18 to 22. Check for hard starting and full throttle ping. If none add more timing but don't go over 22.

- Use the MSD cap and rotor.

If you ever run into an iron distributor, use it. Chevrolet had some of the best factory distributors ever made. There on e-Bay. The 59 to 64, iron, performance unit with dual points, mechanical tach hook up and no vacuum advance is gold!
The weights and springs are the best. These are from the corvette high performance 283 and 327 motors. 396, 401, 427,454, 283, 327 all interchange without issue.

If you want a real strong ignition that will last, add a Capacitive Discharge amp to the mix. By the way, the Capacitive Discharge ignition has been around since the early sixties.

Happy Motoring.

Accel 8104ACC ACCEL Points Ignition Tune-Up Kits | Summit Racing

Accel 110128 ACCEL Points Ignition Contact Assemblies | Summit Racing

 

How much lift and duration does that moderate cam have?

 

Put a vacuum gauge on it and see what it says.
Hook up a timing light and see that timing is correct at idle....and how far it advances when you rev the engine.
Check your fuel pressure and change your fuel filter to insure you are getting enough fuel to the carb.

Since it's not missing, I would think that there isn't any issue with the ignition other than possibly the distributor isn't timed correctly.

If you don't have a vacuum leak, and fuel pressure/supply is good.......then your float in the carb may be set too low and you are starving the engine.

If none of that produces an answer, then check your compression.

 

Your description sounds like a low compression engine, with a poor tune, and possibly a tight converter. I would spend some quality time dialing in the state of tune, i.e. timing and carb adjustment, particularly the idle air/fuel adjstment. This may help with the idle so you can lower the idle speed in neutral and not have the engine die when dropping it into gear. It will also help crispen the transfer from idle to off-idle acceleration. The use of a low speed tuning tach, and/or a vacuum gauge are necessary for this. Adjust idle air/fuel screws 1 at a time for highest idle speed, highest vacuum. I then like to turn the screw in to achieve ~20 rpm drop (lean roll). Then reset the idle speed and go to the other side and do it again. It won't hurt anything to do this a couple of times. Once you get the 2nd side adjusted and you go back to the 1st side you may find your adjustment ends up slightly different. I like to keep adjusting until I'm confident that I've got it the best it's going to get. The only cost is your time, and some gas.

 

A vacuum gauge is probably your best friend and or tool at this point. That is the simplest and least expensive way diagnose these types of engine issues.
Still as mentioned above, points set at .017 with a feeler gauge and set with the rubbing block right on the tip of one of the lobes of the distributor cam. If you have a dwell meter the dwell should be between 28 and 32 degrees.
8 degrees advance isn't a bad starting point on a small block with the vacuum advance disconnected and vacum port plugged/capped. You might just pull the hose off the carb and suck on it or hook a vacuum pump to it and see if the vaccum advance is working. That hidden vacuum leak might be right there in the vacuum advance diaphragm.

Do not go out and start throwing money at it for new parts until you figure out what the problem actually is. Trouble shooting by changing parts is total idiocy most of the time. Ok if you have a known good part on hand but not wise when you run out and buy stuff on a wild ass guess hoping that this tiimee it is the right guess.

If you have the receipts or boxes for the parts you might want to check on what exact intake gasket you used as all small block gaskets are not created the same. It's been way too many years since I dealt with it but I am thinking that some combiinations of heads/intakes and gaskets don't work well without a certain gasket and if you bought a complete gasket set for a 350 including intake gaskets that may be the issue.

 

You have a SJ intake on a LJ block. Could that be a problem? Mr48 may be on to something there.

 

Run that by me one more time!

 

The Accel number is 8104

 

DD: The intake is designed for a small journal (SJ) block and the block is a large journal (LJ), which the heads are built for. Crankcase ventilation was changed when the LJ blocks were designed.
Do things match up correctly? Does the front of the intake match the gasket pattern on the front of the block? Without the breather tube passage in the block the two may not line up. Just asking.

 

When it is idling high out of gear, can you see any fuel coming out of the venturii's? If this is the case, the idle circuit is not working and it will only "idle" if you have the throttle plates open enough to pull fuel from the main metering system. A bad vacuum leak will exhibit the same symptoms because the idle system just can't provide enough fuel to make up for the vacuum leak.

However, you still have to have good ignition, timed correctly and good compression on all cylinders.

 

Don't forget to check valve lash preload when you're checking everything else in the tuneup. A valve lash with too much preload will severely limit the engine's ability to make power. I've seen SBC engines that idled and ran fine at low RPM, but try to rev or accelerate and they fell on their face. Usually they had 1 full turn or more of preload instead of 1/4 turn preload.

 

I have ran many 60s SJC & BJC blocks ,
No issues with intake unless modifications were done to intake ,block or heads, milling , angle milled ,

 

I suspect a sealing issue between the manifold and carburetor.

 

The engine is 1974, the heads 1980, the intake 1965? As to the cam specs I have included a pic.

 

Did you check for intake leaks yet?

I tella you and I tella you...
no one leestens to Reeco.

 

It's never going to run right with hydraulic lifters on a solid lifter cam. It totally screws up the duration on the cam.

Did you not see the lash spec on the cam card?? Comp 270-S is a solid lifter cam.
Or did some "performance wizard" advise you that hydraulic lifters would be ok......yeesh....

 

Try to answer the questions we ask. It's how we narrow stuff down. Sort of like your doctor LOL. If you don't tell us everything, we can't help you as well. Don't be shy. If you filled the crankcase with kerosene and lit it on fire, we need to know. LOL

So before we proceed further, I'll ask what @Happydaze asked way back when.
Did you ever have this engine running well? And if so, what has changed since then.

 

Cam , cam , cam is all wrong . Solid design , hydraulic lifters used and on the radical side . A lot of duration . I hope you used 350 head gaskets , not that it will make things better but if you used 305 head gaskets they will not seal for long .
Back to the cam , even if you adjust the hydraulic as a solid , it MAY help . But itll need a great tuner to get that cam to work ( even with correct lifters ) your probably not on the idle circuit, one way we use to help the problem was to drill a 1/8” hole in the primary throttle plates , start small at 1/8 and close your throttle ( lower your idle ) check your rocker adjustments often . Id stick to 0 lash with the hydraulic s , some dont like to have clearances, the lifter may snap the internal e ring and come apart .
More later

 

Forgot , if you get it running decent , its going to need a loose converter . Having a hi rpm cam with small valve heads isnt a great combination. A stoct 390-410 350 300 hp cam would of been a much more performance oriented package , and better gas mileage .

 

Too many questions right now. Solid lifter cam w/ hydraulic lifters? Maybe you wrote "hydraulic" when you meant "solid"? And with a cam that large I go back to my mention of a tight converter, you'll need a loose converter with that cam.

 

Very first thing I would do is swap out the condenser with a known proven, quality one

 

Okay, back to the earlier question, the engine seemed to run right years ago after supposedly being rebuilt, but developed problems later determined to be intake manifold not seated properly ( backfiring, water in the oil) . The car never saw the road before the problem emerged. The car was mothballed. Fast forward to present and new hydraulic lifters ( that’s what was in it last), different intake, rebuilt carburetor with base plate, distributor changed ( old one broke when I pulled it as it was corroded in place due to antifreeze in the valley). The cam and lifter setup is what the person who put the engine together installed, they claimed to know what they were doing! It sounds like the best thing to do would be to pull the cam and start over. But first determine if there is a vacuum leak.

 

Can you get it to idle slower with out the trans in gear.? Is the balancer and timing cover from the same years. Quick check cam timing pull #1 valve cover slowly turn engine until the exhaust is closing and the intake just starts to open when they are both the same amount check your timing mark it should be very close to TDC if the cam is right.

 

With some of the problems you noted at this point I’d pull the engine and go through the whole thing. I’d also replace the heads, intake and cam and lifters with something more appropriate. Check the bottom end carefully too. Something tells me the engine is a mess inside.

 

It will idle slower out of gear, the balancer and cover should be same year, I did a partial tear down this past winter and while I am no mechanic, I did pull some of the caps from the mains and rods to inspect for possible problems. Things appeared to be okay. I pulled the heads and inspected the cylinders, then replaced gaskets. Everything looked good. I don’t have funds to replace everything that has been mentioned, so I’m hoping that a cam and a couple of gaskets will correct the problem. Since putting it back together it has gone through two cam break in cycles, plus two efforts to adjust timing and carburetion. Low vacuum, vacuum advance replaced.

 

You mentioned base plate . Sorry but if you use a certain intake manifold with a q jet it requires an aluminum adapter to preven a vacuum leak on the side of the secondaries .
Finding it would be easy if the carb is off . Just place the gasket on the intake and see if it covers all openings and then invert carb and place gasket on carb base and check for same .
I can’t remember if it applies to other adapter plates . All adapter plates are not created equal. I had a similar situation and it drove me crazy , until looking at each individual part uncovered the poor fit