sb350 Problems,-Help!

2633 Views 24 Replies 16 Participants Last post by wrenchtwister, Feb 26, 2002

Classic Trucker

Discussion Starter · Feb 4, 2002

Greetings,

I have a sb Chevy 355 in my '56 Chevy p/u and I'm having a problem with hesitation on accelerations and a rough idle. The engine: 350 chevy 030 over, vortec heads (new), mild cam, HEI ignition (new), splitfire plugs (seem in good shape), fuel 91 oct w/2 pints of cleaner/drier in it, flattop pistons, edelbrock 600cfm carb (new). Vacum 21lbs and solid as a rock, accelerator pump squirtin' real well, plugs clean, cap/rotor new, fresh gas, This engine has been real solid although I recently have been putting the miles on it as the other car is in the body shop. Idle is rough and hesitates and knocks on acceleration, runs better when warmed up. Cruisin' at 75mph no problems whatsoever. I can't figure this one out, this truck would smoke 'em on take off, now I'm afraid of hondas. One possible clue the dash voltage guage has been reading slightly lower than usual (44 y/o guage though). The voltage into the hei is measured at 16.5 volts. Alternator puttin out around 16.5V.
Any help or suggestions would be greatly appreciated.

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PAULWELDIT

· #2 · Feb 4, 2002

I'M NOT REALLY SURE ABOUT THE HESITATION BUT IF YOUR VOLTAGE OUT PUT IS 16.5 IT WILL DAMAGE THE BATTERY IF NOT EVENTUALLY CAUSE IT TO EXPLOAD(NO EXAGGERATION HERE).VOLTAGE OUTPUT SHOULD BE 13.8-14.2 MAX. CORRECT THIS FIRST!! THIS COULD ALSO BE CAUSING THE IGNTION MODULE TO ACT UP--NOT ALLOWING ENOUGH COIL SATURATION(WEAK OUTPUT) I SUGGEST REPLACING THE MODULE WITH QUAILTY DELCO OR PERFORMANCE VERSION BE CAUSE THEY ARE A WEAK
LINK ANYWAY. THEN TRY IT --IF THAT DOSS NOT FIX IT START CHECKING FOR FUEL CONTAMINATION OR DRIED FUEL INSIDE THE CARB. HAVE FUN!!!WRITE BACK ON THE RUSULTS.

Phat

· #3 · Feb 5, 2002

I think at 16 volts it will last but NO more(we raced those at 16 volts and they would stay together,2- 8 volt batterys) But anymore as paul says it might blow the batt apart.I would pull the dist cap and rotor and see if the shaft has not siezed up in the mechanical advance(something that happens all the time)Get a timing light and see what you have for total adavnce at @2500-2800(becareful of the fan and stuff) if it ran good before and you have a rock steady vaccum gauge thats were i would look first. Also not to hurt your felling but split fire plugs just dont cut it in the real world.Have seen the things loose hp onn the dyno.they gave them to us free one nite at the race track,i gave then back as did most other guys .The things missfired and just plain did not work.This was in a flat top 355 with 104 oct at about 4500-6800 rpms all nite. One other thing(and i know you will roll your eyes)check the grounds to the motor.You dont know how many problerms i have fixed by just fixin grounds(incl the voltage problem your having) Good luck

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Classic Trucker

Discussion Starter · #4 · Feb 5, 2002

I'll replace those plugs ASAP, I'll check the grounds too, but it worked fine before. The HEI is almost new from Summit. It still looks clean on the inside, nothing sticking. Thanks for the suggestions, I'll let you know what happens.
Thanks,
Charlie

Classic Trucker

Discussion Starter · #5 · Feb 5, 2002

One more question, how do I lower the voltage? That's what's coming out of the alternator...
Thanks again,

Charlie

Phat

· #6 · Feb 5, 2002

Check your meter with another one.I know my muli-meter from sears did that crap all the time to me(drove me nuts) I now have a fluke and its rock steady dead nuts correct. But knocking just sounds like timming to me!! Voltage would not do that. But like i said i have seen bad grounds that made the throttle linkage spark

Classic Trucker

Discussion Starter · #7 · Feb 5, 2002

My ground consists of the negative battery post grounded to the alternator bracket which of course is connected to the block. This has been succesful in the past, do I need more?

PAULWELDIT

· #8 · Feb 5, 2002

I don't remeber if you said but if the alternator is internal style it should be replaced wih a new or rebuilt unit(the regulator is bad). Something else that we might be over looking---high coil spark out put is good on a race motor that's jetted properly but a street motor this could cause lean condition which will believe or not will cause a pinging or ignition knock like the timimg is too advanced----rember retarding the timing fattens the motor/advancing leans the motor.Also you said the accelerator pump is squirting good. Try it more than once with the motor not running.It should squirt good several times if the fuel supply is adequate and fat level is correct. Refering to Holley (but true on most all carbs.)a 3occ accelerator pump rating is the amount of fuel produced after"Ten" pumps of the accelerator pedal. Like the others guys said " junk" those plattium plugs---NGK single digit plugs if you can find them are one many good choices in plugs. keep looking!!!

Classic Trucker

Discussion Starter · #9 · Feb 5, 2002

I have the "one wire" alternator, what plugs would you recommend for this engine? sb350, vortec heads, edlebrock 600cfm carb, edelbrock performer manifold, mild cam, flattops, HEI.
Thanks,
Charlie

brief madness

· #10 · Feb 5, 2002

I had a similar experience as far as the poor performance and idle at low speed. I drove, parked the car and on restart a lot of low speed idle missing and stumbling but ran fine at freeway speed, so I assumed it wasn't a fuel problem. On the way home changed rotor and cap in the parking lot of parts store (easiest things to change) with no help. When I got home I changed the plug wires with a spare set (I am a pack rat when it comes to parts) and that cured it. The defective set was a $65.00 set. The spare set was a $14.00 set from Kragen. As far as the electrical problem I've had bad poitive and negative ground battery cables that looked good with a voltmeter but just wouldn't hold the capacity. Just a few things to check, electrical problems are a bear, good luck.

brief madness

· #11 · Feb 5, 2002

Just a follow up, I forgot to mention that I had checked the sparkplugs first before changing to plug wires, and like other posters had mentioned, be careful with charging problems. I had a bad connection on the alternator to the battery so the charge from the alternator wasn't making it fully to the battery and was blowing out my headlights after starting and stepping on the go pedal. Luckily the fuses protected my stereo but the heater blower motor (it was winter) sounded like a F-16 on takeoff with afterburners full on.

V8Cowboy

· #12 · Feb 5, 2002

Check timing and mechanical advance,also go for higher grade octane fuel,91 is normally only suitable for round town runabouts not modified smallblocks.
Also check for fuel evaporation,try cold air ducting the air filter

madingo

· #13 · Feb 5, 2002

First of all, the resistance check of grounds is not an absolute test. Checking voltage drop( difference from one ground to another). The reason for this is this: you can check a wire with one strand left, and show zero resitance, but the one strand cannot carry any current, rendering it bad.

REDUNDANT GROUNDS:

From battery to block
from block to frame
from frame to body
NEEDS TO A CONTINUOUS LOOP

Make sure the grounds to all of these points are of sufficient size-we use 6 gage or better.

popsz28

· #14 · Feb 5, 2002

Question? Do you have auto tranny with a vacumn trottle modulator. Seen a leak in that fix weird problem. Only fails when in gear and moving which makes vacumn readings difficult.

Good luck!

huffed6

· #15 · Feb 5, 2002

if you just installed the hei dist did you run thru the ballast resister? if you did it may be heating up and cutting voltage even tho when turning on initially you get a good voltage reading .on cranking bypass would show full voltage also. as rpms speed up voltage draw will lesson and resister will cool alowing more juice . just a thought
good luck

troll57

· #16 · Feb 6, 2002

Change the -plugs pronto, I know of no one who has had any luck with them. Watch the amount of dryer in the fuel, as anyone who has run the oxygenated fuel can tell you, it'll clean all the rust and corrosion out of the entire fuel system and lodge it in the fuel filter. Check or replace the spark plug wires. they may be crossfiring too. that'll do really odd things at different times. Check the advances on the dist.. they may be frozen or leaking vacuum and not working properly. Last but not least, check the carb mixture screws, pal of mine had them move.The vacuum modulator on the trans may leak if you've got an auto. run steel line as much as you can and only use rubgber for the connections, full length rubber can collapse in the middle of a long run. Spark plug wires are a good bet. The grounds are also a good idea, make sure you've got a good one from block to cab, don't rely on the motor mounts, they are rubber cushioned and under torque can make contact or not. I have chased many charging system probs down to this. Good luck

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carnutjoef

· #17 · Feb 6, 2002

First that carb cleaner can play real games with you, make sure you've got all of it out of the system, it may take a few tanks as that stuff really hangs in there. It does a good job of cleaning. I would look at the timing, slight changes make a big difference with the cam change, also any vacuum leaks. Any combination of these will make small corrections to performance as you find them, so there may be more than one, good luck, like to know how you make out. You gort a lot of good starts here, everyone seems to be hitting on a good potential, Joe

Classic Trucker

Discussion Starter · #18 · Feb 6, 2002

Thanks for all the replys, I will check out all these suggestions.

Charlie

dave7824

· #19 · Feb 7, 2002

When replacing a point dist. with an HEI it is highly advisable to increase the B+ wire size as the original wire used for point type distributors is too small to provide adequate current for HEI. Will run fine in garage, but under a load in real driving conditions runs like crap. Increasing wire size solved similar problem in my 1964 El Camino. Good luck. dave

dubba

· #20 · Feb 9, 2002

If electrical Don't fix. Pop distributer cap throw a wrench on the crank to see if back and forth movemont on crank is as responsive with distributer shaft. if it doesn't respond quick enough, you've found the problem good ole horse power weakend the timing chain. on accel it won't keep up but cruisin runs fair if this is the problem be gentle till fixed broke chain = bent valves. good luck

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