jaggeedfire

Hello all...I know that this is another question about the same ol same ol. But ....I have tried timeing my 77 l-48 and the thing just wont run right.

First some info...

77-L48
355 running 882 heads- 8.4-1 comp.
performer intake and stock q-jet
i have the hei ign. and all the emissions equip was yanked before i purchused the car. i have capped all the extra vac lines on the carb and run the new vac adv. on the bid port on the bottom plate on the pass. side of the carb. carb model -204.

Problem is that when i time it out to 10 deg initial adv and hook everything up....the car has no power and runs extremely hot. But it i run about 20 deg adv initially, it runs good. this is at about 900 rpm. what am i doing wrong???

is somthing messed up in my dist??? or a slipped balancer??
any help would be appreciated


:cheers:

1979toy

Is the mechanical advance working normally?
Set your car up to check the timing and, while watching the timing marks, rev the engine. The timing mark on the balancer should go out of sight under the water pump.

Chuck Gongloff

An engine that runs hot is a sign of timing too far retarded. You'll also notice a loud or louder exhaust "note" or tone. Could be that the balancer has slipped and your "mark" isn't actually TDC. Could also be the distributor. Try the old "ear" method of timing. Advance the timing till in "pings" when you put a load on the engine while driving. Then retard it just a tad till it stops pinging. Chuck

Frank75

Have to double-check the manual - but most cars have you remove the vacuum advance line before setting initial timing. Vacuum advance at idle is significant (if you're hooked directly to base of carb or intake manifold) and can really throw you off.

good luck

Vetterodder

As already posted, make sure that your readings are with the vacuum advance disconnected. Also, at what rpm does the specs call for? At 900 rpm, many distributors are already into centrifugal advance and that would throw your readings off. My prefered method for setting timing is to rev the engine just beyond where advance stops and set the desired total advance first and then see what initial winds up at. A good starting point is 36º total with vacuum advance disconnected.

A C

You can also use a vacuum guage to see where you get your highest reading. I have found when you set the timing to the best vacuum reading, it is usually right on the money :cheers:. I have used this method twice when the outer ring of my balancer had slipped slightly, and couldn't use a timing light correctly. Each time, when I got a new balancer and timed it...it was right on.

AC


[Modified by A C, 9:03 AM 11/23/2001]

IgnitionMan

OK, here's what will fix it:

Try to find a 375 number center plate and 41 weights off whatever, from a wrecking yard or used dists. This pair of numbers will give you 22/24 degrees mechanical advance timing. Use one stock spring and another to let the curve start at 900 or so rpms, limit at 2,800. I use a spring from an earlier points dist, and play with many until I get the right one.

Initial timing set with vacuum advance disconnected, to 12 deg/BTDC, below 700 rpms out of gear curb idle speed.

Now, for what makes all this work right. Restrict the movement of the vacuum advance pull pin, with a fabricated thin sheet steel or aluminum plate, screwed to the vac adv moounting bar, on the diaphragm side of the pin. I use two 6/32 screws through the plate and into the mounting bar to do this. make the distance from the pin to the edge of the plate .085 inch. This will let the vacuum advance give only 8 crankshaft degres of timing. After getting the initial timing set to the 12 degrees, add the vacuum advance to a full intake manifold vacuum source, and the idle and timing will kick up, the timing to the 20 degrees the engine wants, when it is runing, but not when it is starting.

Do not use ported vacuum as a source for a vacuum advance for any reason. If the engine wants ported timing, the mechanical curve isn't right and should be fixed, and the vacuum advance moved back to the sane and correct full intake manifold setup.

I convert points distributors to HEI and MSD trigger only for a living, and one of the only large cap HEI fixes I do is this one, to new ZZ4 and 502/502 dists, I know it works. The other fix is to get rid of the epoxy coil in the cap of any large cap HEI, and use a remote mount oil filled coil, more consistant spark output and reliability.

This has cured more small block engines like yours for a long time

Rockn-Roll

I believe you have the wrong port. The port on the Q-Jet should be on the driver's side. Check my tech tip: http://www.corvetteforum.cc/techtips...D=86&TopicID=3

This is exactly what would happen if you have the wrong vacuum port which has a low signal like for smog controls which doesn't apply enough vacuum. You also need to set timing with vacuum line disconnected from dist and plugged. After you set the timing and with vacuum line still plugged rev it a bit and watch to make sure mechanical timing is working.

mrvette

Ignition man, my experience directly correlates to yours....same thing....
only variation I have is....the HEI coil leads need to be scraped and soldered in their spade connectors....and that will probably cure a LOT of higher rpm problems, as well as intermittant dead problems...with the HEI....

GENE

Hib Halverson

The first post in the thread says at 10 deg. initial, the engine lacks power and runs hot but at 20 deg. initial it runs better.

First thing I'd look for is either a harmonic damper with an outer ring that has slipped. Secondly, I'd look for a problem with a mismatch between crank and balancer or balancer and timing mark. In both cases, the only way to accurately determine if there is a problem is with the "positive stop" method of verifying the timing mark. Doing that with the heads on the engine requires a piston stop that screws into the #1 cylinder. The procedure is detailed in the Crans Cams catalog along with books like Rick Vogelin's "Engine Blueprinting".

mrvette

Hi Hib, well as usual we can agree to disagree slighty, once again...
I think the positive stop is a good system and certainly accurate within a degree or so,...but I found a quicker method...that is to orient the crank toward TDC by the blow method...finger over the plug hole...and stop when pressure is sensed...now take a wood stick, about 4" long, slide it into the hole touching top of piston....here is where help is needed...rotate the engine back and forth untill you can feel the direction change of the piston, and doit by feel for one thing it's easier on bearings, and quicker too, no tape and marking....well I think so anyway....BTW on a SBC can't use the harmonica balancer bolt to spin engine....on an old original Pontiac no sweat...

GENE

IgnitionMan

Since I only do points dist to HEI conversaions, I always have to build a now loom and add new connectors, so I don't have the problems of corroded or bad connections on the wire terminals to contend with, and I silicone all the wire joints off and use a di-electric grease on the slides.

I do solder all the terminals when I modify a large cap HEI from ZZ4 and/or 502/502 crate engines, when I fix them.

Another tech tip to reduce the ozone ionization build-up in the distributor terminals inside the cap is to coat them with di-electric grease (not on the coil post inside the cap, nor on the end of the rotor). This grease isn't a problem with electrical conductivity, but does help to postpone the ozone ionization build-up problems.

SteveG75

Go to http://www.corvettefaq.com and get Lar's timing articles.

GM set these motors up to reduce smog not make power. :crazy: SBC like to run 36 BTDC max advance all in by 2500-2800 rpm.

Here's how I set my curve. Use 2 medium springs from a recurve kit. Disconnect, and plug, vacuum advance. Using a dial back timing light, rev the car up to 3000 rpm and set 36 BTDC. Reconnect vacuum advance. I use an adjustable vacuum can that gives me 14 additional degrees of vacuum advance. Idle falls at about 14 BTDC vice the stock 8 but I don't drive at idle anyway.

As for vacuum ports, Lars helped me set mine up. I am connected to the lower port, passenger side. It does not matter which port you have as long as it gives zero vacuum at idle then provides vacuum off idle with the throttle cracked open.

My car drives great, makes good power, excellent response. Also gets 18-20 mpg on the highway.


[Modified by SteveG75, 3:20 PM 11/24/2001]