What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Back to basics, setting timing.

TommyD11730

TommyD11730

1/2 ton status
 Premium
Joined
Oct 3, 2014
Posts
454
Reaction score
51
Location
NY
Just for reference, 84 GMC 2500, 350, bone stock with a 700R.

Just wondering how you guys are setting your timing. My non EGR truck spec is 4 degrees. Can't run that, it's a pig. So I'm close to 10 degrees at idle and at or about 2500 all in at close to 30 degrees.

Like I'm sure most of you have guessed on my NYS 10% ethanol junk fuel I get a healthy spark knock at WOT. I'm trying to do anything (short of going 4 a aftermarket dizzy) to get rid of the ping without reducing timing.

Maybe go from 45TS to a 43TS?

Thoughts??
 
Run some higher octane fuel if it runs good but pings...or lose some timing.
 
Premium fuel costs less than new pistons,valves, and rod bearings that got damaged by pinging!..

If the EGR valve isn't opening or isn't the correct one for the vehicle,that will encourage pinging..

Those 80's 305's tended to have some spark knock even with timing and stock fuel mixtures...head design has much to do with it..

You can advance the timing "some" to compensate for the alcohol content in today's gas,but the fuel/air mix will need to be richer too,to avoid pinging..
Two chapters in a "how to run your engine on alcohol fuel" book I have cover the mods you need to make in order to make it perform as good as it did on gasoline,and advancing the timing and richen up the fuel/air mixture are the first two things they say to do--it also covers how to make a "injector" to aid in cold starts ,that is basically a device that squirts some gas into the intake ,as alcohol doesn't vaporize well below freezing..

I know you may be thinking "but I'm running pump gas,not alcohol"--but there is enough ethanol at 10-15% in today's gas to affect engines that use carbs,or were designed to run leaded gas..
 
This 84 has no EGR. Wish I could recurve dizzy to pull some total timing out.
 
It must be "emission exempt" over 8600 GVW not to have an EGR..

Does it have the OEM "feedback" carb and the HEI with a multi-prong "EST" spark advance ?...most people ditched those for pre-1980 parts ,they put an older non-computer carb and HEI with a vacuum advance instead ..but I've seen 305's ping with or without the OEM parts,like I said its partly due to the head design..higher compression with smaller chambers,that is why they used to be sought after for other engines ,to boost the compression ratio and power at lower rpms..

Might not hurt to make sure the advance weights under the rotor aren't stuck or sticking,you can get different springs and weights from Mr. Gasket to change the rate of advance and limit total advance..
 
Straight up HEI, no sort of EST... no electronic /feed back on carb.

Fuel gauge does not read unleaded fuel only... no cat converter. Built north of the boarder if it makes a difference .

First step... cold plugs. :)
 
Oh, timing curve works.. nothing stuck. Just too much total timing as a result of me mechanically cranking in some extra base timing.
 
I think you could pump the base timing up 2 or 4 degrees. I was surprised to see my 73 is spec'd at 12 degrees. I also connect the vacuum advance to manifold vacuum, not ported.
 
The advance is attached to manafold vac (factory ).

Already got initial timing bumped, however like I said as a result now my total timing is too high.
 
TommyD11730 said:
This 84 has no EGR. Wish I could recurve dizzy to pull some total timing out.
Click to expand...

Why can't you recurve it? Just need heavier springs to bring the timing in later. How do you know the total timing and what is it? Have you confirmed that the weights are moving freely? You don't need as much base timing when you run manifold vac because it's adding so much at idle. Why do you say you can't run 4 degrees base timing? Have you confirmed the choke is opening all the way, the secondaries are opening properly, the exhaust heat riser is opening (or not there) and the THERMAC on the intake is opening?

Under what operating conditions (load and RPM) does the ping happen? I would definitely mess with timing first, but after that, you might be just a rod swap away from richening it enough.
 
Ok, honestly I didn't know springs were available for HEI Dizzys. I thought I might be able to lock them, but thats about all. Lesson learned. How do I know the total timing? Timing light with advance/retard.
I cant run 4 degrees base timing because the truck is a dog. Perhaps the advanced timing is hiding another issue, but at 4 degrees you get a pretty decent hesitation when transitioning to WOT at a roll. Advancing it like I have it now and the truck runs pretty darn good. If I keep the throttle to say 80% it doesn't ping and accelerates smoothly.

The Thermac is disconnected (open) and tube still connected to air cleaner/rad support.
Heat riser is free and operates correctly.
Yes choke was converted to an electric and is wide open when "hot".
I believe the secondary's are operating correctly but would be interested to hear how you confirm they are.
As for a rod swap I'm guessing you mean to say meetering rod change? I didnt know you could change the rod alone on a q-jet.
 
The Crane Cams curve kit used to be on the shelf at every car parts store, but I haven't looked in over a decade. You can still get them starting at $5 on Summit. However, the kits are usually used to lighten the springs and bring timing in earlier. Possibly yours has been swapped in the past and you want to go back to stock springs and weights. But what RPM is the issue?

Since your pinging is at high load, you would only adjust the secondary rods. They are pulled out by the top air flap, so there are several adjustments possible. There are lots of old web sites about these units, such as this one that lists all the rods and hangers (formerly) available: https://racepartsunlimited.com/tag/quadrajet/. IIRC there are some secondary rod hangers with two holes, so moving to the rods higher makes it richer. Can bending the hanger a little work? I don't know. There is some kind of adjustment to the secondary air flap tension, but I understand the Q-Jet is fussy about that setting. I think you can still find the Doug Roe book online.

What about temp? Where does it run? I think you can get 180 and 190 T-stats, so a step down might be worth a try.
 
Your timing can only do so much. It sounds like maybe a couple larger jet sizes might be all you need to richen up the mixture to take away the ping.
If your plugs are white, that will be the issue. You want light to medium tan color on them.
 
Could be the timing chain is sloppy and advancing the base timing helps to compensate for that...but increases the tendency to ping..
Hope it isn't that..
 
I run 12* base on my 86. The weights wear on the pins. Springs rust. I LIGHTLY lube my weights with atf. You can also install an adjustable vacuum can on it. Are you hooked to the proper vacuum, i.e. full vs ported? I suspect there's a combination of issues. Getting enough fuel? Fresh fuel filter? Good fuel pump? Are you disconnecting AND PLUGGING the vacuum hose while setting base timing?
 
You must log in or register to reply here.

Latest Posts

Top Bottom