Powerless and detonations with load

[Lars]

Hi,

I haven't been able to drive my roadster for the last 5-7 years because when the season starts something always breaks. Getting parts and fitting them takes months and the roadster season up north is short (3 months). This year I had good hopes, because this winter the brakes were overhauled, the year before that I fixed the carbs, then it was the fuel pump, the alternator, the starter, the differential and so forth. What could go wrong now? Well, hope fell into despair when I heard the first detonation in the exhaust. Here are the symptoms:

- The engine has no power under load. Max speed with full throttle on level ground is 60 mph.
- Detonates under acceleration and up hill
- Hard to start when warm
- Engine idles perfectly and runs just fine with light load

I fiddled with the carbs yesterday in the hope that it was lack of fuel, but it looks OK. Plenty of fuel in the carbs, so I am starting to fear something is a miss with the ignition system.

How should I go about to diagnose this problem? Any advice is highly appreciated.

[Linda]

Coil, plug wires?
How do the plugs look?
Linda

[mraitch]

Might be a long shot, but I had a similar experience which turned out to be in the distributor - one of the steel sprung 'arms' under the advance plate had broken !

[Gregs672000]

Definitely have an ignition timing issue. Make sure your timing is correct, especially if you are unsure what distributor you have. The '68 and later cars are timed at 0 at idle, not 17 for the early cars. Detonation is different than incorrect timing. Go buy a timing light and check your timing, or if needed I can walk you through static timing the engine (setting the timing when the engine is not running, but it's a ball park setting without a timing light.). Do not drive until we have figured out what it's doing as you can damage the engine if you're way over advanced on timing... you're making the engine fight itself by exploding the fuel way too early. If it does not turn out to be that, then we will trouble shoot the issue further. WE WILL HAVE YOU DRIVING SOON.

So, go get a timing light first thing, then report back.

[bakerjf]

If fuel delivery is ok, I’d look at advance as others have suggested. Get a timing light on it and verify centrifugal and vacuum advance are working correctly.

[C.Costine]

When I opened my distributor up to check it out there was considerable rust on the discs and balls of the vacuum advance. It was frozen right up. Condensation is more likely in the north than southern climates due to greater temperature swings. If your distributor is like mine just be careful to keep track of how it comes apart and don't loose the three little balls.

[Gregs672000]

I'm gonna guess that it's a smog dizzy timed to non smog settings. Excessive advance is leading to the immediate "detonation" but what that really is is the fuel is being ignited way way early so the explosion is pushing the piston down while the crank is pushing it up... bad bad bad!

To remind folks, ping is the sound of the fuel being exploded by the spark but the fuel is not burning uniformly, sometimes from too early a spark, other times because the octane is too low for the fuel to slowly burn and it explodes sporadically. Detonation is an explosion of fuel without a spark event due to high compression and to low an octane level. Higher octane numbers refer to the ability of the fuel to RESIST exploding before you want it to. A higher octane fuel is less explosive than a lower octane fuel, which allows you to compress it harder before it explodes, creating more power. It is a trade off however. I run against the ragged edge on 92 pump gas with 11.7 to 1 compression with good spark control.

[Lars]

I will check the timing as soon I can get my hands on a timing light. Hopefully tomorrow. My car has a presmog engine (early '67).
Thanks for all your help so far. Greatly appreciated!

[Curtis]

Which car, 1600 or 2000? It can make a difference.

Reason I ask is my 1600 stroker would run good, run bad and then run good again. Missing, popping, no power but would kind of run at low RPM.

So I ended up replacing every ignition part including the distributor with a 123. Started with the distributor and thought the problem was solved. It wasn't so I put all the rest on. And since I suspected it might be fuel delivery I put on a sealed plastic fuel filter in place of the glass bowl. I thought it might be sucking air some of the time. Did that yesterday and the problem seems to be gone now. Next I will hook the glass bowl back up and go for a drive.

The glass bowl filter top can warp and not seal. Also the cork gasket can go bad.

[Lars]

It's a 1600, stock everything.

[cktrap]

How fresh is the fuel?

[mraitch]

+1 on c.costine - but there are even MORE teeny/tiny balls to watch out for. They are in a small race under the vacuum advance plate.

[redroadster]

Good coolant flow? Full,...real full?
Carb slides smooth
Take a compression test cold
Check the centrif. Advance
Starving on gas?

[fj20spl311]

Check to make sure the coil is not over heating. Possible if the wires are connected in the wrong ends of the ballast resister.
It should be warm, not hot.