Carb question... (1 Viewer)

[spoold97]

So finally got the truck out to Lower Terminator Saturday...TRUCK DID AMAZING! Well anyways...I want to double check the ignition timing. There are so many different ideas on what it should be set at, but I want to see if any locals have done this enough to give me a solid answer.

What * should I be at with advance unplugged and capped off?

What * should I be at with advanced hooked up?

Some info on the truck...

81' with 85 22R (Carb)
LC's K&N air filter kit and adapter
LC's K&N breather kit
4-1 Header
High-flow cat
Adjustable FPR (2.5 psi on-road and about 1.5-2 psi off)
Inline electric pump
35's
5.29's
4.71 TC

Thanks

 

[inkpot]

Howdy! On my 85, I always went with the factory specs. If you advance it from there, then you risk detonation and loose some low end performance. If you retard it, you loose performance and power at higher rpm. Some folks suggest advancing it 2-4-6+ degrees for altitude and performance, but I personally don't like ridding the clutch a lot, so I like having the low rpm lugging power. I have had some good, but limited, results with a Recurve Kit. It allows you to set everything to stock, but the advance weights and springs are setup to increase the spark advance quicker/higher as your rpm goes up. John

 

[Tools R Us]

The eighties were the low point for performance, most were setup (somewhat kludge deal) for emissions. Especially with motor mods, the stock advance setup/curve is likely not ideal for performance. With some playing, it often can be improved.

My first test is see what it has, note idle and full in (~3000rpm) timing. Then remove and plug the vacuum retard hose, note both numbers, remove and plug the vacuum advance hose and note both numbers.

Most distributors from that era have: Vacuum retard; mostly an emissions device, on most setups retards timing only at idle (sometimes the ECU changes/uses it at other times). Centrifugal advance; this is only engaged by rpm. Vacuum advance; this is engaged by ported vacuum, so is better at sensing load.

Say the first test shows 40 degrees of advance, base setting to total, the retard is pulled and it shows 30, the vacuum advance is pulled and it shows 20. Now it is known that the retard changes by 10 degrees, the vacuum advance is good for 10 and the centrifugal is good for 20 degrees.

My first guess setup is about 5-10 base and 32-35 total. Care needs to be taken with the total, too much can cause hot running, pinging, etc, not a good thing in AZ conditions. So using the above numbers I would plug the retard, set the base at ~5, with a 35 total and see how it runs. If I wanted to go further; the next step would be to adjust/limit the centrifugal to bring the base up without over doing the total.

The best advance curve is dependent on you motor, your driving, your preference, etc. Taking others setup maybe a good start, but isn't likely to be best performing for your setup, doing your own adjusting/experimenting is likely to net the best result.

 

[medtro]

Taken from my '85 FSM. For 1985 22R, ignition timing should be set at 0 deg TDC @ max. 950 RPM with vacuum advancer OFF.