tune up speck on a 86 cj7

I put TFI (thick film integrated) ignition on my jeep it is a ford ignition from a 81 f150 300cid i-6 engine. it is much easier to install than HEI there is no need to pull the distributor just screw on the ford distributor base plate and install the rotor,ford cap,wires, and regap the plugs to .0045. I also installed a msd blaster coil to bring the ignition up to

45,000 volts. carmine

Carmine,

Bill is generally correct, but you may want to at least try the weaker spring. Getting the mechanical advance to come in a little sooner will benefit you at lower RPMs, as long as it isn't advancing too much at idle. If this is the case, you will have problems getting the motor to idle properly.

Try putting in the spring, then use a set back timing light to set your total advance to 36 degrees or so at 3000 RPMs. Don't worry about the initial setting, as that will now be a by product of the adjustment for total advance. In other words because you have now adjusted the timing with the engine running at 3000, the initial setting will now be determined by where the distributor ends up being rotated to, and won't really matter as long as the engine runs well, is responsive, doesn't knock, and doesn't kickback on the starter. A lot to keep in mind for sure, but this method usually produces good results.

Bill, someone or several have told me that the 258 tops out the timing around 2300 rpm.

Do you know for sure?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

"L.W.(ßill) Hughes III" wrote:

Hi Mike,

If that is the case, Carmine is probably already getting a decent curve.

2300 is pretty quick for a OEM situation, but all the better as "the quicker the better" is true to an extent. I've worked on many "performance motors", where the mechanical advance was still advancing past 4 grand. That is way to slow, even for a stock motor, irregardless of how many cylinders it has.

Rick

I think you have to figure or I do anyway that the advance should match the 'sweet spot' on the power curve.

These long sixes are low rpm engines with a red line of 4500 that can only be reached if the emissions computer is dead. It tops around 3500 with the computer...

My engine gets the best gas mileage at this point too and for me 23-2500 rpm is where I keep it at 65-70 mph in 4th gear.

I run a ported vacuum with 750 rpm idle set at 9 deg BTDC (with the hose off, sometimes ported can suck a bit at idle, I don't take the chance) so I get an instant punch when I floor it, then it mellows a bit as the mechanical weights take over.

OEM is a manifold vacuum on the timing with the computer adjusting things on the 258's after 82. It will jump about 15 degrees when you kill the computer and wire the distributor to the ignition module direct.

Mike

Red Racer wrote:

Mike, How do you convert to ported vacuum? They pull in opposite directions. Do you go to port and compensate with the distributor position? I would think the increase in vacuum on throttle would retard your distributor when you need it to be advancing... ?

It's convoluted a bit... ;-)

You want the spark to fire in 'advance' of the piston hitting Top Dead Center or Before it, so going BTDC is advancing the spark.

I want a stable idle 'advanced' at 9 degrees 'before top dead center' with no advance mechanism at all turned on, just where the distributor base sets.

To pass emissions this way, the carb needs to be leaned a bit so the engine has a rumble to it. If it is purring, it is running too rich for the sniffer. I split the difference after the test.

'Ported' vacuum has no pull with the throttle closed. It sucks from above the plate. On the BBD it is near the top on the valve cover side and front bottom fender side one too I think.

'Manifold' vacuum has full pull with the throttle closed. It sucks below the carb.

Having the timing advanced at idle will make a lean idle setting on the carb purr, so emissions call for it. It loses the vacuum when you punch it and starts off slowly/sluggish until the centripetal weights start to kick in up in the teens for rpm.

With ported, I get full advance instantly and if I punch it off the line it will light up my 33" muds with 3.31 gears turning them.

With ported, the 'advance' advances the timing spark to 'more' advanced before top dead center, not advancing above 0 but advancing backward before 0.

Basically you sacrifice a bit smoother idle for instant punch and a little more noise. I like the noise, it sounds cool coming down something steep in gear with the throttle closed. If you are old enough to remember muscle cars, they had this 'burble pop pop' sound when the engine was doing the braking, same sound.

Mike

TJim wrote:

mike romain said."I think you have to figure or I do anyway that the advance should match the 'sweet spot' on the power curve". my motor was rebuilt with a R.V. cam in it that hit peak h.p. at 2800 rpm's. when I rev it up the motor starts to flatten out at 3000 rpm's and that is where I shift if I am accelerating. so with that in mind should I install the weaker centrifugal springs(Mr. gasket part # 925d) in the distributor. carmine

I would find a safe stretch of road and time it from stop up to say 60 mph with the stock springs in first, then do the same with the heavier springs.

I don't know what the RV cam runs like, but to get the advance to come up slower so it peaks at a higher rpm means you need heavier springs or lighter weights.

Lighter springs will make the advance peak earlier. The weights work against the springs to advance the timing. Heavier springs means higher rpm before the weights can stretch them out.

Mike

Jet wrote:

It's convoluted a LOT... ;-) OK, it's late. I'll save your post and analyze it after I get a good night's sleep.