Jeep J-10 timing Help

[NBD925]

I have a 1977 Jeep J-10 with 258 engine. I have installed a Motorcraft 2100 carb and HEI clone distributor. I have also purchased the Crane Cams vacuum advance kit with springs and limiter plate.

I need help getting this engine timed correctly. It's up and running right now but I have no idea what a 258 timing curve should look like with these new specs (HEI and Motorcraft). What RPM should the mechanical advance come in and when should it be fully in. How much vacuum advance souls I have for a 258?

I have the initial set to about 8* I have the limiter plate set to limit the vacuum advance to about 14*. For some reason I have a slight loss of power just as you increase speed from idle. I have the vacuum advance adjustment (small Allen Screw that pre loads the vacuum advance spring) all the way loose so the vacuum advance comes in quicker with less vacuum needed. It seems to have helped but I ran out of adjustment and it dosent seem right that it's all the way out.

Another problem is the lack of power if you start with any type of resistance like mud, snow, or a hill. It really bogs down and dies and then is somewhat hard to start. I set the carb adjustments using a vacuum gauge (highest setting then backed off one inch vacuum) is this the best method?

Thanks I hope someone can help.

Adam Corts
Missoula, Montana

[Tatsadasayago]

Hello Adam from a Victor Native!

You might check this post of mine regarding timing. It's a re-post of an engineer's that is very relevant.
I believe 8 Degrees base timing is good for your 258 at your altitude so I suggest you switch to manifold vacuum instead of ported and tune from there.

Here's the link: http://fsjnetwork.com/forum/viewtopic.p ... 028#p78124

Jim

[NBD925]

Hi Jim: thanks for the Responce. I read a bunch of things about the vacuum advance and can't wait to try it out with Manifold Vacuum. It makes sense to me after reading the material and it also makes sence now why so many manuals say to make sure the vacuum advance is disconnected from the distributor when timing the engine.

I see that 8* is a good place to start with the initial timing but how much vacuum advance is good. I can limit the amount given to the engine with the Crane Cams limiter. What should a 258 have in that regard? 9 .... 12 .... 15 maybe 20

These HEI clones can really have allot of timing advance built in you let them go Un-limited.

[Tatsadasayago]

Hi Jim: thanks for the Responce. I read a bunch of things about the vacuum advance and can't wait to try it out with Manifold Vacuum. It makes sense to me after reading the material and it also makes sence now why so many manuals say to make sure the vacuum advance is disconnected from the distributor when timing the engine.

I see that 8* is a good place to start with the initial timing but how much vacuum advance is good. I can limit the amount given to the engine with the Crane Cams limiter. What should a 258 have in that regard? 9 .... 12 .... 15 maybe 20

These HEI clones can really have allot of timing advance built in you let them go Un-limited.

You are most welcome!

Since you are in and around Missoula and assuming your 258 is stock, I would suggest you limit the vacuum advance to 10 degrees for starters and take a timing reading at idle. After that, disconnect the advance and run the engine up to 2500-2700 and take a reading showing base plus centrifugal (Confirm your fly weights are , clean, lubed and move smoothly). Up there running between Ronan and Hamilton my stock 258s loved 8-10 base, 15 vac and a total of 48 degrees at freeway cruise speeds on regular gas.
You're looking for a timing reading of 25-32 degrees at idle (With vac advance connected) and 45-50 at 2500 RPM under full manifold vacuum to simulate a highway cruise condition. If your 258 is fairly healthy, you should be able to pull 18-19" at idle. If you're down around 15" or less you may not get full vac advance when you need it and if you have one or more cylinders with low/lower pressures, you could end up with the "Hunting" idle and timing similar to the big cam-low vacuum engines he described. Your adjustable vac advance and limiter may just be the ticket for final tuning!

You're really going to have to tweak around with the vac advance and base timing to find the sweet spot for your rig. I wouldn't suggest going beyond 12 degrees base timing because you might then experience hard starting and engine 'humping up' due to too much advance.

Best of luck and hopefully you will share your results!

Jim

[NBD925]

Thanks again that's perfect and exactly what I was looking for.

Another question that I thought of: I know it's a matter of playing around with the spring combinations but what might a good centrifugal advance RPM start and end look like. For instance the centrifugal advance comes in at 900 and ends at 2300. Any idea what a 258 would like in normal truck driving conditions. What should I shoot for? I like the gas mileage but also like to drive on dirt roads / snow and hills so might like the engine to lug down a bit.

[Tatsadasayago]

In brief; if you like to wander the hills around town, you want a bit less centrifugal advance sine you will be running a bit rich. When I was exploring the Deep Creek area I found heavier springs seemed to help low RPM lugging around in first gear. Slowing down the cent. advance is very useful at medium to high altitudes like you will see around the 5 valleys and so forth.
As far as the RPM range, I'd say 800 to 2200 since your power range with the 258 is down low. Sometimes adding one step heavier spring on one side of the advance weights is all you need to do.
Just remember that richer mixtures need more crankshaft degrees to burn before the spark plug fires and go from there.

Take Care,

Jim

[NBD925]

Jim: I can't wait to give all the new info a try. I've been battling to get this thing tuned just right but at the same time using ported vacuum. Reading about manifold vacuum makes allot more sense to me now. The whole timing principal, seems to make sense now. It also explains lots of people's problems with knocking at high speeds/full throttle, trouble starting, no lugging down, hesitation off initial throttle and part throttle cruise. It also explains why in most older engine manuals the first step in setting initial timing is to disconnect the vacuum advance. If it was connected to ported vacuum than you really wouldn't be changing much timing by disconnecting it before starting the initial timing process.

It's funny hearing local spots like Deep Creek on a forum like this.

What kind of Jeep do you have with a 258? It's not the one in your signature or did you swap engines or something?

[Tatsadasayago]

I had a stable of J-Trucks from 65 through 82 when I lived near Victor and slowly sold them off. Only 4 out of 12 were V8 equipped. Being a avid coyote hunter, the cabs were just too crampy for two guys, rifles and gear trying to get around so I converted to Cherokees and Wagoneers. I've had 258 powered Trucks, Cherokees/Waggys, a Scrambler, a CJ and a few Eagle Wagons so yeah, I know a bit about and like them
I'm down to just one FSJ these days sadly.

One thing I did learn about the 258 is that no two run the same!
Good luck with your rig and feel free to ask for help/info as there are a great bunch here willing to help a Brother/Sister Jeeper put.

Jim

PS: One of my favorite routes was starting at Big Flat and running the trails north and then east coming out at Alberton. I had a '47 CJ-2A with the flathead 4 and later a 53 Willys 'Davy Crockett' version M38A1 with a 292 Chevy six that made that run often. That was back when we could poach land without too much worry about the MAN
Another fun and challenging route was Deep Creek to Lolo Hot Springs the back way which usually took two days!