with the gas prices going so high i am tying to get my 1986 jeep cj7 258 6 cyl with a r.v. cam (for low torque) to run on pump gas. i have a msd ss coil, lighter centrifigal advance spring in it. i was running 12 degrees advance on super unleaded and had to go all the way down to 6 degrees to get it to stop pinging up hills. but now it is allot harder to start when it is cold. anyone have any ideas what i could do to get it to start better? is 6 degrees to low on the timing? should i put the stock centrifigal spring back in it to not get so much advance at higher rpm's? i just want to get the jeep to run on pump gas and start nice. thanks carmine
Much of this depends on how your vehicle's ignition is set up. The main factor is the vacuum advance. Some people use ported vacuum and some use manifold vacuum. I personally prefer manifold vacuum because it will compensate for throttle opening and engine load. Chances are your vacuum advance is currently using ported vacuum. The easiest way to check is to follow the vacuum advance hose from the distributor and see where it enters the engine. If it is somewhere in between the throttle plate and the head, it is manifold vacuum. If it somewhere before the throttle plate in the intake system, then it is ported.
The problem with ported vacuum IMO is that it increases the timing at part throttle load at the same time the mechanical advance is doing the same thing. This will work OK if you leave the advance springs stock, but this isn't necessarily the most efficient setup.
The manifold vacuum advance setup has a nice advantage in that it will retard the timing under heavy load and or heavy throttle conditions, which is when you need the timing to back down a bit. When you are back to cruising throttle opening and regular load conditions, the manifold vacuum goes up and advances the timing back to its maximum.
What I would do here would be to switch the vacuum advance to manifold vacuum, leave the light springs in place, and then set the timing to 2 degrees more than stock. Take the vehicle for a ride and make sure it doesn't ping. Advance the timing another 2 degrees and repeat the test. Keep doing this until you get pinging, or the engine drags on the starter when it is hot.
Also, most spring kits do not increase the amount of mechanical advance, they change the rate at which the timing advances. You normally have to change the weight's shape to increase the amount of advance.
i am running a weber carb with the vacume advance taken off of the base of ther carb.so i would assume this is manifold vacume. as far as i know the vacume advance is stock. i am running a one line fuel filter with a pressure regulator. i dont know if stock timing would apply to my jeep because it is a 86 with a r.v. cam and all the computer and emmision stuff taken off. thanks carmine
Do you physically have the ignition module connected directly to the distributor or does it still go through the computer?
The reason I ask is if the computer is still a physical presence, then it has gone into limp home mode which messes with the timing advance big time.
You can tell by looking at the ignition module, waaayyy down under the washer bottle. Check the purple wire coming out of the module. If it isn't jumpered to a new wire, you have issues right there. Stock, the purple wire goes nowhere, it stops at the first plug.
If you remove any emissions stuff, the ignition has to be rewired to work right. It is easy, I always add two new wires rather than mess inside the harness.
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One other thing is carbon build up. That RV cam and running low RPM are really bad for carbon build up. This will cause pinging.
I run a pint of ATF slowly down the throat of the carb while keeping it running with my hand on the throttle. It cleans the carbon out great. Some folks use a pint of water to do this and say it works well too.
i traced the purple wire from the ignition module and it goes to the distributer. i dont think the computer is even on the jeep any more. it was removed before i bought it. i will try putting a pint of ATF in it to remove some of the carbon thanks carmine
yeah it sure did dump out some white smoke. even more smoke than the 2 stokes i'm used to working on. but i still cant get the timing above 7 degrees with out pinging. are there different vacume advances i can bolt to the distributer? it seems to me i need more advance on cold starts and less timing advance around 2500 rpm's when i am coming up a hill. i'm just not sure how to go about doing it. thanks carmine
I'll bet the makers have a recommended timing set and curve (spring load) speed.
The total advance is also important. I was told 36 degrees should be total max for my setup. The 258 is quite happy running at 4 or 5 degrees base in some stock setups. I am running 9 base and I think it is maybe causing some overheating at higher rpm or over 70 mph.
You need to pull the vacuum hose off and put your finger on the end to see if it sucks at idle or not. That makes a big difference in how it works and is tuned.
Messing with springs needs serious tuning... A fast advance for short 'power' boosts is different than you want for a street rig.
I have mine set with a ported vacuum advance (no suck at idle, it advances with the gas pedal) and I can hear the distributor plate snap to full advanced when I punch the throttle with my hand with the hood off. I have an Accel SuperCoil, no computer, the stock Carter BBD carb manually tuned and mine rocks. It picks up and flies and will climb ravine or sand pit walls at 400 rpm without a stall.
I can light up and smoke my 33" mud's in 1st and chirp nice in 2nd. 2nd will pull up over 50 + mph at 4400 rpm. Third has hit 80 mph, didn't catch the rpm.
You have soft advance springs so you likely have even a faster snap than mine. Mine runs best with 91 or 92 octane. I get 100 miles better per tank with 91 vs 87!
Just a note. Mine will refuse to run and die under load at 65 mph up hill pinging like crap if there is any amount of alcohol or ethanol in the gas!
My 86 owners manual even says 'not' to use any mixes and if you have to in an emergency to only buy enough to get to real gas. It says 'Performance may be degraded' or something like that. LOL!
Carmine, After thinking about this a bit, your RV cam could be building more cylinder pressure than the stock cam did. These cams generally have a short duration, high lift lobe profile. The extra cylinder pressure could be causing the pinging. With that said, you may want to try another approach by using an adjustable vacuum advance kit. Crane and others make them, but I don't know if they make them for your engine. They do make them for the GM HEI though, and this may be a good time to do this swap if you want. The adjustable vac. advance will allow you to adjust how much advance, and at what vacuum reading it starts. The kits also come with centrifugal weight springs similar to what you have installed already. Here is a link to the product:
Some engines have an adjustment. The aftermarket ones have this adjustment, as well as a stepped limiter plate that is used to limit the amount of advance. The adjustment inside the nipple is for adjusting the amount of vacuum it takes to pull the advance lever. This might be all he needs.
I'm pretty sure the vacuum advance on the 258 IS adjustable. I know for sure the V8 engines were. It's takes a 1/8" allen wrench inserted into the vacuum nipple to adjust it.
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