engine timing question - what does this mean? adjustment question

RedJeepXJ · 09-12-2003, 06:51 PM

I know this isn't the best forum for this but I can't seem to get any help in the cherokee forum

I upgraded my old factory carb with a new weber, the paper that came with it said 30 degrees total advance, when adjusting the timing 30 degrees sounds like to much considering the markings on the engine only go to 24, is there another timing adjustment somewhere

what's the difference between 30 degrees advance and 30 degrees total advance if there is one?

is 30 degrees unreasonably high for timing adjustment, when turning the distributer it runs at 30 degrees but also runs down at 15 degrees (although slower and a lil bit smoother)

misc info:
carb is a two barrell and has been set to the lean-best setting to the best of my abilities, distributer is vacuum advance (manifold) and according to haynes it should be disco'd and plugged when adjusting timing

any help is appreciated

MichiganK9SAR · 09-12-2003, 07:14 PM

I'll try to take a stab at this...

Total advance may mean the standard timing, plus any vacuum advance. Meaning, the timing cannot exceed 30 degrees at maximum vacuum advance.

But I'm not entirely sure. You may wish to call the company that made your carb.

runmanpkll · 09-12-2003, 10:53 PM

you need to fing out what you base timing is at idle & set that (im sure its alot lower than 30). the timing advance is controlled by the distributor either with a vacuum advance or mechanical advance (springs & weights). 30 deg should be total advance at higher rpm's. setting the base idle at 30 is way to high.

whitevette · 09-13-2003, 03:19 AM

What he said^^.

30 degrees TOTAL means when the engine is at full speed.

Base timing is the amount of timing at idle.

What you need to find out is your base timing which should be in the low to mid teens. The higher you set your timing, the higher the octane required is to prevent pre-detonation (pinging).

Find the base specs for any 4.0 and start there. Keep in mind, this number can be changed to suit each engine. It's not a dead set in stone number.

09-13-2003, 03:19 AM	#4
whitevette Registered User Join Date: Jul 2003 Location: Phoenix, AZ Posts: 268 Profile Gallery Classifieds My Jeeps	What he said^^. 30 degrees TOTAL means when the engine is at full speed. Base timing is the amount of timing at idle. What you need to find out is your base timing which should be in the low to mid teens. The higher you set your timing, the higher the octane required is to prevent pre-detonation (pinging). Find the base specs for any 4.0 and start there. Keep in mind, this number can be changed to suit each engine. It's not a dead set in stone number. __________________ Darkness is deaths ignorance, and the Devils time. '96 Grand Cherokee Laredo '93 Taurus SHO '77 Corvette L-48 '74 Land Cruiser FJ40

09-12-2003, 10:53 PM	#3
runmanpkll Registered User Join Date: Aug 2002 Location: virginia Posts: 608 Profile Gallery Classifieds My Jeeps	you need to fing out what you base timing is at idle & set that (im sure its alot lower than 30). the timing advance is controlled by the distributor either with a vacuum advance or mechanical advance (springs & weights). 30 deg should be total advance at higher rpm's. setting the base idle at 30 is way to high.