Hey guys, I've been getting the '78 back on the road and am planning on tackling the carbs. My car does not have anything in the airbox nor does it have a cat. I'm not sure what jets it is running so I figured I would do a little R&R on the carbs. I've not worked on these style of carbs before. I have read the weber manual and have gone through the sync tutorial by Birdman as well. I feel confident that I can get it all to work well, but have a few questions: On the jetting side, people seem to be gravitating towards 55 idle, 135 mains, and 200 ACs. This in concert with the Iridium 6s. Is that generally a successful setup for a '78? Should I sync and then rejet? Does the jetting change the setup? I assume the idle would need to be redone, but does having them in sync help with reducing variables? Is it as easy as popping the top off and then fishing out the parts? Any tips for closing up the throats so you don't lose anything? Is blasting everything in carb cleaner sufficient before reinstall? I do have eyes on a larger full carb rebuild project this winter but would like to get the car running as well as I can for the season. Thank you for any other tips! E
I have a 1978 308. I installed a 308 airbox with the sound deadening fiberglass and steel mesh removed. Helps for additional airflow. I installed the following: Idle Jet: 65 (need this, since stock 55 is too lean for modern gas Main Jet: 135 Air Corrector: 190 NGK 5 spark plugs I get great response on the highway and good acceleration. I presently have my idle mixtures open by 3.75 turns. I bought my jets and air correctors from Pierce Manifolds in Calif. Used their website.
Thanks for the insight. I think moving up on the Idle is probably a good idea! Do you think a 200 AC would work for the catless car?
It just means more lean. Try at 190, the 308 engines love to run a little rich. I went from 200 to 190 and get good acceleration at street and highway speeds.
I went through a fairly comprehensive carb tuning on my car and came up with the following: Idle - 52 Air corrector - 220 Main - 135 Just for reference I have a 1977 308 GTB. Air pumps removed, stock cams, gutted airbox, k&n filter, Nuovolari exhaust. Plugs are NGK BP5ES and all tuning was done at approx. 80 meters above sea level. Tuning was done with O2 sensors in each exhaust and running was done on the road in real world conditions to get the settings right. A combination of plug reading, O2 readings, and driving feel was used to get the car running well. We tried a number of jet choices and the idles were a toss up between 55 and 52 with the latter chosen because the air fuel ratios were a little more ideal and the engine popped less on the over-run. Also fuel was Shell Premium (91 octane) which is ethanol free in Canada. As it happens last week I took the car on the track and it ran incredibly well. Sharp throttle response and the plugs looked perfect. I am very pleased with this setup. To answer your other questions: - Once you do your synch there is no need to do it again after jetting. Always synch first - All the jets are accessible with the airbox off and there is no need to remove the tops of the carbs. That said it is always worthwhile to confirm the float bowls are set correctly and that there is no debris in the bowls. - Cleaning the jets with carb cleaner and putting them to the light to check that they are clear should get you most of the way there. If you have a clog somewhere else it will be fairly obvious so clean jets are your best starting point.
These are great reference points. Thank you so much guys! I really appreciate these tips and can't wait to tune these up. On the altitude piece, how much does that affect these numbers? The car lives in Cashiers, NC (3,484'/1,061m) and in Atlanta (1,050ft/320m) in the winter. I assume the higher elevation leads to less dense air, which means that the jets should be slightly smaller? Thanks!
The gas(with or without ethanol) will determine what jets or AC you will use. Unfortunately, very little ethanol free gas in California and California has special requirements for their gas which is created by a few refineries. Great input by Nuvolari.
