Subject: Tune-up Specification Change
Model and Year: 1968 Corvette with 427 cu. in. Engine, Manual Transmission and Air Conditioning
Source: Chevrolet Service News
Page Number: 5
Date: February 1968, Volume 40, Issue #2
Timing and carburetion changes have recently been made on the 1968 Corvette when equipped with a 427 cu. in. engine (390 or 400 H.P.), manual transmission, and air conditioning. These changes involve: (1) an increase in engine idle speed; (2) the addition of an anti-dieseling solenoid: and (3) a change in distributor vacuum advance control from "ported" to full manifold vacuum.
The idle speed on vehicles with this particular engine-transmission-accessory combination should be set at 1000 R.P.M. with the air conditioning turned ’ON’. The low idle setting is 500 R.P.M. with the solenoid electrically disconnected. The tune-up decal which is used on these vehicles is Part No. 3940925. A note should be added to your November, 1967 Chevrolet Service News Insert to indicate these changes.
If the anti-dieseling solenoid on one of these vehicles requires replacement or adjustment, refer to the procedures given on Page 7 of this Service News issue. The ’Anti-Dieseling Solenoid Diagnosis Chart’ on Page 7 of this issue should be of assistance in determining whether replacement is necessary. Figure 6 illustrates proper solenoid wire routing for either the 390 or 400 H.P. engine. The connector at the use panel should be inserted in the receptacle marked "IGN" for proper solenoid operation.
Figure 7 illustrates proper solenoid installation on both the 390 and 400 H.P. versions of the 427 cu. in. engine and also illustrates the correct intake manifold vacuum fittings for the full manifold vacuum distributor advance arrangement.
Article ID: 893
Created: September 15, 2014
Last Updated: September 15, 2014
Online URL: https://www.corvetteactioncenter.com/tech/knowledgebase/article/1968-corvette-service-news-tune-up-specification-change-893.html