When there is a little wear on the timing chain and distributor gear, there will be a little backlash between engine rotation and distributor rotation.  By turning with the fan, you may be also getting some belt slip which could add to the perceived delay.  If it starts and idles well and responds to timing changes it is probably not the timing chain (but never say never).  When I have had this problem in the past at a sustained higher speed I had two scenarios.  The first was a bum fuel pump.  It kept up at slower speeds and even some acceleration since there is fuel in the bowls but at sustained speeds where you need a constant supply of fuel you may be running out.  Second one was timing related.  I had a vacuum advance that was adjustable.   The adjusting set screw would gradually back out over the course of weeks and under steady driving at higher speeds it produced way too much advance and it would sputter and backfire.  Under higher loads and while accelerating the vacuum signal is low and you won't have the problem.  It usually only shows itself under steady state conditions on a flat straight section of road.  Easy check for this is to disconnect your vacuum advance hose and block it.  Take it for a drive and see if the symptoms repeat.  If it still sputters, I'd look at the pump.  All this assumes that your mechanical advance in the distributor isn't broken which could also give you too much advance.  But this would usually cause inconsistent readings at idle as well.

Either pull the hose at the carb, and use a rubber block off plug on the carb fitting. OR, pull the hose at the vacuum canister, and use a small bolt in the hose to block it.

Last edited by 50vert (11/25/2018 5:04 PM)

Thanx for all the tips. It seemed to have been a bad timing issue, found true tdc and tuned it by ear! Took it on the LIE took it up to 80 (oooh, dont tell!) now to fine tune it.
Now im trying yo find the correct pcv valve. It seems as though theyve gone to a one size fits all format. The pcv valve for the 68 289 was a blue plastic unit-then the damn thing blew up! No clue why, had to actually remove the valve cover to get the pieces before they went down the hole. Sny idea why?

Last edited by rtmjr13@optonline.net (11/28/2018 9:54 AM)

Yup, that pvc just exploded, scared the hell out of me!
The timing was dead on tdc. I used a piston stop, hand rotated both ways, split the diff, it was dead on, and yes, it has no balls at all! Started life as a 2 bbl, had motor done roughly 8-10 yrs ago. Only changes were a Holley 390 cfm 4bbl, edelbrock performer intake, and a rv cam. No idea what cam. So my next step is the whole edelbrock kit, the heads and the cam that comes with it, ill just keep the intake. Im not going to change the rear end, its a 8 inch 3.00 Posi from the factory, nice summer cruiser.

Last edited by rtmjr13@optonline.net (11/28/2018 4:51 PM)