Guest Tim Romans Posted June 15, 2012 Share Posted June 15, 2012 Big thank you to Mark, Grant, Dan, Terry, and 5219! I used a vacuum gauge today and the "ear" method and the 41' sounds like a whole other car at idle, the way a Buick is supposed to run (if a ST8 is in fact supposed to sound like a very menacing sewing machine The hesitation, miss, and backfire seems to have vanished almost as if by magic and here I feared the worse that the cam might have been worn or the valves stuck or shot. I know these gauges we buy vary and are not often precise however the vacuum reading I settled it around was at 27 Hg. Hopefully it's a good sign that she's still going strong.It ran so good in fact that after readjusting the fast idle screw, I didn't even mess with the rest of the carb adjustment (yet, unless it acts up when I take her out in the morning for a fill up.)Can't wait to go for a drive....Cheers!Tim Link to comment Share on other sites More sharing options...
danhar1960 Posted June 15, 2012 Share Posted June 15, 2012 Another happy customer :) Don't you just love it when it all works out. Now get out there and drive it and report back as to how it went.Danny Link to comment Share on other sites More sharing options...
Mark Shaw Posted June 16, 2012 Share Posted June 16, 2012 Just goes to show that us shade tree mechanics still know a thing or two...Congratulations! Link to comment Share on other sites More sharing options...
Guest Tim Romans Posted June 16, 2012 Share Posted June 16, 2012 Well, looks like I spoke a little too soon. While she idles nice and the backfiring issue seems to have gone away, driving was a different matter. She seems very jerky in first and second and while third is smooth, I hit a definite performance wall around 30 mph where the engine just drops off, loses power, and gets jerky again. I had this problem before I tuned her up and set the timing. I tried playing with the carbs (throttle adjustment and idle mixture) and couldn't get any results. I know I'll need to get the carbs rebuilt as there is seepage around the gaskets and "wet" spots around the intake manifold where the rear dumper carb is located. I'm not going to drive her out to the show tomorrow due to the fact that I'm still not sure what's going on and not wanting her to catch on fire. Vacuum gauge readings are around the 24 Hg mark. Not sure if the leaky carbs are contributing to a vacuum performance issue (not to mention potential fire hazard) or if I should readdress the timing, though as far as timing, it seems pretty happy and smooth where it's at at idle.Thanks again guys for all your help!Tim Link to comment Share on other sites More sharing options...
Guest Grant Magrath Posted June 16, 2012 Share Posted June 16, 2012 Tim, spray some carb cleaner around the base of the carb at idle and listen to what happens. Vacuum leaks are a real pain to track down.With all the rough running and mixture issues, it could be worth having another look at your spark plugs. They could have gotten dirty. No backfiring means your mixture is better, so I'd be looking at spark now.CheersGrant Link to comment Share on other sites More sharing options...
Mark Shaw Posted June 18, 2012 Share Posted June 18, 2012 Tim, WD-40 works too. If it speeds up, you found a vacuum leak... Link to comment Share on other sites More sharing options...
Larry Schramm Posted June 19, 2012 Share Posted June 19, 2012 (edited) Here is a chart of Vacuum Gage Readings which will help you tell exactly what is wrong with the engine. Edited June 19, 2012 by Larry Schramm (see edit history) Link to comment Share on other sites More sharing options...
Guest Grant Magrath Posted June 19, 2012 Share Posted June 19, 2012 Great chart Larry! Worth printing and putting up on the shop wall!CheersGrant Link to comment Share on other sites More sharing options...
Larry Schramm Posted June 19, 2012 Share Posted June 19, 2012 Hope it helps someone fix a vehicle easier. :-) Link to comment Share on other sites More sharing options...
Bhigdog Posted June 19, 2012 Share Posted June 19, 2012 Something not right if you are pulling an honest 27" of vacuum...........Bob Link to comment Share on other sites More sharing options...
Guest macmic87 Posted June 19, 2012 Share Posted June 19, 2012 maybe you went a little to far with the timing and you might be over advanced. bring it back a little bit and drive it again. Link to comment Share on other sites More sharing options...
tblack Posted June 19, 2012 Share Posted June 19, 2012 I have been following your problems ...I recently picked up a 40 pontiac and the symtoms were the same as yours....I got lucky it eventually quit and would not restart....too make a long story short I had a slight crack in the rotor and at first I was occasionally grounding my high voltage to the shaft poor performance and eventually I got no spark to the plugs....I ordered a tune up kit and installed it but they omitted sending me the rotor so it still did not run....I pulled an old rotor off a parts engine and the car instantly started...I put the old rotor back in and the car would not start. I have since picked up a new rotor and the car runs excellent...sounds crazy but try another rotor maybe you get lucky....With all the old cars I owned this is the first time I had a rotor be the culprit...good luck Link to comment Share on other sites More sharing options...
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