jeff Posted September 20, 2006 Share Posted September 20, 2006 I am trying to diagnose my '38 Special straight eight with a vacuum gauge. The results look reasonable, but my question is: How steady should the needle be? At a fast idle (7-8 mph, per the manual) mine reads between 19 and 20 inHG. The fluctuation is just less than 1 inHg. All of the books I have checked say to look for fluctuation of 3 - 4 inHg for major issues with a good engine being "steady".Anyone have some experience with how steady the gauge should be expected to be on a Buick straight eight?The engine runs smoothly, but runs out of steam beyond 50 mph and delivers 12 mpg at 45 - 50 mph. Nothing obvious in ignition or carburation systems, but I suppose something could still be slightly out. Jeff Link to comment Share on other sites More sharing options...
Shaggy Posted September 20, 2006 Share Posted September 20, 2006 Hi Jeff. Been away for a while.My "wiggle" is more like 3-5 InHg, so there's something definitely amiss. Dunno about your situation.What I did was replace all ignition components, (less coil) then tuned things as best I could. I'll be seeing the carb kit soon. Hopefully that'll give me a known basline to tune from. Unfortunately, everything I've seen points to a loose valve guide. I may be doing a valve grind this winter. We shall see. Link to comment Share on other sites More sharing options...
old_truck_nut Posted September 21, 2006 Share Posted September 21, 2006 Check out this site: http://www.secondchancegarage.com/public/186.cfmThis guys definition of steady is illuistrated in scenario #1.. The needel does not move. My best runners show zero fluctuation in vacuum.I've found the vacuum gauge to be one of the best engine analysers out there but one of the least understood among us shade tree mechanics. Still learning. Link to comment Share on other sites More sharing options...
Carbuff2 Posted December 7, 2011 Share Posted December 7, 2011 Have you checked your exhaust system .....any restriction will lower your powerand affect fuel consumpton... Paul Link to comment Share on other sites More sharing options...
danhar1960 Posted December 7, 2011 Share Posted December 7, 2011 old_truck_nut This thread maybe 5 years + old but,"Stone the crows and starve the flaming lizards" !!!Now that's a man's avatar !!!!!!Danny Link to comment Share on other sites More sharing options...
Guest Grant Magrath Posted December 7, 2011 Share Posted December 7, 2011 Ha ha!!She's a beauty!CheersGrant Link to comment Share on other sites More sharing options...
danhar1960 Posted December 8, 2011 Share Posted December 8, 2011 Bugger !!! Seems like the avatar police have been here.It was impressive, for a while anyway.........Danny Link to comment Share on other sites More sharing options...
whatdoing Posted December 10, 2011 Share Posted December 10, 2011 Sounds to me your running out of gas or advance during high revs. Check for vacuum advance operation and vacuum leak at vacuum advance unit. Also check for clogged high speed fuel jet in carb. I also agree, check for free flowing exhaust, I have seen muffler baffles come loose and obstruct muffler out let. This can not be seen with out removing muffler but can be tested by removing muffler and test driving car.Good luck! Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now