Miss at idle & at cruise speed

dualquadpete

Well Known Member
#1
This is driving me "NUTS" Have narrowed it down to # 5 cyl. When I pull lead of S/plug, no change in idle, put tester on lead to plug, have spark. Compression test shows 185lbs. changed over to Pertronics & 40,000 coil !!! Have checked plug for spark [yes] Going to pull carb, & put scope down intake for a "looky see" as this car-sat for 17 yrs with very minimal running!!! Either mouse nest blocking fuel delivery or huge carbon build up on intake valve????????? I'm open to suggestions!!!! At 55 mph I can feel a slight miss & as us "old folks" said " It's Hunting" Have timing set at 10 degrees with Vac hose plugged off, new adv. unit as org. was seized from sitting. So I have spark, have compression, also pulled Rocker cover & everything moving as it should!!
 

Fathead Racing

Well Known Member
Supporting Member 7
#6
The miss is anyone’s guess, the searching at light cruise may be over advance taking in to consideration the 10 degrees at idle setting including mechanical plus vacuum. You may have to limit the vacuum advance travel.
 

dualquadpete

Well Known Member
#7
Yuup have switched plug with a known good one, same thing, ran torch this morning NO VAC. leak!! got scope down intake [ tight fit] & can see something "fuzzy" in there???? Ordered a set of intake Gaskets [ $ 52.80 ouch] & will get it off as soon as I can but have company coming up from W V to Ontario tomorrow in their 70 Cutlass. Also going to contact prev. owner & see if this sat with carb off at any time???
 

blkblk63ss

Well Known Member
Supporting Member 5
#8
Why not just rotate engine to close #5 exhaust and remove spark plug and carb ,blow in plug hole with compressed air .Put a vacuum cleaner in intake carb opening in case something does dislodge .Also that will tell you if there is any obstruction. If ok have you check opposite bank same runner as #5 for a broken valve spring ,can affect opposite cylinder. I have seen that happen several times. Your cranking compression would appear normal.
 

dualquadpete

Well Known Member
#9
All other cyl. effect idle when plug lead removed so they are "firing" I did have R/covers off when detailing engine and didn't see anything out of normal, also ran engine with rag over rockers & all moving normal??
 

dualquadpete

Well Known Member
#15
Got manifold off be fore company arrived from W.V. no blockage "BUT" on inspection, gasket imprint around # 5 is not "full" contact!!! Missing imprint on bottom 1/2 . Had to use a "Johnson Bar" to crack loose bolts, really tight. Going to check intake & head surface with straight edge. This looks it it could be the " Internal Vac. leak mentioned!!! Firing order is correct.
 

dualquadpete

Well Known Member
#16
Checked down the head ports, no "excessive" build up on all valves. Rolled engine over, to check cam, all is good there too!!! surfaces check out with "straight" edge!!! Company arrived but I'am into brake repair on their 70 Cutlass, Blew a front brake drum on Sat. on hard braking. complete centre came out of drum as well as some "chunks" from outside of drum, just the brake surface ring left!! NEVER seen on EXPLODE like this!!!! Parts on order.
 

Toms63SSQB

Well Known Member
Supporting Member 6
#18
Not getting "full contact" with the intake to gasket to head, sounds like there may be an angle issue between the head and the intake. Could that be a problem? Wonder why the intake bolts were so tight, was that on all of them?
 
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