8BA Dead cylinders

rick r

rick r

Senior Member
Need Help. have an 8 ba with # 2,3,5,8 cylinders dead . 100 lbs. compression on all cylinders. 10 in hg. vacuum at the intake manifol at idle. lodomatic dist. supplying good spark to all cylinders. double checked firing order and confirmed that all wires are in correct holes. idle mixture screw on dead cylinder side has no effect. have confirmed that there are no external vacuum leaks by spraying starting fluid all around intake and carb base while engine is running. have tried 3 different carbs (94) and same results. confirmed that distributor timing is correct. timing variation either way from spec. does not help. Any and all suggestions greatly appreciated. Thanks in advance.
 
Those are all fed by one barrel of the carb. Look for a chunk of crud blocking the feed in the carb! On a 94, blocking main jet will shut down both main and idle circuits.
 
Testing 3 different carbs with same result...can something have sneaked its way down into the manifold blocking one throath ?
If you take the carb of and crank it over do you have air flowing into both barrels ?
 
What do you mean by dead cylinders?
You said 100 lbs compression on all cylinders
and spark going to all cylinders

If its not mechanical (rings, valves), and its not electrical (spark to all cylinders), it must be fuel related.

Are you doing a cylinder balance test with the engine running?
 
Last edited:
Are the plugs in the "dead" cylinders getting wet when engine is running? If they aren't, and you've tried 3 different carbs, must be as flatheadmurre suggests. Intake malfunction.
 
It would be unusual, but if the exhaust crossover has burned into the throttle bore on one side of the manifold, it would suck exhaust instead of thru the carb. Was the manifold bored at the riser? Your problem is in the passenger side bore of the manifold.
 
With the engine running at idle slowly cover the carb with your hand to reduce air flow. Slowly choke it to richen it up in other words. Will eliminate a lean condition so you can move on to ignition.
 
I alway wonder if it ever run good. There is a motors book out there with wrong order check and see if Mercury is what you are using.
 
Problem was the intake manifold. The engine in question is in a friends shop, so I have not seen the defective manifold. I will post an update as soon as I get a chance to look at it. Thanks to all that offered solutions
 
The manifold in question was a stock aluminum (Canadian) 8ba. Found 2 holes about 3/8 inch dia. in the wall between the heat riser passage and the fuel runner. The holes appeared to be caused by corrosion. There was no sign of any corrosion on the outer surface of the manifold. Live and learn !!!!
 
rick r said:
The manifold in question was a stock aluminum (Canadian) 8ba. Found 2 holes about 3/8 inch dia. in the wall between the heat riser passage and the fuel runner. The holes appeared to be caused by corrosion. There was no sign of any corrosion on the outer surface of the manifold. Live and learn !!!!
Click to expand...
Wow that sucks(ruined manifold)I guess it would have been better to find that ole sneaky shop towel in there:( Pete
 
You must log in or register to reply here.
Back
Top