misfiring

[Anonymous]

Hey,

my '68 200 started a weird habit of misfiring for a period and then coming good, misfiring and coming good again. its now misfiring permanently.

When i pull #3 plug lead there is only a small change in running suggesting thats the problem, the engine behaves as you would expect and runs even rougher when all the other are pulled in turn.

But its been my experience this is normally the case for the centre cylindrs as they must get better feul feed from the inlet? replaced plug and lead and the dist cap looks fine. still rough.

Where to next? points adjustment, timing advance [which is not plumbed to a vacum], carb or compression test for valve?

cheers

 

[addo]

It's worth compression testing for a benchmark. Follow standard procedure for this, and save the results for comparison later.

Then do a vacuum reading. If possible, hook up a remote gauge and log it while driving various speeds and loads.

Now you've got some hard baselines. Next is the standard ignition stuff - verify TDC, set the advance to spec, map out the advance with RPM changes. Use the vacuum readings taken before, to apply vacuum with a vacuum pump to the advance diaphragm as appropriate for that motor speed. See (log) what that gives you.

Typical issues in a nutshell are ring/bore wear, VSR, cam chain slop and a sticky distributor advance.

What city are you in? Nobody here's going to steal your car.

 

[wsa111]

Salty, what does the spark plug look like in # 3 cylinder??

Swap it to another cylinder along with another spark plug wire if that does not change things.

Put a rag over the carburetor or spray carb cleaner in the carb to see if the engine smoothes out due to a vacuum leak.

Then do a compression test if the plug looks the same as the other cylinders.

If that does not pinpoint the problem, give a shout. William

 

[Anonymous]

a belated thanks guys, got called out of town.

Comp test ok and running really rich.

Carby cleaner highlighted vac leaks all over the carbie and vac lines.

Time to find a nice man in brisbane to rebuild the autolite.

cheers