Try and work this one out

[Col.Coleman]

Recently the 11A started coughing and farting and running like a sick dog. There is no power, and it sounds like it is running on a couple of less cylinders than I would like.

Now following the Fuel/Spark/Compression diagnostic routine I found the oil bath filter makes this thing run really rich. time for a clean and investigate as I havn't changed a thing since I bought it.

Running without the filter it ran perfect. Ran all the old fuel out and topped up the tank with Premium unleaded. Now she is running sick.

Pulled the Zenith apart and no water in the float bowl. Plenty of black smoke when pressed telling me it is getting plenty of fuel.

Pulled the top off the dizzy and everything looks good. Wet and dry the points, the rotor button, cap contacts and it was all nice and shiny anyway. Sray with contact cleaner and is all good. The leads are new looking Top Gun items and checked them all out. Pulled the Bosch plugs out and the look good, just a little black.

Now for the weird part. On looking to see which cylinders die while running, I pull the lead on No1 and there is a noticable problem when I do so. Same with No 2. When I get to No 3 there is no change. Same for No 4. When I go to reattatch the leads there is a noticable pick up then back to playing up.

I then held the lead close and made the spark jump mid air to the plug and the engine picked up. Did it on both 3 and 4 and it went back to running properly. I then just laid the leads resting on top of the plugs but not connected and it runs like a dream. All the contact surfaces are clean and making good contact when properly connected.

It seems it either likes having a loose connection on 3 and 4, or there is a slight delay in the spark having to jump the gap, or a power increase in having to jump the gap.

I can provide video if required.

What do you think I need to do to get "Harry" running sweet again?

It's got me stuffed.

CC

[jx2mad]

Have you tried a new distributer cap? My old 2A many years ago developed a miss and the cap had tracked. The NRMA serviceman got me going by carving out the track on the inside of the cap with a pocket knife and then painting the track with acetone and drying it. Worked like a treat and although I bought a new cap I never fitted it as the old one never gave any more trouble. Hope this helps. Jim

[Col.Coleman]

All the ignition parts look fairly new. Had already checked the cap for cracks, so sorry it is not that.

CC

[Blknight.aus]

valve issue, check the clearances, overfuelling from the carby (which may mean you also have a manifold leak that blending #1+2 down the the right mix) and plug break down.

swap the leads and plug positions and combos and see what that does for you...

you should also try rotating the cap 180 to make sure that its not tracking on the cap.

[foz.in.oz]

For what it costs I would be changing the condensor on the dizzy too.

[JDNSW]

Several suggestions -

Air cleaner - take the top off and see how blocked up the pipe down the centre is - this does not often get cleaned and can build up thick deposits if operated in dusty conditions. Removing the aircleaner should not make a perceptible difference - if it does, it suggests you are already running too rich.

Spark plug leads - for 3& 4 in particular, remove the leads and inspect the ends - try swapping to different cylinders to see if the problem moves. I think this is the most likely problem, even if they look new. (the extra spark gap, as you found, can often compensate for other faults)

Carburetter - assuming it is a Zenith, check that the top casting is not warped. If it is, it can be ground flat using fine wet & dry on plate glass or other flat surface.

As suggested, the condenser is a potential culprit, particularly if the points needed attention. Note that you should NEVER use wet and dry on points as it will greatly shorten their life. Always use a steel file. (actually, it is usually better to replace them)

John

[Col.Coleman]

Several suggestions -

Spark plug leads - for 3& 4 in particular, remove the leads and inspect the ends - try swapping to different cylinders to see if the problem moves. I think this is the most likely problem, even if they look new. (the extra spark gap, as you found, can often compensate for other faults)

John

Did this and no change to which cyinders were firing

valve issue, check the clearances, overfuelling from the carby (which may mean you also have a manifold leak that blending #1+2 down the the right mix) and plug break down.

swap the leads and plug positions and combos and see what that does for you...

you should also try rotating the cap 180 to make sure that its not tracking on the cap.

Can't rotate the cap as it has a semicircular cutout on one side where the ground wire from the coil attatches.

When i swapped the plugs from 1 & 2 to 3 & 4 the problem moved. So it seems that both the 3&4 plugs where the problem.

Will have to fit some new ones to confirm this.

CC

[wozapinin]

Reminds me of a problem I've had. What it ended up being in my case was the bush that held the main shaft in the distributer was worn. Tended to make the dwell erratic as the shaft wobbled instead of spinning true. Took a long time to figure out as some days it ran great and some days not.

[Col.Coleman]

Put 4 new Bosch WR7DC plugs in and problem solvered. Seems strange to me though for 2 plugs to go simultaniously. 1 I could reason, but 2 together is a little odd. I will update further if any problems crop up.

Thank-you all for your help. It may not have been the problem this time, but the reference is now there to check those things in the future.

CC

[JDNSW]

Thanks for telling us what the problem was!

John