Thread: General Carb running Rich - killing spark plugs

Just a follow up.

As my RRS needed to go in for a minor smash repair I needed the Haflinger back up running so I had transport.

So last week, I started back from scratch - reset the tappets (were OK). Put a new coil in - old one was OK, has new plugs as discussed above (now all cleaned up again), points, leads, condenser. Points reset but were correct. Increased timing from 7 BTDC to 10 BTDC and will run 95RON.

Pulled the carb off and stripped it down - all clean, and reassembled with new gaskets and new idle mixture screws (set at 1 1/4 turns out which I know is a good static setting). Floats are all OK and the fuel float level valve looked OK but changed for a new one. The float level is not adjustable with this carb and the only way to do it would be some solder on the float arm where it activates the fuel inlet valve or shim the inlet valve so it fits lower in the float chamber. My old valve had a thin fibre washer but the kit had a thicker aluminium washer so I used it so the inlet valve sits about 1/2mm lower in the float chamber so closes a little earlier.

The accelerator pump looked all ok but did seem a bit furry - so this was replaced too.

All went back together OK and bingo problem fixed - so the issue was as suspected in the carb - not sure exactly was allowing it to run rich but I suspect the accelerator pump was allowing fuel past the plunger. When the carb was built by an expert years ago, it did not like the carb cleaner he used and I had some issues. Now I normally do not use carb cleaner and use petrol but when I rebuilt the carb last year I did use it and suspect the seal on the accelerator pump was not compatible hence it looked a little perished and furry.

After about 100km use I dropped the plugs and this is what they looked like

IMG_20191012_165703.jpg

Looks good and not carboned up. I did show them to an acquaintance who races a small openwheeler at Wakefield Park and he straight off said the plug looks too hot. Now that would be correct in line with the discussion above where I did go one hotter to help burn off the carbon. I will leave the plugs as they are for a little while and switch back to the correct heat range if the carbon does not return.

Thanks for everyones help - was extremly informative and helpful.

Cheers

Garry

Thanks for posting the wash up on this Garry.

Its always interesting to read the resolution to a problem and often doesn't happen.

cheers, DL

if the carbon comes back, check the emulsiuon tubes. and the throttle pump if fitted

LaDow-zenith-8-exploded-parts-diagram-CW-sml.jpg
zenith.jpg

mixture tube holder, idle air jet and air correction jet.

if they get blocked up then the fuel rate goes up.

Originally Posted by Blknight.aus

if the carbon comes back, check the emulsiuon tubes. and the throttle pump if fitted

I had to google emulsion tube but once I saw a google pic I knew what it was - yes all checked last week (the carb was exceptionally clean) and a new throttle pump went in and is my number one suspect for the problems I had as I think the pump seal was allowing fuel past and into the carb even when not in use.

The Zenith 32NDIX carb is a "twin carb" in one body so has two sets of just about everything but only one throttle pump. Having pulled it apart a few times now and as there are virtually no internal adjustments, my confidence working on it has grown.

Thanks for your help and advice - much appreciated.

Garry

Just to revisit this.

I rebuilt the carb and things seemed to be Ok but every now and and then the car would miss going up minor hills and would be hard to start sometimes.

I have a mechanic that works on older vehicles and they have a dyno as well. So I sent it to him.

As soon as it went on the electronic tuneup machine the problem was obvious - not so much the rebuilt carb but the coil - the secondary coil was breaking down causing intermittent spark and allowing carbon from the slightly rich mixture to build up on the plugs. Now I have just replaced everything in the ignition system including the coil.

Since the mid 80s I have used the Bosch GT 40 coil where a general service coil is specified. I have one in my Jag and also in my 101 and never had any issues. The Bosch GT 40 in the Haflinger was bought in September and had only covered a couple of hundred km. The mechanic said he had seen many failed Bosch GT 40 coils and by pure coincidence be had the Bosch rep in his workshop the day before my car went in and worded him in about the problem. The issue is that Bosch has moved production of the GT40 to China and these coils are the ones failing. The earlier ones made in Germany are all good.

I now have another Bosch SU12 coil in that is made in Brazil and these are the general coils to get.

The Haf now runs exceptionally well, it is running rich at high revs (better than lean) so maybe the high speed jets are a little large or maybe it relates to the 650m height in Canberra. Not going to do anything until the next time the carb is pulled apart when I will put in the next smaller size high speed jets.

Interesting things that came out of the trip to the mechanic.

The Haflinger produced 15hp at the back wheels, maybe traffic light drags are not on the agenda.

The exhaust pipe is too small to put the emissions/fuel air mixture probe up it - yes it will fit but the pipe is then blocked and the engine will not run - like a banana up the exhaust pipe.

My 85kph top speed is back, fuel consumption is back to 10l/100km rather than 17l/100km so all is now good.

Oh - don't buy Bosch GT40 coils that are made in China.

Garry