DDK - Die Deutschen Klassiker

mycar wrote:After a week of knob wrangling a new muffler should be a walk in the park.

New muffler in fine but the car is still back firing under de-acceleration. There were actually holes in the old muffler that I hadn't seen so it couldn't of been welded.

Could be

-> leak at the front exhaust ports

-> I didn't install the new muffler correctly. However, it was a very tighter fit.

The backfiring only happen when on the main circuit and dropping to the idle circuit. I'm inclined to think that there is another issue

My only experience of this is when the top flanges of the exhaust do not marry up perfectly with the engine and do not make a gas tight seal. The flanges are sturdy and may not pull up if the exhaust is poorly formed.

If this is the case the gaskets will show witness marks where the exhaust gases have been escaping. This poor joint will cause popping on lift off.

I had to resort to filing the flanges, offering up and filing again to ensure a tight fit.

Leaks can also occur at the other end of the exhaust system when these clamps do not nip up well enough.

Thank you Mike. I will check again.

My only experience of this is when the top flanges of the exhaust do not marry up perfectly with the engine and do not make a gas tight seal. The flanges are sturdy and may not pull up if the exhaust is poorly formed.

If this is the case the gaskets will show witness marks where the exhaust gases have been escaping. This poor joint will cause popping on lift off.

I used double gaskets in the hope of avoiding this issue. Interesting whoever fitted the previously exhaust also used double gaskets. I believe this was Larry Markham who has forgotten more about 356s then I know

I did do a quick check before putting it all back together but will check again. I sprayed wd 40 around the joints to see if it interacted with any escaping gases but will do the spray check for a an increased idle too. I believe that Mike Smith also recommended blocking the exhausting and listening too!

"Leaks can also occur at the other end of the exhaust system when these clamps do not nip up well enough."

I had so much trouble getting the old pipes I had to hit the exhaust with a large rubber hammer. When that didn't work I had to heat the joint and hit harder with the hammer not leaving the old exhaust in a good way. I'm hoping too avoid having to do that.

Neil,

Check your idle jets on the carbs. Worth 30 minutes just to see if one is blocked. I presume your plugs are fine.

Roy

roy mawbey wrote:Neil,

Check your idle jets on the carbs. Worth 30 minutes just to see if one is blocked. I presume your plugs are fine.

Roy

I've checked one side

This weekend I'm going to work from valves up. Replace plugs and clean jets and tune it all again.

My gut feeling is that doubling up the exhaust flange gaskets is a terrible idea. To work, a gasket needs to be clamped evenly all around, twice the thickness will not improve things. Flanges need to be flat and not fighting the rest of the exhaust or the cylinder head. All the elements of the system must assemble smoothly and in repose. Achieving this may need heat, filing, grinding and in extreme cases rewelding........ Good luck! W

Your backfiring is likely related to the exhaust but it could also be the mixture is a touch too lean - a quarter turn on all four carb screws stopped mine back firing on overrun.

Neil, now you have easy access to your engine compartment, take the opportunity to lubricate the locking mechanism and fit an emergency release pull.

A length of stainless steel wire attached to the release mechanism, passing through a hole drilled through the engine compartment wall, exiting under the nearside wing will offer a foolproof option for you, or future owners, should the release knob fail again.

Terminate the wire pull with a nice finger loop.



https://www.ebay.co.uk/itm/2mm-3mm-STAI ... 2004268232

Lots done.

Valves adjusted
Brakes bleed
Right carb off to check
Timing advanced a little
Linkage ball joints replaced. Removed play
https://www.berger-tools.co.uk/Din71802 ... nc_Plated/
Checked carbs balanced through the rpm range
Adjusted idle mix and set a bit richer than normal.
Sprayed wd 40 never exhaust gaskets but didn't hear a change in idle
New clamp on exhaust

Rain on and so haven't test drove let

Sent from my Mi A2 Lite using Tapatalk

Still back firing. I will try to seal tomorrow

Sent from my Mi A2 Lite using Tapatalk

Resealed but the lazy way. Didn't take off exhaust entirely but got a gap and put paste in. One of the boots wasn't tight. Took off right carb again because it looked like it had a leak. Not backfiring at much but work still needed.

Bit too much work and too little driving

Sent from my Mi A2 Lite using Tapatalk

Did it backfire before you changed the exhaust ?...from my limited experience i would second Winston's reply.

I changed the exhaust because it was backfiring

Sent from my Mi A2 Lite using Tapatalk

Good plan.

What did you change it for ?

Ah, so any evidence of the old exhaust leaking at ports?