230SL Backfires on idle

[Numbskull]

Hi

My 230SL has started to backfire on idle and is running rough. I have tried adjusting timing which looks correct - any ideas where to go next - injectors? injector pump ? valves ? Any clues gratefully received !

thanks

[BobH]

Hello?, (no way i can call you Numbskull!) and welcome

use the search button above for "backfire", many posts with many possible causes and solutions, see which one matches your symptoms best

Good luck

[rwmastel]

NS (for short!),

How long have you owned the car, and how much work do you do on it yourself?  I ask because if people don't have a long history with their cars and start making adjustments, the adjustments may not work as expected because previous owners or less experienced mechanics may have made other improper adjustments as shortcuts around various issues.

First, I would recommend joining as a full member to get Tech Manual access.  We might be getting into linkage adjustments, mechanical injection pump adjustments, FIP warm up regular test, distribtor diagnostics, and more.  The TM will have valuable info for you.

Second, it's good to start troubleshooting at a healthy baseline.  Read through the Linkage Tour thread, the "sticky" thread in this sub-forum.  Once you have your linkage set to factory spec and lubricated, report back on how it's running.

Regarding what you shared, what's your timing at idle and different RPMs?  Which distributor do you have?  Any changes or work done to the car in the weeks prior to the backfire starting?  Have you done any other testing or tuning?

Regarding what BobH said, getting comfortable with our Search feature is a good idea.  We've been online 20+ years and have discussed (if not solved) almost everything!

Welcome to the Group.

[ja17]

If it backfires or coughs back through the intake it is probably a lean fuel condition (fuel pressure, linkage adjusted wrong, clogged fuel filter or screens). If it backfires through the exhaust, it can be ignition problems, ignition timing, too much fuel, or even an exhaust issue.

[rosch]

Have had same symptoms before.
Identified the culprit - a leaking injector-  causing unburnt fuel ending up in the exhaust system and causing rough running,hard starting and backfiring. This due to uncontrolled fuel supply to one cylinder.
Using a so called "Colortune"  identifies  ignition and fuel problems in a very easy and (cost)effective way. 

[Pawel66]

What exactly is a "Colortune"?

[rosch]

The full name is Gunson Colortune .
In short : it is in fact a transparent sparkplug used to observe ignition spark as well as mixture ( by color ) at the same time and works perfect for troubleshooting as well.
Remove the regular sparkplug from the suspected cylinder and install the Colortune.
Start your engine and observe if you have a spark and judge if your mixture is correct .This eliminates fumbling with split linkages especially at higher rpm's and makes mixture adjustments very easy. It's my favorite tuning tool.
Example : with a running engine you can directly observe the effect on mixture when screwing the baro compensator in or out. It gives good guidance in either to add or remove shims  .
On our engines use the 14 mm variant.

https://www.gunson.co.uk/product/G4074/Colortune-Single-Plug-Kit-14mm
On youtube you will also find some nice video's

[Pawel66]

Wow! Thank you! I had no idea anything like that exists... (not surprising, in fact).

I bought it. If it works as you say and what is shown on video - it is much more efficient than CO measurements.

By the way, on the vehicle example on the video - attached.

[Garry]

Not quite on the BMW.
The BMW 507 is probably the equivalent car for 1957 which can sell for up to $5m


The photo by Pawel is a BMW Isetta

[WRe]

Hi,
The car in the Gunson video is the British version of the BMW Isetta with 3 wheels. This had the advantage that the car could be registered as a moped, which resulted in cheaper vehicle taxes.
...WRe