DDK - Die Deutschen Klassiker

As I continue to fettle with the Modrod, I have a lingering running rich issue.

The engine is 2.2 T, built to E spec with Weber 40 IDA carbs built to spec .125 main jets and .055 idles...The car has got to a point when it pulls great, but smokes like a trooper at idle and stinks of petrol. Also, there is a noticable flat spot around 3500 rpm, if you roll into the throttle its ok, but if you jump on it the car will hesitate slightly and then smooth out.....It also shoots flames when lifting off !!

This has lead me to believe its running rich. I have ordered an O2 sensor to install and see what is going on when its running. Obviously, I could take it somewhere with a rolling road etc and get it figured out......and yes I will probably end up doing this, but as always I would love to understand what's going on and get any insights. As I say the carbs are in spec, I did install some smaller idle jets (.045) to see what would happen...tweaking the mixture screws did reduce the smoke but the car had no pick-up at all in first and second gear. I did wonder if advancing the timing would help, but haven't gone there yet.

My plan this weekend is to put the carbs back to spec, valve adjust, timing check and get the O2 sensor wired in and see what the values are.

Shooting flames is cool....but gassing everyone one out at the Traffic lights is a pain

Any initial thoughts ?


Cheers
Chris

If it is so rich it is burning fuel out of the exhaust I would worry about fuel washing the bores and damaging the engine.

Idle jets at 55 shouldn't be too rich and mains at 125 don't sound too bad but what are the Venturi sizes you are using and do you know what air correctors you are using.

If reducing the mixture volume creates an issue then it sounds as if the progression circuit isn't operating correctly and by running a rich idle mixture you are effectively 'flooding' over the basic problem.

I would also look at the volume of fuel being delivered by the accelerator pump as this also sounds as if it maybe a little out of adjustment.

It sounds more like carb issues than timing.

What about float levels and what pressure is the fuel being delivered to the carbs at?

Agree on floats levels and is ignition timing correct.

Morning Chris, here's Paul Abbot's list for troubleshooting Weebers. Rich running issues a third of a way down.

http://www.performanceoriented.com/troubleshooting

Thanks Guys, really appreciated !

So started from scratch and went back to basics. Went back and refitted the original jets....55 Idles and 125 mains. Adjusted the Valves and re-checked the timing. Valves were all abit tight, and the timing was too advanced. All this made a massive difference, but was still bit smokey. At this point I started to suspect Oil burning so pulled the spark plugs, all look pretty good with 4 and 5 looking bit darker, though they are more carbon than Oily.

IMG_1456 by Chris Jury, on Flickr

IMG_1455 by Chris Jury, on Flickr

IMG_1454 by Chris Jury, on Flickr

IMG_1457 by Chris Jury, on Flickr

IMG_1458 by Chris Jury, on Flickr

IMG_1459 by Chris Jury, on Flickr


Fitted an AFR gauge ( pretty straight forward, just needed to have the bung welded into the exhaust Manifold). Originally it was reading 8 ! Optimum reading for Air/Petrol burning is 14.6...after the above adjustments it was idling around 17-18...so now slightly too lean.

mtx by Chris Jury, on Flickr

IMG_1410 by Chris Jury, on Flickr

afr by Chris Jury, on Flickr

Next step is too check the float level...Replacement shims and a Float level reader are on order and arrive tomorrow. Also maybe try a hotter sparkplug.


Cheers
Chris

One way to set the idle mixture is to measure the CO and there is a value printed on the sticker on the fan strap.

If you don't have a CO meter you can use the 'lean best' method.