I have a stock 280C that suffers from a smelly exhaust at idle. I have rebuilt the carb about 2 years ago (~5k miles) and just recently recleaned it last month. I have NGK BP5ES plugs with a gap of 0.32 installed. I have a dwell meter but I need to dig it up to check that....it should be in spec (what does everyone use for that?). The timing is about 20 degrees advanced at idle with all vacume hoses attached. The car does not have thermal reactors or a cat or an egr (9/1973 model).

I have tuned around and havent been able to get the unburnt fuel in the exhaust smell to go away. Anyone have any ideas on what to look for?

What are the things I should check for that make the exhaust smell like unburnt fuel?

Thanks alot!

Timing should be at about 10 degrees BTDC with the vacuum hoses removed and plugged. 20 degrees with the vacuum retard connected is waaayyyy too much advanced.

The timing should drop to 4 degrees at idle with the retard diaphragm connected.

Hey Mike D....thanks alot. I measured the dwell and its at 34 (%?). I seem to recall that is close, but I am bad with remembering numbers. Is this in the ballpark of what you guys use? I want to get the points right before I tweak the timing.

Thanks again!

I don't use points so I can't help you with dwell. If no one gets back to before this afternoon regarding the dwell, I'll dig out my shop manual and look the dwell setting.

Before you ask, I use the Crane XR-700 optical set-up. Pertronix makes a good set-up which is popular among the board members.

Oh yeah, the 4 degrees I mentioned in the previous post should be ATDC with the engine at operating temperature.

I run mine at 40-42 degrees. After that is set, then set the timing. From then on, as long as the dwell is set correct, the timing will be correct. I haven't touched my timing in years. I do, however, once in a while check to make sure something hasn't changed somewhere in the system. I use the BP6ES plugs in mine.

By smelly exhaust, what do you mean. Is it black smoke (rich), or no smoke eye burning (lean) strange smell?

Sorry, I didnt see the last reply until today. My distributor only has one vacuum port (advance). I took that off and set it at 10 degrees. I also think my dwell is in the correct range.

Since I owned the car I always thought it was a rich smell, it smells like unburnt fuel to me. I may be tricking myself though now that you mention eye burning because it is kind of like that. When you turn off the car and open the drivers door its really fume-y. I may look at leaning her out and see how that goes. I dont see any black smoke from the drivers seat, I could polish my exhaust tip and see if that blackes up to get an idea.

This brings another questions....how exactly do you set the idle mixture on these solexs? I have messed with many solex/webber/dell/bing carbs and usually there is a peak to the mixture setting, a sweet spot where in or out makes it run poorly. These carbs dont seem to have it. As I continue to turn the screws out the idle increases, I lower the idle set screw and repeat, seems like I can put them anywhere.

How do you set the idle mixture without a CO machine?

I may also change the plugs to what MBbuff is using. I switched from bosche to ngk a while back and changed the heat range in the process, I forget which I used to be at (its in my notes somewhere) but maybe another try is in order.

Thanks again...!

*correction: this sentence
I may look at leaning her out and see how that goes.
* should read
I may look at Richening her up and see how that goes.

Do not forget to check the timing with the vacuum tube on the distributor.
I recently found bad tubing for that.
It is hard to see as it is buried behind the mounting panel and the fender.

Good luck.

Doug Q