View Full Version : running lean and "gassy" exhaust smell?

08-09-2012, 01:40 PM
So how normal is this for a pre-emissions control engine (1296 with Stromberg CD150 no emissions stuff at all)

After a drive, my spark plugs are nice and clean, no signs of oil / carbon deposits, (actually a bit orange colored!) If I lean out the engine any more, I have drivability problems.

But the exhaust still smells like I am spraying gasoline...

now to get avoid being super rich I had to adjust the fuel float level about 2mm lower than normal, when I had the height set according to the manual the mixture was very rich no matter how I set the jet. I checked the weight of 3 different floats I have and they were all identical so I don't think that the float has a leak???

08-09-2012, 01:51 PM
The plug color is mostly set during cruise. I assume what you are smelling is at idle. Not sure, but you could have a rich idle with a good cruise mixture.


08-09-2012, 11:55 PM
Yes obviously I am smelling the gassy smell at idle, I was mostly wondering what other peoples cars smell like at idle since it is really noticeable.

08-10-2012, 05:26 PM
I don't know if this would apply to a CD150 or not, but maybe ... especially since you had to lower the float level to get mixture within range.

On the earlier SU carbs, the jet has to be moved slightly in the housing until it is perfectly centered around the needle. If that centering is not done exactly right, the needle rubs on the side of the jet which, over time, can wear both the jet and needle. The result is that the mixture goes way rich at idle, even after the centering is reset to be correct. I don't think the CD150 requires jet centering, but wear (or damage) to the jet and/or needle might be a possibility.

Another possibility (again for a SU H6, may or may not be applicable to a CD150) is that there is a fuel leak past the outside of the jet. The H6 carbs use a seal that rides on the outside of the jet; if that seal leaks then the idle mixture will go rich (as the extra fuel gets sucked into the engine). Since the leak is fixed, the effect becomes much less at higher rpm.

With the engine warmed up and the choke off, there is no "gassy" smell from my TR3. Very little odor at all, what there is just smells like car exhaust.

08-11-2012, 02:13 PM
Thanks Randall
The CD150 does require the jet being centered basically just put it in place and run the piston up and down a few times before tightening it in place. The piston does go up and down nicely but there still could be a leak around the jet maybe... I guess I could take it apart without taking the carb out.