exhaust / gas smell in cabin

[advtracing]

ok heres the deal , 1976s 911 coupe r-gruppe stripped out . running 40 ida's and extractors etc... all heat gone and my cover plates on the heater tubes in the engine bay. all sound proofing etc removed and rs carpet installed .

the carbs are not quite tuned right so we get a little spit back on throttle , using cis fuel pump to fuel reg and return to tank .

when driving i am getting exhaust fumes in the cabin and a slight raw fuel smell . so
1 is the exhaust getting sucked back in via the center tunnel holes / shift rod hole or through the vents at the bottom of the back window ? can't be the heat system

2 is the fuel pressure and return stirring up the fuel tank and causing venting in to trunk maybe via expansion tank or is the fumes maybe attached to the exhaust smell with the raw spit back from the carbs ?

not sure where it from , so any other ideas

[douglas bray]

The smell of fuel/exhaust is common on cars that do not have a catalytic converter. (It's amazing how much cats impact the exhaust smell) That said, I'd sure check the tunnel for a pin hole leak in the fuel line and make sure the frunk isn't filled with gasoline vapors from a bad line.

[Workhorse]

I've been told that sometimes the accumulator doesn't hold pressure and "releases" pressure over time. Was told that the older smaller accumulators do this. The fix is to buy a newer (SC type or newer) larger accumulator and it usually solves the issue.

My 911 is a 1974 CIS though, not sure it would apply to a car with carbs?

Let us know what you come up with.

Ross-

[Michael T]

I would get a new gas cap from our host as a first step. It worked for me and I was sure there was a fuel leak.

[Dave Colangelo]

Its a long shot but I recently had a gas smell in my cabin and it was a result of the small piece of fuel hose from the tank to the pump. It had degraded to the point it was leaking a bit. Enough that there was not a substantial build up of fuel on the ground (or it was evaporating fast enough) but causing a serious smell issue. Worth checking out.

Could also be coming though the heat exchangers if they are having an issue.

Regards
Dave

[Neilnaz]

Is it possible that the fumes are entering the cabin from the engine compartment via the normal path for heat (i.e. the heater ducts through the sills) despite the removal of the heat exchangers? I also get some exhaust fumes in my car when I 'open up the heater flaps' which I take to be because the heat exchangers have some pinpricks.

Is it possible to seal the heater ducts to make sure they are not guilty in this instance.

I presume the slight smell of fuel is unburnt fuel as you are running rich?

All the best,

Neil

[Dave Colangelo]

My mistake I did not read that the heat was removed, not the first time I have answered the title of a thread after only skimming the body of it...

Regards
Dave

[advtracing]

The heater ducts are sealed tight with the set up I make. I think I will replace the front lines and run the breather straight out of the car , then make a run and see .
Will gasket the tunnel holes into the engine bay also.

[BoxsterGT]

Here are a set of E-85 rated fuel hoses I make up.......



for you or anyone else in this situation. They are crimped at one end, and will last a reasonably long time when you use the good "Norma" clamps........



at the tunnel end. For details please email me.

Len at Autosportengineering dot com