Thanks Rick/miniestate. Can you tell I used to be a specification writer?

What I didn't mention is that I also have done most of those things and STILL have exhause fumes coming in. MY remaining suspicions are that I have the head-to-manifold gasket on backwards (they should be labelled!), that my RC40 with the tapered tailpipe allows the exhaust to slow down a bit and not get pushed out behind the car and/or that my carb needle is too rich at higher rpms and throttle opening.

As in baseball, there's always next year. I put Desiree to bed for the winter today. (Sigh)

Moffet definitely gets the 'Best Explanation Award', (seriously Dan, very excellent and thourough coverage on the subject!) I think I'm going with 'too short' of an exhaust pipe, although the old rubber shifting gaitors are good at hiding a split in them allowing exhaust fumes to enter in more than one of my pre-'67 MKI Minis over the years!!! (check the rubber shifting boot Rooster and see) 'RacingFlea' gets the 'Best Creative Solution Award' (and probably the most effective results for our curious visitor Rooster). Last but not least, 'CA2SBL1275' gets the 'Best Way To Identify Most Problems Relating To A Mini Award'. Congratulations to all!!! And remember Rooster, nothing is normal on a Mini.                        Mini Estate/aka Masking Tape Estate

thanks Tina...

i sealed all the tiny holes i see around the car, i tightened the manifold bolts , tightened the exhaust nuts,made the carb a liytle leaner..

i'd say i did it successfully, no more fume smell.

thanks to all who gave advices.. 

Come on guys, I thought this was a good question and Robster was actually listening.

I had an exhaust in cabin issue. Turned out I was missing the seal around the parking brake. I also had to reseal my manifold. 

all sealed

oh good idea, i just have to get an oxygen tank and an oxygen mask and ill be good.. 

smells like Shabu.... google it and you'll find out!!  muwahahaha!!!

dont worry about it. roll up the windows turn the heat on full blast and take a long drive

Robster:

Does it smell like Exxon or Chevron?

How about Salems or Winstons?

Does it smell like Crack or Grass?

How about Valvoline or Penzoil?

Could it be wet cat or wet rat?

Is it like Limburger or Cheddar?

Maybe it is Gardenia or sage?

Russ

it's the fumes comming from the exhaust, i believe its a backdraft at 40mph, i would suspect too that its running a little rich because it bogs quite a bit going uphill at 4th gear and at constant speed of 40sh mph. i dint know if thats one indication that its running rich. 

i dont smell any raw gas, purely carbon monoxide from exhaust. 

i dont think too that the culpritis the joint between manifold and pipe because i tighten the 2 bolts really good. 

i will seall all the tiny holes that i see inside the car and maybe turn the carb tuner 2 more to the right to make it a little leaner

A typical Mini car body has lots of small openings that can allow fumes in. The shape of a Mini tends to cause low pressure air eddies at eac side of the winshield and behind the car. At about 40mph it become significan enough to pull some air out of the cabin, reducing pressure. THe make-up air comes in through the many openings - holes for wires, controls etc. in the firewall, holes in the floor for parking brake cables, holes between the cabin and the boot (each big enough to put 4 large fingers into), in the bottom of the companion boxes each side of the rear seat, around side windows etc. PLUS any rust holes that haven't been found... yet. There are also holes and gaps often between the boot and the exterior wich allow fumes to be sucked in.

As Jeg says, first you have to determine if they are raw fuel fumes or exhaust fumes.  It does get a bit complicated when the mixture is very rich or combustion poor.

Raw gas:

• leakage from the carb or fuel lines, including the float bowl overflow/vent or mechanica fuel pump (if fitted)
• leakage from the fuel line under the car, including the electric fuel pump (if fitted)
• leakage from the fuel tank due to rust perforations in the bottom or around the filler neck within the boot
• loose or missing fuel tank vent tube, which should lead from the top of the tank through the boot floor and hang down at the rear subframe near the fuel pump.

Exhaust fumes: at about 40mph, there is enough low pressure behind the car to pull a cloud of fumes along in the wake of the car.

• leaks from anywhere in the exhaust system including the exhaust manifold gasket and on back
• too much back-pressure in the exhaust system that is too small for the engine fitted (like when a 1275cc engine gets put into a car with an exhaust system for an 850cc or 998cc engine
• too short a tail pipe that doesn't extend past the bumper
• a centre exit exhaust pipe that doesn't properly release exhaust into the air stream making a fume cloud behind the car

Semi-raw gas or heavy exhaust fumes:

Most Minis don't have catalytic converters or effective emission control systems, so the exhaust smells different than modern vehicles - it does have more smell -the efficiency of combustion affects how clean the exhaust is

• proper timing and the appropriate spark plugs of the right heat range and gap (it isn't just gap)
• a good spark and coil and the right distributor for the engine
• a carb in good condition - throttle shaft bushings not worn and all gaskets in good condition
• the right sized carb for the engine
• a good air cleaner to which the carb is tuned
• the choke mechanism working and adjusted properly
• the right weight of oil in the dashpot damper
• the carb float set properly
• the right main jet and needle - there are probably a thousand possible combinations (most of them wrong!)
• the right idle speed and mixture setting - some (not all) SU carbs have a special lift pin to set the idle mixture correctly
• All these procedures are shown in the Haynes manual.

Since it is nearly impossible to make the Mini body airtight and you may want to open the windows sometimes, you need to eliminate the fuel or fiume leaks first, then optimize the tuning, make sure the exhaust is released into the air stream to be carried away from the car and lastly try to seal up some of the body holes. (The old 50's and 60's VW Beetle bodies were much better built and sealed - they would float if the windows were closed.)

The fact you only smell at speed indicates probable back draft from the exhaust but also means your mixture is too rich. If adjusting the mixture nut doesn't help you might need a leaner needle. 

I seem to recall a thread on this subject last year.  Try searching for that thread of info.

I think those that had exhausts in the centre of the back end had more issues than with the exahaust off to the side.  Could be a leak in the exhaust near the firewall... or fumes coming in from the rear...  

But as suggested, are you sure its not fuel fumes?  

Generally my mini "smells" a bit on the inside... but not like a fuel or exhaust fume...  Have a good look around.

Tony, are they exhaust fumes or fuel fumes?

Being more specific about what kind of fumes might help.  Center exit exhaust systems are oftentimes the cause of exhaust fumes being drawn back into the car.  As for basic carb adjustment, well, you know the drill - have you consulted the usual reference materials first?

is it normal that you can smell the fumes inside the car?, i mean my car doesn't smoke, but i can smell the fumes inside, when i get about 40+mph, is it normal?

i have my windows up, sunroof closed, all little tiny holes were sealed, the front hole where the speedo assembly is were also sealed.  i dunno where that smell are getting in??, or am i running rich? if yes, i'd like to know how you tune your carb,i'd like to know your way not haynes way,lol..i know there is a little tiny flat bolt(size of a penny) that i need to adjust, left to make it rich and right to make it lean..

i did adjust it,but i just want to know if i did it right..thank you much!!