exhaust fumes/ smells

[cheezee]

k guys im having trouble with my exhaust fumes from my exhaust smelling like crap! it stings my eyes, nose, and makes me cough, it also gives me a major headache if i leave the car running for a long time. also number four cylinder is not firing, i know cause i pulled the spark plug and it had no hesitation on the idle, i also did a compression test and adjsted my valve already. the car is running on triple mikunis and back firing out of cylinder 4 is that whats causing the smell and hesitation on WOT? it is the choke?

[grantf]

Try the search. LOTS of info there. and after you search you can tell me how to fix the fumes in my car.

[JLPurcell]

First, I would test the simplest things. Check the spark plug wire to number 4, check the gap on the plug and make sure it is firing. If you have good spark at the plug then it could get complicated. Valves or carburetor, as I am sure you know the triple Mikuni’s are like running a single barrel carburetor for each cylinder the only thing they share in common is the float bowl. I could very well be a problem with number 4’s carburetor.

JLP

Edited April 27, 2011 by JLPurcell

[FastWoman]

Maybe you mean raw fuel/air from the #4 is causing afterfire (out the exhaust) not backfire (out the carb)? Certainly if #4 isn't firing, you'd have some stinky exhaust. There's no way for any of us to know your headache tolerance, though.

There should be no choke once the engine is warm. If you've got your choke engaged, then that would certainly be a problem and would certainly cause strong exhaust fumes.

[JLPurcell]

On the Mikuni's if properly set up all chokes work together. When I ran them we simply wired the chokes all together, let the springs hold them open and never used them. FastWoman is correct in that over fueling or unburnt fuel will give you a heck of a headache in short order.

JLP

[Walter Moore]

I thought that the Mikuni/Weber style carbs didn't have a choke... But I have no experience with them, so that is just hearsay. Anyway, if you have a cylinder that is pumping out raw fuel, the car will smell really bad. I agree that you need to check for spark first. Did the #4 cylinder look low in your compression test?

[JLPurcell]

Walter, I don't remember how the Weber's worked but the Mikuni's choke is not a butterfly but increased the fuel flow to both barrels. Contrary to my earlier post that the only thing the single barrels have in common is the fuel bowl, the other thing they share is the enrichment circuit. Which would rule out the choke being the problem with only cylinder number 4. It also would rule out a float problem. JLP

[grantf]

sorry read though half of youre post now I feel like an arse.

[cheezee]

i did a compression test and cyl #1 read 119 and the rest 120 this is after i did a valve adjustment to spec .010 exhaust and .008 intake, i also checked the distributor and its set all the way to retard, im guessing that may be the cause of the back firing? spark plugs all look like some one rubbed charcoal on it.

[cheezee]

K guys I checked my timing and set the timing light gun to 0 and adjusted the distributor, guess what? Idled like crap so I set the gun to 10 degrees and adjusted the distributor ran good and idled great, reved it couple of times with no back firing came back to check I totally forgot to plug in #4 spark plug wire earlier when I was checking the plugs, plugged it back in and idle went up again reved it and it backed fired through #4 again

[JLPurcell]

I can't make sense of a car running better with one plug wire off. Your sure you don't have a tight valve on number 4?

JLP

[Walter Moore]

The other possibility is that the intake seat on the #4 cylinder leaks back into the intake manifold. But you should see that on a compression check... unless it is a small enough leak that there is only enough leak to allow the just enough burning gas into the intake to detonate the fuel air mixture.

Maybe you need to do a leak down test on the #4 cylinder. That will tell you more than a standard compression test.