My 65 is running awfully rich. So rich that I smell like I've been mowing the lawn after a cruise. No black smoke, and the plugs actually look ok. I have had the timimg and dwell set by my mechanic and he says it must be something else. The car has side exhaust, and I had tears in my eyes last night after a 20 min ride (no, I didn't watch Ol' Yeller) from the fumes.

I have come up with a few ideas:

1) Bad Coil
2) Need to rejet carb
3) Need to get new carb
4) need to get new mechanic

Anybody have any ideas on what to do? I'm not a wrench, I went the paint and body route, so please don't be afraid to be remedial in your suggestions.


BTW, the car has a 74 corvette L82 engine that has been rebuilt to be around
300 hp. It runs real strong when it's not running poopy like now...
This is the greatest forum on Earth!
:steering:


[Modified by NuckingFuts, 4:18 AM 5/14/2003]

 

I'd look at the carburetor. My guess would be either the needle and seat are leaking, or the float is sinking. For some reason the fuel level in the float bowl, either primary or secondary, is too high, and it's dumping gas into the intake. For certain it'll get worse, rather than better.

 

thanks for your reply, The car has the stock fuel pump - so too much fuel pressure should not be the culprit. Anybody else out there have any suggestions before I replace or rebuild the carb?

 

how about switching to rear exhaust?
.
the only way i tune anymore is with oxygen sensors.
.
But, sadly, 99% of forum members find this topic too difficult. That's why i suggest rear exhaust 'cause you said THE PLUGS LOOK OK. If they were sooty black it would be another story. :smash:

 

Rear exhaust is not an option - no offense to our rear-exit friends, but I'd never consider that as a solution. I'm sure it's something minor, but I just need to find out where to start looking without just swapping out a bunch of stuff.

Thanks for your reply :cheers:

 

Have you ever driven a side exhaust c2 that was OK? If you have then there is hope.
Otherwise,
The reasons i would never run side exhausts:
1. fumes
2. noise(at certain rpm)
3. heat(can burn leg)
Good luck, no offense to side exhaust lovers :seeya

 

"the only way i tune anymore is with oxygen sensors.
.
But, sadly, 99% of forum members find this topic too difficult. "


SAY WHAT???????


too difficult because _______ (you can fill in the blank with anything like "i can't describe it myself" or " 99% of the forum members find me incomprehensible")......you wanna try that again? :rolleyes:

 

Nothing you said would necessarily suggest that it is actually running too rich.
Like the others said, you would see black smoke exhaust, jet black soot on the exhaust pipe tips, even blackened rear tires. You would also see evidence on the plugs.

I have side pipes also (and I love em!!!). At various points in time over the last year, my carb has caused me problems. At times it was running rich (later fixed). When it was too rich, I had all of the symptoms I mentioned above.

Even when running fine, I end up smelling a lot of unburned gas (un-smog controlled) exhaust. And yes, you get it in your eyes and on your clothes,especially when the convertible top is down.

Could it be that you engine is ok, but you're just getting a lot of exhaust blown back up into the passenger compartment???

Mark

 

4) need to get new mechanic

If you cant do it on your own.

Holley used to re-manufacture the correct carb for your car,
I bought one and it worked out great on my 365. If you dont care about that stuff a Holley 650 should work out fine.
Whats on it now? Has it been rebuilt? Is it worth rebuilding?
Did it run good, but now does not? Is this problem new?
Has it always ran this way? Does it flood when cold?
Did the mech check the dist? elect system? carb air and fuel mix?
Floats?
Need more info.
As far as not liking side exhaust? Maybe a name change to "Goober" is in order? Just kidding! :lol:
I would throw a "borrowed" carb on and see if it solve's the problem.
I would think it would. Sounds like unburned gas is getting to you... :crazy:

 

You can't be so rich that you stink and still have "OK" plugs. Don't blame side exhaust. Get it on a chassis dyno and pay the extra $20 for a exhaust check on A/F ratio, or just do the ratio check with a good garage (they stick a sensor up your pipe). My car shows rich (11:1-12:0) throughout the rpm ranges (ideally 13+:1) and runs sidepipes and no smell.
You could try changing gas stations, some gasses just stink!
Daffy

 

Whats on it now? Has it been rebuilt? Is it worth rebuilding?
Did it run good, but now does not? Is this problem new?
Has it always ran this way? Does it flood when cold?
Did the mech check the dist? elect system? carb air and fuel mix?
Floats?


Ok, now we are getting somewhere. Good questions, here are the answers (in order):

2 year old Holley 650. Bought new out of the box. Ran good up until recently. Ignition system checked by mechanic. Must be fuel related - he says. No flooding when cold. Plug electrode looks fine - there is some black sooty stuff around the bottom of the plug threads. Good strong spark is present at each.

I'm thinking maybe a carb rebuild is in order. Also, PCV system a little funky and installed improperly - so I have fixed that. Raining here so I can't road test to see if that was the problem.

If having side exhaust is wrong - I don't want to be right! :cool:

 

2 years seems too soon for a rebuild.
Keep us posted!

 

An improperly operating PCV will richen the mix (among other things). The PCV valve is a "controlled" air leak that normally leans the mix. If it is blocked (even partially), then the mix is automatically richened. Check the PCV valve by removing and shaking (you should hear the valve rattle when shaken). Also check to see that a good suction is being drawn when the PCV valve is installed with the vacuum line connected and the engine running at idle. Put your finger over the end of the valve opposite to the vacuum line connection and check the "draw". If it does not rattle or the draw is weak, replace it (they are cheap!). Also check the filter at the PCV inlet (can be either a separate filter or draw from the main carb filter base).

Can also check out the air bleeds in the carb. Should be clean, and even on a low milage carb can be partially blocked to offset the mix with just a little "dirt" in the right place.

Several other areas to be sure can upset the mixture, but really difficult to diagnose via the Internet!

Frankly, your mechanic's comments leave me cold (in other words, Get a new mechanic!).

Plasticman

 

Just an idea about why the plugs look fine - this would especially apply if it only runs rich when its not idling. If you let the car idle after cruising (i.e. while rolling into driveway) before shutting it off, and the mixture is ok at idle, the plugs will give a false reading. As it idles, it could burn off the soot that would show from cruising. Seems unlikely, especially if the cam is a hot one from back then, but its a possibility.

 

I wouldn´t bother running awfully rich !! :jester

 

Kid_again
congrats on tuning with O2 sensors. :cheers:
as far as the other 99%, i can only speculate on why it's too difficult:
possible reasons
1.They don't have Vizards book.
2. think it can't work
3. don't want to drill holes and weld bungs in exhaust(this could be the biggest reason)
4. don't care all that much about an extra 20-25hp
5. need lots of peers to convince them
6. Never thought to call me on the phone to have their questions answered.
.
Maybe you could write up your experience for others to learn from? I have carpel tunnel and can't type enough for complete directions.


[Modified by Matt Gruber, 9:06 AM 5/15/2003]

 

This site tells you how to do it: http://www.bob2000.com/carb.htm

 

VG

Thanks for the link! :thumbs:
I added it to my web page. :thumbs:
Now there is no excuse for a poorly tuned engine! :D

 

hot1corvette1

Mark,
I'm having the same problems you were having, on my 67. Black soot at tips (sidepipes), heavy carbon deposits on plugs after 300-400 miles, mild gas smell sometimes. Running a stock 66 Holley carb that was rebuilt, but only slightly improved situation. What did you do to fix your problem?
When I put new plugs in, the car runs great til the plugs foul again.
Thanks for any help.

 

User9ryan:

One could write a book on the problems I was having with my Holley carb. It is the correct carb for the L72 engine: List 3247.

Over the years, owners/mechanics had changed jets (incorrectly), removed one of the power valves and replaced it with a plug, and tried to stop various leaks. Also, the vacuum mechanism on the secondary had failed, the accelerator pump had failed, and the choke cam had broken and so it had no choke or fast idle. There was a strange leak onto the throttle valves that only started after 3 hours after stopping engine. One of the float bowl attachment bolt holes was stripped. There was a loud whistling sound coming from somewhere on the carb. A mess.

I had one mechanic who tried to fix it and got about half of it working. Finally, took it to a local carb/fuel injection specialist who specializes in these old carbs. On the first try, he got everything working perfectly, except for the weird leak. Finally resurfaced all of the mating/gasket surfaces and used special gaskets. Installed the carb and carefully adjusted everything.

A miracle!! The car runs absolutely perfectly. I think the primary source of the leak, whistling, and poor mixture problems was coming from warped mating surfaces. If you had a carb rebuilt and they did not resurface the mating surfaces, you may have fuel and/or vacuum leaks. The good news is that these old beasts can be made to work very well as long as you find someone who has the experience to deal with em.

Good luck,
Mark

PS. Ace Fuel Systems, in Santa Clara, California.