gas smell at exhausts
 

Hi there,

I think my engine runs really good but there's always a certain smell of burnt gas at the exhausts. is it usual also in nicely tuned engines?

here are some some specs about my engine:
-the carb is an Edelbrock 1406 -unmodified I suppose-600cfm ( this carb is the leanest of the line)
-MSD distributor and new spark plugs with modified negative contact ( filed a bit to improve the spark). I didn't checked the new spark plugs but the older ones were just a bit more than tan
-made 900 miles in 4 months and only 200g oil loss ( the fourth part of a 1/4 gal)
-please check the pic of the back of my car. the black spots are the result of about 600 miles
-gas consumption is really good. better than a stock 190hp 79 owned by a friend
-I think I have a 160 F thermostat because myengine takes lot of time to reach the 190F temp
-The gas smell is there also when engine is hot
-some, few, smoke from the exhausts, same as other vettes I've seen on youtube videos.the smoke is really few when engine is hot. smoke is white at cold engine, clear when hot

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RE: gas smell at exhausts
 

androus, gas smell at exhausts huh?white at cold, clear when hot? who is driving thevehicle when you've noticed this?

RE: gas smell at exhausts
 

Forgot what year you have but does it have a catalytic convertor?

RE: gas smell at exhausts
 

73shark,
1979 and cats

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RE: gas smell at exhausts
 

Aldo,
How have you been? Are your exhaust pipe tips black? Sounds like you're running "rich." Short of going into the carb, you can go "in" w/ the two mixture screws in the front. Other-wise, it's jets and/or metering rods and springs.

RE: gas smell at exhausts
 

Hi Aldo, I agree with Jim on a little bit of fine tuning on the carb. You can hook up a tachometer and vacuum gage to help adjust the idle mixture screws to the fastest leanest idle speed, it may help some on the rich odor. The white/grey smoke on cold starts is typical with older and/or high mileage chevy engines, normally it's a little oil running down the valve guides after shut-down and it burns in the combustion chamber on re-start. You can install new valve stem seals with good results if the valves and guides are not worn badly.

RE: gas smell at exhausts
 

Don't know if this matters or not but those particular cats are designed to have fresh air pumped in from either an air pump or intake pulsations. If they aren't plugged, then you'll probably have some exhaust leaking out of those elbows on the side of the cats.

Have you considered putting a heat shield above the driver's side cat? Because if they are working correctly, they get very hot. [:o] Also the exhaust will have a sweet smell. I'm guessing that they probably aren't working anymore. That style cat also has a honeycomb matrix inside and sometimes it breaks down and then partially plugs the exhaust.

RE: gas smell at exhausts
 

If indeed, like "shark" is saying, the convertersmay beclogged, hook up the vacuum gauge and from idle, crack the throttle wide open real quick, not holding it open, and see if the needle drops down to zero. The fast complete drop indicates the exhaust is clear, if the needle doesn't drop quickly, the exhaust is clogged/not free flowing.

RE: gas smell at exhausts
 

Thanks everybody,

I have reduced the a/f mix with the 2 screws in front of the carb and now it's a bit better. very little smoke at cold engine and no smoke at all when hot. The gas smell is always a bit there, probably slightly less than before.

I'll check my Cats conditions soon. Actually i should remove them since there's really no need of them. But that's not so easy to me...
Now I have other troubles... yesterday my mech has replaced various parts at the front suspension : tie rod ends, idler arm , PS control valve. But my car doesn't behave good : when I turn left , the behaviour is very scary! The car seems to continue to steer even if I stop steering...
After the parts replacing , my steering wheel has become harder than before and not straight anymore ( high point of steering ar 2 o'clock). We kept tie rod ends same size as olders, but possibly made a mistake at the pitman arm , loosing the high point of steering
keep you posted

RE: gas smell at exhausts
 

Aldo, you need to get an alignment, that should help alot.

RE: gas smell at exhausts
 

Hi Aldo, if your steering wheel is not centered at 12 o'clock when you are going straight down the road then the "Centering" is out of wack.
To adjust the centering loosten each tie rod end and turn it one revolution the same way on both sides. Then see if you get an improvement, if not turn the tie rods the other way eaqually.
this will "Center" the steering Wheel.
If you turn the tie rods in oppiset directions that changes the tow.
The Centering gets changed because the new Control valve is in a differeft positoin than the original. PG.

RE: gas smell at exhausts
 

the problem was the alignement...

made the toe in at the shop and now the car rides great! I think anyway that the steering gear box should be remanufactured for really perfect steering.too much money...

now I have to replace the rear monospring ( waiting for a composite one to arrive) and I have to replace the bushings at trailing arms and at rear camber rods. Then make the final alignement both at front and rear. I hope to be able to do everything in about a month

RE: gas smell at exhausts
 

The new control valve may need to be balanced if your mech didn't do it. Procedure is on page 9-65 to 9-66 in the Service Manual. If you don't have access, let me know and I'll try to scan it in and e-mail it to you.

RE: gas smell at exhausts
 

http://jimshea.corvettefaq.com/?page_id=4
Aldous, check this link out very informative

RE: gas smell at exhausts
 

Great link there batesy80, I'm sure that will help a lot of forum members, PG.

RE: gas smell at exhausts
 

I agree, especially since I'm going put new seals in mine.

RE: gas smell at exhausts
 

Batesy80,
thanks for the link.
I solved my steering problem finding the answer in that link.

I had my steering wheel out of center because I centered the steering wheel by turning from one side to the other and then diving by 2. But was not correct.

in the link I found that the steering gear box center is marked by a flat surface between the rag joint and the the gear box input. I readjusted the steering wheel placing that flat surface in the right manner, then I made the front wheels realignement. Now everything is OK.
I'll possibly work a bit on the 2 gearbox adjustments ( screw and big nut) if necessary.
thanks again

RE: gas smell at exhausts
 

your welcome. I saved that link from this forum from last year, cause I knew I was going to use it for my own car. Nothing but good info from the contributors on this forum, hats off to all. Drive it like you stole it, but don't break it.hahaha

RE: gas smell at exhausts
 

If you decide to adjust the steering gear, be sure to do so with the steering centered in order for the sector gear to be on its high point.

RE: gas smell at exhausts
 

73shark
to find the gear box high point , I followed the picture attached below.
I feel that the steering wheel has a good feeling now, but it's still not perfect.
when i go straight, OK , when I turn right , OK too-very smooth and precise. But when I turn left the steering wheel needs a bit more effort and the steering is less precise and smooth and it's "faster " than when I turn right.I mean bends at 40-50mph

after replacing the PS control valve, the steering has becomeharder than before

I have still to adjust the front camber, now is pretty bad. But to do so, I'm waiting for the new monospring to arrive , balance the car left-right ( now the car is still low at driver's side in respect to passenger's)

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RE: gas smell at exhausts
 

"when i go straight, OK , when I turn right , OK too-very smooth and precise. But when I turn left the steering wheel needs a bit more effort and the steering is less precise and smooth and it's "faster " than when I turn right.I mean bends at 40-50mph

after replacing the PS control valve, the steering has becomeharder than before"

Hi Aldo, I agree with 73shark, it sounds like you have to balance the new control valve. Go back to where batsey80 said and look under " Control valve replace and balance instructions".
The picture you posted is the steering box, the control valve is under your car. PG

RE: gas smell at exhausts
 

when we fitted the new PS control valve ( a Lonestar Caliper) seemed that no centering was needed, since the wheels were not moving by themselves.

At the shop, I wanted to check the control valve centering with the PS piston detached from frame, as suggested by GM instructions, but with car jacked up , the engine fan was touching the fan shroud due to chassis warping...

So , may I adjust the control valve centering with the car on the floor and without detaching the PS piston? turning the nut just a bit and trying the steering wheel turning effort?I'll do this step by step until I have a more balanced steering wheel...

RE: gas smell at exhausts
 

You are very close to having it centered 100%. I did mine in the driveway with the front wheels on ramps. I took off the rod from the piston and slowly turned the adjustment nut left than right than split the difference. Sounds like turning the nut 5* from where you are now will do it. PG.

RE: gas smell at exhausts
 

If jacking your car up flexes the frame enuf to cause the fan to hit the shroud, then you might want to check your motor mounts (maybe you already have, I can't remember) or look for some places on the frame that have serious rust as that is a problem with some that have seen a lot of road salt and weren't flushed out.

RE: gas smell at exhausts
 

PG . I'll try to balance the valve asap. I hope to solve the problem.good idea the ramps...

73shark . the car was totally jacked up, not the front only. look at pic. the nose isa bitdown due to nose weight. the clearance between the fan and the shroud at the top is sosmall that I'm not surprised of fan hitting the shroud on certain conditions. Anyway I have only surface rust underside ( california car).Possibly the motor mounts... Anyway when I rev the engine I see little-usual movement of it. How to check motor mounts?

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RE: gas smell at exhausts
 

Look at the gap between the bottom of the fender and the door, it closed up. The pic of your car on the ground shows a normal gap.

When my left motor mount broke the left side of the motor would lift up and the fan hit the shroud. To test yours power brake it in 1st gear and see if the motor moves. To test the right side power brake it in rev. PG.

RE: gas smell at exhausts
 

PG,

the gap at door seems ok to me too. A friend's 79 vette has a wider gap than mine, for example...

I already made a braking test both forward and in rev ( for other reasons: after replacing front coils and shocks). I heard no strange noises from the fan.

I suppose that the reduced clearance between fan and shroud, it's possibly due to 2 things

- my engine it's not the stock one , but was replaced about 20 years ago, I suppose
-the radiator seems replaced too.

So possibly , when reassembling the things , not so much care has been took to perfectly fit the parts.
anyway, I'll post a pair of pics of fan and motor mounts soon, so you can judge the situation

RE: gas smell at exhausts
 

PG , some pics , but not the motor mounts : too hard to take good pics

Anyway , I think that the shroud is fixed too low, simply. check pics

Ah... look at the second pic. My fan's shroud has a "door" underside. My friend's 79 doesn't have it and can't find this thing on the assembly manual. fresh air to radiator and engine I suppose...Indeed my car has no overheating problems ( till now...)

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RE: gas smell at exhausts
 

The fan should have pretty equal clearance all the way around the shroud. So the clearance on the sides should be the same as on top. If it's closer on top, then something is not right.

RE: gas smell at exhausts
 

Hi Aldo, I had a chance to look a my fan clearance today, I have more at the top, more still at the left and less at the right. My opionon, just live with it. Check your transmission mount and if that is ok, than so be it. Your fan shroud may be off a little, I have bolts where you show a screw. If you want pic's let me know.
I have seen post's where someone finds out months or years after the purchasethat there car is 1/2 inch lower or higher on one side or the other, so what! Our cars are up in years and they were not made perfect from GM. Enjoy your ride! PG.

RE: gas smell at exhausts
 

PG ,
I have made the balance at the PS control valve. I did a short ride to check the thing...
Now it seems that the effort to turn the steering wheel left-right is the same. far better than before but still not perfect when I turn left ( less precise than right). when I turn left in bends at 30-40mph , I have still to make some corrections. I think I have to check and tighten the steering gear box, since I have still excessive lash, in my opinion. Unfortunately I can't send my gear box out for a rebuilt ( too expensive) . So i have to live with it...