exhaust manifold question

[Anonymous]

guys, I think I am sucking raw gas from the choke tube up into my carb. I have a question about the hole in the exhaust manifold. there is one hole at the top of the (where the tube goes in) and one hole at the bottom. Shouldn't there be free passage between the bottom and top holes i.e. should be able to snake a piece of wire from the top to the bottom with no restrictions? this is a 200 ci engine. manifold is a repo from NPD, approx 2 years old. thanks for the help!

 

[addo]

That is correct. The bore for that tube is isolated from the exhaust gases, and there are conventionally two tubes used - one jammed in each end of the bore.

I don't think there is an insert like the SBF manifolds used, for these two tubes to press into - they just go straight into the casting.

 

[pedal2themetal45]

HI
I beleve that the hole in the bottom of the exhaust manifold is plug with a plug with a real small hole in it so it doesn't create a large vacuum leak persay... thou the choke... its NOT open to the inside of the exhaust manifold it just passes thru to pick up heat for the choke on the inside of the manifold it is cast into the construction of the manifold and its about 1/2" in outside diamitor. 3 & 4 shair that exhaust port and it kind of divides it. Theres no raw gass there it would be exhaust gasses...
What kind of prob are you experanceing that makes you fell this..
tim

 

[Anonymous]

Tim, thanks for the response. The problem I am having is that I can put new plugs in the car, drive for 20-30 minutes, pull the plugs and I have a shiny black spot on the insulator. It's almost as if something is burning the insulator just on one side of the plug. Honestly at this point I am grasping at straws. car runs great, I'm just stumped. If you look at a spark plug diag. chart, I am splash fouled guy! I've checked and/or replaced the following..

compression: 150 accross the board
vacuum 23" at 2000 rpm
a/f mix ok, just a tad lean
timing ok, no pinging
plug wires/fuelfilter/coil/vacuum advance all new

no one local (including myself) can seem to diagnose. I had read that raw gas/exhaust getting sucked into the choke tube could possibly cause.

thanks guys!

 

[Anonymous]

Danance;

What year is that engine?
The 1978-82 engines had 2 coils inside the exhaust manifold in between the two ports. However, most of those burned completely away from the years of MTBE fuels we all had to use. Then, you get raw exhaust gases into the Holley 1946C carb, which warps the top plate, which then causes the power valve to be always open (a rich mixture). The lower hole should then go to the air filter (cleaned air) and the upper hole to the choke housing. This is to warm up the electric choke to above 55 degrees F so the little switch inside will close and make it open the choke electrically.

The other thing to check, if you have these later engines, is the EGR. If you've disconnected it, or if the valve is permanently closed, the engine will run rich from just above idle to 2500 RPM with the Holley 1946C carb. This is by design: the carb expects a "vacuum leak" of EGR gases, so it runs rich in that range to compensate the mixture back to 14.7:1 or so.

 

[Anonymous]

it is a 1966

 

[pedal2themetal45]

HAY DANANCE
Could be the power valve.... dumping raw gas in..... I'd maybe go there. the power valve # should be half the vacuum at idle.. If you have had any kind of back fire thou the carb it can take one of these out.. and check the float level maybe if it is to high it might cause fuel to be pulled in throu the bowl vent tube.
tim

 

[pedal2themetal45]

HI GUY
I just went and looked at the plug reading page as to what it says... Look down you carb does it look dirty??
If so maybe you should spray some carb cleanner down it.. I'd maybe do it anyways. Something I always do when spraying carb cleanner down a carb is I pull the a/f mixture screw out and spray in it as well as thats what mixing the fuel.. then put it back in and readjust as if the carb was dirty its going to change anyway and well have to be adjusted anyway.. and I well know that that passage is clean. To help get the right setting I'd screw it in and seat it gently counting the turns befor I take it out.. then put it back where it was the adjust from there...
tim

 

[Anonymous]

thanks guys, I'll clean the carb good, see what happens and let y'all know. thanks again

 

[pedal2themetal45]

Spray it down the carb while the motor is running that way it well clean the passageways from the carb to the valve.. You well have to work the throtell to keep it running as it well want to die while you spray down the inside...
good luck
tim

 

[Anonymous]

I had a similar problem with my auto choke. The passage through the manifold had ruptured and was sucking exhaust into the carb. I don't think it effected the plugs, but it fouled the carb real good.

Check and see if you have much carbon in the carb throat. Or pull the manifold and see if it is ok.

 

[JackFish]

The other thing to check, if you have these later engines, is the EGR. If you've disconnected it, or if the valve is permanently closed, the engine will run rich from just above idle to 2500 RPM with the Holley 1946C carb. This is by design: the carb expects a "vacuum leak" of EGR gases, so it runs rich in that range to compensate the mixture back to 14.7:1 or so.

Hey, my EGR recently failed and I capped it and plugged the vacuum line. So now I'm running rich?
What can I do to alleviate the problem? Jetting?
Should I fix/replace the valve or bypass it with a block-off plate?