Spark plug

[granthendrickson]

Has anyone seen this on a plug? If so what is causing it? Engine is a 355 with 3,000 miles and is running rich. It makes what I think it’s a knock sound coming through the exhaust. All the plugs on the right side of the engine look like this however the left side plugs look normal.

 

[Ricko1966]

I'd check for an intake leak. Top side spray with carb cleaner around all the intake ports,listen for an idle change. Bottom side, pull the dipstick, put a vaccum gauge on the dipstick tube. Pull and plug the pcv line, duct tape over valve cover breather and pcv openings. You shouldn't be pulling vacuum at the dipstick, if you are you have a leaky intake gasket.

 

[granthendrickson]

I'd check for an intake leak. Top side spray with carb cleaner around all the intake ports,listen for an idle change. Bottom side, pull the dipstick, put a vaccum gauge on the dipstick tube. Pull and plug the pcv line, duct tape over valve cover breather and pcv openings. You shouldn't be pulling vacuum at the dipstick, if you are you have a leaky intake gasket.

Okay thanks, will do. Do you know why only half the plug looks brown and the other half is white?

 

[Ricko1966]

I do not know why one side is clean and the other not,but that is how plugs look with a leaky intake gasket,clean on one side.

 

[DoubleDingo]

I do not know why one side is clean and the other not,but that is how plugs look with a leaky intake gasket,clean on one side.

Would the butterfly being not fully open on the right cause that? Or just vacuum leak? I know the butterfly in normal operation closes when cold and opens when hot. Just curious if partial blockage could cause that to happen. Of course that would mean the OP is not running headers.

 

[granthendrickson]

Would the butterfly being not fully open on the right cause that? Or just vacuum leak? I know the butterfly in normal operation closes when cold and opens when hot. Just curious if partial blockage could cause that to happen. Of course that would mean the OP is not running headers.

Something that I stupidly left out of the post is that the right side idle mixture screw is wollowed out and isn’t able to lean out.

 

[DoubleDingo]

Something that I stupidly left out of the post is that the right side idle mixture screw is wollowed out and isn’t able to lean out.

DOH! That is most likely your problem with running rich

 

[Ricko1966]

Would the butterfly being not fully open on the right cause that? Or just vacuum leak? I know the butterfly in normal operation closes when cold and opens when hot. Just curious if partial blockage could cause that to happen. Of course that would mean the OP is not running headers.

I doubt it but you may be on to something, I've only seen this with an intake leak, But he says he hears a knocking that could be EFE flipping open and shut,and we may have found another situation that can cause this plug reading,or just 2 separate problems First let's fix the obvious and see what happens. O. P. passengers side right behind the exhaust manifold is a butterfly valve that is suppose to shut on cold start,to warm the intake. See if it is bouncing open and closed. If so see if you can wire it open, put in fresh plugs and check in 3000 miles. If you do find an intake leak,definitely fix it ASAP. Back to fix the obvious, fix the carbureator You may have 3 problems.

 

[granthendrickson]

I doubt it but you may be on to something, I've only seen this with an intake leak, But he says he hears a knocking that could be EFE flipping open and shut,and we may have found another situation that can cause this plug reading,or just 2 separate problems First let's fix the obvious and see what happens. O. P. passengers side right behind the exhaust manifold is a butterfly valve that is suppose to shut on cold start,to warm the intake. See if it is bouncing open and closed. If so see if you can wire it open, put in fresh plugs and check in 3000 miles. If you do find an intake leak,definitely fix it ASAP. Back to fix the obvious, fix the carbureator You may have 3 problems.

I’m running headers so it couldn’t be the butterfly on the old manifold. I will check for a leak in a minute, the sound goes away when it’s off idle.

 

[AuroraGirl]

whats your ignition timing with a timing light look like at idle and off idle but not necessarily WOT? im curious

Also, what heat range you running?