RPMs surging, smell of fuel in exhaust

[Finnerty]

This just started recently, rpms occasionally surging up/down 100 rpm at 2000 rpm slow cruise, occasional smell of gas in exhaust, especially when reducing throttle, engine sounds a little rough, not purring. Vacuum readings at 2000 rpm are rock steady. Quadrajet carb on a 454.

 

[alldodge]

Smelling gas would think you need a carb rebuilt. Look to see if the tygon tubing (yellowish clear tubing) coming from the pump does not have any gas in it. If gas is present then the fuel pump diaphragm has ruptured

 

[Finnerty]

No gas in the sight line, fuel pump is good, recently replaced and gives proper pressure to carb. It’s the original 40 year old carburetor, I wonder if I should replace it with a reman carb instead of trying to rebuild.

 

[achris]

Seen this before on other engines. How old are the spark plugs?

Chris........

 

[alldodge]

No gas in the sight line, fuel pump is good, recently replaced and gives proper pressure to carb. It’s the original 40 year old carburetor, I wonder if I should replace it with a reman carb instead of trying to rebuild.

Rebuild or replace is the same thing. There are no new ones, so it all depends on how well your clean and rebuild over the one which is replacement is cleaned and rebuilt

 

[Finnerty]

Plugs were replaced at the beginning of the summer. I’ll pull them and have a look. I’m guessing a bad one will look different and smell like gas?

 

[wahlejim]

The mercruiser manual gives an excellent review of spark plug wear, color and what kind of fuel condition you are running. I would browse through that.

 

[Finnerty]

So I pulled the plugs, all looked the same until I got to the
last one. Instead of white the insulator was brown varnish colour. Looked in my manual and it said this can be due to a misfiring plug. So I thought I’d try a new plug and while in there noticed the plug wire was badly burnt. Happy ending, easy fix! Thanks for your suggestions!

 

[alldodge]

The plugs should have some light tan color to them for running normal. White plugs which have been used for a while are showing their running lean.