May have a carbon problem with my Cad 425

[Rumble]

It appears that a faulty choke pull-off, or possibly other issues, has caused carbon build-up in my engine. Last time I cranked it, it was running very ragged and knocking. I pulled the plugs and they were fouled with dark soot. Car is a '79 with 16K.

New choke parts are on the way (Rochester Quad). So, when I get the choke back to working correctly, how do I deal with this carbon? I've read all kinds off stuff using water, Seafoam, Techron and what-not, but I want to use a tried and true method that will not damage anything.

 

[HerrStig]

A "southern European" tuneup, out on the highway.

 

[chrisri]

Water spraying works very well on wet manifolds, but you need to be extra careful when doing it otherwise you could hydro lock the engine. Warm up the car before.

 

[29662]

The proper way to deal with it is an "Italian tune-up" take it oun on the highway and drop the hammer for a good while. I know an old mechanic who works at a Cadillac dealer. He says that back in the days when cars were carbureted they would have customers bring in their cars with this issue all the time. Mostly older folks who just putted around in thier cars at low speed. They would take them out on the highway and blow them out for about 20 miles on the highway. Problem solved.

 

[Olas]

X2 on the Italian tune up, might work even better with SI1 or similar in the tank

 

[Rumble]

Thanks for the replies everyone. I'm assuming it's ok to run it regardless of the knocking sound?

 

[Olas]

If its carbon knock just hoon till it stops. If its rod knock be very careful.

 

[Rumble]

Originally Posted By: Olas
If its carbon knock just hoon till it stops. If its rod knock be very careful.


Lol, I had to google "hoon". Hopefully, it's not a rod, but I'll take it easy just in case.

 

[Phishin]

I'm a big fan of getting the motor hot and setting the idle around 2500 RPM's and feeding the carb a stream of water until it starts to flounder, back off and let her catch up again, and do it again until you've given her a gallon of water.

Then take her out on the highway for a good 15 minute run.

Works wonders in my older cars/trucks/boats.

 

[eljefino]

Disconnect a washer fluid sprayer hose and plumb that to the intake somehow, then hit the highway, and hit the button.

Alcohol and water are both effective at this.

 

[Rumble]

I'm gonna try the easy method as recommended in the first several posts, if that doesn't do the job, I'll try the water or some sort of combustion chamber cleaner . My choke parts will not be in till next week, so it will be the middle of the week before I can fire it up. Thanks for the suggestions everyone, I'll report back with an update once I'm done.

 

[The_Eric]

You could just wire the choke open and nurse it along until it's warm, instead of waiting.

 

[Rumble]

My replacement front choke pull-off came in yesterday evening (the rear one still works). So I installed it this morning, along with some new vac lines (and another set of plugs). The car had a problem starting, so I pumped the accelerator a few times and it fired up. It was still making the clanky-noisy sound, but I could tell it was sounding somewhat better. I took it for a spirited 10-15 minute drive, and the noise finally cleared up. No water or cleaning solution was required.

When I returned home, the wife and I took it for a 50 mile cruise, and it's running/sounding like new. I'll install the rear pull-off when it gets in tomorrow. I also have the Doug Roe "Rochester" book on the way, so I can learn how to tweak the choke settings.

Just to be safe, I'm gonna probably change the oil as I'm sure it may have taken a hit from all this. Thanks for the suggestions everyone!

 

[splinter]

I’ve had good luck with GM’s own ‘Upper Engine Cleaner’ (PN 88861803) for removing stubborn piston and combustion chamber carbon deposits.


Originally Posted By: Rumble
..I also have the Doug Roe "Rochester" book on the way, so I can learn how to tweak the choke settings..


That’s a great book…got mine back when I was flogging Q-Jets. Paid for its $9.95(!) purchase price many times over.
Still holds a revered place in the reference library.

Best wishes with your sweet Cadillac!

 

[andyd]

I do not miss carbataters a single bit. The best had a manual choke. Talk about about taking a simple task and over complicating it. My 80s Wag 360 V8s had about 35 feet of vacuum hose connecting various 50 cent widgets to pass smog and shift the front end. Even those dinosaurs had an electronic ignition. Glad you got the old boat going . My brother had a 75 Fleetwood with a 500 ci. What a car.