Heavy Carbon Build-Up in Old Carb'ed Gasser

[Conan]

Scenario: '79 Celica sat for many years, but very rarely driven. 118K original miles. Runs rough, but looks like it has had good maintenance over the years.

Plugs 1-3 had very heavy carbon build-up, with one actually bridged across with carbon. At least 2mm of hard black carbon on the outer electrode, to the point where it has cracked and broken off in places. #4 plug had light oil fouling, which I'm hoping is just a stuck oil ring. Cleaned up the plugs as best I could, and it runs much better. Dumped in fresh gas with fuel injector cleaner additive, and have been running it some to clean out the fuel system. (Hydraulic clutch is kaput, so no driving yet.)

So, I imagine the valves and piston crowns are coated with the same nasty build-up. My theory is that the PO would keep the battery up and run it now and then, but it never was driven hard enough to blow the carbon out. It does seem to be running rich, too.

I've heard of this "Sea Foam" stuff-- is it any good? Short of pulling the head and manually removing the crud, what are the options? I think I'll go ahead and rebuild the carb, since the car has spent so many years with old gas in the float bowl. I've never done that, but I'm not afraid to tackle it. Only book I have is Haynes, which is just about useless. I'm on a quest to find a real shop manual.

(I'm just posting here because I know a lot of you are long-time mechanics, and this is probably Gasser 101 to you.)

Thanks,

Lee

I'm not that familiar with old, carbureted gassers, so this is new territory for me. The car ran rough when I picked it up, so I've been assessing its condition to determine if it will be a runner.

 

[RabbitGTI]

Run a few bottles of Techron through it.

 

[White Crow]

The carb is pretty complex just be very careful as you take it apart there are a few BB's many small jets and lots of pieces. The carbon maybe nothing more then a rich mix. Sea Foam I think is way over rated actually water will do the same thing as far as removing carbon. Some older engines would build up carbon so bad the engine would knock as the piston collided with the carbon in the head 396 CID Chevys were famous for that often a gallon of water and lot of steam would take care of it.

 

[GoFaster]

Here is what you do ...

Do whatever you need to get it running on all cylinders - probably new spark plugs are in order.

Fill up a squirt bottle of some sort with water. Start the engine, warm it up, and hold it at some moderate revs (2000-ish) then squirt water down the air intake (air filter off - directly into the carb). If there's no noticeable effect on how the engine runs then squirt more. Ideally you want to have it just short of bogging or misfiring. If it tries to stall then stop squirting water until it recovers.

The water acts as a steam-cleaner. I've found this treatment to be more effective than any of the chemical wizardry.

 

[migbro]

If you can get it running OK you might consider an Auto-Rx treatment to decarbon the piston ring packs. Auto-Rx is the least bogus of the snake oils imo and appears to be effective at freeing stuck piston rings and improving compression.

 

[Got Bearings?]

I know a few friends that swear by MotorVac for carbon cleaning

 

[TDIJetta99]

GoFaster's method works wonders.. I do it to a lot of older carboned up engines.. It seems to work best when the engine is hot..

 

[RabbitGTI]

So if you just gently squirt water in until you notice a slight difference in how it is running, there is no chance of hydrolocking it?

 

[GoFaster]

Think about this. A 2 litre engine is drawing 1 litre per revolution. If the compression ratio is 8:1 then it is 125cc per revolution "compressed volume". At 2000 rpm that's about 4 litres per second "compressed volume". So it would take 4 litres per second of water to fully hydrolock it. Ain't gonna happen. Squirting in 250 - 500 mL of water over (say) 30 seconds doesn't significantly impact the compression ratio. Just make sure the water doesn't puddle anywhere in the intake. A carb'ed engine like that, is designed to not puddle fuel in the intake manifold, so it won't puddle water in the intake manifold either.

 

[TDIJetta99]

Do it with a windex bottle.. I did it to the leaf blower last season and it's only 175cc and it didn't hydrolock..

It'll take more than you think to make it bog down.. I tried it with the big block and I had to resort to taking the sprayer off and dumping it in LOL..

Edit.. GoFaster beat me to it

 

[RabbitGTI]

Think about this. A 2 litre engine is drawing 1 litre per revolution. If the compression ratio is 8:1 then it is 125cc per revolution "compressed volume". At 2000 rpm that's about 4 litres per second "compressed volume". So it would take 4 litres per second of water to fully hydrolock it. Ain't gonna happen. Squirting in 250 - 500 mL of water over (say) 30 seconds doesn't significantly impact the compression ratio. Just make sure the water doesn't puddle anywhere in the intake. A carb'ed engine like that, is designed to not puddle fuel in the intake manifold, so it won't puddle water in the intake manifold either.

Thanks, I didn't want to think about it and I knew you have, so why re-invent the wheel Thanks man!

 

[GoFaster]

I fixed a Yamaha FZR400 motorcycle engine that had been running too rich for too long, and was burning oil, probably because the rings were starting to stick from carbon build-up. This engine has a separate carb for each cylinder (standard practice for motorcycle engines). Straightened out the carb jetting (made it a lot leaner at part load) - put in new spark plugs - engine still burned oil. Last thing before committing to a top end overhaul ... Got it warmed up with the airbox cover off and the air filter out, and ran a siphon hose from a water container into each carb one at a time with the engine running. Probably ran 50 - 100 mL of water into each cylinder although I didn't measure it. PROBLEM SOLVED. Never had to do that top end overhaul and it no longer burns oil! And with the carbs properly leaned out at part load, it hasn't had that carbon build-up issue again.

 

[hevster1]

You probably need to replace the AAP diaphragm and the air horn gasket. The pump plunger is a good idea as well. Pull the main jets and make sure the are clean. run some wire through them. Use NGK or ND plugs ONLY. Check the valve clearance and set it on the loose side of .07 intake and .011 exhaust hot preferred. If using the water trick, do not drizzle too much. This will only clean the top cylinder, not the valves. If you have access to a borescope, check the valve carbon. If heavy, pull the head and clean it. Replace the valve seals with OEM, and use oem gaskets. If it was sitting for years running once in a while or not, it will probably need valve seals anyway along with vacuum lines etc. Good Luck.

 

[White Crow]

Water will not clean intake valves even 50 gallons. You'll need to run solvent through your carb the jets do gum up some are small enough that they are hard to see through. If you reduce the diameter of a jet by 1/2 it reduces the capacity by a factor of 4 it will never get that dirty but it will lean out the mix. Carbs are hateful things hope I live long enough to see them all in the junk yard. Actually a good up grade for the 20R was a Weber carb kit.The Toyota engines of that vintage were as bullet proof as it gets I would suspect once it is running properly your problems will go away with use.

 

[Conan]

You probably need to replace the AAP diaphragm and the air horn gasket. The pump plunger is a good idea as well. Pull the main jets and make sure the are clean. run some wire through them. Use NGK or ND plugs ONLY. Check the valve clearance and set it on the loose side of .07 intake and .011 exhaust hot preferred. If using the water trick, do not drizzle too much. This will only clean the top cylinder, not the valves. If you have access to a borescope, check the valve carbon. If heavy, pull the head and clean it. Replace the valve seals with OEM, and use oem gaskets. If it was sitting for years running once in a while or not, it will probably need valve seals anyway along with vacuum lines etc. Good Luck.

Great advice. I happened to know the name of the shop that has done all the maintenance on this car since '85. The owner was super nice, and remembered the car well. I told him I had a carb kit, and was getting ready to rebuild the carb. He told me about the AAP diaphragm, and to definitely rule out every possibility before rebuilding that carb. I really didn't know how crazy that carb job would be until I got into it-- water choke, a bazillion vacuum-operated doo-dads, etc. -- YIKES! Not a good project for someone who has never rebuilt a complex, Japanese car carburetor! The air cleaner housing is hiding a crazy tangle of vacuum hoses-- it would be a major deal to r/r/r that carb, to put it mildly. I got my clutch issues sorted out, so hopefully I can drive it enough this weekend to get it hot, then try the water trick.

Hevster-- do you know of a source for the AAP diaphragm? Toyota can't get 'em any more, and I haven't had any luck at the chain parts stores, either.

Thanks all for the help! I knew there would be some smart folks here on the club.

Lee

Edit to add: I mistakenly assumed that Toyota wouldn't stock the AAP diaphragm, based on other carb parts being unavailable. They do have them-- $27 for a 2" square piece of rubber-- ouch!

 

[hevster1]

I was going to say, I thought they still carried them at the dealer. Get a camera and photograph the vac lines. This will help in putting them back. If you need a full rebuild kit, look on the net, I am sure there are some around still. If you run into a problem, you can ship it to me and I can do it for you if you like. I haven't done one since the early 90's but you don't usually forget.
A weber conversion if still available is an alternative but they are troublesome. Do not go bigger than a 32-36 and make sure it is a legal kit in your state.

If you can find it, a can or 2 of BG 44K added to the tank is an excellent idea. You might want to try this before doing a rebuild. If you cannot find it, let me know. I will ship it to you.

 

[MrMopar]

Does anyone still do the old de-gunking trick of removing the spark plugs and filling the cylinders with Sea Foam to let all the rings and stuff soak?

 

[Dieselfitter]

There used to be a product called carb-out. Start and warm up. You would fast idle the engine and pour it down the carb opening. The last 2 oz are poured in quick to stall the Engine.

Then you would let it sit overnight. Best to start the engine the next day while it is still dark if you live in a Densely Populated area! Lots of White Smoke.

 

[nicklockard]

Here is what you do ...

Do whatever you need to get it running on all cylinders - probably new spark plugs are in order.

Fill up a squirt bottle of some sort with water. Start the engine, warm it up, and hold it at some moderate revs (2000-ish) then squirt water down the air intake (air filter off - directly into the carb). If there's no noticeable effect on how the engine runs then squirt more. Ideally you want to have it just short of bogging or misfiring. If it tries to stall then stop squirting water until it recovers.

The water acts as a steam-cleaner. I've found this treatment to be more effective than any of the chemical wizardry.

^^This. Except add 2 drops of Dawn dish soap per quart of water. It helps the droplets break up into smaller drops, which improves the chances that all 4 cylinders get a dose.

 

[Conan]

I was going to say, I thought they still carried them at the dealer. Get a camera and photograph the vac lines. This will help in putting them back. If you need a full rebuild kit, look on the net, I am sure there are some around still.

I got a "GP Sorensen" kit at AutoZone. It includes an AP plunger and cheap-looking AAP diaphragm. ($30). I ordered the OEM AAP, and I'm going to go look at it. If it is much nicer than the one in the kit, I'll probably go ahead and pay the $28 for it. I started the car up with the air cleaner off, and gas is leaking everywhere out of (apparently) the top of the AP plunger. I got a 20R Toyota shop manual (engine-specific) on CL, and it makes it look like I can replace the leaky parts just by removing a couple of linkages and pulling the air horn.

There's a sight glass on the side of the carb-- the book says it should show half full at idle-- it's empty when sitting. Seems like the float bowl should stay full after shut-down-- I may have to do the whole kit after all.

 

[ocshaman]

^^This. Except add 2 drops of Dawn dish soap per quart of water. It helps the droplets break up into smaller drops, which improves the chances that all 4 cylinders get a dose.

Methanol or ethanol would do the same thing, and they will burn.

 

[Antsrcool]

AC Delco top end engine cleaner. You can buy it at any GM dealer. It was used for throttle body Cadillacs and other throttle body applications and works wonders.