Blocked carbs- How to clear them?

[JamesWilson]

1275 Engine with twin SUs that doesn't run.

Ws running fine, then sat for a while and developed problems- would idle OK but wouldn't run under load.

After much aggravation and puzzlement, I found water had gotten into the fuel tank. I drained that, flushed out the fuel lines and mopped the old fuel out of the float bowls. Refilled with fresh fuel.

But it still doesn't run. Electrics all OK- sorted those out before discovering the real problem. Good fuel pump and flow.

I suspect some grit from the fuel tank has gotten into the carb(s)and is blocking their internal passages, despite having a filter between tank and pump.

The fuel bowls fill OK.

Is it possible to see the fuel being sprayed when the engine is cranked to start? I see none, but don't know if that's normal.

Is there an easy way to clean these on the car? I'm not enthusiastic about pulling them off, though I've resigned myself to that....

Any advice would be appreciated greatly.

 

[spritenut]

SUs are very simple, no fuel is sprayed.
Fuel is fed by gravity from the bowl to the jet, the needle on the piston is the regulator, piston down, fuel shut off.
Piston up, fuel comes out of the jet and air sucks it into the carb.
To clear a clogged jet, remove the float lid, remove the dashpot lid, pull out the piston, and gently blow air down the jet into the float bowl.
Too much pressure will blow gas all over the place.
A simple check is to have the bowl full of gas, and lift the piston out, you should see gas coming out of the jet. If not blow it out.

 

[Guest]

Take it from a guy who's tried, there is no shortcut for optimum performance. Bite the bullet. I can't speak for others, but I'd bet Dave and Doc will agree.

I tried straight SEa Foam in one durring the winter months and tried to start it last week. That would be the truck I caught fire last week. After I put the flames out, still had to pull it and "rebuild" it.....ants and all.

Buy the juice and teach 'em to swim. New juice aint like the old but it still does the job. I find it works preety well but still like the snot yellow stuff.

 

[Guest]

If he's had water, best to pull it down as it might have corrosion in there.

 

[jlaird]

I bet the float valves are stuck just one prob.

 

[dklawson]

Remove the float bowl lids again and check for fuel as Jack suggested. The valves may simply be stuck. Since the car sat for a while, the other possibility is that your jet tubes are blocked and the needles gummed up. You can clean those without removing the carbs but you have to be careful.

Work on only one carb at a time.
Carefully remove the vacuum chamber. Lift is straight up. Use spray carb cleaner on a coarse rag or paper towel to remove any gum on the carb needle. There should be no deposits or gum on it. Put it carefully aside when you are done.
Remove the float bowl lid. Use paper towels to sop up any fuel in the bowls. Use the spray carb cleaner in the jet (not in the float bowl, the opening of the jet in the carb body). Spray down into the jet and you should see the cleaner come out into the float bowl. Allow the spray some time to work and then spray again. Do this until you see the cleaner flow freely into the bowl and that it is "clean", not amber colored from gum. Empty the bowls by sopping up the cleaner with paper towels.
Carefully put the vacuum chamber and float bowl lid back in place. If you carbs were plugged they will be open now.

 

[JamesWilson]

Thanks everyone- that's my afternoon fun 'n' games now.

I'll let you kow what happens....

 

[DrEntropy]

Doug cover'd it well enuff. A couple cans of a good aerosol carb cleaner and good supply of paper towels. Needles/jets can have green swarf built up from water and sitting, just take yer time and they can be fairly well serviced in situ.

 

[bugimike]

I might add that a useful "tool" for the job is to use the little red tube on the carb-cleaner spray nozzle (If the carb-cleaner did not come with one, "steal" one from a WD40 can!)to spray down into the jet with! :wink:

 

[Sarastro]

When you say "electrics are OK"--does that mean you checked for spark?

When you say it "doesn't run"--what exactly is it doing? Starting but dying, cranking but not starting, not even a sputter, or cranking, sputtering, but not starting to run?

If there's crud in the carbs, it would have to be pretty bad to prevent even a sputter. If the carbs are reasonably clean, put together right, the float bowls are filling, and the ignition is working, plugs are not fouled, and initial timing is OK, it's pretty much gotta run. So, in my mind, these are the things to check.

 

[dklawson]

I might add that a useful "tool" for the job is to use the little red tube on the carb-cleaner spray nozzle to spray down into the jet with! :wink:

That's a good point. I just assumed the spray tube would be used. It's really necessary for cleaning down in the jet tubes.

On a similar note I will share a recent personal experience. For years I bought "store brand" spray carb cleaner. No more. The last two cans I bought from Advance Auto do not touch carb varnish or gum... AT ALL. It is like spraying water on there. I have gone back to buying national brand carb cleaner. Costing less doesn't mean much if the product doesn't work and you end up "buying it again" to get the job done.

 

[JamesWilson]

When you say "electrics are OK"--does that mean you checked for spark?

Yes, indeed. The issue was that I pulled it out from the garage and let it sit outside for roughly two weeks and during that period it seems that water from snow that laid on the car and subsequent rain got into the fuel tanks. I drove it over to a friend's to pull the engine and swap geraboxes and it ran very raggedly there and back. Then, it would start and run OK at idle but when would stall under load for no apparent reason.

Previously it had run fine, and I checked dwell, which was right, the timing I'd checked and it too was right, I checked the coil and it was ok. I pulled all the plugs and wires in turn and they each would spark when grounded. About the only thing I didn't check was the condensor, but those seldom fail and wouldn't cause such extreme problems if they did, I believe. I checked the fuel pump and that fuel was getting to the carbs and then I discovered that there was water in the fuel.

I siphoned all the old fuel out, ran the pump to clear the lines and used rags to dry the float chambers.

I filled the tanks with new fuel, installed a new glass-bowl type filter/pressure regulator and it's showing fuel pumping in that's clean and fuel being delivered to the carbs, with the float bowls are filling properly, it seems.

My first inclination was to suspect the electrics, but they seem OK; I then thought that the fuel delivery was messed up, but everything up to the float bowls seems OK.

I'm going out now to see what works, or not....

 

[Guest]

Is anyone else enjoying the irony of the fact that the ~first~ time I ever say don't take a short cut everyone else does?

 

[JPSmit]

so?