DCD Weber problem

rubyalpine

rubyalpine

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Can someone please help me?
Ive got a 36DCD Weber on my R10 1300, which was running fine. I removed and re-fitted the cylinder head to fix a top end rattle and after re-fitting every thing, the car will not run. It fires up o.k. but will only run for a few seconds before flooding and cutting out. After all the usual checks, jet cleaning (with compressor), etc.
I tried it with the air filter removed and then noticed that the main jet discharge nozzle (was pumping out a lot of fuel while cranking and when running (1000 to 2000 rpm). This is causing the engine to emitt black smoke and then cut out. The needle /seat is almost new and no leaks in floats.

Acording to my limited knowlege and experience, I'm sure the main jet should not be operating at such low revs with no load. Whats even more puzzling is that I have tried 2 different carbs(after transfering the jets and choke tubes) and the still the problem persists! I have tried lowering the float level to 6mm in lieu of the specified 5mm, but the problem remains. I've stripped the carb and cleaned jets and fuel ways/air ways a half a dozen times....no luck.

I need help, or a box of matches!

Cheers,
Henry
 
Do a compression check, if 3 different carbs all splutter then revisit the cylinder head and valve timing.
Also check dizzy, could be a tooth out, or rotor not aligning.
 
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Alex, I doubt it's timing, a couple of times I got it to run for 2 to 3 mins and it was very smooth, until the plugs fouled up and it cut out.

Col, I suspected that too and have just fitted a new Facet elec pump, no difference.

Henry
 
Check needle valve attached to float, will probably have some grit in there causing flooding

Otherwise

Check out 36 DCD fix <click left
 
rubyalpine said:
It fires up o.k. but will only run for a few seconds before flooding and cutting out.
Click to expand...
Running for 2-3 minutes with retarted timing can also foul the plugs due to incomplete combustion.
Incorrect valve timing can also foul the plugs due to incomplete combustion.
 
I have run car without fuel pump by removing in-line fuse to pump; no difference.
I have stipped and cleaned needle valve 3 or 4 times.
New in-line filter fitted; not yet been on the road.
 
You say the main jet is flowing? Yeah you should only be getting fuel via the idle circuit.

Does the DCD have idle mixture along with speed adjustments? Get them backed all the way in?

Also check the linkage, I once had a linkage jammed against something forcing the throttle open enough to idle super rich then stall out.

And it has a choke? not open?

Oh and do you have that restrictor in PVC system. There is a little boss with a tiny orifice that sits inline that meters the pollution control stuff? Without that it will run like sh1t.
 
Bowie, I think your first statement is spot on! I have tried all positions for idle mixture, linkage checked, all o.k.

It has maual choke, not using in the warm summer weather. Ther is no "pvc" system, only breather pipe from valve cover to air filter, I have tried with connected and with it disconnected.
I tried advancing ignition timing but just runs rough and cuts out even sooner.
The root of the problem is main jet squirting fuel when running at low revs with no load. WHY?

Thanks to all for suggestions/recommendations, keep them coming.

HENRY
 
Curious. There can't be too many things that force an activation of the main jet circuit.

And you say you have tried 3x carbs? Sure it's not linkage / throttle / choke related? :S
 
I think the issue is with the needle and seat or too high pressure. I would fill a 500ml petrol in a tin and hold it high, gravity feed, start the car then and see how it idles and revs.
 
The other thing that you could do is hook up a fuel pressure gauge and see what the actual fuel pressure is.

The only other thing that I can think of checking is the float, has fuel leaked inside the float? An easy check is to shake the float and see if it rattles.

What ever the cause it seems like you have excessive fuel in the carby.
 
I am baffled that three carburetors can show the same symptom. Would be inclined to say the problem is not with the carby.

Secondly, I am baffled that fuel gushes out of the main jets. There is no direct passage out of the mains on any carby ever made directly down. Fuel has to go up, through the emulsifiers to a level above the float and then it can come down. Otherwise, your entire fuel bowl would never fill because all the fuel pumped in the bowl would drain directly into the engine. What powers the circuit is vacuum created by the engine sucking in air otherwise fuel would never make it past the emulsifiers. Similarly with the idle circuit (sometimes this is partly or entirely shared).

Which leaves one option, as many have implicitly assumed. Something is pushing/sucking fuel out of the bowl through the mains. But this is nothing to do with one specific carby, because three carbies have displayed the same problem (are we sure these other carbies were good runners?). Stupid question, I know but are we sure the emulsifiers are in? In three carbies, no less.

Which only leaves the rest of the fuel system, or other systems like others have already suggested.

Or is there another source of vacuum? Something not to do with the engine/cylinders? Or not directly anyway.

I have no idea what this other vacuum source could be, but then again I don't have the engine in front of me. Perhaps more investigation is warranted in this direction.

I would run a simple test just to make sure this horse is dead. Take the carby off, take the cover off the carby fill the bowl with petrol and see if fuel drains that way. Just sitting there.
 
Col, no fluid in float, all good.
I will try schlitz and Frans' ideas after xmas, too busy festive schedule right now.

Cheers, Henry
 
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I tried Frans' gravity feed idea: still no good, fuel still flows out of main jets and floods .

Schlits, if i leave fuel in the gravity "tank", it drains away into the carb and then who knows where! Must be going through carb to inlet manifold. There is no sign of fuel running down head/block, must be running into inlet then cylinder head. I tried another (used but good looking) needle and seat, but no difference.

If I don't get this sorted , I wont be having a happy new year.

Henry
 
Sooo it has to be coming in via the needle seat / float. Your carb bowl should remain full. Like, for weeks.
 
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rubyalpine said:
I tried Frans' gravity feed idea: still no good, fuel still flows out of main jets and floods .

Schlits, if i leave fuel in the gravity "tank", it drains away into the carb and then who knows where! Must be going through carb to inlet manifold. There is no sign of fuel running down head/block, must be running into inlet then cylinder head. I tried another (used but good looking) needle and seat, but no difference.

If I don't get this sorted , I wont be having a happy new year.

Henry
Click to expand...
Does not look like an over fuel pressure problem.

I would try this, remove the top off the carby and hook up the gravity feed can. put some fuel in a small container that the float will fit in (to simulate the float bowl). Put some fuel into the gravity feed container and watch what happens in the little container under the float.

If you get fuel coming from the needle and seat when the float is in the upper position you will have found your problem.
 
I tried Col's idea and fuel stops flowing with very minor upward pressure on float, seems like needle/seat is o.k.
But then this happened! I changed the plugs (the old ones very carboned up) and got the motor running. I warmed it up and set timing, idling mixture and idle speed, all running fine, no funny noises and instant pickup from idle to 4000 rpm. Revved and idled smoothly. Happy days! I left it to cool for an hour and then restarted it with a touch of the key, no problem, no throttle required.

The next morning (Sunday), I tried to start it up and back to square one, fired once and fuel poured out of main jet nozzle into auxiliary venturie, flooding motor and unable to start again. BUGGER

I have ordered a new "repair kit from EBAY , which includes new needle and seat, and will see what happens thereafter.

Henry
 
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Just another thought that I have had, is the hinge for the float nice and free and not jamming up when the float is in the lower position? The reason I ask is because I have had this happen to me on a DCOE carb in the past.

It seems weird that you have had to running fine for awhile and then it starts to play up as soon as you start it the next day.
 
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