New out of the box 45 DCOE's on a TMW manifold, Carter 4070 electric pump, 4 psi fuel pressure with pump running.

Engine fires but won't catch, plugs removed and are bone dry. Carbs full of fuel, evidenced by dripping.

Timing checked and re-checked.

Assumed float levels should be within spec from factory. Only modification was installing 165 main jets.

Fuel doesn't seem to be making it to combustion chambers...am I missing something obvious?

Thanks for any and all advice.

I wouldn't assume anything. You would think the levels are correct, but who knows. They could have installed some foam or other packing inside the float bowl to protect the floats/needle from handling damage. I'd check that first.

Frank

Mikuni-driven L24

Questions: Was it running ok prior to fitting the 45's? Have you altered the timing since fitting them? Do you pump the gas pedal prior to trying to start?

Check that the Accelerator pump jets are squirting gas into the chokes of the carby's. Use a mirror and light to look down the carby throats while someone flattens the gas pedal for you.

Also make sure the butterflies are opening when you press the gas pedal.

If you are getting fuel from the Accelerator pump jets then it should fire. You normally have to pump the gas pedal (quickly all the way to the floor) 4-5 times before trying to start, that is assuming you have not connected the choke cables.

I had similar problems with my Dellorto's and found the pump jets were blocked despite my cleaning and blowing air through before installing them.

Warren

Thanks for the responses. I'll be doing further examination today. As I mentioned, these are factory new carbs right out of the box.

This is a brand-new 12:1 engine, and the timing has been checked several times. In my past experience with Weber dcoe's, they have always been on the rich side, I've never encountered a set that don't even wet the plugs. Over the course of the several starting attempts made yesterday, there should have been fuel running out of the headers.

It's even more astounding that they are all doing the same thing, which makes me think that there may be some oddball "packing material" or whatever within the bowls...to me that seems unlikely but I'll tear one down today to verify.

Thanks again.

Edited September 7, 200816 yr by Kronoss

Removed carb 1 to verify accelerator pump operation...no fuel squirt from pump jets when butterflies pumped. Accelerator pump linkage bound up...lubricated linkage and was then getting fuel squirt during throttle pump.

Float level checked out okay, main jets clear.

Reinstalled carb 1, removed bowl covers on carbs 2 and 3, verified accel. pump linkage was free on both.

Ignition on, pump on...end result same. Intermittent firing but no start...plugs still dry.

Still something amiss in the carb starting circuit. Hoped to avoid pulling all three carbs off the manifold for a teardown, but now it seems unavoidable. So much for buying "new" carbs.

Got the thing started. Had to further massage the accel pump linkages...now getting a good pump shot across the board.

Thanks for all replies.

Just to reinforce the concept of "checking" even new carbs - when I bought a brand new set of triple webers some 4 years ago - we discovered loose ball bearings rolling around in the float chambers!

That's really strange for new Weber carbs. That's some kind of QC issue from the factory. Why should anyone have to tear down a new carb to see what's wrong? And they're not cheap. Go figure.....