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It's alive!
by Anders Dinsen ... October 05, 2008, 07:58:10 am
As already revealed on the forum, the engine is alive. The carburettors actually work okay!

I ran the electric fuel pump to fill the float chambers, and checked for seeping fuel from the fuel lines. I then checked the bottom lids on the carbs, which were sealing well too. With no serious fuel leaks visible, I pumped the pedal one time and turned the ignition.

Nothing happened  Shocked
The starter didn't engage!

This was a sign of luck, but I must admit I didn't see it as such... it's a "known problem" (and one of the reasons I'm making a new engine wiring loom) and it is caused by a bad connection in the green connector in the engine room. A bit of twiddeling with the connector cured it and the starter turned the engine.

And it fired up! It died again, of course, but second time, I kept it running on the accelerator. I noticed that the engine was steady (good syncronisation). It took a few minutes before it could idle by itself, and the idle was then too low. But it idled Smiley

I did a quick run around the block to visit a fellow Matra owner (Bagheera, lives just 200 m from me) who popped by Friday night when he was walking the dog and I was doing the throttle cable. You have to share your successes Smiley

There was a loud clicking noise coming from the engine. I thought it could be either valve clearance (but why now?), or something stuck in the distributor. It turned out to be the vacuum advance mechanism on the distributor, which being fed from only one cylinder was banging back and forth as the engine was running. I cured this by fitting a stud with a smaller hole in the manifold, but the correct solution is to balance the pickup between two adjacent cylinders.

There was also fuel leaking out on top of the carburettor around the fibre seals on the banjo bolts and the cover for the integral fuel filter. Fuel pressure is about 30% over maximum due to the type of pump I run - I'm going to replace it with one that's "gentler" and correct, as this is critical on the circuit I have here, which does not include a return line to the tank. Fuel pressure is thus maintained only by the pump. I might implement a return line, but I think not as it will reduce the amount of fuel which the pump is able to supply. First solution will be to replace the fibre washers with the copper washers that were on the carbs when I got them, and a rubber o-ring on the lid. This will be able to withstand the pressure.

There was also a slight fuel leak from the starting mechanism. This is not uncommon with Webers that are inclined as they are here at 15 degrees. I will try lowering the float level and replacing the plungers that operate inside the carburettor to open and close the starting mechanism. For some reason, the starting mechanism (choke) didn't seem to have any effect on the engine's running, which could indicate that something is fundamentally wrong, but I can't imaging what it could be.

There is a flat spot and hesitation in the lower end. I did suspect the emulsion tube was too "lean", and it is probably necessary to change to one that puts the main circuit in operation earlier, but it could theoretically be fixed by the ignition by advancing it by a few degrees. Idle is very low (but it's stable), and a bit more advance will also improve that. Due to the close proximity of the first progression hole to the throttle plate, turning the idle screw will upset idle mixture and ruin progressen, so the way to increase idle is to drill larger holes in the throttle plates than those which are already there.

Noise level is very high. Running without the engine cover makes it worse of course, but I definitely need an airbox. Ram tubes are also needed as there's a lot of whisteling coming from the carbs and it could also improve the low end a bit if they are long enough.

Speaking of the noise, I noticed some "singing" or apparant resonance between the carbs. I know that the manifold does not align them correctly - the throttle shafts are offset by 1 mm or so, so they are not 100% syncronised over all throttle openings. Fixing this will require the manifold to be modified as the root cause of this problem is that the carb studs on the manifold are not located correctly. I will need help from a pro. I will therefore have to live with it for now, but I do think there is a problem.

I haven't adjusted idle mixture, which is next of course, and mixture checking with my colortune plug will also be done.

But it works Cheesy, and I'm sure I can get it running perfectly. I'll refit the old carb again to correct the problems that require the carbs to be removed from the engine, but it's my aim to tune them as well as possible on the road now.

It was a very good day, indeed! Cheesy
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