Fuel starvation. Tiny washer in carburettor.

[Axolotl]

This had me baffled for a bit, but the cause and cure may be useful to other people with the same symptoms.

I'd been getting an occasional misfire, which I'd worked out was due to "tea leaves" (dirt) in the carburettor bowl occasionally blocking the jet tube where it exits from the bowl.

I took the lid off the bowl and removed the tube at the bottom so I could clear it out. Sure enough, there was sufficient crud in there to have caused the intermittent misfiring. I cleaned it all out and reassembled the carburettor. Result, no misfire, but no power either.

It started fine, tickover was fine, but I couldn't get above 60 on the flat, and the slightest incline felt like I had an 803cc engine, not 1098.

It turned out that in reassembling the jet tube to the bowl, I'd got the little rubber washer/grommet out of alignment so it was squashed sideways instead of square-on to the tube. In that position, it was masking some of the diameter of the tube, so that not enough fuel could flow through at full throttle. I should have known, because it leaked petrol at first, and I had to tighten it more than I was expecting to stop the leak.

Cure was a new washer from a service kit, carefully lined up in the hole in the bowl with the aid of a small screwdriver before I fitted the tube in place.

Does anywone know how you are supposed to fit this tiny thing?

[wibble_puppy]

yikes! thanks for the tip, axolotl. *goes off to check own carb assembly*

[Packedup]

Fit the rubber seal into the hole in the chamber, making sure it's square.

Push the end of the jet tube into it, you'll feel a positive soft thunk as it slots into place. Screw in the 7/16 union till it feels like it's nipping the lot together nicely.

Worst case then is a slight leak from the joint, just tighten the union a little more till it stops.

The above works for me

For cleaning out jets I now use a syringe from an inkjet printer refill kit. The needle is nice and long and the syringe holds about 25ml. I fill it with petrol, take the top off the carb and stick the needle down the jet. Then squirt petrol back through into the float chamber, and drain the fuel and any crud with either a normal syringe without needle, or lots of kitchen roll.

[alex_holden]

I use a cheap inline fuel filter to stop crud getting to the carb in the first place. It has a transparent plastic body and I can see loads of dirt inside. The mesh filter in the pump will stop the big lumps of rust but not fine particles.

[Axolotl]

inline fuel filter

Yes, I'm thinking about getting one. Trouble is, I've just fitted a new armoured flexible fuel pipe, so there's nothing to cut in half to fit the filter. I replaced the pipe because some of the crud appeared to be bits of rubber from the lining of the old (original) pipe.

Guess I'll need to buy a non-armoured one as well and use a small section to fit the filter to.

Pump-armoured pipe-filter-non-armoured section-carburettor?

[rayofleamington]

I should have known, because it leaked petrol at first, and I had to tighten it more than I was expecting to stop the leak.

yup - that's a dead giveaway that it's not gone back in correctly.

I cleaned out my carb half way to Orkney - also due to a missfire, and because it had probably never been cleaned out by the previous owner. Mine had the usual red sandy silt in the bottom - although more than the average car (the bottom of the bowl was choked full of it).
After doing that I delved in my box of 'road trip spares' to find the inline filter and fitted this in the middle of my (old) armoured fuel pipe. Armoured or not, a hacksaw will cut it in half ;-)

Needless to say - my missfire came back the day after That was only cured whe I worked out that I was doing 49mpg and not 44 that I'd previously estimated (error caused by a yet unknown combination of diff and speedo)

My only tip for the rubber seal: Fit it to the pipe first and then put both in at the same time - on mine I couldn't get the pipe to go through the washer so tried this way instead. I was very glad I'd not kept fiddling to fit the pipe into the washer whilst the washer was compressed in the housing.

[bmcecosse]

Bet that washer was an excellent economy device!