Club Triumph

Hi All,

Have been putting back together a GT6 Mk3 over the last few years. Got to a point of starting up the engine only to find things not quite so good, so over the winter months removed the cyl head  only to reveal that the head gasket must have blown at some stage in its prior life out on the road. ( some 14 years ago )

Have had the head refurbished by a local company in Pitstone, and now back on the engine ready to fire up the engine.

Good news is that the engine will fire up and run few a few seconds having floaded the carbs with fuel, then cuts out. we have fuel feeding the carbs all ok but obviously not further than the float chambers. On removal of both chambers found that the needle valves were sticking. Removed and recleaned ok so that they were free to move up and down.Again after initial flooding the carbs the engine starts up ok but soon runs out of fuel.Unable to see if fuel is getting past the main needles ! Even if the main needle jet is adjusted incorrectly surely the engine should run ! and then adjust eliments of carb as required !

Any ideas would be great fully received .

I can also be contacted on my Mobil 07756-442160

Hear from anyone soon,

Martin

OK, first off... if you're able to start it with the fuel in the float chambers (i.e. not using any spray-down-the-inlet tricks) then the fuel flow from the float chambers onward is working. So please be a bit more precise about how you're "floading the carbs".

Also, how long does it run for? When you say "soon runs out of fuel", is that half a second? Half a minute?

Hi Rob,

Thanks for your reply, to get the engine started it is by forcing fuel through the carb / inlet manifold. So engine will fire up for a few seconds until that has burnt that fuel off.

Dosn’t seem to be drawing fuel from fuel chambers up through the main jets.

Carbs have been thoughly cleaned out in special cleaner system and rebuilt, so still may need that fine tuning, but unable to do so as it’s not running long enough.

Back at home so I can call you if need be to have a chat

Cheers,

Martin

OK, so the next question is whether there is actually fuel in the float chambers. This is easier on SUs as you can whip the top off and look, whereas Strombergs need you to remove the bottom and spill petrol everywhere. If they're dry (or only have a dribble in) then you could have a faulty pump or the floats set way wrong, or the valves still stuck shut.

Where have you set the jets and/or needles to after the rebuild?

Do the dashpots lift and drop cleanly?

Is the cold enrichment device properly set up and connected?

The float chambers and both full with fuel. Also the float valves move up and down freely as do the pistons. The only thing we don’t know is if the jet is set up correctly in the piston. Waiting on the special tool to arrive. Is there a correct set up sequence to follow? Also would this stop fuel getting up there?

Fuel is drawn up through the orifice round the needle by the depression in the CD chamber. If the needle is too fat (e.g. has fallen out of the piston - a common fault on some later SUs, apparently) then no fuel will flow. If there's no depression (piston permanently lifted) no fuel will flow. If the float chamber vent is blocked, so that there is a depression inside the float chamber, no fuel will flow. Also, if you have a huge manifold leak, the engine will probably fire on a squirt down the intake but not draw enough fuel to keep running.

The correct initial setup is described in the WSM, I think, or search online. I know the SU / early Stromberg base line is two turns down from flush but that's for movable jet types, not the CDSE adjustable needle.

Went round everything and tightened it all. We have fuel to the plugs now as we just flooded it, so going to leave it a while and try again later. 

Still in the same boat, will fire on starter fluid but won’t draw the fuel through, really puzzled in where I’m going wrong.

When you say fire on starter fluid are you meaning easystart or similar? and how fresh is the fuel that is being drawn from the fuel tank. Petrol can go stale in a matter of months and stale fuel is only fit for cleaning parts.  

Hi, Having had the same problem some time ago sympathise!!

In my case it was sloppy re-assembly in that I had connected the choke on the Strombergs 180 degrees out, so the choke wasn't working! Once sorted it started OK.

Sounds silly but maybe worth a re-check?