View Full Version : Turns over but won't start

01-28-2005, 11:14 PM

I'm trying to start my TC2500 for the first time in ages. It turns over and over but won't fire at all. I tried squirting a quick-start aerosol into the carbs, and that gave a brief firing-up but then it died again. There is fuel in the float chambers. There is spark. Any ideas please?

p.s. how do the cylinder thingies in the carbs get moved up and down?

Webb Sledge
01-28-2005, 11:21 PM
Remember that engines take 3 things to start and run: air, fuel, and electricity. If it's getting all three, it will run. Given that you sprayed stuff into the carbs and it ran then died, I'd say you have a fuel flow problem. Check your jets and mixture adjustment.

I'm not real familiar with all the intricacies of carbs, but it sounds like you're talking about the floats, which control fuel flow to the carbs. Very similar to your toilet, when they fill up enough the float will rise and cut off the fuel flow. When it drops enough, it opens up a valve and lets more in.

01-28-2005, 11:28 PM
Wombat, how long has it been since you last started it? It could be clogged jets or stuck needle valves, or a bum fuel pump.
The pistons in the carbs are moved by vacuum.(Actually by differential pressure.) Make sure they are moving freely, as when they rise, it pulls the needles from the jets allowing fuel to flow.
Are the chokes working properly?

01-28-2005, 11:36 PM
Thanks guys. It's been at least 8 months since I started it (maybe longer). The pistons in the carbs are moving freely. How do I check if the chokes are working properly?

01-29-2005, 12:09 AM
SU choke is very simple -- when you pull the cable, it pulls the jets down on the bottom of each carb. Simply gaze at the bottom of each carb, then go in and pull the choke, then look again. You'll see a difference. By pulling the choke/moving the jets down, more fuel gets by the needle at idle.

If your fuel pump has a priming lever (it's a little lever on the bottom of the fuel pump) pull it a few times. It's very possible that there's not enough fuel in the float chambers, and there's not enough fuel in the line for the pump to get it all in there without some priming (or a ton of cranking of the starter.)

You might also make sure there's no junk in the bottom of the SU float chambers and look into the fuel pump sediment bowl to ensure nothing is blocking the fuel flow.

If you spray some starter fluid in both carbs, pull the choke, put your foot to the floor (hold it so the throttle is totally open) and start it...and if it runs for a second on the fluid then dies as it is used, I'd guess you either have a fuel line block or your fuel pump needs to be rebuilt/replaced.

01-29-2005, 12:28 AM
Wombat, I'm not really that familiar with the 2500TC carbs, as we didn't get them in the States. Does that have Strombergs on it? I think it's time for more experienced hands to jump in here.

01-29-2005, 03:45 AM
OK I've taken the carbs off to inspect them and here's what I know so far...

I definately have spark and compression. That just leaves fuel as a problem.

The fuel pump is definately working, and filling the float chambers with fuel.

The choke is working: when I pull the choke knob out the brass bit in the bottom of the throat (i.e. the jet) moves down (on both carbs). The choke also opens the throttle a tiny bit, via a cam pushing on a grub screw.

The pistons in the carbs move freely up and down. Normally they rest in a fully-down position.

The float chamber needle valves are OK: I can blow through them when the floats are down, and moving the floats up cuts off the flow as expected.

The fuel flows freely from the float chambers to the throats: when I fill the float chambers with fuel then tip the carbs to the side I can see the fuel rushing out of the jets into the throat (through the middle of the bit that the choke moves down).

So it all seems to be working as intended, but I must have missed something!

p.s. these carbs aren't like any I've ever seen on other cars: there doesn't appear to be any idle jet, and it looks like the throttle (when closed) completely shuts off the throat, which sems odd.

01-29-2005, 11:21 AM
Wombat, sounds like you are on the right track, just one more little item, is the gas old or did you mix some new in with the old. If this is in fact what you did, let the fuel run out of the tank for a quart or two as the old fuel will settle on the bottom right where the line picks it up. Wayne

01-29-2005, 02:37 PM
Wombat, You've proved that it must be a fuel problem by starting it briefly on an alternate fuel source.
Most fuel problems are related to the fuel level in the float chambers as controlled by the needle valve being pushed on by the floats.
Assuming there is no evidence of petrol running out all over the place then the chances are that the float chamber level is too low rather than too high. I would suspect that the pressure from the fuel pump might be marginal or a blockage in the delivery line, or as trrdster2000 says it could be bad petrol (that's the 1st thing to check).
Bad/leaky fuel pumps are not uncommon and often appear to be normal unless you test them.
Of course it could just be that in Australia the fuel swishes the wrong direction owing to coriolis effects which the carbs wern't designed for :-)
Good luck, let us know how you are getting on.

Geo Hahn
01-29-2005, 09:02 PM
I definately have spark and compression. That just leaves fuel as a problem...

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Maybe, maybe not. I would check the point gap and then the static timing as spark will do you little good if these aren't in spec. The starting fluid is much easier to fire than normal fuel/air so a poor spark or timing could work for it but not for gas. I have known points to lose their gap after sitting a long time. If the gap becomes small the spark is weak and timing is retarded.

01-30-2005, 05:14 AM
Q. When is fuel not fuel?
A. When it's really old!

I've got it running by draining & flushing all the old fuel out. With fresh fuel it started first time, with less than half a second cranking.

Thanks for all your help and suggestions. This weekend I've learned a lot about the fuel system and carbs in my Triumph, and I reckon next time encounter a fuel problem I'll be able to figure it out for myself. Thanks!