Starting

[Ian Cooper]

Can I conduct a 'straw poll' please?

I have a MkII GT6 which runs sweetly, has been rolling road tuned and is absolutely glorious except when starting.

Has anyone out there got a Triumph, running twin CD150s, that starts first pull without priming?

 

With priming mine will start first pull but without it needs loads and loads of cranking, so if you've got one that starts, what is the secret please?

[Colin Lindsay]

If you need to prime the fuel then I'd guess the pump is allowing the fuel to run back, probably due to worn valves or incorrect valve seating and without priming, the pump first has to get the fuel to the carbs under the power of the starter before it will run. You could replace the pump / valves to create a better seal, or fit a non-return valve into the fuel line close to the carbs.

[Pete Lewis]

much to do also with modern fuels evaporate quicker, the float chambers are open vented and the bowls soon drop fuel levels 

so you have to wait till it refills before it will start.

drain back will not take fuel out of the float chamber , evaporation does ,

you could fit a low psi electric pump or just hand prime as you have found that works 

might be worth checking the float heights  at 18mm  

have you checked the choke discs are all clear of corrosion ??? 

i take it its only cold starts after inactivity ???

and are these CDSE with temperature compensators  as if they are open when should be closed you cannot set the mixture 

and at idle can just be too weak as the bypass is open 

Pete

Edited May 30, 2023 by Pete Lewis

[Ian Cooper]

Hi, thanks for the responses guys.

I've tried a brand new fuel pump and also refurbed my original pump with new valves etc, tried fitting a one way valve and really there is no improvement, leave it overnight and back to cranking. don't have the compensators and, as she will go on priming, I'm pretty sure the 'choke' discs are good. So I guess I'll put it down to evaporation and say no-one has cracked it🤔

[Ian Foster]

Ian

I have a Huco electric pump on my mk2 (as I was having hot running issues), which primes the carbs as soon as the ignition is switched on. (I do have 175 CD2 carbs, so not quite standard)

It's surprising how much fuel is heard gurgling into the carbs, so there must be a fair bit of evaporation from the float bowls.

Do you have the separate choke spindles or a starting box on the front carb?

Ian 

[johny]

12 minutes ago, Ian Foster said:

It's surprising how much fuel is heard gurgling into the carbs, so there must be a fair bit of evaporation from the float bowls.

Yes even in the early 70s California was horrified with the carb vent arrangement...

[dougbgt6]

Ian,

I have the same problem at the moment, it used to be OK but now, churning and churning to start. I grudgingly decided to do something about it at the last Area meeting parked next to Andy Cook's GT6. He got in, turned the key, and Varoom! I waited for him to leave to save embarrassment 

I've checked spark and  compression, all OK. It used to start OK and timing hasn't changed and it runs OK when started, so not timing?

I've a one way valve in the fuel line having suffered drain back and found a new pump no better than the original.  The pump is getting fuel to the carbs but a slight smell of fuel. So I've replaced the "O" rings in the reservoirs and opening them up, yes they're now retaining fuel. So why won't it start?

Air leak? I've taken off the temperature compensators and sealed the holes with tape, no difference. However I think I will take Uncle Pete's advice and block them off all together, turning the manifold gaskets gaskets top to bottom does it, apparently.  Next, new manifold gasket. I hope to get around to that today.

I'll let you know how I get on.

Doug 

 

[Gully]

Seems I'm one of the lucky ones! Mine has generally always started 'on the button', even after a few weeks of inactivity. Evaporation does play a part - in hot weather, if it's been a couple of weeks without starting, it might kick and stop, then start immediately on second pull, but otherwise I pull the choke out and it starts straight away.

The only failures to start for me were a fuel pump diaphragm failure (after 2 months stored in my parents' garage) and a fuel pump valve failure (again, whilst stored in my folks' garage when building work was occurring at home).

Something I have done recently is replace the short lengths of rubber fuel hose connecting the rigid sections around the carbs - might be worth checking that they're not deteriorating?

Gully

[Stratton Jimmer]

My Mk3 has a Triumph Tune engine but has been fitted with a pair of HS4 SU carbs. First start of any day involves around five or six, three second bursts on the starter and full choke. Thereafter it starts first time every time without the choke.

[Pete Lewis]

as the myths that surround drain back cannot take or return fuel to the tank if the bowls drop in level till you prime it then 

it can only be evaporation or a float bowl leak there is no alternative 

Pete

[Iain T]

My front carb even after a full professional refurb leaked. I had assumed it was the jet housing O ring but on inspection it was the bowl gasket. A clean up and nipped up the screws and (up until yesterday) dry as a bone and the engine bay now doesn't pong of fuel. 

I agree even with a Huco I leave it a good 20 seconds to prime the carbs as the petrol does evaporate. 

Iain 

Edited May 31, 2023 by Iain T

[johny]

19 hours ago, Pete Lewis said:

as the myths that surround drain back cannot take or return fuel to the tank if the bowls drop in level till you prime it then 

it can only be evaporation or a float bowl leak there is no alternative 

Pete

Yes and additional non return valves dont help because they just add another resistance for the pump to overcome....

[chrishawley]

On 30/05/2023 at 09:43, Ian Cooper said:

Has anyone out there got a Triumph, running twin CD150s, that starts first pull without priming?

My GT6 (150CDSEs, Facet Pump, conventional points) starts pretty much on the button even when cold or after layup. So such a thing is possible.

Hard to point to, or lay claim to, any special factors; but pre-engaged starter, beefiest battery possible and trickle charging may help things along. Perhaps another thing for consideration is the precise relationship between the enrichment mechanism (whatever form that takes) and action on the butterflys; such that first movement of the choke cable gives a predominance of extra fuel over butterfly opening. Can be worth a look.

[Mark B]

Had similar problems on my gt6 mk2 for years if not used for a while. It always started after a time, so never really looked for the cause after replacing all the obvious parts, and assumed it was Down to worn engine. Then I read Nicks thread, https://sideways-technologies.co.uk/forums/index.php?/topic/9896-stromberg-cold-start-device/ In my case it was already on the winter setting, but I did find I wasn't getting full travel when the choke was operated. After a cable adjustment, the extra 1/4" travel of the choke, made all the difference, and now starts  a lot easier.

Edited June 1, 2023 by Mark B

[Pete Lewis]

yes  later CDSE can  have a small brass  push and twist adjustable stop to restrict choke travel  

its not really a summer winter adjustment but that would suit the explanation 

Pete

[Iain T]

On 01/06/2023 at 10:42, chrishawley said:

Perhaps another thing for consideration is the precise relationship between the enrichment mechanism (whatever form that takes) and action on the butterflys; such that first movement of the choke cable gives a predominance of extra fuel over butterfly opening. Can be worth a look.

A good point. On my 150cds with the disc choke I had to increase the screw gap so I had more disc rotation and therefore enrichment and only 1200rpm on full choke. You shouldn't be able to get 2000rpm with the choke full out. 

Iain 

[Ian Cooper]

Just a quick follow-up. I removed the 'new' fuel pump, refurbished the original pump and refitted it, I then opened up the float chambers, cleaned and checked the free movement of the floats and shut-off valves (the floats were sluggish/sticking on the front carb) reassembled all and now, miraculously NO CHURNING😁 she always fires first or second pull🤗🤗😁