Ian Cooper Posted May 30, 2023 Report Share Posted May 30, 2023 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? Link to comment Share on other sites More sharing options...
Colin Lindsay Posted May 30, 2023 Report Share Posted May 30, 2023 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. Link to comment Share on other sites More sharing options...
Pete Lewis Posted May 30, 2023 Report Share Posted May 30, 2023 (edited) 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 Link to comment Share on other sites More sharing options...
Ian Cooper Posted May 30, 2023 Author Report Share Posted May 30, 2023 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🤔 Link to comment Share on other sites More sharing options...
Ian Foster Posted May 30, 2023 Report Share Posted May 30, 2023 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 Link to comment Share on other sites More sharing options...
johny Posted May 30, 2023 Report Share Posted May 30, 2023 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... Link to comment Share on other sites More sharing options...
dougbgt6 Posted May 30, 2023 Report Share Posted May 30, 2023 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 Link to comment Share on other sites More sharing options...
Gully Posted May 30, 2023 Report Share Posted May 30, 2023 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 Link to comment Share on other sites More sharing options...
Stratton Jimmer Posted May 30, 2023 Report Share Posted May 30, 2023 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. Link to comment Share on other sites More sharing options...
Pete Lewis Posted May 30, 2023 Report Share Posted May 30, 2023 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 Link to comment Share on other sites More sharing options...
Iain T Posted May 31, 2023 Report Share Posted May 31, 2023 (edited) 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 1 Link to comment Share on other sites More sharing options...
johny Posted May 31, 2023 Report Share Posted May 31, 2023 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.... Link to comment Share on other sites More sharing options...
chrishawley Posted June 1, 2023 Report Share Posted June 1, 2023 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. Link to comment Share on other sites More sharing options...
Mark B Posted June 1, 2023 Report Share Posted June 1, 2023 (edited) 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 Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 1, 2023 Report Share Posted June 1, 2023 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 Link to comment Share on other sites More sharing options...
Iain T Posted June 2, 2023 Report Share Posted June 2, 2023 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 Link to comment Share on other sites More sharing options...
Ian Cooper Posted June 25, 2023 Author Report Share Posted June 25, 2023 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🤗🤗😁 2 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now