Hot weather causing vapourisation?

[daverclasper]

Hi. put this in fuel section, though not sure if something else causing it.

In the past years during hot weather have had the old chestnut of car switched off and 10 min's later bit more difficult to start and stumbly/stalling when driving at low speed/stopping at junctions, lasts for a minute or so. (very, very hot weather, then stumbly etc, continuously while slow moving/idling etc.

Recently with warmer weather, has been more more prone to this, and today (pretty warm), has been worse than ever, using handbrake to stop it, then keeping up the revs to stop it stalling at junctions. Fine when on the move.

Mixture/timing has not been altered and seems normal with checks.

Only engine work done since last summer was fitting a used exhaust manifold (cheap and had better gasket surfaces than mine). I seem to remember that new one was noticeably lighter for some reason?, if so could be chucking out more heat at carb bowls?. Can refit old one, if need be.

Also fixed the cooling system not pressuring (as had never done so), so now car running cooler (from the gauge) in traffic, which should improve under bonnet temp and help this this, I assume?.

Can try a heat shield to help?, though wondered if anything else I should look at?.

Cheers, Dave  

Edited March 30, 2021 by daverclasper

[Iain T]

Dave, I think fitting carb heat shields is a good starting point. How do your plugs look? 

Iain 

[Nigel Clark]

I was out in my Scimitar GTE today and had exactly the same problem when in traffic. Fuel vaporization in warmer weather is certainly a problem with modern petrol.

The Scimitar' s Ford V6 is particularly prone to such trouble, work carb nestled in the middle of the V, fed by a hose that runs across the top of the left rocker cover, where it picks up plenty of heat!

For a Triumph inline engine, non-crossflow layout, carb heat shields will help. Also check the route of the metal fuel pipe that runs from the fuel pump, around the front of the engine above the water pump, to the carbs. Make sure it doesn't touch the block, cylinder head or water pump.

Nigel

[Pete Lewis]

changing the metal pipe in proximity to the engine for a rubber one  is  more insulating 

make sure your mixture is not on the rich side of OK     lean it a bit may help

Dave make sure the short hose on top of the fuel tank dip tube is good and not loose or sucking air 

Pete

[johny]

I know this might be a bit controversial but my hot tickover problems ended when I fitted a decent electric fan. Alright it had a new rad at the same time so does run cooler but the flow of hot air I can feel coming out of the engine bay when stationary now must help keep the carbs cooler...

[Peter Truman]

My Vitesse wth Stroms hasn't had issues with vaporization, but the daughters Mk2 Spit gave us grief several years ago I even pulled the head! The issue was the plastic bush that orientates the SU float bowl vertically had failed allowing the float bowl to rotate from vertical towards the exhaust manifold hence it was getting to hot and vaporizing the fuel.

I also fitted heat DIY shields pic's attached, notice the shiels are bolted behind the manifold flange so they can be removed without disturbing the carbs.

Also had vapor locks on a Series 3 XJ in the early 80's issue was the fuel filter was full of sh*t. In the mid 70's we had a 2500TC which from new always suffered vaporization on 38C plus days worst when in traffic, probably accentuated by the aftermarket air conditioning installed.

[Pete Lewis]

one easy way to increase air flow under the bonnet with a std fan set up ( as dave has) is to up the idle speed a bit 

I neve had any supposed vaporisation on my Vit 6 and with the 631 unwrapped  it would idle for hours never to miss a beat 

heat shields  are worth adding but im sure most vapourising is a myth its other effects showing themselves 

i would start by leaning it to best running and lean to drop 50 rpm so youre on the lean end of best 

 

[68vitesse]

See Pete added extension to the air filter stub pipes to pull cooler air through the grill rather than the hotter under bonnet air.

Regards

Paul

[johny]

yes as standard they came with flexible hoses fitted in a similar position but over the years most have been thrown out...

[poppyman]

The flexi piping can be had cheaply from fleabay as pond piping

 https://www.ebay.co.uk/itm/BLACK-CORRUGATED-FLEXIBLE-POND-HOSE-PUMP-GARDEN-PIPE-TUBE-FISH-MARINE-FLEXI/322205804990?_trkparms=ispr%3D1&hash=item4b04f669be:g:7ncAAOSwHnFVgXSB&amdata=enc%3AAQAFAAACcBaobrjLl8XobRIiIML1V4Imu%2Fn%2BzU5L90Z278x5ickk5v8gVt3hEWLVg%2F253w6XCc1PlmQo1UiHf8iPGqw%2B61XgF6lq9NlHbpP2iHLfg0s1cE%2BMHOGmg1zyI%2BZ1%2Bek4TkP2MVcz7cLkcP737gQiHhVRdA2qEIVJh%2F8TkAFKnAPjmHIsvoYheyz1kMZkJmF3RFooDt5Fm45nZywbqFCuKqMRED58opN%2BvgfvHWH4sTOvUDoF1iG8rxUh%2BRcQR05NROVfL4pyVURbPWwvhfFjk3SL2pbFjE993BD%2FpNwVOjqHa8PYggvklWhO6x0mPTGJfbQoqFdmmiCyZKhB6zQ0WTey%2FiH1IWrq8ATqExc%2FGTJIFbbrON12u4cxezP5mw4X50rEArQBmcdvybkfPtRv7yoj0QmZErGrZsFmFzjX3Pqzrs4oiGD1qYoIJbaKeJeEtZLmXSxw3RIZzAfRwBr%2BPl%2BdAsOn5CiCGI7pLeMMo9BrT51eQ77Ha40%2BcW%2F1azJu3gBAIPnC8TsgN8BvZ%2FTtxxhZ7sQkBTaFRS7e%2FwRIN77Xk7W2iALM2Y8o818dvdBDOEdk6b5tmvpLlXwOLf%2FW7Z5y7hSdE5y%2Fr1WNhUTw43TsaONHFU0vmVNyBltj8KEwd7%2BP96OuNVn5bRKUvzw57%2ByLJ0NMCo3agCBJn%2Beqjnq2StC8vgQmgQb7OIBNqeOIG03Dbw7PNdg%2F2KKmThkLx%2Brkqr4FOsNWSUJ76lfJ6ALOS6M0u2GAOOwIkvZtAJc8AkmlLRQ%2FYWAzgII1PBjUi5jMK9KwAycvwvIDu6GQ6fUr%2FDtoohd2OVEsIm8ngAnPwQ%3D%3D|cksum%3A3222058049903dc5427673fe44a98f96e55c4044e2c6|ampid%3APL_CLK|clp%3A2334524

Just measure the id, perfect for the job.  

Tony.

[Pete Lewis]

mine were just waste pipe , pond pump hose is good  especially if the inside is not all a convoluted helix  smooth walled is the preferred 

cold air is King 

pete

 

[johny]

9 hours ago, poppyman said:

The flexi piping can be had cheaply from fleabay as pond piping

 https://www.ebay.co.uk/itm/BLACK-CORRUGATED-FLEXIBLE-POND-HOSE-PUMP-GARDEN-PIPE-TUBE-FISH-MARINE-FLEXI/322205804990?_trkparms=ispr%3D1&hash=item4b04f669be:g:7ncAAOSwHnFVgXSB&amdata=enc%3AAQAFAAACcBaobrjLl8XobRIiIML1V4Imu%2Fn%2BzU5L90Z278x5ickk5v8gVt3hEWLVg%2F253w6XCc1PlmQo1UiHf8iPGqw%2B61XgF6lq9NlHbpP2iHLfg0s1cE%2BMHOGmg1zyI%2BZ1%2Bek4TkP2MVcz7cLkcP737gQiHhVRdA2qEIVJh%2F8TkAFKnAPjmHIsvoYheyz1kMZkJmF3RFooDt5Fm45nZywbqFCuKqMRED58opN%2BvgfvHWH4sTOvUDoF1iG8rxUh%2BRcQR05NROVfL4pyVURbPWwvhfFjk3SL2pbFjE993BD%2FpNwVOjqHa8PYggvklWhO6x0mPTGJfbQoqFdmmiCyZKhB6zQ0WTey%2FiH1IWrq8ATqExc%2FGTJIFbbrON12u4cxezP5mw4X50rEArQBmcdvybkfPtRv7yoj0QmZErGrZsFmFzjX3Pqzrs4oiGD1qYoIJbaKeJeEtZLmXSxw3RIZzAfRwBr%2BPl%2BdAsOn5CiCGI7pLeMMo9BrT51eQ77Ha40%2BcW%2F1azJu3gBAIPnC8TsgN8BvZ%2FTtxxhZ7sQkBTaFRS7e%2FwRIN77Xk7W2iALM2Y8o818dvdBDOEdk6b5tmvpLlXwOLf%2FW7Z5y7hSdE5y%2Fr1WNhUTw43TsaONHFU0vmVNyBltj8KEwd7%2BP96OuNVn5bRKUvzw57%2ByLJ0NMCo3agCBJn%2Beqjnq2StC8vgQmgQb7OIBNqeOIG03Dbw7PNdg%2F2KKmThkLx%2Brkqr4FOsNWSUJ76lfJ6ALOS6M0u2GAOOwIkvZtAJc8AkmlLRQ%2FYWAzgII1PBjUi5jMK9KwAycvwvIDu6GQ6fUr%2FDtoohd2OVEsIm8ngAnPwQ%3D%3D|cksum%3A3222058049903dc5427673fe44a98f96e55c4044e2c6|ampid%3APL_CLK|clp%3A2334524

Just measure the id, perfect for the job.  

Tony.

My 2L Vitesse MK1 has 1 3/8" (~35mm) OD airbox intake pipes and I cant find that pond hose in a suitable size. The 32mm can be bodged on with heat and force but I wonder if the 40mm OD electrical flexible plastic conduit thats available wouldnt be a better fit...

[poppyman]

You can get the right stuff Johnny  https://www.ebay.co.uk/itm/35mm-1-3-8-ID-40m-OD-Flexi-Pipe-Tube-1-metre-Exhaust-Flexible-Excellent-Quality/274263527383?epid=2205266000&hash=item3fdb614fd7:g:YVoAAOxyqUpQ8B0e

But look at the price, the pond hose went on my dolly with no problem, just warmed up as you say.

Tony.

[johny]

hmmmm think I'll try the conduit and report back...

[Pete Lewis]

you can make a lot from  8ft  of 40mm waste pipe  its cut and chop to go round things  thats tricky 

flared the end with hot air gun and push  over the end of  a socket .

but used pond pump hose on the 2000 as tube passes through an aperture and you have to allow for engine  movement 

pete

 

[Mathew]

I have tried the sheild between the carbs and still had it. First thing if you have waxstat jets is to ditch the wax capsule and replace with a penny. Then as everyone else is saying cold air flow, i had k and n's so got some 4 inch silver foil house ducting and a scoop to under the carbs . This supplied cooler air just where its needed.

[Clive]

A friend who has been a pro mechanic, and also owned Vitesses since the mid 60's (so knows them pretty well) started having fuelling issues a couple of years ago. Made the car undrivable. 

After much faffing and trying different ideas, the think that solved it was insulating the fuel pipes in the engine bay, and I think he tweeked the routing slightly.

I have wondered if using a fuel return pipe would help, it would need a restriction to make sure te carbs were kept full. But other cars do use a fuel return. It would drastically reduce the time the fuel spent in the pipework. But of course, my spitfire already runs the fuel at about 60-80psi, with a return so no problems for me😁

 

[Mathew]

1 hour ago, clive said:

A friend who has been a pro mechanic, and also owned Vitesses since the mid 60's (so knows them pretty well) started having fuelling issues a couple of years ago. Made the car undrivable. 

After much faffing and trying different ideas, the think that solved it was insulating the fuel pipes in the engine bay, and I think he tweeked the routing slightly.

I have wondered if using a fuel return pipe would help, it would need a restriction to make sure te carbs were kept full. But other cars do use a fuel return. It would drastically reduce the time the fuel spent in the pipework. But of course, my spitfire already runs the fuel at about 60-80psi, with a return so no problems for me😁

 

That would require a pressure relief valve , running an electric pump. I do remember someone moving the fuel pipe from the back of the engine to the front. My 2500s has it at the front.

[Clive]

40 minutes ago, Mathew said:

That would require a pressure relief valve , running an electric pump. I do remember someone moving the fuel pipe from the back of the engine to the front. My 2500s has it at the front.

I was wondering if putting something like a restrictor (eg solder the return pipe solid, then add a 2mm hole?) would suffice to keep the carbs full. It would solve the issue of the repro mechanical pumps producing too much pressure too. A quick search throws up this, which looks remarkably like a simple T with a small jet screwed in one outlet https://classiccarbs.co.uk/product/weberdellorto-carbscarburettor-fuel-return-t-piece-re-stricter-union

[johny]

Yes youve got to ensure that there would still be enough flow to the carbs for sustained full load (long uphill stretch on a motorway?) so I think adjustability of any return orifice is essential....

[Nigel Clark]

1 hour ago, clive said:

I was wondering if putting something like a restrictor (eg solder the return pipe solid, then add a 2mm hole?) would suffice to keep the carbs full. It would solve the issue of the repro mechanical pumps producing too much pressure too. A quick search throws up this, which looks remarkably like a simple T with a small jet screwed in one outlet https://classiccarbs.co.uk/product/weberdellorto-carbscarburettor-fuel-return-t-piece-re-stricter-union

The Weber 38DGAS carb on my Scimitar has exactly that setup as standard, with a return flow via a small restricted orifice, the return pipe going back to a separate connection to the fuel tank.

That's with an engine-driven mechanical fuel pump.

Nigel

[daverclasper]

9 hours ago, clive said:

After much faffing and trying different ideas, the think that solved it was insulating the fuel pipes in the engine bay,

Interested in this one, as I was thinking of slitting fuel hose down the length and wrapping the metal pipe?. What did he use?.

[daverclasper]

7 hours ago, johny said:

Yes youve got to ensure that there would still be enough flow to the carbs for sustained full load (long uphill stretch on a motorway?)

Also this one. Have at times had some miss firing, that felt like fuel starvation on long motorway inclines.

I guess to bowl fuel level lowers at bit at that angle, or is it "something completely different"?.  

Edited April 2, 2021 by daverclasper

[Pete Lewis]

17 minutes ago, daverclasper said:

 slitting fuel hose down the length   (it was Clive) 

so  back to why not just replace the metal with rubber  hose    ???? as it doesnt conduct the heat 

Pete

[daverclasper]

Well yes Pete. Though, thought a quick? wrap around in summer and take the bits off in winter and check any pipe corrosion (steel on mine).

Your idea may well be more simple, though just about the more rubber to metal joints (is there?), pos failers of these, and the lasting qualities of rubber hose comparted to steel, even the good stuff (was thinking of using any old crap for this insulation purpose.

Don't really know

Cheers, Dave     

Edited April 2, 2021 by daverclasper