Can ambient temperature affect mixture

[cliff.b]

Drove my 1500 Spitty about 130 miles on Tuesday and used the opportunity to coast onto a layby and take the plugs out after driving at speed for a good few miles. They were too white for my liking so I richened the mixture one flat on each carb and the performance was noticeably better. Checked again later and colour was improved but still lighter than I would like so a little richer still and further improvement to performance observed.

So, to my question. I was previously happy with the mixture but that was set in the summer when temperatures were hitting over 30C. On Tues it was about 14C so I was wondering, as cold air is denser, is that enough to change the mixture to a noticeable degree, or will it be due to something else?

[Pete Lewis]

yes it does   thats one thing from the 80s when they introduce a thermac valve in the air filter to always give a mix of hot/cold to arrive at the carbs at a steady 70F

so emmisions kept more stable than any old temperature intake

pete

[cliff.b]

8 minutes ago, Pete Lewis said:

yes it does   thats one thing from the 80s when they introduce a thermac valve in the air filter to always give a mix of hot/cold to arrive at the carbs at a steady 70F

so emmisions kept more stable than any old temperature intake

pete

Hmm, interesting. I will check it again next Summer when it is hot, if I remember to do it that far in the distant future 🤔

[NonMember]

Yes, this difference in mixture with ambient air temperature was the reason they fitted waxstat jets to the later carbs. If only they'd worked reliably.

[cliff.b]

2 minutes ago, NonMember said:

Yes, this difference in mixture with ambient air temperature was the reason they fitted waxstat jets to the later carbs. If only they'd worked reliably.

I was just thinking about that myself. I splashed the cash on the penny trick with mine lol

[Pete Lewis]

the thermac  idea has a vauum operated temperature sensed valve  that operated a flap to mixed hot air from the exhaust with cold air from outside to give a modulated steady 70f  

not easy to convert a triumph air box to add any gizmos inside 

the dreaded waxstat was triumphs( and others) way of some degree of air temrperature control

Pete

[cliff.b]

1 hour ago, Pete Lewis said:

the thermac  idea has a vauum operated temperature sensed valve  that operated a flap to mixed hot air from the exhaust with cold air from outside to give a modulated steady 70f  

not easy to convert a triumph air box to add any gizmos inside 

the dreaded waxstat was triumphs( and others) way of some degree of air temrperature control

Pete

Also, I presume that sort of setup wouldn't be able to compensate for ambient temperatures above 70f. So maybe the idea was to just limit the range of inlet temperatures that the carb had to cope with. Perhaps to allow a weaker mixture on the basis it would never have to deal with very cold inlet air 🤔

[daverclasper]

5 hours ago, Pete Lewis said:

yes it does   thats one thing from the 80s when they introduce a thermac valve in the air filter to always give a mix of hot/cold to arrive at the carbs at a steady 70F

so emmisions kept more stable than any old temperature intake

So, with older carbs, not an issue that can cause damage, when running a bit weaker in winter, if carbs aren't richened up a bit?

[NonMember]

No, it's usually fine. This is partly because the summer setting is normally slightly rich, and the engines are quite tolerant. It's more important to get it right for emissions reasons. Also, in winter, the engine probably doesn't get as hot, and most of the "weak mixture" problems are caused when things get hot.

[cliff.b]

So maybe best to choose an average, moderately warmish day to set up you carbs 🤔

[daverclasper]

On 20/10/2022 at 19:38, NonMember said:

No, it's usually fine. This is partly because the summer setting is normally slightly rich, and the engines are quite tolerant. It's more important to get it right for emissions reasons. Also, in winter, the engine probably doesn't get as hot, and most of the "weak mixture" problems are caused when things get hot.

Thanks, Great, as difficult to get this sort of info (even though, it's sort of basic)

[Wagger]

Peugeot and BMW used Kugelfisher mechanical injection way back in the late 1960's/early 1970's. It was quite easy to fit a 'Choke' cable to the enrichment lever. I did this but had to watch the tempeature gauge very closely in hot weather. I could really feel the difference in power when it was 'Spot on'.

Shame other manufacturers never adopted it. Once set, no fiddling necessary for over 50,000 miles.