Smaller engine Emission DHLA40s - Jetting

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Dig up this old post

 

Been too busy with uni work to touch the car recently but now easter is here i get a bit more time...

 

i managed to get hold of some .1 vents, a couple of .10 e-tubes and two 115 mains second hand over the past few weeks.

 

seems to me that smaller engines benefit from responsive/early e-tubes, and since the .10 is an earlier starter than the .11 (which i have) its heading in the right direction....... but the .8 tubes are earlier still and would perhaps be an even better choice?

 

for the main jets i see that often the emission carbs run slightly larger mains than non-emssions. this i assume is to do with the fact that main meters the fuel to the idle jet stack as well as supplying more fuel to the greater proportion of air as a result of holier tubes. dropping the mains to 115 on the .11 tubes would make it run perpetually too lean..... the lower numbered e-tubes are less holey and more responsive so they may well accept a smaller main. i assume the fuel metering to the idle stack will be unaffected? i think they did this on the smaller engined alfas....?

 

fitting the .1 vents will make the main jet stack more responsive and bring it on earlier in the rev range? am i right in thinking the emission carbs have longer progression phases than the non emssions due to the increased number of progression holes, fixed air bleeds and larger idle jets? would fitting the .1 vents mess the progression phase? my thinking suggests that there will be a "lump" of richness in the mixture at the point of progression to mains? hence here i would reduce the idles to the minimum allowable, say 57, to try and make it "fit".

 

airs no idea, but i doubt small airs will work with emission e-tubes

 

could you see making these changes will have any affect? i'd need to get two more mains and another pair of .10 e-tubes before that though. i know there's no harm in trying its just that i need to start looking at getting the car moving again. i'm still interested to find out if these emission carbs can be successful on small engines.

 

But saying that i still have money set aside for some non-emissions, any news on that pair dave?  ;D  ;D

 

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Right I had the car out today and spent sometime adjusting the float levels to the correct height as per the article. After driving it for a bit i checked the plugs again and they were still blackened, although not quite as bad as when i last drove the car around Christmas time. the car still felt 'flat' with a more wider throttle usage and after say 2500-3000rpm. i think the 128 mains are too big and will aim to drop down to something around 115 to see what happens. after all dave you suggested 110-112 mains for non-emissions so 115 will be a good start?

 

Sunday i'm going to look at testing the .1 venturis i picked up as spares, to see if the .11 tubes respond better. i'm not holding out on these though and would want to try an earlier starter. emission carbs aren't the most desired items, anyone here have any spare/unwanted .8 .10 (.9?) emission tubes they would like to get rid of?

 

I'll also see if a drop to the 57 idle makes a difference.

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It didn't go too well, after fudging around for a couple of hours with a poor idle I eventually discovered that one of the sets of floats had perished   The carb on cylinders 1 and 2 was perpetually drowning the plugs in fuel, bollocks. the carbs were fine when i last used them before christmas, time off must have ruined them.

 

But the good news is i have a acquired some non-emissions   so i'll try and get another set of floats for that carb and they'll be sold on for good...

 

I have two sets of .5 emulsions to use with the non-emissions and will consider getting the lower waist of one set machined down to .7s. A friend of mine is a development engineer for a valve company down in Poole and he has a lathe, or two, and offered to do it for me

 

What changes do i have to make to the .5 tube to make it a .7?

 

chris