Hello and regards from Spain.

Recently I have installed a wide lambda air fuel ratio meter to my orion with CVH engine. My goal is to fine tune my Weber DCOM 40 carbs and I want to know what AFR is best for this engine.

I think at cruising I may be at 14.7 or 15 ? But at full throttle what is the best value? I think 12.5 or 12 but don`t know if this is correct or if this engine requires richer or leaner ratios.
Also what are good ratio when lifting the throttle? I think my pump jets are too small because the carbs came from a peugeot 205 rallye that has a 1.3 engine.

My engine is standard apart of the DCOM carbs, newman phase 1 cam and slightly ported head. Also my engine is post 86 so I have heart shaped combustion chambers.
Has anyone running this engine with DCOM carbs? I am running with the 1.3 jets, and the engine runs fine but I think it may be underfuelling.

Thanks in advance, any help will be appreciated.

 

Your best bet, and the cheapest in the long run is to get it on the rolling road, to get set up, a lambda is ok, but what you think the engine needs might not and most likely won't be what it works best with.
tabetha

 

you need to either get a load of jets or a set of small drill bits and some solder.
each jet is labelled and that refers to how many mm's the hole is, i.e. 115 would be 1.15mm.
you should aim for around 14.7-15 ish for cruising and idle, and head for about 13.5 for full throttle, any richer and you'll lose power and fuel economy would drop drastically.
you may have read about 12.5 afr, but this is for turbo engines to aim for as they need extra fuel to cool the mix and avoid det.
as for jet sizes, then sort the idle jets and then accelerator sides.
can't comment on the carbs you've got, but just test idle as is and cruise, if it's too lean then drill the holes in the jets a tad bigger, if it's too rich, then make a note of the jet size, fill the holes with molten solder and drill out a bit smaller than the previous size.
and try again.
you can get carbs mint within a hour or two, just try a setting and then go for a drive, the outlay on equipment has been made and now only a little cost on fuel and time to go.
not worth sticking on rollers really, unless they're cheap down your way.

hope this helps.

 

A few hours on the rollers is going to be a much better bet, so turbo engines need 12.5 to avoid det do they, depends on a LOT more than just that, my own car runs down to 11.6 at full throttle, but only runs 17.5psi, on low setting.
Up to you whether you want top piss about with jets, and then wonder if it is as good as it could be, as you have NO WAY of measuring any change you make, unlike a change that can be SEEN in BHP terms by your very own eyes on the rollers.
They certainly can be done on the road, and you can get a good job done with experience.
tabetha

 

Thanks for the responses, the rolling road is an option but here we have very few rolling roads. Also I am a student so my funds are very limited so I want to know what AFR is best at cruising and full throttle and tune my carbs around that.

The idle jets are actually sorted and the AFR is between 14 and 15 which is acceptable. Now I need to sort the main jet to get the most of my engine.

If anybody has a configuration for twin DCOM carbs on 1.6 CVH I`ll appreciate some help as I have seen DCOE configurations, but the DCOM need slightly differente jets.

Thanks again and regards mates!

 

rollers are better than road tuning, i totaly agree, but if on a budget and you want to learn more, then there is nothing wrong with road tuning on a N/A engine, turbo's are more complex as you say.
i was also just stating that certain engines tend towards certain figures, my cvh turbo ran about 12.3:1 at peak boost, down to EGT's, det issues, timing advance etc.
merely a guide to head for as all engines differ.
i did however get a very good level of tune out of carbs i've setup in the past on N/A and carb turbo setups.