Baseline settings for triple OERs

[AK260]

Hello wise ones.

 

I have a friend who is about to install his triple OERs onto a brand new high-end engine for his first start up and initial run-in.

 

 

 

But given what a critical time those first 20-30 mins are, there isn’t much latitude for messing about to get them dialled in.

 

So, I have advised he starts with his good known SUs set a little richer (say 3 turns down) than previously to account for a more thirsty engine and then once initial run-in is complete, he can swap them out. Also easy to get the adjustment right quickly with his afr guage.

 

However, what if? What if he threw on the OERs and kept them there from the very beginning? How do you set them up so that the engine starts and is able to rev out to say 4k rpm without being overly lean or rich?

 

Has anyone set a “base tune” on these carbs either off the car or with the engine off and is there any advice for my buddy?

 

My assumption is that you can turn all mix screws out equally from closed to a ball park / best practice first setting, balance the throttles to “nearly there” using a feeler gauge.

 

Or is it just a bad idea to start the engine and run-in with the OERs?

 

I know there are different / opposing religiously held views on how to run-in an engine but that’s almost irrelevant as the engine builder has recommended the start it and hold it at xK rpm for y minutes. (My personal church preached a different method but let’s not get into that as it will divert us from our purpose).

 

Or indeed, am I asking a question asked many times before and can be pointed to a previous thread?

[Patcon]

I would use the SU's if the engine isn't too wild. I think it will be hard to get the OER's close enough

[heyitsrama]

Borrow the OERs from him and let him borrow your nice SUs. :^) 

[jonbill]

sell the OERs and get ITBs and injection. 

[AK260]

42 minutes ago, heyitsrama said:

Borrow the OERs from him and let him borrow your nice SUs. :^) 

I like the way you think!!!! 👍

 

22 minutes ago, jonbill said:

sell the OERs and get ITBs and injection. 

And there speaketh the voice of experience! 

[AK260]

16 hours ago, Patcon said:

I would use the SU's if the engine isn't too wild. I think it will be hard to get the OER's close enough

I have to agree with that - but never having set up a set of triples, I wasn't sure if I was being pessimistic 😉

 

[Patcon]

Lot's of jetting in DCOE style carbs. Somebody really familiar with DCOE's might get the jetting pretty close first try but I would try it. Much less getting them balanced on a break in run. The nice thing about SU's is their simplicity. Mixture is easy to fatten up or lean out.

I will violate religious protocol and say I'm not sure how critical a continuous break in run is. I have broken in a number of engines and never had a failure due to the break in period. These engines are incredibly tough...

[datsun-man]

the oers are far better than itbs having had a rebello engine on oers no contest 

[Patcon]

I would expect ITBs to surpass all carbs.

Fuel injection is almost always superior to carbs if tuned properly

[datsun-man]

sorry to disapoint you but that is a myth i have the pleasure of putting to the sword i current have webbers  on my z be oers knock spots off them old school still rules

 

[jonbill]

Yeah, I don't think injection can necessarily beat well tuned carbs, but its a damn site easier to tune injection well. 

[AK260]

At the risk of starting a heated debate, please help me understand this - why can carbs be better than ITB / injection?

Except for the obvious other points, I had always understood that DCOE carbs suffer with reversion / standoff when the air pulses back and forth past the jet. Not forgetting low air velocity atomisation issues (read below 4k rpm) if not choked right down - which in turn takes away the benefit of better breathing up top. But an injector isn’t affected by how many times the air passes it back and forth or by the shockwaves in the same way as a carb jet. It just injects fuel once, at the ideal time and with great atomisation.

So what am I missing?

I’m not questioning factual experience but I’m keen to learn.