3.0CS jetting problem for m30b35

[72b35CS]

Hi everyone,
My fathers e9 3.0cs received a m30b35 5-spd transplant but maintained the dual zeniths from a 2.8L which were in better condition than the original 3.0 ones, my brother says everything is fine with the car he doesn't want me to try and fix it. But I know in theory the jets can't be the same, given the carbs are tuned for a 2.8 and now it's a 3.5 in there. I feel the engine just flatens out when reaching 4000 rpm when it should be pulling much better than it is, It can still reach 6300rpm but it takes forever. Can this lead to problems? If I install the jets from the 3.0 engine will this improve? Do I need to change all jets or just the main jets? or does it need bigger jets or drill existing ones? recommendations on the sizes?

Also when the engine is warm and you stop it for say 10 min, it doesn't start right away, as if the gasoline evaporated not like when it's flooded so it needs some insisting on the starter, could it be a stuck float? It also smells of gas in the car when you accelerate harder.


Hope you can help me
Cheers

 

[Jan Gullett]

Jetting

Perhaps my experience my help you.

I have sport cam, ported heads and a high flow exhaust on my 3.5 liter in my coupe with a 528i US LJet fuel injection system. I had the same problem as you.

Consensus advice was that the stock LJet provided sufficient fuel flow for my engine. However I upgraded the injectors to a higher flow rate, solved the problem and have more power. Perhaps my old injectors had lost flow with deposits over the years and new stock LJet 528i injectors would have been fine, but I am skeptical.

 

[decoupe]

Fuel Delivery

72b35CS - In all likelihood your mains are too small (probably they all are) and the engine is running lean as the rpm increases - possibly this will lead to damaged valves/pistons if extreme. Pull either #3 or 4 plug and check the colour of the tip - should be light tan colour. Best tuning aid is a dyno and wide band air fuel meter but the plug colour is a good rule of thumb.

Jan - If the 528i injectors weren't sent in for cleaning and calibration, I can pretty much guarantee that the flow rates would be well below spec and vary considerably. I've had injectors for both the L Jet 528i and motronic b35 serviced by RC Engineering and the before and after numbers are enlightening as to how much gunk effects fuel delivery rates.

 

[61porsche]

72

Your secondaries are not opening. Stuck ( operate the throttles while opening wide, bad diaphrams, etc.)

To alter the mix:

1. Check the preopening on the secondaries. Unlike the manual, close it up untill it is just off closed by holding your thumb over the butterflies and feeling. To check your self- briefly hold your hand over the throats to see how much air is coming in. it shouldn't be much.

Before you ream jets 2 sizes up, do this- next to the primary air bleed ( jet on top) is a small hole drilled in the casting. That hole is your idle air. Place your finger or a pencil and briefly close the hole. The engine should respond. Speed up, slow down, smooth out, get rough. Tell me that and I will say more.