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Running Rich On Rear Cylinders


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#1 Rtiny

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Posted 09 November 2017 - 09:38 AM

Hi. I need your help.

 

Overview of setup:

- Triple 44 mikunis - 

- Dual exhaust system, so 1 pipe for cyl 1,2,3 and 1 pipe for cyl 4,5,6.

- Dual AFR

- MSD and Coil

- Pertronix sender unit in dizzy, +18 degrees

- carter pump at 3psi

 

Concern / Issue

At idle AFR

front is at 13.8 and goes to 16/17ish

rear is  at 10.8 and stays consistent.

 

On Decel AFR

front is fine.

rear goes to 11.5 and then back to 10s

 

Every other time its in use the 2 sensors read pretty much in sync. with load and WOT it will become the same. struggles and splutters a little to begin with, i think due to excess fuel. Pops on decel on exhaust and sometimes at the carbs.

 

Diagnosis

- Had the carbs tuned so we reading the front 3 cyl it should be good but rear is not at idle and decel.

- Swapped carbs front and rear made no difference.

- Adjusted float, made no difference.

- Tested vacuum booster, found when the pipe is blocked off it runs better slightly. tested all lines, one way valve, booster. all okay. still suspected booster to got rebuilt and refitted last night. better brakes and doesnt struggle as much on accel. but idle and decel still same.

 

Factors

- I dont have a working tacho atm, so we did not sync the carbs but they were pretty good before.

- clearances were checked 1.5 year ago

- last service was about 2000miles ago, due for one now. noticed it was low on engine oil and coolant also dropped. i dont have the breather pipe connected atm.

- When i had SU carbs the rear was pretty much always rich as well. i always thought it was the SUs were just over fueling.

 

if i think of more information ill add to it or if anyone need more info please ask. its doing Skot and my head in. dont know whats causing it. I want a slightly more economical weekender and save some coin haha.

 

Please, anything i can try :D



#2 Rtiny

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Posted 09 November 2017 - 09:53 AM

Engine picture

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#3 Agno

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Posted 09 November 2017 - 10:12 AM

Not helpful I know but I have the same issue. I think that's part of the reason why the six pack Chargers have a different carburettor on the rear 2 cylinders compared to the front pair.



#4 Cozza

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Posted 09 November 2017 - 11:40 AM

Not helpful I know but I have the same issue. I think that's part of the reason why the six pack Chargers have a different carburettor on the rear 2 cylinders compared to the front pair.


I can see this being an issue under load/ acceleration but not idle.

Sounds like the rear carb has a high float level or similar. I know you mentioned you’d swapped carbs front to rear and the problem remained at the rear. Any chance there is higher fuel pressure on the rear carb? Maybe leave the carbs as they are but run the fuel lines so the rear outlet of the fuel rail feeds the front carb and vice versa and monitor the afr’s.

Checking the valve clearances would be a wise idea too.
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