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Gas difference

luhrs_40

luhrs_40

Contributing Member
1989 454s with flowscan installed Up to 2500 RPMs both engines showing around 7.5 gallons per hour Once around 3000 rpms starboard engine 10.5 Port engine 18.5 Why the difference?
Is it something wrong with the port carb secondary? Thanx in adavance
 
There's a few things that could induce that behavior.....I'd be inclined to start with an inspection of both carbs, while operating at the 3000 rpm mark....check the secondary air valve positions. My hunch is the port will be 'partially open' and the starboard still 'closed'....if it is, the tension spring will need to be tightened...
 
luhrs_40 said:
How the secondarys suppose to react at high RPMs ?
Click to expand...


they usually 'open up' with increased RPM....the throttle valves are linked to the primary side but not linearly....eventually, the RPM obtained requires more fuel than the primary side can supply and the secondary air valves begin to open....
 
Mark gives you some excellent suggestions. Take heed!


You may also want to try using the P of E...... process of elimination. You have twins, so this adds a level elimination!

Map out your ignition advance on both engines, and within the usable RPM range. Use engineering paper and make line graphs!
In other words, look at the "progressive" advance as per RPM, and the "total" advance as per RPM and plot this out on paper.
The two ignition advance curves must be the same (or extremely close)!

Try swapping Port/Stbd caburetors.

Also try swapping the Port Floscan sensor for the Stbd unit..... and visa-versa.


See if the odd fuel consumption reading follows any of the above component swaps!


.
 
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