New carb poorer performance?

My 2006 volvo penta 3.0l was recently recalled to replace the holly carb. Prior to the recall the boat was running fine and had no problems. Since then the carb has been replaced and the boat is running a bit rougher at idle but also does not seem to have the hole shot that it had prior.

On my way back to the lake I filled up at a gas station in a small town that didnt have premium gas so I used regular (87 octane Canada). My question is would the lower octane rating from 91 to 87 noticeably affect the boats performance? If so would octane booster help for this tank until I can get some more premium in it? Or does it sound like the new carb needs to be fine tuned a bit?

Thanks

Re: New carb poorer performance?

Lower octane = less performance? Ah, yeah.... You may need to adjust the idle mixture screw for a smoother idle too....

Chris.............

Re: New carb poorer performance?

Lower octane does not mean less performance unless the engine calls for the higher octane. Using a higher octane when not needed will not increase performance. What does the manual call for? Usually only engines with higher compression and/or more advanced ignition timing would require anything above 87.

Re: New carb poorer performance?

Yup, performance is not a direct product of "octane".

If your engine does not call for higher octane, you're throwing money away. Use the minimum octane rating required, unless you have knock issues...

The dealer probably just failed to properly tune your carb.

Re: New carb poorer performance?

The engine does call for a higher octane gas which I have always used, unfortunately the gas station that I was at didnt have it.

Is it appropriate to use an octane boost in the gas tank?

Re: New carb poorer performance?

What octane rating method do the gas stations in Canada use?

There are 2 most common methods.

• (R+M)/2 (AKI)
• RON

The first one listed is what the US stations post. 87 AKI (first method) is the same as 90 in RON. 89=91, etc...

Your 2006 VP 3.0l manual calls for 87 AKI for non-EFI engines.

Re: New carb poorer performance?

my manual says 87 in hte us and 91 outside us? Not sure what method canada uses

Re: New carb poorer performance?

It should show the method on the gas pump somewhere.

If "(R+M)/2" is on the pump then that is the US formula also may just show "AKI" or may have both shown with "(AKI)" after.

"RON" is the "other" formula.

The "R" in the US formula is "RON" and is averaged in with the "M" method which is why it is a lower number than just "RON". The "M" method is "Motor" and is from actual tests and is almost always a lower number than "RON" .

Re: New carb poorer performance?

Found this online, It was free so take it for what it may be worth. It does echo the same things I have learned from numerous other sources, plus it mentions Canada! and the method there appears to be the same as the US R+M/2 (the lower numbers).



Octane Rating Calculation Methods
There are various calculation methods, RON, MON, and PON or AKI.

RON: (Research Octane Number). Most common fuel used in Europe, Australia and some other Countries. It is determined with measurements of fuel behavior in a variable compression engine. Results are compared with other iso-octane fuels, wich means, compared with other fuel types with equal number of similar octane molecules present, but not the of the same organic compound.

MON: (Motor Octane Number). Determined also with a variable compression engine, but with the fuel already preheated, variable ignition timing and higher RPMs than the RON method. This method is more precise on determining fuel behavior on an loaded engine.

PON or AKI: (Pump Octane Rating or Anti-Knock Index): This is the method used in USA and Canada, expressed as [R+M]/2, wich means RON number plus MON number, divided by 2. In other words, it is the average between both methods above.

So, due to the fact that RON is always from 4 to 5 points higher of its equivalent to PON or AKI, the number conversion between USA and Europe octane ratings will approximately be as follows:

USA (PON) Europe (RON)

87 = 91
89 = 93
91 = 95
93 = 98