New FPR, new vacuum pipes, still 22mpg

Hello friends,

I recently brought my Silverwing up to date. I replaced the Fuel Pressure Regulator FPR with a brand new one, since I knew it likes to go bad and mine looked still to be the original. (Yellow Dot on the fpr and fuel rails as torque marking. Also my oil was smelling of gas very very intensely. No signs of fuel in the vacuum hoses tough!). While replacing the fuel pressure regulator I also replaced the vacuum lines with brand new Continental hoses.
Oil is fresh
Rear handbrake is adjusted.

Around town - which is what I use the scooter for mostly atm - I still get around 21-22 US mpg. I know that the Silverwing 600 is thirsty, is old, but still, its consuming as much fuel as my 6 cyl. Mercedes Benz automatic sedan with stron airconditioning.

Is that mpg number simply what I can expect from the Silverwing 600 around town, or do I have to inspect further?

Thanks!
Alex


Edit: it’s a 2004 Silverwing with 28580 miles / 46000km on the clock. Exhaust pipes are clean (BP Ultimate gas) and the plugs are nice and brown.

Another thing I noticed: no matter how I set the idle on a hot engine (set to appprox 1300rpm) during warmup I’m always getting slightly above 1000rpm. See picture. Rpms are also slightly fluctuating up and down during warmup. 


Another thought: Since the Silverwing is so old and the fuel pressure regulator is known to fail, may ethanol in the gas be the cause / a cause? I try to find ethanol free but it’s becoming increasingly difficult. Maybe an ethanol additive might prolong the life of the fuel pressure regulator? Back in the day when the Silverwing was designed and built there was no ethanol in the gas - so no one payed attention to it.

That seems VERY bad mileage. What year is the scooter and overall mileage? Most newer than 2008 can get over 50 MPG, mine on back roads can top 60 sometimes. Under 2008 usually in the 40's... Check and/ or replace the spark plugs? Are any of the brakes dragging?

Others on here may have better suggestions, good luck.

Edited the initial topic.

It’s a 2004 with 28580 miles / 46000km on the clock. Exhaust pipes are clean (BP Ultimate gas) and the plugs are nice and brown.

Brakes are not dragging, parking brake is adjusted a bit too light just to rule out it dragging. 

Plugs are brand new NGK Iridium.

PEA based gas additive to clean out the fuel system from gunk has been used multiple times.

Exhaust smell is strong, but it’s a 2004 only with basic cat converter and no o2 sensor, so I assume that’s normal. No smoke, no soot on the tail pipes.

112mph is easily reachable on the motorway.

My rpms cruising and accelerating in town are between 3500 and 4000, not more than 4000, with 1/4 of throttle to max 1/2 throttle but 1/2 throttle is usually not needed. RPM wise I’m mostly close to 3500 rpm. 


I have to do a throttle body sync. I’m waiting for the professional tool to do it.  But I can’t imagine that that is causing massive fuel consumption. 

Otherwise the scoot runs great!

Tickover rpm is low, is that as it’s supposed to be?
When cold cold started then its 1800rpm.

Mine is a 2006, so the same basic cat system as yours, and just over 40k miles.
I usually get about 53mpg UK (about 44mpg US) and that is running on E10, which the bike is designed for.
Your mpg does sound excessive, what mpg does the bike do on a longer cross country run?

If your oil had gas smell, usually there's 2 possibilities, bad FPR or leaking fuel injectors, have you checked fuel tank for rust or contamination, dirty fuel can make both FPR and fuel injectors stick or not fully close/drip, causing a rich condition. Since the 2003 has an open loop fuel injection (No 02 sensor) makes it worse. Fuel system cleaner/fluid sometimes works.

Are you sure you got the correct pressure FPR ?, several older Honda's use identical appearance part, but different PSI/KPA settings. Is there suction/vacuum at FPR hose at idle ??. This video show only diaphragm rupture/failure, the normal issue with FPR's https://www.youtube.com/shorts/8Lb2I6iysL8

My limited understanding of these systems is that the only way gas can get into the oil is via the fuel injectors. It's possible that the extra fuel is washing the cylinder walls. Perhaps a compression test is in order. Also, does the oil level raise at all on the dipstick over time?

Another thought: Might it be worth cleaning or replacing the injectors? My impression is that they are basically electrically controlled fuel valves, and maybe they are not closing completely.

I am by no means a mechanic; I'm just throwing out ideas. Good luck, and keep us posted.

Ron in AZ.

" My limited understanding of these systems is that the only way gas can get into the oil is via the fuel injectors." Usually, but on a SW600, a broken FPR diaphragm will allow fuel to be sucked thru vacuum hose, see video above.

" It's possible that the extra fuel is washing the cylinder walls." Absolutely .., not good for bearings, etc., either.

" Perhaps a compression test is in order. " Is never a bad idea when troubleshooting performance/efficiency issues.

" Also, does the oil level raise at all on the dipstick over time? No, maybe slightly when hot, oil level is checked, with bike level with cap fully unscrewed.

Injectors on SW600 rarely fail or need extra care cleaning, an occasional can of seafoam, etc., does not hurt, but neglected with dirty/old/contaminated fuel or rusted fuel tank are the real issues.

Thanks everyone!

@steve_h80: I'm not sure, since I use mine atm 99% in the city. I might buy one of these new Honda E-M1e 50cc equivalent electric scooters for running around short distance around home and use the Silverwing 600 out of town for leisure rides. Makes my Ducati Supersport 939 a bit obsolete, but to be honest, I prefer riding the Honda for comfort reasons.

When I bought it I rode it home on the highway, 110mph all the way, I made about 105 miles til I reached the reserve last block on the fuel indicator.

I stay away from E10, in my opinion the bike isnt designed for E10, even tough Honda says its compatible. Back then when the bike was designed and buiilt - gas was gas. No ethanol, therefore all the components that are in contact with fuel might not be designed / tested for ethanol compatibility. So BP Ultimate gas, 98 octane for me only. Maybe I'll use a ethanol fuel additive for extra lubrication of the FPR diaphragm, just to be safe.

@zrx212: I should have the correct FPR, since Honda ordered in via the VIN. I also have on of these tre rosso aftermarket ones from poland, bought from ebay, 3 Bar just for testing. Since the FPR is a known issue, maybe its not a bad idea to have a few of these in storage. Right now Honda still has them and delivers on order, but who knows for how many years to come? The Silverwing 600 wasn't exactly selling like hot cakes....

I will check my gas tank with a inspection camera as well as the fuel lines simply by sucking fuel out with a vacuum pump. Then I will know more.

But this will have to wait until I put it in winter storage, theres where all my tools are.

My oil has had a very strong gas smell, but I didn't notice the oil level increasing. I'll keep an eye on it, right now I'm running a mix of 10W60 and 10W50 1:1 of Liqui Moly Street Race 4T motorcycle fully synthetic oil. Just in case I'm dumping fuel in the oil not to thin out the oil too much.

While in winter storage I may take out the injectors an clean them in an ultrasonic bath as well as pump some gasoline cleaner through them undiluted, should be doable with a battery, pump and a few  meters of pipe.

I'll defintely check the fuel tank for rust, but with contaminated fuel supply shouldnt I experience uneven acceleration, stronger rpm fluctuation, vibration, hesitation to accelerate and so on?

Alex if you got over a hundred miles with the motor running flat out there is nothing wrong with the fuel consumption. Or there wasn't until you did that