350K performance

[Tufftrax]

My bike is near perfect but I have always had doubts over it's top speed. I've never managed 90mph plus and my Sport is supposed to exceed the ton.

It handles well, picks up well through the gears but seems down on top speed so not sure if my expectations are too high or whether the bike has a fault? Could be gearing/sprockets I suppose but I think they are standard issue so less likely.

Tappets seem OK, carbs seem balanced, air filters changed and there's no hesitation when snapping open the throttle. The only "problem" I get is vibration through the bars at around 5,000 rpm (60-70mph) which disappears at higher revs/speed - do any other Sport owners have similar tales and how were they overcome please?

I love my 350K but this lack of top end speed has always been a concern, just not sure if my expectations are too high (and there's nothing wrong at all)!

Thanks in advance,


Keith Holyoake

[smotorboy]

Flat road, no wind, and no traffic then high eighty's is normal....

Down hill or a good tailwind then the low to mid nineties is possible.....

As measured by GPS,,,,plus it takes a while to get the last few mph....

I did some testing before I started the modification to make it into a land speed racer...

Tach is very accurate,,, Speedometer was only 2 to 3 mph fast.... Not bad at all,,,I'm impressed by the allover quality of this little bike...

Robert in California

[smotorboy]

A few more thoughts,,,,,,,,,, if your gearing is too "tall" then the bike will be faster in 5th than in 6th....

I had an old 1958 Harley "74" Duo-Glide when I was twenty, and it would run 93 mph in 4th (high) gear and 97 mph in 3rd gear.

If you are over 5' 7" and 150 lbs, then your size could be slowing the bike quite a bit at top speed,,, your "tuck" is also very important..Pro racers (the good ones) can get "under the paint" as we say.

I remember ridding a new Honda OHC 350cc twin WFO for 5 miles on a deserted country road back in 1973... 80 mph up a steep hill and 96 mph down the other side,,,,87/88 mph everywhere else....

350cc is 350cc after all , and bikes have such horrible aerodynamics that high speeds are not our best area...

Your speedometer may just be very accurate, and telling you the truth....That old Harley was registering 115 mph with the needle swinging about from all the vibration when it was really only doing about 95 mph.... Stop-watch and a measured mile told the real truth then... Today GPS is the way to go....

Robert in California

[3potjohn]

My K has Sito Black chrome silencers. I have read that these may restrict top end but the bike runs well with no hesitation. I just did a 300 mile round trip and cruised in top at 5500 RPM for straighter bits, which was plenty fast enough. Obviously had to cog down on long hills. I have revved the thing hard but it feels like it is beginning to struggle above 8000 rpm, and I always run with both taps on. I tested the elecric tap for flow already.I rebuilt the carbs and put in new filters.New HT leads and plugs.I played around with jetting a little but its running the standard stuff. i try and use Shell V power when I can get it.For road use I am not so interested in revs at the top end of the range as log as it pulls cleanly but as the Sitos are beginning to go am wondering if an alternative system might have an advatageous effect. So might getting rid of some flab in my case.

[unreal]

Performance of my Sport has deteriorated over the last 20 years.

I suspect a failing power-to-weight ratio...

Best i've seen is 93 mph (GPS) on the flat, but may be momentum helps here!

Simon

[mgelder]

My K has Sito Black chrome silencers. I have read that these may restrict top end but the bike runs well with no hesitation.

The black chrome Sitos on my 350K are collapsing internally through corrosion and are definately capping performance at the very top end. It's nice and quiet though...

...as the Sitos are beginning to go am wondering if an alternative system might have an advatageous effect.

I'm trying a set of short "perforated tube" baffled megaphones on mine. As they arrived, with the minimum of packing, they were a bit anti-social for me. Now that they're re-packed with decent material they're on the loud side of acceptable but they're still nice and fruity. I haven't tried putting them through an MOT yet, but they're quieter than a lot of Harleys.

They would have been too loud for the club trackday at Cadwell so I used the Sitos there, but I used the megaphones at Mallory for the Festival of 1000 Bikes a couple of weeks later. The top end performance with the megas on was noticeably freer; I haven't adjusted the jetting yet as the plugs suggest that the mixture is a little rich anyway.

I'll be putting a report on RealClassic.co.uk at some point soon...