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Discussion Starter #1
i got back from a motorcycle trip that was approx 600 miles and took my bike into the shop the next day. i needed to get my second service, but i also needed a new tire. between the the nasty roads, and long stretches of highway, i was riding over in the texas hill country, i had worn my tire down to the cords. i also noticed that my top end was beginning to suffer on my way back home. it was becoming difficult to reach speeds above 85mph.
my engine temp didnt seem to be any higher than usual, and my fan was working, but it still scared me enough to put it back in the shop. i dont know if this is because of the stop leak stuff i put in my radiator, which did stop the leak, at least... i told the shop guys to go ahead and flush it out, replacing the coolant with engine ice. i cant remember what tire i wound up getting, but the guy said it should be wider, which i am hoping will give me just a couple of extra inches, so that i'm not scraping my pegs.

also, for any other texas d390 riders, pedernales falls st park has a really fun entrance road.
 

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NEVER use stop leak! It will stop up your leak all right as well as any other passages and can lead to a fatal failure of your motor.Ask me how I know, $3700 wiser. Hey, I was a kid what did I know. Glad to hear your bike is still saveable.
 

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Discussion Starter #4
i dont typically resort to such rash actions, but in this case i wanted to do what i could on a very limited time and money budget so that i could go on this long planned trip. i got to get out, and knew i'd be getting the bike into the shop, at least for the 2nd service, so the tire and rad flush hopefully wont add up to too much... at least i get a little discount there for being on a local forum they support... :/
 

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Matt, I thought about the "engine bogging"/perceived loss of top end speed that concerns you. A couple of thoughts:

I saw in the photo that you have a generously-sized tank bag on your bike. I surmise that on a camping trip you might also have had some additional luggage hanging off your Duke.

You say that you could not get the bike to run beyond 85 mph (as opposed to its normal top end of just over the ton). My thought is that you were retarded by aerodynamic drag rather than loss of engine performance.

To greatly simplify a complicated formula that accounts for several variables, let us just observe that aerodynamic drag increases as the SQUARE of velocity. For example, if you are riding at 60 mph, your aero drag would be 3,600 units above what it would be at zero speed. But if you increase speed to 85 mph, your aero drag soars to 7,225 units, about TWICE as much as at 60mph. Any extra obstacles to aero flow at this speed (ie, rider's body, external luggage) will create correspondingly large increases in drag.

Riders who like to do the ton on a Duke typically ride solo, with no external loads or attachments and they lie down on the tank to minimize drag. Clearly, with a large tank bag it would be impossible for you to assume a racing crouch. In addition, your external luggage would be creating heightened drag, magnified by riding at high speed. My supposition is that the combination of an upright/semi-upright riding position, along with additional drag from luggage, would be sufficient to create a level of aero drag that would impede you from reaching theoretical top speed. This is particularly true if you were riding into any degree of headwind, which would aggravate the bike's coefficient of drag.

I believe your engine is probably OK and normal. When you get your bike back from the shop, if you are worried I suggest you find an isolated road, then try a top speed run, with no luggage, no headwind and using a racing crouch, flat on the tank. I think you should be able to do the ton or thereabouts. Top speed is subject to variables such as rider size, weight, position and clothing, engine tune, optional equipment, fuel type, ambient temperature, wind direction, tire inflation, road surface, sprocket sizes, chain lubrication, tension and alignment, etc.
 

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Discussion Starter #6
thanks, diplo, but i dont think that's the case here.
the only luggage i had on the bike was the tank bag. my friend in the kia was the designated pack mule.
even if i had my small amount of baggage on the bike, i dont think it would be enough to slow me down that much. everything i brought fit into my back pack and tank bag.
i was fairly spartan, while my compadres were packing dig folding chairs, full size pillows, several outfits, that big tent, and a bunch of other crap we didnt need.
 

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Interesting that the shop would suggest a wider tire, as the 150 that is on there is kind of too wide to begin with, at least it terms of allowing the rider to access the edges of the tires when leaning. Most of the RC Cup riders have gone to a narrower 140 tire.

Good luck, hopefully the speed issue is just a tight valve and the shop will catch it with the valve adjustment. I agree the luggage was not the problem, as I had a large tank bag and tail bag when I rode from Texas to Florida and I was still able to crest 100 with ease.
 

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I agree with BSH: If your shop recommended a wider rear tire than the already-too-wide OEM 150, it sounds as if they don't have the slightest clue about tire dynamics. Perhaps they have a 160 in stock that they want to sell.
 

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Discussion Starter #9
i got the bike back this morning and the **** thing tops out around 91mph and it's working hard to get there.
i cant call the shop yet, because my phone is in the middle of a lengthy restore. my phone got crippled somehow on last week's trip. battery life went to a few hours and it ran super hot. yeah, my luck... so while my phone is being activated, i'm hoping yall can provide me with some good material to talk to the shop when i call them.

they didnt even touch the radiator. if i'm off work tomorrow, like i am supposed to be, i intend to do another radiator flush on the bike. i want to put some clean engine ice in there, and get rid of the remaining stop leak crud.
i dont think that the stop leak is why my engine is running poorly. the bike doesnt appear to be running any hotter than it normally ran before all this trouble.
 

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Running your rear to the cords means it has a greatly reduced circumference, since speed is taken from your front wheel this could very well be the "problem". Other than that I'd be looking at chain tension (know how to set it that it isn't too tight) or possibly a faulty thermostat.
 

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Discussion Starter #13
the bogging isnt severe. it's like if i had a good size person on the back of the bike, so i doubt it's a bad connection on the battery.

the **** thing overheated on me and died at a traffic light this morning.
i just did a radiator flush with engine ice yesterday.

really regretting not buying the cheaper honda competitor.
 

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the bogging isnt severe. it's like if i had a good size person on the back of the bike, so i doubt it's a bad connection on the battery.

the **** thing overheated on me and died at a traffic light this morning.
i just did a radiator flush with engine ice yesterday.

really regretting not buying the cheaper honda competitor.
Blown head gasket, or your OEM fan blades aren't connected to their shaft anymore, which would be a SPAL fan as a recommended fix to a known issue. Don't worry, once you've sorted teething issues out, you'll never look back.
 

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Discussion Starter #15
the ride home from work was better than the ride to work. i think i have some air bubbles in the system. i might have gotten some of the air out on the way to work or something... i dont know. all i know is that it was 1 bar cooler than it was on the way to work. it seemed to have a slight bit more power too. that could just be in my head though.
i took the car to work today. when i get home, i'm going to open the rad and run it for a while, to warm up the engine and hopefully get more air out.

i also have a guy offering a straight trade for his 07 harley street bob. it's got about 13k on the odo, and it's in good shape. title in his name. sounds good to me! i'd prefer a simple, big, air cooled v twin bobber right now. it can eat miles all day. i can put a sissy bar on there and hit the road. with my job, i have 3 days off one week, and 4 days off the next. i think once it cools down here, i'm going to be doing a lot more weekend camping trips.

i dont hate the duke at all... it's just not what i had expected. it is a lot of fun... just not for long distances.
 

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What is the calculation for tire roll-out (diameter) and its effect on gear ratio?

Taller tire = lower gear ratio. Shorter tire = higher ratio.

i cant remember what tire i wound up getting, but the guy said it should be wider, which i am hoping will give me just a couple of extra inches, so that i'm not scraping my pegs.
 

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The OEM fan has demonstrated two failure modes: The familiar mechanical self-disassembly with radiator eating: and the lesser-known but more insidious electrical failure, where it simply refuses to switch on at the required temperature. The electrical failure mode is sometimes intermittent, and thus difficult to diagnose. It sounds as though your fan could have the latter malady, Matt. If you have a properly working fan the bike should not overheat, even in very hot conditions.

A SPAL fan will cure both of these ills.
 

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Discussion Starter #18
the thing is, i can hear and see my fan kick on...

a local shop owner (not the place that i got the bike from) suggested that i remove my rad cap while the bike is cold and let it run with the cap off until the bike has been running, warmed up, for several minutes. re cap it while the bike is warm, and that should give me a pressurized system with no bubbles.
the guy has been very helpful in the past, and freely dispenses sagely wisdom. i think he likes to educate his customer base so that he can avoid working on trashed bikes.
i really wish i was better at retaining this knowledge. i can watch a video on how to tune carbs, or rebuilding forks, and then i go to do it, and my mind is completely blank.

i'm going to see if i can go through with this street bob trade. its a more expensive bike. the owner just wants something new in the stable. he has like 4 other bikes to play with, and never rides the bob. if the street bob isnt to my liking, i can trade it or sell it and gain a cbr300r and maybe even a grom. definitely a grom if i do this next year.
 

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Well with all due respect if the Duke isn't to your liking when it comes to distance capabilities, the Grom or even the CB300 are even less suited for that application. The Street Bob would be fine with a good windshield and some bags, but waaaay heavier and less agile.
I've had great luck touring on my Duke, and a buddy of mine with an RC390 just rode Chicago to Portland OR and back (shade over 4500 miles) in eight days so the bike itself is very capable. But I realize it is not for everyone, and I hope you find the ride that makes you happiest.
Good luck!
 

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Discussion Starter #20
i hear you on distance riding on the grom and cbr300r. i figure that the cbr, at least, would have a much better aftermarket than the duke.
the grom, i was thinking more along the lines of tossing it in the back of my mazda 5 and then i can ride it around town. i love it out here in the country, but it sure would be a lot easier if i lived in town, lol.

if i dont like the hd, i can resell it after i clean it up a little, and make a decent profit. maybe i will have enough money to get a used fz07 or a good sv1000 or vfr800
 
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