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General Category >> Rubber Side Down! >> Engine Cuts out at 70-75mph
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Message started by bmc2k7 on 06/26/10 at 13:18:34

Title: Engine Cuts out at 70-75mph
Post by bmc2k7 on 06/26/10 at 13:18:34

It's a 1998 with about 16000 miles. I've owned it for over a year and put about 3500 miles on it myself. I had the carburetor cleaned, the air filter replaced and the oil changed with some mobile 1 10W40 when I bought the bike.

The thing is, it's got nothing apparently wrong with it until I'm hitting about 70mph, I'd expect the bike just to top out but it doesn't. It will run very strong and then, unexpectedly, sputter for a few seconds and cut out completely.

It exhibits this problem less when the tank is full, so I've thought it might be a full pressure problem. I have not spotted any fuel leaks.
Also, I can take it up as high as I want to if I pull the choke out all the way and switch it to prime (Carb need to be replaced maybe?). I generally don't worry about running out of fuel, but it does decrease the mileage to about 30mpg, however, I can get on the freeway and not worry about random engine cut outs.

Another weird things it does do, which I don't know if it matters or not is, it sometimes sticks or makes a weak feeling shift into 5th gear. All other gears have a defined and solid feeling when shifted to. So sometimes I need to downshift back to 4th and re-shift back to 5th so I'm confident that it went correctly.

I want to get it fixed, I was wondering if anyone else has seen this and has a solution, let me know. That would be awesome.

Title: Re: Engine Cuts out at 70-75mph
Post by BurnPgh on 06/26/10 at 13:28:35

it runs better with the choke out because its jetted lean from the factory. Rejet. Your cutting out at highway speeds is likely the vaccuum line between the carb and petcock. Replace it with reinforced fuel line, replace the petcock with a yamaha raptor 660 petcock, convert the stock petcock to manual (in the tech section), or just keep running in prime.
The "shifty" 4th-5th shift is normal. Keep upward pressure on the shifter until you let the clutch lever all the way back out.

Title: Re: Engine Cuts out at 70-75mph
Post by Serowbot on 06/26/10 at 15:07:20

sounds like your vac line is sucking air,... or you're just not pullin' enough vacuum at 70mph to work it...
Running on prime should fix it...

30mpg's is way too low... something else is wrong there... try going to prime without pulling the choke on...

3500 miles,.. time for another oil change too...

Title: Re: Engine Cuts out at 70-75mph
Post by Routy on 06/26/10 at 21:56:56

Well, at my age I like crusin at 50-55. Today I ran it up to 80, just to see if it would do it, and it did, no problem. But if it would have started crapping out at anything above 70, I don't think I would have concidered it broke ! :o

Title: Re: Engine Cuts out at 70-75mph
Post by justin_o_guy2 on 06/27/10 at 01:41:22

I hope youve looked at the csm chain on that. 16 k miles , its time to have a look.

Title: Re: Engine Cuts out at 70-75mph
Post by Oldfeller on 06/27/10 at 02:03:59

I agree you are having vacuum actuated petcock issues -- interstate running at 75 mph used to cause me to have "false low fuel incidents" that would put me on reserve and have me headed for a gas station -- same story it stumbled like it was out of gas.

When you are running fast your vacuum level drops a lot, sometimes down to less than what will run your petcock once it gets old and flabby and the rubber diaphragm and valve seals have degraded a bit.

Solution for me was to switch to a $24 mechanical raptor petcock. Now I have no issues at all on the super slab (except my legs get tired and start to cramp after enough of it)

====================================

quote from tech section post

2003 yamaha raptor 660 petcock fits

Franch posting today at 02:47:14

fuelcock part # 5 Lp-24500-01-00
$20.89 from bike bandit plus shipping. it's a direct bolt on.
comes with o-ring.
not as pretty as the original part.
no vacuum line needed.
has on, off and reserve.
must manually turn off.
the nice thing is this petcock doesn't go under the tank towards center of the bike nearly as much as OEM so taking the tank off and on won't be such a tight fit.

===============================

At Ron Ayers Motorsports, it cost less money.

http://www.ronayers.com/browseparts.cfm?SearchString=5LP-24500-01-00&adv=5&kw...

$15.61 isn't that bad a price.

Ron will charge you $9.00 flat rate for shipping.

$24.61 to your door

===============================

Now, Franch gets full credit for his marvelous find. But please, somebody who does this who owns a camera please fill in all the blanks by posting appropriate additional information below.

Title: Re: Engine Cuts out at 70-75mph
Post by bmc2k7 on 06/27/10 at 09:06:11

Thanks for the great advice. I'm going to first look into raptor petcock and see how that goes. The oil should be fine, I've never had a problem with full synthetic after 3500 miles. Might look into the reinforced fuel line as well.

Title: Re: Engine Cuts out at 70-75mph
Post by BurnPgh on 06/27/10 at 12:28:23

the reinforced fuel line i suggested was intended to replace the crappy vacuum line that comes stock. If you switch to the raptor petcock you wont need a vacuum line as its gravity fed. You will need to plug the vacuum port on the carb though.

Title: Re: Engine Cuts out at 70-75mph
Post by jsarsfield on 06/27/10 at 19:45:17

Get yourself a new spark plug .... I had the exact problem you were experiencing .... I put in a new plug and that was the issue. It also does sound like you might have some vacuum issues so I suggest replacing the lines but if your plug is old and worn out it won't burn the fuel/air mixture like it is suppose to. A new plug seems like the cheapest thing to try IMO.