"Slow" XT600 ??

[Martynbiker]

Hiya, firstly thanks to all of you that answer my many questions and panic calls for help.

Here is a strange problem I have with my XT and the steps I have taken to overcome it.

Flat out is 120kmh. 4500 rpm no more. engine revs freely to redline through gears, but not in top.
stripped carbs off and replaced the Diaphraghm as it was a bit floppy looking, also the needle valve assembly as that was leaking and causing carbs to overflow.
Now the bike is MUCH more responsive through the gears, a lot more fun to ride, but still 120kmh (75mph) flat out!!

I was wondering if maybe the gearing was wrong? the rear sprocket is 39 teeth the gearbox is 15? is this correct?(parts supplied by wemoto ) it is a 1987 2KF XT600.......

Im not a speed merchant, but overtaking power at 100kmh is handy and also the parts guy at Flitwick motorcycles says it SHOULD do 150kmh or 95mph.

your thoughts please.....

[*Touring Ted*]

Im not sure of the reduction difference in the gearbox but my 2003 XT600 does about 85mph flat out with 15/45 sprockets.

It should have enough power to pull your 15/39T to 100mph.

What are your sprockets meant to be ??

There are many problems associated with a feeling of low power. I dont know the history of your bike so I woudnt like to speculate.

[Boxer]

Mine has been to 75 with a (light) passenger with 15 to 45. Is your rear sprocket a bit small - you may be overgeared. I don't have any references to look at, but a change from 39 to 45 on the back seems like a big change to me.

[Martynbiker]

thanks guys! looks like I will be dropping the gearbox sprocket a tooth....... should make up for things ( equals 4 on rear i think)

Martyn


****Just looked in the official Yamaha partsbook.pdf for my model bike and it specifies 15tooth gearbox and 39 tooth rear sprocket! stuff it, im still goin 1 smaller...... may make it better off road on the hilly rocky tracks round here.

[stuxtttr]

Have you checked your inline fuel filter, sounds crazy but if its flowing the wrong way it will upset the bike. I only know this because I managed to ride to Portugal with the same problem. Silly thing is I stripped every part of the bike 3 times and the problem was so simple to fix. I just kept missing it.

Originally Posted by Martynbiker

Flat out is 120kmh. 4500 rpm no more. engine revs freely to redline through gears, but not in top.
.

Hi Martyn,
On the face of it you have a gearing problem. A reduction of 6 teeth on the rear sprocket is very large. The standard 15F 45R is a reduction of 3 to 1 and the gearing you have at the moment is 2.6 to 1 and if you reduce the front sprocket by 1 tooth you will achieve 2.79 to 1 which may make things better but not much. At the moment you have a 14 % difference over standard.
Another consideration, with the smaller sprockets, is the route the chain is taking could be causing extra wear on the swinging arm chain guides.
If you have not tried it go back to standard and see how it suits your riding. The reasons to change the gearing are because you have more power, or the terrain. I might suggest your fuel consumption could increase with the correct gearing. You’re going to need a longer chain with the 45 tooth sprocket. It’s going to feel like a rocket with the standard gearing.

Steve

[*Touring Ted*]

I tried a 41/15 combo on my XT600E. It would still pull a fully laden bike to 100mph.

I now ride a 15/43 combo which although is slower and taller to accelerate, it gives me a better cruising speed at lower revs.

I think his sprockets would allow him to reach 100mph if he allowed the revs to climb sufficiently before changing up.

You cant swap from 15/45 to 15/39 and expect not to have to dramatically change your shifting habbits.

I would agree with leaving the 15T on the front and get a larger rear.

[pottsy]

My '02 xt600e is running 14(std 15?)/45 gearing and sits happiest at 70-75mph(5000/5500 rpm) on the motorways, hitting low 90's head buried in the clocks (grinning inanely...).I reckon this is a useful cruising speed as i don't have to worry about Plod so much.She generally pulls 60mpg at m/way speeds, so i'm happy enough with that.Hope this is useful info

[bruken]

Before you go and run off to buy sprockets to lower your gearing.....how does she pull in 4th?

Because tbh, I have had a XT500, a XT550, a TT600, a XT600 (1VJ) and a XT 600 (3AJ) and to add to this list a Honda XL500 and XR600R. What I can tell you is all of them could cruise very comfortably at about 100km/h (60mph) at 1/3rd throttle. AThalf throttle a 120km/h (70mph). To get to 140 km/h (90mph) you would start labouring the engine and using full throttle just to get there and maintain it @ about 7/8ths. Depending on the weather (barometric pressure / wind resistance) you might on the very odd occaission get the bike up to 160km/h (100mph)
The higher in elevation you rode the faster the cruising speed (up to a point of course...where I rode ranged from sea level to 2000m). Best height, about 900-1200m which would add about 15km/h. This may account for some posting higher figures?

These bikes do not do motorway well. If that's what you want, you got the wrong bike.

can do, and does do are sometimes two very different things

Bruce

[Martynbiker]

to Stu, Steve, Tedmagnum, Potsy and every one else..thank you.


nope. problem still not solved.

the gearing I am running 15 Gearbox 39 Rear is std Yamaha factory gearing. ( as it says in the official yamaha parts book no less.) if you ask me they got it wrong.

The fuel filter? there isnt one! just 2 little strainers in the feed tubes in the brand new fuel tap i bought.

Rather than go to the exspense of a new chain for the 45 tooth sprocket. the chain is already new and just right for this set up..darnitt! , and having made my own swing arm protector from INDUSTRIAL HD Poly ( takes forever to cut with a hacksaw but wont wear out the chain)and riveted it on ( yes, im a heathen bodger but it works )

I think I will go 1 tooth smaller Gearbox. I know its not ideal, but I have thrown a load of money at this once wrecked bike and have run out of funds. A gearbox sprocket im afraid is the cheapest option.

The good thing is, she does run like a dream and as soon as I figure out how to put pictures on here I will post some pics of the bike and the mountain tracks near where I live here in Spain.

Thanks again everyone!

Martyn

[Martynbiker]

Just had a blast up the Motorway about 3 Km to Carrefour ...gave the bike a bit of welly.......... she coughed a bit and spluttered as I overtook a lorry and then surged forward... and kept surging.........120, 130, 140, 145...... then I had to pull off on the slip road!.......hmmmmmmmmmm!

Now im confused as hell:confused1:

was it a blockage I had missed? I have stripped the carbs about 20 times in the last 6 weeks! then rebuilt them with new diaphragm cos the old one loked like this......



not pretty, and not cheap at 68 quid for the replacement...... but I think worth it for the peace of mind if nothing else.

she has been stood for nearly 18 months outside, before I rescued her.... and the more I run her the better she seems to be getting. I Have changed the Oil and Filter too... Oil was like tar! but no metal bits

Hi Martyn,
Sounds like a fueling problem.

Things to look at if the bike has been stood, check the jets are not partially blocked and drillings in the carb body are free. High pressure air line will be best.

Check the jets and needle are the correct size.

Check the float height and make sure it's moving freely.

Remove the fuel tap from the tank and check the gauze is clean. Check the petrol tank is venting, not sure where the vent will be located, it’s usually in the petrol cap.

I take it everyting else is at it should be, valve clearences, clean airfilter, good plug.

Plug caps and HT leads can be a problem with age and cheap to change.

Maybe stick with gearing you have until it's running right.

Steve

[bruken]

Good news then

[Martynbiker]

Hi Steve thanks for your reply....... Here is what i have done so far.
didnt have compressed air ( no compressor) so used high pressure Co2/Argon mix from my 6 foot high bottle I have for my MIG welder!!

The jets are new, the needle valve is new, the fuel tap is new, the diaphragm is new. Air filter is new, plug, cap, HT lead is new, have not checked valve clearances I will admit as A.) it didnt sound tappety and B.) the book shows a tool I dont have for adjusting them. so was going to wait till I could get a local Bike shop to check the valve clearances for me.

I use a lead additive and 95 octane fuel.

The only thing I havent done is reset any of the mixture screws etc.
if they were for instance 2 turns out when i stripped it, i re set it to that.

any tips on that??

cheers

Martyn

Martyn,

I found this, post 2 may be of help setting up the carb.
http://www.horizonsunlimited.com/hub...ut-65mph-23582

It's worth checking the valve clearences even if you can't adjust them, may be a tight if you can't hear them.

The mixture screw is a fine adjustment on the idle jet and will not have any noticable effect at large throttle openings.

Tank Vent? you could try opening the cap a fraction during a test run.

I am trying to think what we could have overlooked.

Steve