topspeed as indicator for full horsepower...

[Tom125mx]

hi all,

I have to admit, that I was a little bit disappointed about the topspeed of my 78 dt125mx.

--> not more than 90km/h (55mph) .. maybe the speedometer in inaccurate...

my kawasaki ke 125 (1978) appears more powerful and is faster as well..

... how fast should it go?

... any obviouse modifications to improve power?

... does the 175 barrel/piston/barrelhead fit?

if yes: what else need to be changed in order to have the full dt175 power?

thx in advance

tom

[Airhead]

morning Tom, first check the exhaust header, you may find a sleeve in there that you can take the dremel cutting disc to.

Yes the 175 barrel and head will fit straight on.

Also some of the early bikes had a 22mm carb but it would go better with the 24mm version fitted

[Tom125mx]

oh. fast response thx!!!

is the barrelhead of the 175 identical with the 125?

the 125-175 conversion seem to be the most obvious change

cheers

tom

[Airhead]

yes if you can find them a 175 convert is easy

[Tom125mx]

is 90km/h resp 55mph ok for the dt125mx? shouldn't it be a bit more????

tom

[Ttaskmaster]

Topspeed as indicator for full horsepower. My kawasaki ke 125 (1978) appears more powerful and is faster as well.

Top horsepower for any given bike kicks in at a certain number of revs, depending on your bike model.

Yours reaches its maximum of 14HP at 6500rpm.

Your statistical top speed is given as 68mph (110kph), meaning you'd have to rev it pretty hard to get much faster than you already are.

The '78 Kawasaki, by comparison, is rated at only 10HP at 6300rpm, topping out at 58mph (94kph).

Bear in mind though that as these things get used, they do drop in performance.

Also, it depends how you rev it and govern the throttle.

If you're going along and whack the throttle open, you will be stressing the engine too much and it will actually lag in performance. If you gradually increase the throttle, building your speed up you'll find you eventually get a higher top speed... eventually.

A trick I used on my 125 Dragstar - Gear 1 was for moving off. Gears 2-3 were for playing in traffic. Gear 4 was for high speed moves (50-65mph, overtaking, etc) and getting up toward top speed. Once at around 65mph, I'd then shift to gear 5 and just cruise along, but slowly increase throttle over about 30 seconds to a minute. I'd then end up with a top speed of about 74mph.

[Airhead]

my 175 will do 70 if I cane it but it's more comfortable at 65...I wont do it for long stretches though it seems a bit risky and I dont trust modern ethanol fuels!...I have one more tooth on the front sprocket to raise the gearing slightly

[Cynic]

Same here. She will do 70 but 7krpm is my normal max.

I think the 2 compare on top speed. The extra cc counts for plugging the muddy lanes not tarmac tearing.

[blackhat250]

One other factor " How heavy are you ,,, 60mph will be tops, and remember Twinshock barrels are 4 stud . and MX 5stud...

[Airhead]

MX 125 = 4 Stud John

[Tommy xs]

One other factor " How heavy are you ,,, 60mph will be tops, and remember Twinshock barrels are 4 stud . and MX 5stud...

In other words if your a fat bastard that's why your bike is slow

[Tom125mx]

75kg... Not that fat ;-)

And it's the topspeed of the dt that is less than the 10hp Kawa ke 125.

Adjusted the ignition Timing yesterday. Plus I took away the airfilter. This added another 5 km/h in topspeed

Still far away from where i'd like to be ;-)

More Tipps?

The realistic tip that bring's the 100km/h+ will get a Free Pint!!!

T.

[Airhead]

some of the early 125cc bikes had a 22mm carb venturi and the later ones a 24mm vanturi which is better, what is the number stamped into your carb Tom ?

Also mr Yamaha had a thing about fitting smaller diameter inserts into the exhaust header pipe, what is the number stamped into your exhaust and have you checked the header, I suggested this earlier but you didnt respond ?

It's not advisable to run without an air filter on a long term basis

[Tom125mx]

Stamp on the carburator is MIC 2A8 00

The numbers on the Exhaustor pipe is 2A8 14610

Does that tell anything to you?

Cheers

Tom

[Airhead]

Not sure about the carb, you will have to measure it using some inside calipers

but the exhaust has a restrictor tube, I know this because I just bought one myself, I use a dremel speedclick arbor and the smallest cutting disc they supply for it...even then you may have to wear it down a bit in order to gain access

looks like the pint is mine then

This is the sort of thing you'll find, you can see the end of the tube in this pic although the 2A8 has a longer tube so you'll need a torch

[Tom125mx]

this Sounds promising!!

Would the ( unrestricted) exhaust of a dt 175 fit?

Any idea where to get an exhaust? .. I'like to keep the original one...

Are there any Tuning Exhausts for that Model available on the market?

Cheers

T.

[Airhead]

I've tried various exhausts

aftermarket exhausts were made by several manufacturers over the years, of course being a 35 year old model they were mostly withdrawn from production

personally I have found that the performance of the original pipe is hard to beat, I say remove the restrictor in yours

[Tom125mx]

ok. cool..

since I want to keep the original pipe unmodified; i'm looking for a second exhaust.

any idea where to get a original part from? either used or new?

AND: would the exhaust from the 175mx fit to the 125cc barrel?

tom

[Cynic]

looking for a second exhaust.

Best of. There are pattern ones by Big One but they are in the later front expansion chamber type. Pick a bodypart for an oe system in good nick.

[Tom125mx]

hi cynic,

maybe my english is not good enough, but I don't understand what that means: "Pick a bodypart for an oe system in good nick"??

can you help me out?

tom