YZ 125d Porting specs

[philthy]

Hi
I am needing some original porting specs for my 125d.I am having trouble finding much power under 11000rpm.It is being tuned by a well respected tuner in SA and he has just rung me regarding information on original port specs,as he suspects it has been wildly ported some time in the last 30 years hence the problem.If anyone has any information regarding original specs it will give him some guidelines to work from.If anyone has a barrell for one of these bikes that is unmolested I would be keen on buying it,as I'm too old and unfit to keep it at 11-12000 revs for any length of time
Cheers     

[vandy010]

these are old measurements i took some time ago from a stock barrel but given my measuring practises back then were a bit on the mediocre side i'd suggest them as a guide only.
i no longer have the barrel as it was moved onto a mate.
hope this helps

if more bottom end is what you're chasing, check the "stinger" diameter on the pipe is not too small.
i changed to a larger diameter on my 125F and it now makes respectable bottom end for a 125.
i'd also be looking at reed material for improved bottom end.
cheers,
Vandy.

[Lozza]

If vandy's measurements are correct you will have to get used to keeping up in rpm, that cylinder is road race spec rather than mx.

[vandy010]

If vandy's measurements are correct you will have to get used to keeping up in rpm, that cylinder is road race spec rather than mx.

i knew you wouldn't be able to resist

[Hoony]

i had a YZ125D back in the day when i was 15 and i always remember it as a torquey engine and not peaky at all.

[Nathan S]

The 25mm exhaust port height is pretty standard for Yammie 125s of that era - and usually the first place that 1970s tuners attacked with the die-grinder.

A stock 125D is pretty easy to get along with. Yeah, they need to be revved to go well, but they're a hell of a lot more tolerant of a less than balls-to-the-wall riding style than the CR or RM of the same era.

[philthy]

Thanks guys for the input,The tuner said that the port specs were similar to a 125 roadracer,problem is he carn't put metal back.Options are to run methanol and gear down,but running at such high revs makes getting off the line hard ,and reliability?? 

[philthy]

I forgot to add ,I am running boyson reeds and a 78 E model pipe!

[Lozza]

Thanks guys for the input,The tuner said that the port specs were similar to a 125 roadracer,problem is he carn't put metal back.Options are to run methanol and gear down,but running at such high revs makes getting off the line hard ,and reliability?? 

Options a many and varied and more low end is a pretty easy fix(methanol isn't one of them). Reliability goes hand in glove with performance and maintenance, what ever the spread of power has to work with the gearbox.

[vandy010]

I forgot to add ,I am running boyson reeds and a 78 E model pipe!

stinger diameter will be about 19mm id on the "E" pipe.
which for my money is small.
my "F" runs an "E" pipe but now with a larger 23mm id stinger
i believe it's helped the bottom end

[Freakshow]

who the tuner whos got it may i ask ?

[Mike52]

Your tuner could always drop the exhaust port down and start again.

[Nathan S]

Thanks guys for the input,The tuner said that the port specs were similar to a 125 roadracer,problem is he carn't put metal back.Options are to run methanol and gear down,but running at such high revs makes getting off the line hard ,and reliability?? 

Depending on how far the port(s) have been raised, machining down the barrel on the base gasket surface on the barrel will lower the port height.
This might require re-machining of the head, but then you can put a modern profile into the combustion chamber.

The stock exhaust port height 'seems' like it would create a much peakier engine than it actually is.

[philthy]

I think this was one of his options as well as running methanol,but as he said ,would be a lot simpler to find another barrell if possible and start from scratch

[vandy010]

the monoshock DT125 barrel and the YT125 trike barrels will bolt straight on but have the disadvantage of having smaller reed blocks making the rubber boot to carby/set~up a bit of a challenge.
not impossible though.
but a well sorted DT125 barrel could be quite nice too.