PORT JOBS

[vandy010]

ok, i'm no wizard but have done a few to my bikes over the years with some success so am still convinced to do them myself.
my question is in relation to the transfer ports, see picture attatched,
we're looking at a yz125d barrel.
side A shows the shoulder of the bore flush with the base gasket
while side B shows the transfer port to be raised by 5mm.
i'm think of doing this to my little mx125a but would really like some feedback before i do it.
both the mxa and the yzd share the same bore and stroke with the distance fom the top of the barrel to the base gasket being equal distance, so to my way of thinking, it should be ok but what will it really do?

[attachment deleted by admin]

[Lozza]

What do you want to do? Making the transfer cut away there will have 3 parts of SFA difference. Would be 30 things to do before worrying about this. Have a look and see how it relates to the cut away in the piston.

[vandy010]

the main aim of it all is to be able to run a larger carby as the standard barrel just won't cut it.
the usuall larger inlet, lower/wider/higher
raised exhaust,
open up the transfers then smooth it all out.
i was curious as to whether this "step" in the D model barrel was done in order to smooth out the power delivery.
just trying to understand it a little better.
i don't have a piston for this D model barrel on hand as it's just something i've had lying around

[Lozza]

OK, I see, from what size carb to what size carb? Before you start attacking why don't you clock or degree the opening and durations of the port windows?In most old engines( a few new ones to) scavenging can be improved by filling ducts rather than making the ducts or port windows bigger.Your plan for the inlet is sound but would go for width with the exhaust over height.Even in highly developed engines like an RS 125 road racer benefit from a reduction in ex duration. Their idea was just whatever the current thinking was it has little overall effect the extra bit of cylinder wall.

[vandy010]

ok, so with the exhaust port,
current hieght is around 28mm and i was planning on raising that to 25mm measured from the head gasket face.
current width of exhaust is at 38mm and i've read it's not wise to widen by more than 70% of bore {which would take it to 39.2mm}, bore is 56mm but yet the D model yz barrel has a width of 40mm, hieght of 25mm so i guess that in itself is a contradiction to that theory of width.
by the way, the D model barrel looks to be totally stock so i'm guessing thats the standard factory width & hieght.
std carby size is 28mm, i'm currently running a 30 but would love to step it up again to a 32mm, another bloke has already tried the 34 on these motors and he said they were just too big.
i know these little mx's will never run with an elsinore but it sure would be nice to just have it move forward when the throttle is opened.

[Lozza]

Is the timing edge of the piston flush with the top of the barrel?
Assuming a 50mm sroke and a 100mm C to C rod length 28mm from top of barrel is ExO 89deg ATDC which s fairly conservative the 25mm equates to ExO 83 deg ATDC which is close to what an RS 125 would run. 72% is maximum you can go for a single exhaust port with a resaonable radius on top and bottom of the port.
Based on your figures 1.5mm off the top of the port and out to 40.3mm with a 150mm radius top and bottom with 6mm radi on the corners.You will need at least 32Deg of blowdown time.
A 125 should easily work with a 32mm
Reed block size and petal material?

[vandy010]

thanks Lozza,
i get a little lost with the degrees of it all but followed the measurement part of it.
reed block,
have already doctored in a reed block from the DT2 which is the same size as the YZ125D and about as large as i can go, petals will be boyseen as i already have them on hand.
another person i spoke with ages ago did this same reed mod and was happy with the outcome hence my trip down this path.
this barrel probably won't get on the bike till january or so
but when it's all done i'll let you know how it goes with a 32 mikuni as planned.
as for timing edge being flush, i'd be a day away from confirming but will guess a yes. same with 100mm rod length.
my figure of 25mm hieght from the exhaust port comes from a workshop manual with "hot" porting specs for this bike, although they still use the std reed set-up.

[Nathan S]

Lozza, Vandy: MX125A is basically the same thing as DT125A.  What's good for the goose should also be good for the Vander...

[Lozza]

Your DT barrel is now more TZ than YZ Got that piston for me?

[Freakshow]

Not port related per-say, but i had a new 1.5mm wisco in that TM 250 i ran this year, i pulled the head off last night just to check it was still ok before i stored it till next year ( im making 2 piles - the fix before next season and the she'll be fine pile) 

Any how when it ran it would alway have a load rattle and i put it down to the fins/ no rubber blocks, with the head off there is no movent in the piston (think it was 2oth clearance) anyway there is no movement back or forth its tight, however there is a flat spot running down the front edge of the bore ( the rest is still perfectly cross hatched) right down the centre of the exhaust port up to the top, from the angle i was looking i cant tell if its on the thrust, but it looks more like the piston or ring is getting dry or a hot spot on the EX - bridge and dragging on the way up.  Should this piston have had a few holes drilled on it to lube up from the inside ? does this models stock piston have bridge lube hole in them ? i never saw the suzuki piston so i never put any in, but i think it really needs something there as its wearing a very distinct shiny patch / groove up  the barrel the exact width of that bridge ( about 3-5 mm wide) and all the way up -  or is there somthing else going on here ?

[Lozza]

I think you answered your own question there Freaky

[DJRacing]

There is always another way to cook the goose guys, lets say the MX/YZ-A runs a 28mm carb and it fits into the intake boot of the reed block ok, but you want to run a 30 or 32mm carb and it doesnt fit the intake boot. Bore the carb out and do less work to the reed block area and see how that goes before porting. If all is good then start porting and you can probably port the barrel similar to a YZ-C. Anyway, just a thought for you guys to have a beer over. It is easier and alot cheaper to stuff up a carb than a barrel. 

[Freakshow]

I think you answered your own question there Freaky

well thats my thought but im no expert so i was looking for a tick or a cross on my thinking from someone who knows somthing?

 im guessing your saying it needs some oil holes to settle down the bridge ?  Do the stock suzi have them in the piston or not ?

[TonyB]

83% vs 87% eva portblowjobsdegrees btc kk*76^ blah blah blah if you want more BALLS just buy a 465 

[lukeb1961]

Do the stock suzi have them in the piston or not ?

Haven't got a std at-hand, but the Wiseco definately does - has two.
Luke