T250 Race Bike will not start

[dannaz94]

Hi Guys
Having issues getting my newly assembled t250 race bike to start.
i have spark courtesy of the new powerdynamo ignition system. have checked the timing and am pretty certain its correct.
i have cleaned and rebuilt the carbs. they are standard carbs with standard jetting. the engine dosent run an oil pump as the previous owner did the crank work and oil slinger removal as required to remove the pump.
am running 50 to 1 premix. Is that too much?
getting compression values of just over 100psi on both sides. is that too low?
and what i think may be the thing stopping it from starting is the barrels have been ported? i dont the know the specs on the porting just know that i compared the barrels to a standard set i have and they are definitely larger.
so can porting cause hard starting issues?

Cheers

Dan

 

[onefromexile]

Barrels ?? Head port ??
Or over bored
Pistons??


Sent from my iPhone using DO THE TON

 

[crazypj]

Your going to need larger jets when you run without oil pump.
50:1 should be fine depending on what oil your using (don't use 100:1 pre-mix no matter what oil your using, motor was designed for oil pump or 25~30:1 pre-mix)
Timing needs to be right. You would be better off removing heads, making spacers and clamping cylinders down tight then using DTI to make sure you have timing set at 2.8mm BTDC. (I think that's right for T250?)
Do you have measurements of port sizes? If the intake was lowered too much you may have a 'free port' where piston skirt doesn't close it so you get no crankcase compression. (or if piston skirt was shortened) Where is bottom of exhaust port in realtion to piston top at BDC? How tall is the port? (should be around 21mm~22mm) 100PSI isn't too bad for a ported motor, stock corrected compression ratio is only about 6.8:1 and will be lower with a raised exhaust port. Have the heads been machined to raise compression? You do have the right spark on rigt side and left spark on left side?

 

[dannaz94]

Timing is now spot on

Exhaust port is 22.5mm. Intake haven't measured yet.
Bottom of exhaust port is level with top of piston at bdc. Pistons are untouched. Brand new old stock.

Borrowed a set of rollers. And she fired!! Only to rev to the moon. Hit the kill switch. And then unfortunately it started raining. Any suggestions for carb settings and jetting size. I know stock carbs are no good. But it's only for testing the engine.

 

[2_DONE_THE_TON]

Timing is now spot on

Exhaust port is 22.5mm. Intake haven't measured yet.
Bottom of exhaust port is level with top of piston at bdc. Pistons are untouched. Brand new old stock.

Borrowed a set of rollers. And she fired!! Only to rev to the moon. Hit the kill switch. And then unfortunately it started raining. Any suggestions for carb settings and jetting size. I know stock carbs are no good. But it's only for testing the engine.

what kind of carbs are you running?Mikunis VM´s?
Did you install your slides correctly?When mounted in the wrong direction the motor will stick WOT.

Angled part of the slide should point towards intake-airfilter side.

 

[crazypj]

It's more difficult to fit the slides worng in the early Suzuki carbs as they use a pull rod through the cap for idle adjustment. Yamaha RD is very easy to put slides in backwards when you swap left for right.
I modified the carbs I have to use a normal slide adjuster screw plus made new low profile tops as there isn't a lot of clearance fitting VM's on CB360 I also drilled and tapped for vacuum take off 8) These are 'old' carbs off T305, not normally spigot mounted
You'll notice a swapped enrichener plunger to make them easier to use (rather than have the lever style and mess around between carbs)

 

[HollywoodMX]

It's more difficult to fit the slides worng in the early Suzuki carbs as they use a pull rod through the cap for idle adjustment. Yamaha RD is very easy to put slides in backwards when you swap left for right.
I modified the carbs I have to use a normal slide adjuster screw plus made new low profile tops as there isn't a lot of clearance fitting VM's on CB360 I also drilled and tapped for vacuum take off 8) These are 'old' carbs off T305, not normally spigot mounted
You'll notice a swapped enrichener plunger to make them easier to use (rather than have the lever style and mess around between carbs)

Those look old! And obviously modified.

 

[crazypj]

Yep, probably been kicking around since the very early 70's ;D
I started 'playing' with bikes in 1968
They have been on a few different bikes over the years, set up for XS650 at present 8)