amazing little 50cc going to park some bigger ones!

[Street Ryderz]

I had received this Starfire gen II engine from 2009-2010 as a basket case from a customer who really messed it up breaking both exhaust studs and a mounting stud in the case and then tried drilling them out with no luck and just making it worse! When he brought it to me I saw the broken studs and just quickly looked it over and thought it may still have some useful parts and he only wanted $20 for it so why not right!I put it aside for quite some time thinking when I need something from it all good then years later my son's 48 needed a clutch rebuild so I took it apart to take what was needed and was shocked to see it had a 17mm crank, solid weights,6203 main bearings and was allready trued and balenced quite well!I took what was needed from it and put it aside again then just last fall I was comparing port timings and looked at it's cylinder and again was thrilled to see that firstly it's walls were mint not even fine wear marks in the chrome plating and also the transfers were 2mm lower than any cylinder I have ever had or seen!The intake was also at 43mm at the top of port and 55mm from the deck to the floor of port, The exhaust port was at 27mm from deck to top of port not bad for stock.I have changed the intake and droped the floor 1.5mm,raised the exhaust port 2mm and added 10mm in width to both 5mm per side other than correcting the angles on the side closest to the exhaust of the transfer walls and blending the ramps I left the transfers alone and ended up with a port map that sings and still has bottom end torque that honestly seem's stronger than most 66's It's port timing durations are now 164 exhaust,110.43 transfers,127 intake blow down is 27 it's piston crown comes flush to the deck and has a 6cc head yet still only has 6.25 to 1 comp ratio the compression gauge says 190 p.s.i though that will drop as the rings seat during break in!Right now it's rich for break in and is running with a potatoe pipe with two of the three baffles removed no tuned pipe (expansion chamber) yet and still as soon as the rpm starts to climb say above 2500 it just wants to keep pulling and hit 40mph in under 100 yards with the stock 44t gear thats just over 9000 rpm and it still wanted to go more! The mid range throttle responce is awesome quick and strong this thing is going to be fast!

 

[Street Ryderz]

This is the bike I put the little guy in! nothing special it's an aluminum road bike with a nice sis bb so I put heavier wheels and the front suspention with disk break on it just have to put rear v break and good enuf to mess around on!

 

[FurryOnTheInside]

Looks sweet.

 

[Street Ryderz]

Looks sweet.

Thanks!

 

[Street Ryderz]

I wonder why grubee stopped bringing these pipe's in and how sbp has the closest varient? makes me wonder big time! look at the one's in the top corners looks like the same chamber to me just different header tubes!

 

[Street Ryderz]

It was quite nice here today so messed around with the 50 and put a speed carb on it! Well the speed is 15mm and jetted with a 70 jet and it's not enough the bottom end sounds like it's sucking air starving for fuel!Once it's rolling it just keeps climbing but it can be better yet!And this is still prior to putting a real pipe on!

 

[gary55]

I had received this Starfire gen II engine from 2009-2010 as a basket case from a customer who really messed it up breaking both exhaust studs and a mounting stud in the case and then tried drilling them out with no luck and just making it worse! When he brought it to me I saw the broken studs and just quickly looked it over and thought it may still have some useful parts and he only wanted $20 for it so why not right!I put it aside for quite some time thinking when I need something from it all good then years later my son's 48 needed a clutch rebuild so I took it apart to take what was needed and was shocked to see it had a 17mm crank, solid weights,6203 main bearings and was allready trued and balenced quite well!I took what was needed from it and put it aside again then just last fall I was comparing port timings and looked at it's cylinder and again was thrilled to see that firstly it's walls were mint not even fine wear marks in the chrome plating and also the transfers were 2mm lower than any cylinder I have ever had or seen!The intake was also at 43mm at the top of port and 55mm from the deck to the floor of port, The exhaust port was at 27mm from deck to top of port not bad for stock.I have changed the intake and droped the floor 1.5mm,raised the exhaust port 2mm and added 10mm in width to both 5mm per side other than correcting the angles on the side closest to the exhaust of the transfer walls and blending the ramps I left the transfers alone and ended up with a port map that sings and still has bottom end torque that honestly seem's stronger than most 66's It's port timing durations are now 164 exhaust,110.43 transfers,127 intake blow down is 27 it's piston crown comes flush to the deck and has a 6cc head yet still only has 6.25 to 1 comp ratio the compression gauge says 190 p.s.i though that will drop as the rings seat during break in!Right now it's rich for break in and is running with a potatoe pipe with two of the three baffles removed no tuned pipe (expansion chamber) yet and still as soon as the rpm starts to climb say above 2500 it just wants to keep pulling and hit 40mph in under 100 yards with the stock 44t gear thats just over 9000 rpm and it still wanted to go more! The mid range throttle responce is awesome quick and strong this thing is going to be fast!

You might want to check that comp. gauge. I'm guessing you are around 600 abv. sea lev.. So 190/14.37=13.2 to1 comp ratio.. 6.25 to 1 would be 14.37X6.25/1=89.9, oh now I see. It's 90psi not 190psi.. Had me scratching my head for a second.

 

[gary55]

Glad you found that case you were looking for.

 

[Street Ryderz]

You might want to check that comp. gauge. I'm guessing you are around 600 abv. sea lev.. So 190/14.37=13.2 to1 comp ratio.. 6.25 to 1 would be 14.37X6.25/1=89.9, oh now I see. It's 90psi not 190psi.. Had me scratching my head for a second.

Corrected and uncorrected compression ratios calculator
Bore: mm 40
Stroke: mm 40
Height over exhaust port, top of port to top of barrel mm 25
head volume (head cc) 6 cc

uncorrected 9.38 :1
corrected 6.24 :1
This is how I came up with the comp ratio that I posted it's from lambretta's port timming calculator.And it seemed a little odd to me aswell!because the comp gauge is mint and kept in it's box when not in use and it reads correctly on other engine's!And yes it reads 190 p.s.i every time and I checked it three times. When doing a comp check I'll kick it over three times to make sure it hit it's peak .Oh yeah I look at the plug while it was out for comp check and just as I thought just about right now with the jet drilled out to 72 it seems alittle lean in the bottom end and almost perfect on top mind you thats with stock ignition and stock plug lol so I guess thats not bad!

 

[zippinaround]

wow! 190 psi! surely that'll removing your chrome from your cylinder pretty quick? i like that tester though where did you get it if you dont mind?