Dyno testing 'performance mods'

[DieselTech]

Thx

I wish you could get smaller main jets for these carbs. Make the adjustments a little less sensitive. I wonder if I can't turn one down on the lathe, I think there's some brass stock here somewhere...

So far there's no real gains to the Tilly vs the BoFeng so I'm considering putting the BoFeng back on. It sure is easy to tune though

You should be able to get jets. They might be hard to source where you are at. Yes the Tilly is super temperamental as far as fuel settings. I lil bit goes a long ways. Lol I think I spent 3 days tuning b4 I got mine the way I liked it. Also pop off pressure can affect your fuel mixture. I cant remember if the higher the pop off pressure is, the richer they run & tune on the fuel screws. Or if it's the other way around.

 

[DieselTech]

I also agree that the bofeng will be easier to tune. I think also more people is going to use a bofeng carb on their builds. I think if time & funding allows you to test both would be nice to see & hear about.

I think when you get around to testing reeds the Tilly might come out on top. Reeds should also help to restore some low end power.

 

[robe]

Interesting stuff as always. Thanks for sharing all your hard work.

 

[robe]

I've been thinking about the big Tilly carb. Oh, dear.

I think that model may be too big for this size of engine. May be why it is hard to tune. This size is similar to the ones used on the old Husqvarna 2100 chain saw, those were a 100cc 9 hp monster you could put a 54 inch bar on and bury the bar all day long. Most guys ran a 48 inch bar with lots of power to spare.
One of those would make quite the bike motor.

I'm thinking maybe a smaller sized one for a 60 to 70 cc saw may work better. I think I will send this one back according to your observations.
I put the BoFeng back on mine and went for a long ride in the country and it had much more power across the RPM band, what a difference from the HP.

All good until I sheared off the disc brake mounting from the rest of the hub. Worked out that it was the last hill before home.

 

[Chainlube]

Ahh ok, yeah that'll be ideal. A stock ms660 maxes out at 8krpm?

According to acresinternet max is 13,500.

Model Profile: MS 660, MS 660W, MS 660 Arctic

 

[WillitBoost]

if there's power up there at 13500, that'll be one powerful bike!

I think you're right that this carb is a touch oversized. It still runs fine and once tuned it shouldn't need touching again. A BoFeng is just easier though

 

[WillitBoost]

So, given that this CDH jug will not make power over 8000rpm no matter what we throw at it, I should probably design a pipe for a 5000-6000 peak RPM to get the most out of a stock Chinadoll...

I also want to try a 3rd bend axis in the hydroforming. I'm thinking if i bend before I weld the halves together, when it inflates it could potentially make a corkscrew kind of shape which would clear the frame and wrap up the top like the CDH66 does.

 

[WillitBoost]

a little more data.

I widened the exhaust port and leveled out the roof. the yellow and blue lines are with the porting and my hydro pipe and comparing the bofeng with the tilly. Both jetted as best they can be, the tilly is producing an extra 1.75HP than the bofeng at higher RPMs. This is still the junk jug and piston.

So while the BoFeng can flow 4HP, this is only true at ~4000rpm or so. It can't flow enough up at 7000RPM to make even 3HP.

The Tilly is too big for this motor down low.

The stock muffler without cap, and bofeng with no filter makes the beset average power compared to anything we've tried.

Widening and raising the exhaust port does shift the power band up.

Knowing this - I feel the best combo will be a BoFeng with a pipe tuned for 4000RPM.

I think I need to try a different carb. Something smaller than the tilly but just as tunable,

 

[GW's Motorized]

Now i really want to see that tilly on a phantom

 

[DieselTech]

a little more data.

I widened the exhaust port and leveled out the roof. the yellow and blue lines are with the porting and my hydro pipe and comparing the bofeng with the tilly. Both jetted as best they can be, the tilly is producing an extra 1.75HP than the bofeng at higher RPMs. This is still the junk jug and piston.

So while the BoFeng can flow 4HP, this is only true at ~4000rpm or so. It can't flow enough up at 7000RPM to make even 3HP.

The Tilly is too big for this motor down low.

The stock muffler without cap, and bofeng with no filter makes the beset average power compared to anything we've tried.

Widening and raising the exhaust port does shift the power band up.

Knowing this - I feel the best combo will be a BoFeng with a pipe tuned for 4000RPM.

I think I need to try a different carb. Something smaller than the tilly but just as tunable,

Yep mine is a doggy down at a low rpm, it dont come alive on mine till about 18-20mph.