More low end - engine guys

[stylenb]

long time reader, first time poster...lol

So this is what I got
86 short rod, 86 head
ported (RB Porting) dune port
120 over
38mm Airstryker (58 pilot, middle, 180 main)
Cool Head (21cc pump gas, stock comp)
Cr250 ignition 2001
Dynoport pipe
reed spacer
open lid

So the bike runs great(midrange and up pulls real hard, snappy, etc), but I am having trouble in the tight stuff. I already have pretty much the lowest gearing possible(11/40) so scratch that.

I need more low end.

I have my eye on a flywheel weight, slow down the revs, hoping to help starting on steep inclines?

also a pwk 36mm?

maybe a diff pipe?


Was even considering raising the compression, but striaght race gas is to much $$, can I mix with 93 and jump up the comp? Anyone doing this? what gas do you mix? leaded? unleaded? ratio? will this help?


On the esr ignition adapter, I have it to one side of the oval, can't remember what side, but where should it be?


Ok thats a lot of questions, any help would be appreciated. :)


Just need to make my bike more well rounded, ride all kinds of diff terrain.

[stylenb]

forgot to mention, I ran the bike with the stock PJ at first, throttle response, lower rpm chugging way better, However, the a/s is way better in mid to top.


Is a 36mm pwk, middle of the road?

Can I have my cake and eat it to?

[450rJam]

dune porting usually favors the mid/upper rpm range
(loses a little on the low end)

bump comp will help buy your right about gas $$$$$$

your running an 11 counter sprocket? thats tight on the chain

you done a comp. check ? when the rings start to go the low end
goes with them

[mineralgrey01gt]

my bike pulls its nuts off 1, 2, 3. After that it doesnt pull as much at all. All mods are in sig. Also im running a 13/39 set up

[norcalduner]

I'd start with getting another cylinder and have a woods/mx port done on it which will be IMO the biggest improvement you can do.

[my88r]

PUT A PAUL TURNER TYPE 6 PIPE ON IT.:macho

[wilkin250r]

Originally posted by stylenb
Can I have my cake and eat it to?

Not really.

As others have said, your problem isn't gearing, or even carburetor. More than anything else, it's your porting.

And unfortunately, one high-rev component and one low-rev component together will not give you the best of both worlds, it will give you the WORST of both worlds. Your carb might want to work at low revs, but the porting/pipe won't let it. Then at high revs when your porting/pipe want to come on strong, the carb chokes it off. They don't give you all-around power, they give you all-around garbage, because they're fighting each other.


If you want more low-end, you need to revamp your porting/pipe combo.

[ct350trx]

I have a 11 oz flywheel weight on my cr250 ignition and it really helps on the lower rpm's

[86 Quad R]

Originally posted by ct350trx
I have a 11 oz flywheel weight on my cr250 ignition and it really helps on the lower rpm's

thats what i'd try and maybe a 36mm carb. it should help a bit but, as mentioned your porting is a factor.

[stylenb]

Unfortunatley, a diff jug/porting is out of the question.

Also, so this doesn't get mixed, I am very happy with the work that was done with my jug, excellent price, great work and support, overall running is fantastic!!!


I know I can make this better, My b-in-law has the same porting,same pipe, 38 pj, with stick ignition, same bore, same pistion, but he has an 88 head and spacer plate.

His bike is lot more well rounded then mine, and we run the same gearing and weigh the same.



any answers to the more specific questions about the ignition? or mixing race gas/to what compression?

[Buttermilk]

With out knowing what your port timings really are (dune port is too generic...) it's really hard to say it's your porting - and it may not be....

Something you can do with the CR ignition is advance it, if you haven't already (there's about 5 degrees or so that you can play with...you'll have to remove a small plate on the stator mount or remove it... I slotted mine...)

Advancing the timing will give you better throttle response, improve your bottom end and mid range acceleration, plus increase your top peak hp (but will also **** the curve to the left....).

Bump up your compression some too will help with bottom to mid power, but at some point you would need to run higher octane fuel.

If you're b-n-law has a similar setup, but is running a long rod engine, then that will contribute to different power characteristics. Longer Rod motors tend to be a bit torqier.

[stylenb]

Thanks buttermilk, thats the kinda info I am looking for. If I remember correctly I can adjust that ignition, a little each way. I just don't which way to move it?


I am willing to run like half/half mix with race gas, I can afford that. What compression would that allow? What dome do I switch to?


I know the point of race gas is to eliminate detonation, kinda looking for a starting point.......or someone doing this already with good results.