Reed Spacers and the two stroke

[TR]

Can anyone generalise about the effects of using reed spacers on two strokes ? If the crankcase volume increases and pumping pressure decreases what is likely to happen ? Reed spacers are being sold for ATVs claiming that the reeds can be allowed to open further, improving low end torque and throttle response.

Anyone had experience with these type of mods ?

Thanks in advance.

 

[Jman271]

My 02 CR125 came w/ one stock, it ran better w/o it. I think the idea behind the spacer is to try to get low-end out of the motor. I heard that in some cases like the 01 CR250, as well as some others, it "kinda" worked. Other models like mine, it didn't at all. Don't know about the ATV's, though-

 

[125 rider]

They are supposed to provide better low end torque and response but like most pipes, it is a trade in power and usualy hurts top end.

 

[marcusgunby]

I have tried mine in and out on the 02 CR125 and find it really hard to tell any difference.

 

[DEANSFASTWAY]

They seem to work best on bikes where the top reeds block the rear transfer port , if you pull the reeds back it helps to uncover the port and also makes the intake tract longer . It usually works best on 250s and mostly on bikes with the reeds in the cyl not in the cases like most current 125s . They used to work on older YAMs p[retty good ,thats what I recognized anyway . They work good on blasters and banshees .

 

[TR]

DEANFASTWAY, did you try using a reed spacer on the husky 360 ?

thanks,

 

[EricGorr]

Dean said something important, the original reed spacers were made for Yamaha YZ motorcycles dating from the early 1980s where the reed stops blocked the rear center boost ports that linked the crankcase to the top end. Putting a reed spacer on those bikes made a huge difference. So aftermarket companies made them for everything and claimed 5hp, no matter if its a KX60 or a CR500. Every once in a while they resurface under extravagant advertising claims and sell for a while then disappear.

This is what a reed spacer does;
1) Increase the volume in the crankcase
2) Lengthen the intake tract
3) Lengthen the distance from the piston face to the reed tips

The crankcase volume and compression ratio is different for all engine displacements. Whats the optimum? There is a range of standards from 1.2 to 2.0 to 1. Large displacement bikes tend to have high ratios because of inherent geometry, just the normal sizing of the cylinder, crankcase, and crankshaft flyweight diameters. Small bore engines are challenged to get the crankcase compression ratio high enough for quick throttle response.

If you look into the early karts of the 1970s, there were all sorts of aftermarket accessories that took up volume in the crankcase including piston stuffers that were plastic inserts fastened to the cases and fitted to the underside of the piston. They had ellaborate porting to channel the gasses being squeezed out from the underside of the piston towards the transfer ports. They called them turbo-squeezers, piston superchargers, and high speed gas funnelizers. All funny stuff! I'm surprised that no modern aftermarket company has copied and recreated that old stuff from karting. In 1975 Mercury produced a snowmobile called the Snow-Twister that featured a shielded crankcase with a knife shaped connecting rod that protruded from a narrow slot in the crankcase. The case was fitted tight to the flyweights to reduce windage and volume in the crankcase. KTM copied that shielded case design for the late model 125 and now shifter kart tuners are fitting aluminum tubing to the cases of CR125 and CR80 engines.

I guess all I can say about reed spacers is that they may or may not work for your bike and riding situation. My friend Jim always puts them on his 144s that I build him every year. He swears by them and I swear at them. But as long as he thinks they work and it makes him ride better, who am I to argue.
Two-stroke tuning is subjective and the world of unsteady gas dynamics is a turbulent one :eek:

 

[Rich Rohrich]

Originally posted by EricGorr
the world of unsteady gas dynamics is a turbulent one :eek:

:confused: :aj:

 

[125 rider]

Good info, eric.

 

[DEANSFASTWAY]

TR I used to work in a Husky shop where and when bikes came out sometimes we needed to find a quick or easy way to fix problems on them . We built the spacers on the Huskys to help the MIK carb bowl clear the top of the engine case L/S The spavers were like #/8 thick and helped alot . We think it helped spread the power of those huskys a little further also but at the same time we were putting in good dual stage reeds which shifted the power curve around , The 360s had enough powere for just bout anything except maybe a drag race with a CR/KX500 or a hillclimb . We also raised the cyls by using thick base gaskets and did different things to make them start easier. The 250s were really good bikes actually I liked the earlier 250/360 with the showa suspension rather than the MZ forks becuse the MZ s were usibng up seals alot unless you used forkboots and it seemed everyone wanted to see those shiny fork tubes just notwith oil leaking . I dont really subscribe to some of the new go fast mumbo jumbo that is out there like turbo veincrank mods and junk .

 

[Zig-Zag]

I just took my Moose Reed Spacer off my 01 Cr250. It did make a difference in the power curve IMO. It actually felt like too much for me down low, but then again I am slow compared to hard-core racers. I am now gonna try riding without it now that I know what it does to see which way I like it. It was worth the cash just to see a difference and in some cases I may prefer it on but the track I ride (sandy whoops) I don't want that much hit right off 1/8 throttle. I'm gonna give it to my 220 lb. friend to put on his 96 CR to see if he likes it for his riding style. My .02

 

[Guaryzzzpode]

With the reed spacer you increase the crankcase volume, thus decrease the compression. This would result in a lower final compression, and in my head lower compression=lower torque (ceteris paribus). This could mean that reed spacers provide mor Top-end, sacrifizing Low-end.

Please let me know if I'm wrong. :uh:

 

[marcusgunby]

Some bikes will respond well to spacers-it all depends on the original spec of the engine and any mods done to it, ed a std cr125 may not respond well but after lowering the cylinder and say stuffing the transfers with epoxy it may suddenly like a reed spacer-thats why i dyno my bikes-its the only true way i can tell if something works.I did a few mods to my 02 a while ago and it felt good to ride, on the dyno it was down 1hp from the mid upwards and no better bottom end(which i was after)it was just on that track it didnt need much hp as it was nice a dry and cool.

 

[Durt Cycler]

The only thing I get confused about is Moose claims it helps bottom-mid range while Trinity Racing says their reed spacers increase the topend???

 

[marcusgunby]

I beleive a reed spacer is meant to lower crancase compresion that should increase low end, but you cannot generalise on a 2 stroke as some just dont follow the rules.eg if a 0.5" spacer gives more bottom end does a 1" spacer work 2* as well?