i am trying to tame a 2003 yz85, i have installed a flywheel weight and moved the carb needle to a richer setting, this has helped some but i need to tame it more. someone suggested to me to reduce the ID of the exhaust pipe at the slip joint between the head pipe and the silencer by 25% by welding in a washer. does anyone know if this helps and what are the long term effects to the engine.
ever tame a yz85?
- Thread starter W00TsP0P
- Start date
- Dec 26, 1999
- 19,765
- 1
Maybe just pay attention to how much throttle ya' feed in to it? No really. The bike doesn't have a PV so the power is never going to be very linear. The flywheel weight is a good choice and the above mentioned trip to Eric Gorr would be another great suggestion but mine is the least expensive ;)
- Dec 26, 1999
- 19,765
- 1
Porting is more permenant but i's not something that would hinder a developing rider. It would just improve the delivery which makes it feel more easily controled.
I guess you could also place a little spacer in the carb to limit how far the slide opens if control of the throttle is an isse.
I guess you could also place a little spacer in the carb to limit how far the slide opens if control of the throttle is an isse.
Dirtbike'n man
Member
- Feb 20, 2004
- 241
- 0
i had a pipe restrictor in my first bike (pw 80) and recall when my dad took it out
really opened the bike up so i guess it made it mellower
really opened the bike up so i guess it made it mellower
- Dec 26, 1999
- 19,765
- 1
I think the exhaust restrictor idea is bad news on a performance bike. I really really really think the throttle limiter may be your best bet if you are worried about the rider not being able to control the power. It doesn't make any permenant changes and is easy to remove. A small piece of brass tubing that is just big enough to slide over the cable end cut to whatever length you desire based upon how much you want to limit is safe and non-damaging. You can even cut it down as you feel more comfortable letting the rider have more throttle.
gwcrim
~SPONSOR~
- Oct 3, 2002
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Yamaha PW80s (and others I assume) come with a'washer' between the pipe and the heads. Makes a pretty big difference in power. I can't imagine that you'd "hurt" anything other than maybe a spark plug if it fouled.
Doubling up on the base gasket is a good idea too.
Doubling up on the base gasket is a good idea too.
W00TsP0P said:
Yes, double up the base gasket. I haven't tried these mods myself, but have seen this written up several times to detune a 2 stroke motor. Try retard the timing first. It's the easiest and cheapest thing to try.
This might be a crazy idea, :eek: over oil the air filter rather than welding washer on the pipe. Remember though you will probably have to rejet the motor with just about all these ideas.
Patman's idea is the cleanest and very easy to do, and NO rejetting required. Good luck.
- Dec 26, 1999
- 19,765
- 1
The 360 KTM's used the 250 exhaust to save money. Problem was the stinger section of the exhaust was way undersized so getting the bike to run clean was a huge problem, it might bog or it might be lean or someplace in the middle for a while but they never ran correctly. Change that pipe out to one designed for the 360 and it was an entirely different story! The undersized stinger was basically an exhaust restrictor on a performance 2 stroke design and it was nothing but a huge PITA. Additionally limiting the travel of the throttle does not change how the power is delivered just how much is available so when the modification is removed the rider will not have to relearn how to deal with the different power delivery.
Limiting the throttle travel shouldn't require any jetting changes if the bike is setup properly to begin with and is easily modified for more travel or removed. I'll venture an educated guess based on past experience this isn't going to be the case with a restrictor in the exhaust.
Then again it's your call to make it as easy or difficult as you want. I've been there and given the directions for a couple of short cuts, take it or leave it.
Limiting the throttle travel shouldn't require any jetting changes if the bike is setup properly to begin with and is easily modified for more travel or removed. I'll venture an educated guess based on past experience this isn't going to be the case with a restrictor in the exhaust.
Then again it's your call to make it as easy or difficult as you want. I've been there and given the directions for a couple of short cuts, take it or leave it.
Put a restrictor washer between ex. port and headpipe with a hole about 1/2 the size of the stock hole. Works great and you can make the hole bigger weekly/daily as experience increases. Do not raise the cylinder as that would just make it come on later and harder. I did the washer on a KTM pro 50 until my son could get his brain and wrist connected. Never fouled a plug nor hurt any parts.
Wes Gilbert
Boyesen Precision Porting
Wes Gilbert
Boyesen Precision Porting
- Thread starter
- #19
fastwes
Put a restrictor washer between ex. port and headpipe>
please clarify for me (between the head and the pipe)?
someone else recomended to cut the pipe at the silencer and put a washer there.
i was figureing since the YZ85 had a slip joint in the pipe about 6" before the silencer i would do it there. they also recomended a 25% reduction. at the slip joint the pipe ID measures .804" so i would put in a washer with an ID of .603".
would there be any preference where it is done or the difference in effect?
Put a restrictor washer between ex. port and headpipe>
please clarify for me (between the head and the pipe)?
someone else recomended to cut the pipe at the silencer and put a washer there.
i was figureing since the YZ85 had a slip joint in the pipe about 6" before the silencer i would do it there. they also recomended a 25% reduction. at the slip joint the pipe ID measures .804" so i would put in a washer with an ID of .603".
would there be any preference where it is done or the difference in effect?
- Dec 26, 1999
- 19,765
- 1
Another alternative is to take a hammer and smash the expansion chanber a few times. Then just remove the dents as you want to gain the power back. Now of course it may change the power delivery a bit like any exhaust restriction will but it is yet another alternative.
OR you can weld a washer to the end of the exhaust. This is yet another spin of the exhaust restriction theme but instead of having to remove the pipe to insert a larger one or drill it out it's right there in front of ya'. Two little tack weld should be plenty and it's easy to remove.
I'm pretty sure any of the methods discussed so far WILL work to some extent. I am equally sure that some will work significantly better, will make the transition to full power easier and will require less effort.
You might be suprised how quickly your rider will actually adjust to being able to deal with the full power available.
OR you can weld a washer to the end of the exhaust. This is yet another spin of the exhaust restriction theme but instead of having to remove the pipe to insert a larger one or drill it out it's right there in front of ya'. Two little tack weld should be plenty and it's easy to remove.
I'm pretty sure any of the methods discussed so far WILL work to some extent. I am equally sure that some will work significantly better, will make the transition to full power easier and will require less effort.
You might be suprised how quickly your rider will actually adjust to being able to deal with the full power available.
freightrain
Member
- Nov 17, 2004
- 19
- 0
I'd also check to see anyone makes a flywheel weight for the bike. My dughter's LT 80 came with a restrictor in the carb that kept the slide from opening all the way. I still have it lying around if you want to see if it fits.
xsnrg
Member
- Jul 20, 2004
- 728
- 0
See "Making a Bike Girl Friendly" on this page: http://www.ericgorr.com/faq/new_dirt.html
I stumbled on to it shortly after reading your post. Hope it helps.
I stumbled on to it shortly after reading your post. Hope it helps.
- Thread starter
- #23
this weekend i installed a washer in the pipe at the slip joint between the pipe and the silencer.
just tacked it in so it could be removed later, it did make a difference in power. the bike still has quite a bit of yank still in it though even with the flywheel weight but i am headed in the right direction.
i thought that i would try the throttle limiter but was concerned about climbing hills and needing the use of the full power range. i was thinking maybe a short heavy spring would give the feel of limiting the throttle when it made contact with the slide but you would still be able to twist harder and still have full throttle if it was needed. (any thoughts)?
just tacked it in so it could be removed later, it did make a difference in power. the bike still has quite a bit of yank still in it though even with the flywheel weight but i am headed in the right direction.
i thought that i would try the throttle limiter but was concerned about climbing hills and needing the use of the full power range. i was thinking maybe a short heavy spring would give the feel of limiting the throttle when it made contact with the slide but you would still be able to twist harder and still have full throttle if it was needed. (any thoughts)?
I set up my sisters woods race bike. I started out as a KX80 big wheel, was bored to 107.4 by RPM (excelent people to deal with). Also had Rick neck down the exhaust port, he welded in an aluminum sleeve and machined it out some so that the end result was a smaller, lower exhaust port. He also bumped up the compression a bit, polished the intake ports etc. I played with the jetting until it was nice and crisp. The result was an engine that felt more like a late modle YZ125 than anything else. The power was boosted everywhere, but especially at lower rpms. The power curver was much smoother but still pulled strong. She won the women's HS championship on the bike and even holeshot a 200cc class race:).
good luck
good luck
