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Tuning a 150R down some?

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I'm wondering if anybody has ever DE-tuned a 150R at all. I'd be interested in dropping about 20% of it's power for greater reliability/longevity, and to make it a better ride to run on pit bike tracks.

We've been talking about converting a 150R chassis to accept a 150F motor, then building up the 150F motor... Wouldn't it be easier, cheaper, and less of a hassle to tone down the motor that comes in it, and just race the bike like that in the pit bike races? --L*64

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If you leave the engine stock and do regualr maintaince it should be extremely reliable. If you are wanting to reduce the power output slightly or tame it, I'd suggest a flywheel weight and one of the "quiet" aftermarket exhaust with a spark arrestor.

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Adding another base gasket under the cylinder will drop your C.R. and lower power, make the motor run cooler too.

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Adding another base gasket under the cylinder will drop your C.R. and lower power, make the motor run cooler too.

That's a good one. On some of my strokers I built I used up to three base gaskets, just so I wouldn't have a 14:1 CR.

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That's a good one. On some of my strokers I built I used up to three base gaskets, just so I wouldn't have a 14:1 CR.

:thumbsup: Please, don't anyone else construe that to mean that this procedure is an acceptable method of reducing CR.

No reputable professional engine builder would consider doing that.

Easiest/safest way to detune an engine is to reduce throttle opening. I.e. a throttle stop. (although reducing power in a bike you are going to race seems "counterproductive". But, hey, that's just me....)

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Tons of engine builders do that. That's why you can get custom head gaskets in different thicknesses. It's achieves the same thing. That idea has been around for as long as people have been building motors.

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Tons of engine builders do that. That's why you can get custom head gaskets in different thicknesses. It's achieves the same thing. That idea has been around for as long as people have been building motors.

Very true...

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( I was addressing your original post of using three base gaskets, not addressing the issue of using a custom-thickness head gasket. Try to stay on track....)

You seem to feel that stacking multiple gaskets (under the cylinder) is the same as using a custom-thickness (head) gasket.

It's not.

Are you taking into account the change in cam timing that occurs when you do this? The professional engine builders make allowances for this where the amateurs may not.

Bottom line: using three base gaskets is a terrible idea....just ask the real engine builders.

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( I was addressing your original post of using three base gaskets, not addressing the issue of using a custom-thickness head gasket. Try to stay on track....)

You seem to feel that stacking multiple gaskets (under the cylinder) is the same as using a custom-thickness (head) gasket.

It's not.

Are you taking into account the change in cam timing that occurs when you do this? The professional engine builders make allowances for this where the amateurs may not.

Bottom line: using three base gaskets is a terrible idea....just ask the real engine builders.

So you're telling me flycutting a head or a cylinder doesn't? There are four things that affect your compression ratio: 1) Combustion chamber 2) Dome Volume 3) Valve relief volume , and finally 4) deck height. A thicker head gasket or base gasket will increase your deck height. About the only real difference it will make is take up the slack a bit in the cam chain and have barely any cam timing effect. So the answer: Degreeing your cam. You can read all about here: http://www.webcamshafts.com/pages/degreeing.html

This is what real engine builders do, they all have a degreeing wheel. You can't customize an engine without one.

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Hi Mr Remote check the cam timing before you fit your '3 base gaskets' recheck the cam timing after you have fitted it all back up,measure how many degrease the cam timing has moved,then pull the cam flange of the cam and refit in the correct position,trust me its alot harder to do correctly than it is to describe how to do it! Martin.

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I am not going to be using 3 gaskets. I was just curious. As I was typing an extended response to this I realized how it changes. Thanks for the info.

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Three base gaskets is obviously extreme, but I did it because it's about $40 cheaper and 2 or 3 weeks worth of riding rather waiting for a custom gasket. But it worked, it lowered the C/R so I wouldn't break a kick starter gear and it ran much cooler. I couldn't take it to my friend's machine shop to mill the dome down, so I improvised. Besides with XR motors, the tolerances are pretty wide. I NEVER said for him to do, I just said I've ran three before. But back to the running one extra base gasket, lots of people do it to lower the C/R or because cut the head or cylinder too much or for a lot a reasons. Bottom line is, if you don't want to do it, don't do it. But it's an easy option to lower the C/R down. Remember he wants to tone it down a bit, not increase power. That's the whole point of the post.

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:lol: Please, don't anyone else construe that to mean that this procedure is an acceptable method of reducing CR.

No reputable professional engine builder would consider doing that.

Easiest/safest way to detune an engine is to reduce throttle opening. I.e. a throttle stop. (although reducing power in a bike you are going to race seems "counterproductive". But, hey, that's just me....)

I just re-reread this and this does absolutly nothing to detune a bike. The power is still there but this is just a governor on the throttle. This is great for a klx110 or XR80 but it wouldn't have the same effect on a race bike. To de-tune the bike you actually have to de-tune the motor and yes that means one would actually have to work on the motor to do it. You can build a pipe to do it and the jet accordingly, custom cam, machine a restrictor for the carb, map the ignition, lower the compression ratio, smaller valves, and a ton of other things in various combinations. A dyno would help too. All take a lot of knowledge of fabrication and engine building. It's a lot of work, that's why you have to think, "what would the average person do?" The easiest to me, and this is just me is a smaller head pipe and an extra base gasket, and probably some gearing changes. Remember, This isn't Pro-Ciruit or Factory Honda, it's just a guy who wants to tone down his bike a bit and not spend a fortune doing and have everything reversable. I try to look at things as a do it yourselfer type way. If the person has $1500 to send it off to a pro to have it done, then by all means do it. That's why there are professional mechanics, factory mechanics, and garage mechanics. I'm just a garage mechanic that doesn't have big bucks to send it off to have it done. So I do everything my self. Actually, I have a few factory mechanic friends, so it really wouldn't cost me a whole lot, but I'm just cheap. But anyway me and a lot of other people have done the two base gasket thing and the world didn't come to an end, my motor didn't explode into the abysse, it just had a bit less hit, that's all. Shhesh everyone likes argue on this forum. I say let's all meet at Milestone Racepark and I'll buy the beer. :banana: :banana:

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I just re-reread this and this (throttle stop)does absolutly nothing to detune a bike. The power is still there.... :

No, xr, it is not.

That's what a throttle does: controls an engine's power output.

At least mine all do... :lol:

it's just a guy who wants to tone down his bike a bit and not spend a fortune doing and have everything reversable. :

I know. That's why I recommended a throttle stop. :banana:

I'm just a garage mechanic :

Really? I would never have known....

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Really? I would never have known....

Take a walk over to the XR/CRF/80-200cc section. We have the trickest most factory bikes around. All done by us. When you take a xr100 and convert a CR85 frame (lots of fabrication), then take a 6.0 hp and get 14+hp (133% increase) out of it, you need obvious motor and bike skills. For instance, for about twenty years before there was a Wisco 58mm piston or any BBK's, we used a Kawi GPZ550 piston and machine them to work. We had special cams made for our specific applications, custom needles, carbs from other motors, handmade dynod pipes, custom valves. We did this because unlike the CRF150R which is basically pre-built, nothing else existed and it's fun to do. Well that and beating big bikes on a bike that has 1/10 the hp is a blast. You may say garage mechanic as if it's a bad thing, but some of us worked for pretty big names throughout our lives: Factory Honda, Team Green, DG, FMF, Chapperal (when MC rode for them), and DMC. Not bad for garage guys. :banana:

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You may say garage mechanic as if it's a bad thing, but

I didn't say it.

Someone else did, I just quoted him...oh, wait, it was you that I quoted!

:banana:

"Credentials" like that and you put three base gaskets on an engine to lower its compression ratio? Where were all these "custom parts" when you were using "three base gaskets"?? Something doesn't add up here.

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When you can build this you can talk, otherwise don't bother. You can look at it in the Primm Museum, Nevada. It's a CR125 in CR85. If you would like to to reply just do it in a PM so you don't waste any more of this post. DSC00336.JPG

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This thread has degenerated into a credibility war, and you are right; it's a waste of time.

When you can build this you can talk,

I can build that....no doubt about it. But, talking to you won't help the OP with his question. If you still want to get the last word in, go ahead.

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