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Old 08-06-2010, 03:36 AM   #1
Mike Butt OP
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RD400 Project

So I bought an RD400, 1977, off of Road Rash.

Promptly I did the equivalent of this to it:



So we threw a party to fix it:



Everyone gathered around (particularly Dagwood who seemed to know what he was doing):



Dagwood calling me an idiot:



And me making idiot moves:



But none the less we are getting close:



Until:


Racing carbs, they took the floats off to save weight.

(inside joke)

Many thanks to Dagwood, Direwolf, Helikron, Twisty Sister and Beth for the garage time.

Floats are on the way from Spec II, I'll update then.
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Old 08-06-2010, 03:51 PM   #2
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What is that nicely welded aluminum thingy behind the head?
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Old 08-06-2010, 04:45 PM   #3
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Looks pretty great! Any pics of the engine rebuild? Any signs of what caused the failure in the first place?
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Old 08-06-2010, 04:53 PM   #4
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Quote:
Originally Posted by klp
What is that nicely welded aluminum thingy behind the head?
It's some sort of period equalization pipe for the carbs.
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Old 08-06-2010, 04:54 PM   #5
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Quote:
Originally Posted by MayerMR
Looks pretty great! Any pics of the engine rebuild? Any signs of what caused the failure in the first place?
I had a local shop do the rebuild. It failed so badly that it literally whipped out the bottom end too.
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Old 08-06-2010, 05:50 PM   #6
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Quote:
Originally Posted by klp
What is that nicely welded aluminum thingy behind the head?
Actually its called a boost bottle. Someone pls. correct me if I'm wrong but I believe it takes unspent air /fuel mixture and stores it until it is needed on the next intake stroke.
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Old 08-06-2010, 05:57 PM   #7
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Quote:
Originally Posted by welder
Actually its called a boost bottle. Someone pls. correct me if I'm wrong but I believe it takes unspent air /fuel mixture and stores it until it is needed on the next intake stroke.
Think it works?
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Old 08-06-2010, 06:23 PM   #8
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They're supposed to help in the low-end and mid-range.
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Old 08-06-2010, 06:29 PM   #9
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Old 08-07-2010, 02:57 AM   #10
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Boost bottles were introduced on the early LC's - they are intended to even out the pulses for better low/mid range as Welder says

Can't do much harm, but not ever really proven 100%

I had a mildly tweeked RD400 - and did the std carb mods - drill out air jet on intake side & fitted the Y tube with a TDM850 K&N filter, etc ....



But ny favourite was back in the day (late 70's) - my RD250 with 400 race barrels and 350 pistons - that thing flew - had 220 main jets in std carbs, would power wheely in 3rd - but coz std gearing still only do 100 mph

BEFORE



In action in the FRONT -



AFTER THE MODIFYING -

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Old 08-07-2010, 03:10 AM   #11
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Spotted this at the Swiss earlier this evening...

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Old 08-07-2010, 03:05 PM   #12
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Sweet.. An RD thread.. keep it comin!
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Old 08-07-2010, 06:40 PM   #13
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Quote:
Originally Posted by FLYING EYEBALL
Spotted this at the Swiss earlier this evening...

Fuck yeah.
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Old 08-07-2010, 09:40 PM   #14
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Quote:
Originally Posted by welder
Actually its called a boost bottle. Someone pls. correct me if I'm wrong but I believe it takes unspent air /fuel mixture and stores it until it is needed on the next intake stroke.
It's a Helmholtz resonator http://en.wikipedia.org/wiki/Helmholtz_resonance

They have a measurable but small effect. They are tuned for a specific RPM - just like an expansion chamber. If all the little goodies are tuned for the same RPM - look out . If they are tuned for slightly different RPM, the power gets spread around a little bit (in a two stroke "spread around" is relative) .
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Old 08-08-2010, 12:32 AM   #15
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Quote:
Originally Posted by Mark G
It's a Helmholtz resonator http://en.wikipedia.org/wiki/Helmholtz_resonance

They have a measurable but small effect. They are tuned for a specific RPM - just like an expansion chamber. If all the little goodies are tuned for the same RPM - look out . If they are tuned for slightly different RPM, the power gets spread around a little bit (in a two stroke "spread around" is relative) .
YICS before it was YICS.

Otherwise known as the yamaha vacuum leak induction system.
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