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Aircooled RD Tech Help 250cc and Above / Re: RD400C
« Last post by 5port on Today at 11:58:34 AM »
Certainly would indicate soda blasting as it easily disolves in warm water.

Soda will compact in passages and even though soluble, it isn't always easy to remove.  Also, it does promote corrosion in alloy.  Possibly carefully used, if you have to clean a carb with blast, soda is OK. 
Overall, many owners comments and threads over the years have proven that folks have problems cleaning their carbs out. They say they've done it but, not well enough.  I don't use blasting on carbs and I avoid it on cases with passages or even just blind threads.  Heads are a good subject for careful blasting, and cylinders if you put screws in the threaded holes.  Another factor is the surface finish. Harsh media give a non-standard rough finish.

5port   
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Aircooled RD Tech Help 250cc and Above / Re: RD400C
« Last post by pidjones on Today at 11:27:27 AM »
Certainly would indicate soda blasting as it easily disolves in warm water.
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Aircooled RD Tech Help 250cc and Above / Re: 1973 RD250 crank rebuild
« Last post by Whitey on Today at 10:47:56 AM »
They would not rebore my 350b cylinders without using YPVS pistons , so obviously didnt get the job. They tried telling me they were  better piston for my cylinders.  >:(
Mmmmm, slight concerned that I may have the LC pistons you mentioned… is there a easy way to tell, I haven’t had them out of the boxes yet.

If they are LC pistons, is an absolute no?


Sent from my iPhone using Tapatalk
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Restorations Diary / Re: RD250DX resto
« Last post by 5port on Today at 09:44:34 AM »
Hi Zed1000th!
Just wondering how this is going?  :)

Cheers

5port
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Aircooled RD Tech Help 250cc and Above / Re: cannot identify pistons
« Last post by 5port on Today at 09:22:50 AM »
Also, I posted this recently.  Old original exhausts can have a thick internal layer of oil carbon and crud that restricts their working badly.  Decoking them is not easy but, it is worth it, and I mean for the whole system!  Caustic soda is the best way, just needs serious care and reading-up before doing it!
"The removable baffles can be best cleaned by putting them in a wood fire that is burning clean.  They don't need to be too hot, just hot enough to burn off the oil coke.  You will need to wire-brush and oil them afterwards.
However, the whole pipes will have a fair amount of carbon/coke in them.  The only real way to remove that is a warm soak in Lye (caustic soda) at about 1lb caustic crystals to 1pt water.  Heating it and keeping it at about 80*F will do the job in about a week. I do them cool without heating about 50*F and it takes a month. You have to circulate the solution inside about every few days.  This is what Chrome platers do to strip/clean items before plating, they hate 2T pipes because they spoil their hot Lye bath with all the crap that comes out.  Some members have made their own hot baths with large dia plastic pipe and thermostat controlled immersion heater.
Beware, Lye (caustic soda) is deadly and dangerous.  You must read it up before using and it is dangerous to everything, so don't do it where it can hurt/damage anything, like things,people,children,pets animals etc.
So, have a think about that and read it up. BTW, It is safe with Chrome and Steel."

5port
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Aircooled RD Tech Help 250cc and Above / Re: RD400C
« Last post by 5port on Today at 08:20:41 AM »
Bazzer is correct, the old Mikuni's do suffer from partial and full blockages in the passageways and drillings.  Not just from blasting, also normal use dirt and gum and corrosion.  This can be very difficult to clear properly, but not impossible.
So, we know about the balls out proceedure for clearing the Air corrector. But don't forget the passages that lead to that as well, including the rubber tubes and the nozzles in the airfilter box, I have seen them bunged solid. Possibly the worst is the tiny angled pilot orifice. Tested with WD, it often just lets a dribble through, but it must be clear with a strong jet or, you get the typical faults of poor idle, poor response to Idle air adjustment and..Bucking on the overun!
So, we are not going to sort this out overnight but, spread the word!  :)

5port
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Aircooled RD Tech Help 250cc and Above / Re: cannot identify pistons
« Last post by 5port on Today at 08:05:03 AM »
Modern 2 stroke exhausts (about 1960's onwards) that use the divergent/convergent pressure wave designs do have a restriction to raise the pressure. This is usually done by the stinger dia and length. The extra pressure increases the strength of the pressure waves but, it is a very precise value, the effect has to be optimised.
The RD exhaust systems do have quite efficient expansion chamber functions. They have been found to be just about the best possible compromise for the normal engine range in many tests over the years.  Just like the intake side, you can only really trade flexibility for power at higher rpm.  Of course, we are talking the state of the art.  RD400 2T technology is early 70's. Today, a modern design 2T road bike could provide twice the power with total flexibility.   
So, our old RD tinkering is not earth shattering, but we can make some improvements.  The difficulty you always face is finding the right person to do the clever stuff (porting and exhaust pipe building) and, knowing what you are trying to achieve.  Also, these changes are not cheap because they are usually bespoke.  There are many people who have failed in their attempts to improve their road RD, and many almost unrideable bikes have been created.  ???

5port       
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Aircooled RD Tech Help 250cc and Above / Re: RD400C Rear Brake Switch
« Last post by Cooky1961 on Today at 07:59:06 AM »
Thanks I've managed to get one from CMSNL
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Aircooled RD Tech Help 250cc and Above / Re: RD400C Rear Brake Switch
« Last post by chrisg.007 on Today at 06:42:54 AM »
Obviously not stock, but Ive used these in the past.

https://www.ebay.co.uk/itm/384961335172?hash=item59a17bcf84:g:Qy8AAOSw~IhisXmH
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This is so more complicated than I thought. I have always known about reflected waves in the exhaust expansion chambers. But now I learn that a similar thing happens at the intake, if I understand it. It makes sense that a positive pulse of air when the intake port opens will jam more mixture into the crankcase. But the intake air restriction is still a mystery to me. We do not restrict exhaust flow for more power (or do we?) I need to find a good book that explains it for a dummy like me.
I understand you to say that without the restriction, the carbs will also suffer from too rich or too lean at certain RPMs. That makes sense. I found that on my old 250 Suzuki X6 Hustler with port timing, if I removed the hoses to the carbs, I could see a mist of fuel mixture coming from the carbs. I reasoned that if the mixture goes back and forth, it gets richer for each direction and each pass.
Do the stock RD400 mufflers have any "expansion chamber qualities" of reflected waves?
And, the website, https://www.motorcyclespecs.co.za/  claims that the stock RD400C will go 106 MPH.  How true is that? I would be more than happy with that.
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