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Restorations Diary / Re: RD350 Track Bike build
« Last post by 5port on Today at 12:12:19 PM »
Intake Flow.

So, we have the modified cylinder assy and the modified reeds but, standard size carbs (28mm).  Where is the extra intake airflow coming from?  :-\
Of course, the modified engine working as an "air pump" is hopefully going to be able to pump more air through and use it at higher revs, 8500ish against 7500 standard.  But, it is not good if the air through the carb is restricted too much. Common knowledge shows that you don't get far with a lawnmower size carb on an R1, for instance.  :D     This is where we can look at the carb air feed.   Standard RD roadbikes have air filters.  These function as dirt traps and, as sound absorbers.  The dirt trapping is especially important on a roadbike to ensure long engine life. The sound absorbing is required for other reasons.  Both functions restrict the airflow, and cause reduced air pressure into the carb compared with an open carb with no filter.  Unfortunately, that reduction of air presssure at the carb inlet reduces the air mass flow through the carb.  This effect is minimised by the designers but, it is there.  Aha! You say, what about resonance?!  ???  Well, to keep it at my level, yes some air boxes use design to take advantage of the intake pressure pulses and cause the positive pulses to be at the carb when the engine is on it's intake phase.  This is certainly used on the RD250/400C onwards plastic airboxes.  However, the advantage is mostly in the low/medium revs and, overall, this is making the best of a situation with some pressure reduction by the filter and sound absorbtion unavoidable.
I think you can see why the standard carbs(28mm) are actually quite big for the RD's.  In fact, they are right at the top of size for a 25bhp cylinder in the Mikuni guide, Yamaha wanted to minimise the airflow(pressure) losses through the carb by using as big a venturi as possible-combined with the losses of an airfilter and filterbox.   :)
Now, if you remove the airfilter and airbox, the carb gets an immediate big increase in the air pressure it has at the bellmouth.  This is a bit like supercharging!  However, you need completely new jetting to adapt the fueling to the new airflow and, you get any muck etc down into the engine.  For pure racing performance, many people will run open carbs and some will have a high power/speed optimised bespoke airbox.  The changes to the airflow in the carb with no airfilter/box are so great that you really need to go back to the older style of Primary jetting in the carb.
Fortunately, many racers in the past have proved the best set-up and it is not expensive!  No, it is not just open carbs!  ::)
Dale Alexander has written that the optimum intake for a race RD is the Y-boot and large K&N filter.  Dale quotes improvements of 0.2sec over the SS1/4mile over pure open carbs, and that is with correct jetting.  Many others have attested to the fact that this is correct.  You can see that the carb is getting much better flow with reduced pressure drop because the main jet has to almost double in size, compared with the standard airfilter/box on a standard bike. 
So, this is what I have chosen for my track RD.  The bonus is that the filter gives the engine some protection from dust, and 100% protection from stones, nuts, bolts and washers..etc!
I will be using mine with absolute minimum oiling on the filter, to me it is an intake gauze. So, why is it better?  I presume that the filter is very low resistance (if not over-oiled!) but, I also guess that the Y-boot provides a good airflow feed and, the characteristics just suit the carbs/engine. 
For info, I am starting with the 169 P-0 Needle jet (one whole size range bigger than the R5 O-0), 5DP7 Needle, Main jet 210 and Pilots #30.
Those figures are in the bracket for this set-up but, are my interpretation for my engine.  Will be interesting to see how it runs with that?  I know the mid range will not be strong but, I hope that it will run fairly well mid range with good power above 5500.  We will see!  Cheers

Aircooled RD Tech Help 250cc and Above / Re: yds7 head light
« Last post by Gr8uncleal on Today at 11:54:13 AM »
Thanks Dave.

Member "Grey Duck" from the US fitted this item to his own DS7 (although he adapted it to take, I think, a H4 bulb).

This is the lens off the earlier YDS6 where you could replace the bulb, prior to the US bringing in their sealed beam legislation. If you compare it to the image of the sealed beam unit on CMSNL, you will see that the various brackets/mounts are the same.

I note what Doug says about US bikes having an inner ring and I agree that some do. However, CMSNL do not show the US DS7 as having one.

I don't know if the DS7 headlight bowl had two holes in the top, although the diagram on CMSNL only shows one. My 1972 RT2 (ie from the same period as your DS7) has two holes and the parts manual shows the high beam warning light in one and a bung in the other. I always wondered if the second hole was for the speed warning light that Japanese domestic market (JDM) bikes had to have fitted, although Doug could well be right about it being for a park light switch.

What would be handy would be an original UK DS7/YR5 parts manual (being lazy, I haven't checked in the Tech section!).

As yours is a box of bits resto, it could be that you don't have an original headlight shell.

If you were thinking of going for the lens that I provided a link for, maybe contact the seller for dimensions first, just to make sure that it fits your shell. If you don't have one already, you will also need a bulb holder, although I think that Yambits sell them.
Swear I've read this discussion before but when I searched could not find. Not got the search skills of others.

However someone suggested old school electronic ignition.

Its not suitable for magnetos but the 200 uses a dynamo ie its got a commutator for DC take off.
You keep the points but as they are now make/break switches of low voltage, they don't suffer pitting and wear is just the heel plus you get better spark at plug.
I'm presuming this means the starter will still work as its on a separate circuit.

Now I know a lot of you like to kick your engines over, but the number of twisted and severed kickstart axles out there. I've got two engines that have poor ones  :'( no doubt from some teenager jumping 2 foot up in air imaging their on a Harley or kicking in frustration to get engine to start  :o :o. There are no NOS axles out there :( :(
Plus the Electric is the distinguishing character of the 200's. However each to their own.  8) 8)

Aircooled RD Tech Help 250cc and Above / Re: yds7 head light
« Last post by Doug_R5C on Today at 11:28:38 AM »
The USA model has an inner rim, that the adjuster pivots, you need a UK rim and headlight.  I have a USA R5C and it only has one hole for a high beam indicator.  Back in the day when they were new, my friends YDS7 had a switch on the headlight for running with the pilot light only, so maybe that's why you have two. 
Aircooled RD Tech Help 250cc and Above / Re: yds7 head light
« Last post by davegsx on Today at 11:11:29 AM »
it is a USA import, the head light bowel has two small holes in the top of it , and I have the headlight rim.
Restorations Diary / Re: UK Pre A 350 'box of bits' Resto
« Last post by stevie747 on Today at 10:39:59 AM »
Bit of a panic as I couldn't find the angled brackets for the front number plate that got chromed a few years ago, I put them somewhere safe....
Aircooled RD Tech Help 250cc and Above / Re: Exhaust ID
« Last post by tractorman on Today at 09:27:51 AM »
Possibly late Suzuki A100
I did read somewhere about it being used on 200's from what I saw  they claimed it was fine, maybe even better, but no more electric start.
ignition timing should not change, no points that alter with wear and heat .

Hardest part now is maybe getting the armature off, they can be a git to remove, I lean the bike over as much as I can , and pour some oil
down the end of the armature, put it in gear, then use the bolt, seems to work much better than trying to do it dry, gives it a kind of hydraulic action.
Only ever worked on 1 cs5, mine, but worked on loads of RD's back in the day.
Aircooled RD Tech Help 250cc and Above / Exhaust ID
« Last post by yellow peril on Today at 01:00:42 AM »
I'm hoping that someone can identify this pipe, I got it with a job lot of Yamaha parts.
Looks like at least a 250 if not bigger.
I'm going to sell it on if anyones interested, thanks93507-093509-193511-293513-3
Events and Regular Club Meets / Re: RAVEN CAFE Shropshire 1st sun in month
« Last post by Kickstart on July 14, 2020, 11:49:18 PM »
good show of bikes. I see the pink bike is at the front  :D

Really Tez  :'(

Thought you wouldn't lower yourself to Blue Oyster Gimp comments

 :D :D
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