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Author Topic: Yam RD "Blue Dream"- Ride,Maintain,Tune  (Read 53393 times)

Offline davedogg

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #70 on: Jul 28, 2015, 21:56:39 »
Sorry. I should have been more clear. Jpmobious is correct with the yz125 petals. 2 strokes are addicting and the search for power is real and adds up. When I built my 350 I spent more money than I intended but have a machine I will be buried with. Here's some of the engine related performance work I did just to give you an idea (if I remember it all)

K&N y boot
yz125 petals in stock cages (better low end power)
rz manifolds with crossover tube (have to cut the tongues/flanges)
Dale A/ Dave F carb mod
new top end/ pro-x pistons
rebuilt crank
heads squished
heads o-ringed
Coffman expansion chambers (started with DGs)
NO porting work done.

I think thats it. I got suckered into spending more money but I don't regret it. The results are a bike that has get power throughout the revs low through high. Please do not send your machine work out to people that do not specialize in 2 strokes. I know you're in Austria but I sent my work out to Scott Clough in California. He's been racing the bikes since they were new. He has good turn around time and his work speaks for itself.

Offline jpmobius

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #71 on: Jul 28, 2015, 22:25:34 »
Sounds like an excellent plan.  I run cranks until they have an issue.  Very nearly always the crank becomes to wide for the cases.  Either the center flywheels become farther apart than they should be or the two on one side or the other drift apart.  I weld the crank pins in if it is going in a hot rod motor, but I'm coming to think it is a good idea in a stock motor.  Probably the scarcity of un-rebuilt cranks is partially responsible - after the first rebuild the interference fits have to be compromised.  Bearings rarely fail before something else does, but I replace all the bearings with upgrades.   Suzuki RG500 big end bearings are good on the rods, and better mains can be had with a little looking.  Bearings do fail though, and in my experience without much warning.  I had a drive side main bearing fail very suddenly last year, and it did a dreadful amount of damage to pretty much everything.  Saw massive smoke in the right side mirror and bang!  But that was a first - otherwise most crank related failures make a lot of bad noise and you can shut it down before you really suffer too much.  If the counterweights start coming adrift (common), or the flywheels separate (also common) to the point they contact the cases, you usually can fix the crank and all is well.  When that bearing disassembled itself at 9 grand, it destroyed pretty much everything - piston, cylinder, case, crank.  It is a transmission parts only engine now.  Don't get me wrong - Rd's are not as fragile as all that, but I pretty often ride around with guys on much bigger bikes, and consequently abuse my own bikes pretty badly.  Not recommended!
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline TranceMachineVienna

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #72 on: Jul 29, 2015, 05:16:17 »
I can fully understand your last sentence mobius.
I tend to get a little stupid child when bigger bikes stand beside me on the traffic lights :-) and then i abuse the RD too....completely for nothing.

Dave Dogg,thanks for your mod list.as for the dale A dave f mod...did you see any performance changes?
We had the discussion earlier and teaser said its completely useless...

Offline davedogg

  • Posts: 73
Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #73 on: Jul 29, 2015, 10:41:03 »
Compared to my stock RD400 my 350 with mods is a totally different bike. The mod is supposed to "get smoother, more
responsive power"

I look at it in layman's term because I am not as knowledgable as the other members chiming in. But this is my explanation... two strokes are peaky, you want to even out the power while hopefully creating more power and make it a comfortable street bike. Simple mods like the crossover tube are to even out the flatspot around 5k. YZ125 petals give the bike better response down low. The carb mod is supposed to do the quote above. I can't tell you why it works. I just know it worked for me.

Offline jpmobius

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #74 on: Jul 29, 2015, 11:12:44 »
I have to partially disagree with Teazer - I wouldn't call it useless, but certainly it is not the "solution" many claim it to be.  I had a set of Rd carbs with the mod.  Fooled around with them on several motors.  I didn't experience any additional power - at least with the combinations I tried, but there are definitely changes to the running characteristics.  I don't have them any more because I sold them with a bike I built.  They ran better than the un-modded carbs on that setup, but not by a lot, and I wouldn't say you couldn't get the stock carbs to run as well if you wanted to fool around with the needles. 

In my experience, I would not alter my only set of carbs, because you can not undo the modification.  But another set of carbs is easily had if you want to experiment.  Davedogg's setup is a very good way to set up a street bike motor - I have built several very much like that and highly recommend it as an excellent compromise for the street.  How you end up setting up the carbs will depend greatly on the exhaust system.  My suggestion is to set up and tune whatever set up you decide on with the un-modded carbs first.  If you are not satisfied, try out the new parts and see.  Just FYI, the "Dave F mod" pretty much duplicates the carbs from an R5 piston port motor (1970-72 Yamaha 350 twin), so if you find a pair of those unmolested you can try them.  No ports for the oil injectors though.
« Last Edit: Jul 29, 2015, 11:14:27 by jpmobius »
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline TranceMachineVienna

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #75 on: Jul 29, 2015, 11:56:56 »

In my experience, I would not alter my only set of carbs, because you can not undo the modification.  But another set of carbs is easily had if you want to experiment.  Davedogg's setup is a very good way to set up a street bike motor - I have built several very much like that and highly recommend it as an excellent compromise for the street.  How you end up setting up the carbs will depend greatly on the exhaust system.  My suggestion is to set up and tune whatever set up you decide on with the un-modded carbs first.  If you are not satisfied, try out the new parts and see.  Just FYI, the "Dave F mod" pretty much duplicates the carbs from an R5 piston port motor (1970-72 Yamaha 350 twin), so if you find a pair of those unmolested you can try them.  No ports for the oil injectors though.
[/quote]

as for the carb mod i stated earlier i want at least try it.i already had the parts ordered for my birthday.
so iŽm gonna let you guys know the results.

y boot
kn filter
r5 emulsion tubes+needles
bigger mains
idle jets
+ 2 air jets (2MM) for the main air port-->it needs to get opened and threaded for the air jets

if it doesnt do anything i will close the threaded air port with a screw and switch back to the RD emulsion tubes.

what i read is that this mod changes the fuel curve,the power band starts earlier at 3,500 and gets a kick at 6,000,so again a modification of the standard "behaviour" of the motor which is just lame below 6.000.

Offline jpmobius

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #76 on: Jul 29, 2015, 12:24:42 »
In my experience, I would not alter my only set of carbs, because you can not undo the modification.
Well I suppose that technically this is incorrect - you CAN go back, but only if you thread the carbs for the new air jets.  The stock jet is just a drilling, and I think most people just drill it out to the needed size.  Then you will have to also buy smaller air jets (don't know off hand what size) to replace them if you want to restore the carbs back.  Be advised you can make large changes just altering the needles and needle jets (emulsion tubes) in the same series without altering the main air jets.
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline TranceMachineVienna

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #77 on: Jul 30, 2015, 04:54:33 »
This is exactly what i was going to do.
I ordered all parts from mikuni,including 2MM air jets to screw them into the air passageway.
Do you have a hint how to get that brass 'cap' out that is currently blocking this passageway?
How would you go about threading?

Offline jpmobius

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #78 on: Jul 30, 2015, 12:31:51 »
Need a pic.  Early carbs are cap-less.  Most caps come out pretty easily by drilling a hole in them and using a sheet metal screw to pull them out.
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline TranceMachineVienna

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #79 on: Aug 02, 2015, 12:41:31 »
Got some work done today.the RD is hibernated for about 2 weeks now to renew the paint on the bottom of the tank.

Cleaned the carbs and made a pic of the caps that close the air jet.my plan is now to remove the cap,thread the hole put in a screw to close it up again,cause i will ride the RD stock till the end of this season.

Took out the floats and sanded the tang with 600 then 800 where the needle pin touches the tang (damn there was nearly a hole in there).now its smooth and nice.

And i found out why my bike constantly drips fuel....put a catch can on the disconnected carb fuel hoses turned the petcock to off....the next day the glass was half full :-(  petcock o ring was renewed 1 week ago....grrrrrrr
« Last Edit: Aug 02, 2015, 12:43:06 by Ryan Stecken »