Yam RD "Blue Dream"- Ride,Maintain,Tune

2_DONE_THE_TON

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davedogg said:
+1 on getting the heads squished, o-ringed, and yz125 reed petals. I have that on my 350 and it the tits.
by yz125 reed petals you mean replacing the whole reed cage of the 350 with them dont you?
what does this change performance wise?
there are these v force membranes out there too,but terribly expensive!
 

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Tune-A-Fish

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I won't try and answer for Mobi... But We ran those V-Force reeds in our bikes before the 4-Stroke took over and they are/were an improvement over stock reeds, much better power curve, still a big hit when it comes on and when you stay in the pipe the reeds respond to throttle input very well.

Then it all changed with 4-strokes, we had to beef up radiators, add better impellers to the water pumps, dig out the valve seats and replace most of the top end, squish and widen the intake ports all in an effort to run cooler and build in some HP to match the torque... Can you say "Parts Unlimited" LOL!... ruined MX IMO... now you have very few riders with the training or money to compete at the very top, even with everyone under the top ten being faster than most brains can even process the obstacles in front of them. Everything leads back to video games mang :eek:
 

jpmobius

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For me, replacing the reed cages falls into the "I am willing to spend unlimited amounts of money on my bike" category. There are benefits, but they are expensive, and need to go hand in hand with a lot of other expensive changes to realize them.

I was suggesting using the petals only on your stock cage blocks. The YZ reeds have 3 petals, but the petals are the same size as the RD's, so you can cut off one and throw it away and install the remaining two just like stock. It will be a minor change to the engine - seemingly more valuable to some combinations than to others. Likewise to banshee crossover tubes, enlarged crossover tube reservoirs, and carb/reed spacers. All can effect how the bike drives but I am not sure that any of these changes actually make more power. However if the combination you use gets you better drive off of corners, or makes the bike more pleasant to drive, the benefits are obvious.

In your pic, the left cylinder is the style of early US 250/350's with the early ring copper gasket. Very hard to seal on stock good running engines - impossible to seal on high output motors. However, it is the best style for modified heads because you can machine the head with a step that makes it sit down inside the recess previously used for the copper gasket. It is then a simple matter to cut a groove for an o-ring, and then cut the center for the squish you want and combustion chamber volume. The benefit here is that the interlocking steps force the head to be exactly centered over the cylinder, or more importantly the piston. Your new squish area will be very close to the piston at TDC, (.035"-.040", or 0.9 to 1.0 mm). Because the piston is crowned, and the stock head arrangement is exceptionally sloppy and you can easily install the head considerably off center, the squish can be way too thin on one side and way to wide on the other. The alternative is to machine a centering tool to perfectly center the head on the bore, and install some alignment pins to locate the head. The only downside is that the early heads are thin and prone to cracking, but my opinion is that this is primarily caused by the gasket design and over torquing. If you start with good condition heads you should be fine.

The right cylinder is the later style 250/400 scheme which has flat topped cylinders and uses the gasket you are familiar with. This is a huge improvement over the early style as tightening the head does not bend the head over the gasket causing it to leak and crack. With care and copper gasket spray you can reliably get heads to seal, but this is no match for o-rings. You need to center and pin these heads for optimal performance.

I do not have a picture of altered early heads, but I have an aftermarket RD o-ring head sitting here. It has a good squish and chamber, but has not been fitted to an engine yet and has no alignment pins or other engine specific modifications. This head was made by Ottoco before they sold to HVC. It is a 350 head without the step so it can not be used on a stock 350 cylinder.
 

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2_DONE_THE_TON

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune

I guess this is again a question of budget.the vforce 4 reeds cost about 180 euros in europe a piece....crazy!
If these yz 125 petals are cheaper and bring reasonable improvemenr i will buy them.
 

Tune-A-Fish

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jpmobius said:
For me, replacing the reed cages falls into the "I am willing to spend unlimited amounts of money on my bike" category. There are benefits, but they are expensive, and need to go hand in hand with a lot of other expensive changes to realize them.
Although I don't disagree, I would say that the money spent above the base plate gasket is minor pocket change in comparison to below and we are spending for the expansion chambers already. Machine work if well thought out to add a grove and align the squish with the world seems basic bucks well spent and well a little "mild" buzzing with a porting guru shunt cost the moon or you need to buy more drinks at the pub :eek: mang...

I guess it boils down to what you said about driveability (performance) and what you want as a reliable but racy sport classic. As for the over rev... put a dollar sign on your tach where the box should come on?? (smile face)
 

Tune-A-Fish

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune

Ryan Stecken said:
I guess this is again a question of budget.the vforce 4 reeds cost about 180 euros in europe a piece....crazy!
If these yz 125 petals are cheaper and bring reasonable improvemenr i will buy them.
If you were in the US I would give you some carbon petals off V-force cages to try, but seems if the budget is this tiny one failure would set back the project a millennium LOL... eBay?

Just kidding of course :eek:
 

jpmobius

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Tune-A-Fish said:
As for the over rev... put a dollar sign on your tach where the box should come on?? (smile face)
Indeed! Maybe that is a good summary. While maybe not technically true, in my experience, everything you do hunting for more power out of a 2 stroke ends up with more revs. Oh you may decide to not exceed the red line Du Jour, but inevitably your creation will spend a great deal more time knocking on the door. THAT ultimately works out to expensive in my experience!
 

jpmobius

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Tune-A-Fish said:
I would say that the money spent above the base plate gasket is minor pocket change in comparison to below and we are spending for the expansion chambers already. Machine work if well thought out to add a grove and align the squish with the world seems basic bucks well spent and well a little "mild" buzzing with a porting guru shunt cost the moon or you need to buy more drinks at the pub :eek: mang...
Agreed. I probably should have been a bit more clear - from a "bang for the buck" perspective, chambers, air cleaner, and the described head work take you a long way while keeping a nice, rideable and reliable but faster motorcycle. I am promoting stopping at this point. You can add some port work to that, but that is a sure enough slippery slope so I place it on the other side of this equation. You can fool around with some inexpensive intake bits like the reeds, spacers etc for small money and slight performance changes. Past this point, the money starts to grow dramatically, but more importantly the time and talent required to realize the benefit. And there are invariably big trade-offs in practicality both day to day and long term. The lifespan of air cooled Rd motors fall off rather precipitously once you start widening the ports and upping the output past the just chambers and heads point, and for me that factors heavily into the cost. If the engine lasts half as long - and that is not an unrealistic expectation - it DOUBLES the original cost that at the time may not have seemed so high. On the track, it is just the cost of doing business, but on a street bike it make a big impact.
 

2_DONE_THE_TON

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune

Thank you guys for the interesting insight you give me!

My plan is:
250 configuration:
DG chambers
KN filter plus carb work

In winter i will do:
350 conversion
Squish band mod
O ring mod
Reeds (costs :)?)
Crank rebuild

How long do yoy guys run your cranks?do you wait till it breaks :) or do you have certain intervala to check them?

It will be hard to find someone in austria do the trueing.
Theres a guy in schwechat near vienna but he mainly build speedway cranks for rich russians so he wknt be that motivated to do that poor students crank :)
 

davedogg

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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.
 

jpmobius

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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!
 

2_DONE_THE_TON

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune

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...
 

davedogg

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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.
 

jpmobius

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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.
 

2_DONE_THE_TON

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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 i´m 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.
 

jpmobius

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Ryan Stecken said:
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.
 

2_DONE_THE_TON

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune

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?
 

jpmobius

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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.
 

2_DONE_THE_TON

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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
 

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