Looking for engine opinions

[73novaguy]

I'm building my street tracker and am torn between some options as far as building one of these motors. The bike will be ridden mostly short cruises and on 55MPH highways with the ocassional trip couple hours away. Alot of that will determine gearing though.

The things I will for sure be doing are rephase, cam (grind depends on what motor combo I go with), ported head, full exhaust, 36MM Mikuni flat slides.

Now I am torn between just honing and throwin a new set of piston's in, going with a 750 big bore kit with heads from Mikes or Central, going with a 750 kit with new sleeves pressed in from Hoos, or going with a set of Hoos 700cc pistons, or boring stock cylinders out to get a 707cc motor. Any opinions good or bad are welcome.

And also looking as to any engine builders near southern WI that will be able to press apart and rephase crank with proper runout and such. I currently have a Pamco ignition that Ive never used that I would be able to send back and upgrade to the dual rephased igntion.

Thanks, Justin

 

[dagored]

Justin,
I'm headed out the door as soon as I finish this post. I'm taking my crank assembly to Bob Donahue at Donahue Super Sports in Wisconsin Rapids.http://www.donahuesupersports.com/ Bob has been the Yamaha dealer there since 1966. He did performance work for me on my brand new XS1B back in 1972. I highly recommend him.
John

 

[73novaguy]

Thanks, I'll throw them an e-mail and see what kind of bites I get on it. I just e-mailed Hoos as they are about 2hrs and 20min drive for me also. Basically looking for someone to do the rephase and head porting. And peoples opinion on what to do with the bore on this ole girl. Looking for more of a torquey motor with some upper range. I would sacrifice some upper for torque. I am currently riding a 125HP, 117 FT LB, 113 c.i. Harley engine and my CRF450 MX bike is torquey, Ive also got a 502CI big block in a 73 Nova that is around 570Ft Lb toque. So once your used to that, its hard to not want it. LOL

 

[yamaman]

G'day novaguy, unless you've already got the VM 36's, I'd go in favour of VM 34's. 34's are well up to the task of pushing along a 650 (or a 750 also) along very nicely. The 34's will give a better low end response, the 36's will only be a real benifit at higher revs!

You say your torn.......hone, bore, replace............Well that's more up to the engine than you! If you want to just hone it, you need to get the bores & pistons measured up to see if it's close enough to hone, or if not what re bore you need.

If $ is no object, I'd go for Mikes 750 barrels, look pretty cool! Otherwise just do what is needed

 

[73novaguy]

Well the motor has over 60,000 on it's ticker, so she will need some freshining! Just got an email from Gary over at Hoos with some price figures. I need to get back to him with what kind of rods I'm interested in before can final quote the rephase. So any opinions on crank rods? And I dunno who doesn't have a budget!! Lol. But the cost of Mikes 759 big bore kit is only couple hundred away from reboring stock cylinders.

 

[73novaguy]

Oh, I don't have carbs yet, and I agree with you on the 34's. I am gna run TMs , not VMs! Just to be different. Better throttle response from what I read!

 

[yamaman]

Yeah cool on the TM's, I've no experience at all with them.........I think they come with & without pumps, is that right.....Non pumpers would jet up pretty similar to VM's i'd imagine.....Pumpers would be a different game.

Well carrilo rods are no doubt the best........They run to $500 each here in Aus, and I think that's without bearings etc!

I've never heard what the difference is between Mikes std rods & heavy duty, be great to hear someones thoughts on that! Std rods got your motor the 60,000 it's got, so std rods would probably get you another 60+ more....

 

[inxs]

- std rods should be fine, carillos are good for racing applications but you can do a lot for their cost...if sourcing new rods check the number cast into the original, 256, 447, 533... theyre all different lengths and dont interchange except as complete with crank and pistons...when doing so you can have problems with oil feed to the bottom end if you dont check the oil galleries, sometimes there are holes missing
- the 750 kit is a good bolt on fit, the larger cooling fins match the head profile, has greater cooling surface area and is a good compliment for a rephased crank

 

[dwyatt]

Definately go with the TM's, you'll get a power boost from the better effeciency. I also suggest you purchase the Modification Guide from 650performance.com, big help for what you are doing. Check out this note on the carbs from Craig Weeks at 650Performance:

A savvy XS650 builder recently did a dyno comparison between 34MM modern flat slide Mikunis (TM) and the older 34MM round slide (VM) versions. His engine is a 750 with 10.5 - 1 compression, a Jemco exhaust and a (he thinks) Shell-prepared head. He is running a Shell #1 cam.
On a Dynojet 200 the flat slides improved power 1 HP @ 4500 rpm and 1.5 HP at 7500. Max power with the flat slides was 64 @ 7500.
His jetting was 210 mains, 27.5 pilots @ 2.5 turns, no air jets, P-4 needle jets and 6F9 needles in the #3 position (one leaner than mid).
He claims throttle response is crisper than the round slides and while that is a seat-of-the-pants analysis, he describes the overall feel of the flat slides to be very good.
On the other side of the coin, he writes that the flat slides are way more difficult to fiddle with and more sensitive. One advantage is the flat slides are smaller and make a denser package.
He's very curious about how his new CNC head will work with the flat slides. So am I.
Thanks for the information, Tony.
Craig Weeks

Also, a dyno comparision of the different sizes:

 

[73novaguy]

Yes, I've got a couple articles booked about flat slides and what the owners dud for jetting. They also suggested that they are harder to fiddle fart with mostly due to the throttle slide being harder to remove out the top to access needle settings.

As soon as I hear some more tech on rods, it sounds like I'll be going the big cylinder 750 kit, rephased crank (purely for vibration and out of sync firing), ported head, bigger valves, exhaust, and carbs. Looking at a 2500 motor roughly! Yikes. So any more rod info? Hoos also said you could go crazy with Carillos, but I'll be looking for something little easier on the budget! Does anyone know if the Mikes 750 with new cylinder us a steel sleeve inside, or aluminum. I have a good freind who owns Max Power Cylinders ANC can coat the cylinder walls if there aluminum fir better friction control.

 

[650Skull]

Mikes 750 is a steel sleeve. Be careful with over sized valves , Pistons designed for standard size valves don't have enough relief

 

[jay760]

Not sure how much of a hurry your in, the last time I looked on the mikesxs site they didnt have the 750 kit in stock.

 

[xsjohn]

Won't make much of a highway bike all hopped up.........you asked for opinions so if mine I would buy a bigger bike with a lot more potential for all that money and work.....and use the xs for what you said in the beginning of the thread....suppose I will get beat for this but that's nothing new for me............

xsjohn

 

[73novaguy]

I appreciate all opinions John! I know you have a ton of experience with these lol scoots and you are very involved in alot of XS sites! I geuss I wasn't thinking big bore, porting and exhaust and fuel was to "radical". I've already got big bikes for highway use. The 125hp in my 113ci VTwin with 6 speed makes some easy work outa highways! Lol. This bike is strictly for playing and cruisin! The rephase is a must! Lol I just can't get used ti the parellel twin sound after so many VTwins. And I've been racing Yamaha bikes on motocross for the last 16 years. So I've got that soft spot for this XS! About 5 years ago I saw one of Mules bikes (blue one) in Cycle World and hung that picture up in the shop! Lol.

Anyone got any input on rods? Just freshining up bearings in stock rod assembly?

 

[73novaguy]

And correct as of today, Mikes or 650Central are both out of stock on big bore kits. I'll be sending the motor out in roughly couple weeks to get rephase crank and head ported, so I've got a little time before I'll be chomping on the bit! I appreciate all your guys input.

 

[Jack]

If you want to replace the rods, use MikesXS HP rods,good bang for the buck if the stock rod small end is worn out. As far as the flatslide go,I've been using them on BMW for the last 15 years and they do offer an advantage for a smoother and wider power band that no round slide can match. They simply permit higher velocity through the venturi and intake port which in return packs the the cylinder with higher fuel mixture velocityto enhance the combustion efficiency. It's the next best thing to forced induction. I find the F/S no harder to tune or take apart than a R/S,just a matter of what you're a customed to I guess.

 

[inxs]

- i enquired about another 750 kit last month and was told february 2010

 

[650Skull]

If you do a few 2 hour rides you should consider Mikes 5th gear mow you have the cases open, even with the rephase the gearing is still low. With that gear and a 32 rear sprocket it will lower the reves by 400 at 60mph without any loss of tourque. Here is a link to Pamcopetes Exel spreadsheet on gearing, http://xs650temp.proboards.com/index.cgi?board=sprocket&action=display&thread=11068 over at the Garage.

 

[yamaman]

As far as the flatslide go,I've been using them on BMW for the last 15 years and they do offer an advantage for a smoother and wider power band that no round slide can match. They simply permit higher velocity through the venturi and intake port which in return packs the the cylinder with higher fuel mixture velocityto enhance the combustion efficiency. It's the next best thing to forced induction. I find the F/S no harder to tune or take apart than a R/S,just a matter of what you're a customed to I guess.

I see in the Sudco site,
http://www.sudco.com/mikuni3.html
yes TM's are available with or without Accelerator pumps in 33mm & 36mm (others listed these are what we'd want though I guess) I take it yours are no pump?

Dwyatt, as your data refers to 34mm, I'll assume they were no pumps too.

So anybody run the pumpers???????

 

[Jack]

Yamaman.........Those are not TMs,they're called RS series.At one time Mikuni did offer a pumper for the TMs. Don't get caught up thinking you need pumpers for the XS,the only time pumpers should be consider an option is when vacuum signal in the venturi can't draw enough fuel from the jets to prevent leaning out the mixture during cylinder filling on hard acceleration or an engine with very long intake tracks or a long armed motor.