Were Your Engine Mods Worth The Bother.

[jay760]

[QUOTE="xjwmx, post: 700799

Wondering what mods Jay has done if he would reveal them. Got to be fast, going by the clothing...[/QUOTE]

JE pistons 750cc, worked on head not just ported, unknown cam, not high lift but long duration with exhaust longer than the inlet, 2mm over valves, crank is welded, using electrex world ignition, still setting up after a change to the engine, I tried a mega cycle cam but decided to go back to my old cam as I hadn't tried it with the 2mm over valves, mainly running 1/8th this year last time out although times were slightly down, but that was due to me struggling with the heat top speed was up to just over 92mph, over the quarter best is 11.88 at 110mph bearing in mind I'm over 200lbs it's not too bad

 

[jay760]

And 36mm dellortos on tapered inlets so there is no step

 

[MacMcMacmac]

Hmmm....I just reread Mac's original question--are mods worth the bother? Definitely not! If the work is a bother rather than a pleasure, performance modification isn't worth doing.

Tough crowd ..ha ha.

Let me rephrase that, did the results justify the effort? Was the time and effort spent performing the mod worth it?

 

[azman857]

During the last top end I did late winter, I unshrouded the valves. Took away the build up around the valves in the head. A very common mod on classic VW heads to help then breath better. I didn't imagine an extra 20 HP. Can I feel any difference? Not really. Would I do it again? Yes. Why? Bragging rights! It's listed being done on OU-72 racing head modifications. I could be wrong on the designation. I did try to smooth the edges in the ports too. Nothing major. Same expectations and results and reasons.

 

[jay760]

During the last top end I did late winter, I unshrouded the valves. Took away the build up around the valves in the head. A very common mod on classic VW heads to help then breath better. I didn't imagine an extra 20 HP. Can I feel any difference? Not really. Would I do it again? Yes. Why? Bragging rights! It's listed being done on OU-72 racing head modifications. I could be wrong on the designation. I did try to smooth the edges in the ports too. Nothing major. Same expectations and results and reasons.

Do you mean like this, this is one of my heads

 

[azman857]

Yes. Or something very close to it.

 

[motormike]

I've built a few 750 engines ... the sleeve type.. the big bore kit with the replacement cylinders don't look " right ". The big juggs might work but they just kill the balanced look of the engine-frame. Never had a problem with a 750 kit except add'n three heavy clutch springs to cure the slipping. If I went with a bigger displacement.. I'd entertain weld'n the cranks.. but the 750 adds plenty of twist the throttle fun. Of course.. with the 750 kit.. I went with slide carbs... and pea shooter mufflers... dual brakes recommended. I owned a phased engine... and to me... ran ok.... I didn't see any performance improvement worth the $$$ but the " potato potato " idle and rip down the street was great.

 

[Jan_P]

I like stock
If it is performance one is after a 20- 30 -40 years newer sports bike. Does it.

Back in the day I know of many mechanical jobs that went wrong and modifications Kits for fex Hondas that did not last long.
So it depends on the competence on the person the one doing the job.

There is a reason why untouched Cars and Motorcycles are bought / sold at higher prices.

 

[dps650rider]

Engine mods:

700 cc and Megacycle cam: Nice torque boost, good especially when riding double
277 rephase with welded crank: Love the sound and the lowered vibration
Elephant foot adjusters: Never going back to stock tappets
Boyer ignition: Never going back to points
Mikes oil filter: Don't know for sure but a real filter has to be better
Hi volume oil pump: Should improve oiling especially at lower RPM
PMA: No more brushes!

Other mods:

Tapered roller bearings in steering: Nice improvement in handling
Bronze swing arm bushings: Ditto
40/75 ratio belt final drive : Never going back to chain
Halogen headlight: Don't ride at night much (deer) but when I do quite a bit better
Modified stock mufflers: Sound nice, don't know if it helps otherwise

Currently getting 58-59 MPG, really nice with the Special's 2.9 gallon tank

 

[GLJ]

40/75 ratio belt final drive : Never going back to chain

Tell use more about the belt mod. Pics?

 

[dps650rider]

https://xs650temp.proboards.com/thread/17140/belt-drive

 

[Mailman]

https://xs650temp.proboards.com/thread/17140/belt-drive

That is impressive! I’ve never seen anyone with a belt drive XS650, no small feat. Man it’s close to your clutch pushrod. Nice work.

 

[dps650rider]

Thanks. Was some work but well worth the effort. Probably have about 45k miles on it now and the only thing I changed was the rear to change gearing. Original belt is still fine.

Best of all, NO MAINTENANCE REQUIRED.

 

[GLJ]

Thanks. Was some work but well worth the effort. Probably have about 45k miles on it now and the only thing I changed was the rear to change gearing. Original belt is still fine.

Best of all, NO MAINTENANCE REQUIRED.

Links to where you bought the stuff needed? Could be a great mod. I've dealt with belts on industrial equipment and they work well.
How tight do you tension the belt?

 

[dps650rider]

Sprockets came from ebay. Got the belt from http://www.royalsupply.com.

Tension is tricky since it changes as the suspension is compressed. I bought a tension gauge but mostly set it so it plays a low note when plucked with the shocks fully extended. I added the ball bearing idler to keep the belt from getting loose when the suspension is fully compressed. When I'm riding solo it occasionally contacts the top of the belt (you can hear it if you listen carefully).

 

[dps650rider]

Belt is a 8MGT-1760-36 - Gates 8MGT-1760-36 Poly Chain GT Carbon V-Belt 92742220
I think the rear sprockets I used are 8MX-80S-36 and 8MX-75S-36
Front sprocket is 8MX-40S-36-2012

 

[thechickenman]

First time posting, This might be better off in its own thread but it seems like there are a lot of 750cc owners in one place so here it goes.

Recently did the 750cc kit upgrade with mikes xs kit. Im noticing when engine braking or letting off throttle the engine has almost a rich (glugging) gurgle sound that seems odd. It wasnt there before the big bore and I'm wondering if anyone else has experienced something similar? just to clarify up some things heres what Im running.

81 xs650 special with 750cc kit from mikes xs
mikuni vm 34 carbs with aluminum intakes. jetted with 22.5 pilot and 185 main
cam chain and valve clearances checked and double checked. I have them at .05 and .10 intake exhaust
compression is at 150+ in both cylinders
bike has straight pipes with cocktail shakers


Im trying to diagnose why it would be so loud only on engine braking. It runs through all the gears and accelerates great but when I lay off the throttle thats when the gurgle shows up pretty loud and only for a few seconds then it sort of mellows and goes back to normal.

I'm thinking of changing out sprocket sizes with the idea that maybe different ratio would help with the engine braking I currently have 17-34 set up.

Thanks for your time and sorry if this should be in a thread of its own I'm new here.

 

[jetmechmarty]

First time posting, This might be better off in its own thread but it seems like there are a lot of 750cc owners in one place so here it goes.

Recently did the 750cc kit upgrade with mikes xs kit. Im noticing when engine braking or letting off throttle the engine has almost a rich (glugging) gurgle sound that seems odd. It wasnt there before the big bore and I'm wondering if anyone else has experienced something similar? just to clarify up some things heres what Im running.

81 xs650 special with 750cc kit from mikes xs
mikuni vm 34 carbs with aluminum intakes. jetted with 22.5 pilot and 185 main
cam chain and valve clearances checked and double checked. I have them at .05 and .10 intake exhaust
compression is at 150+ in both cylinders
bike has straight pipes with cocktail shakers


Im trying to diagnose why it would be so loud only on engine braking. It runs through all the gears and accelerates great but when I lay off the throttle thats when the gurgle shows up pretty loud and only for a few seconds then it sort of mellows and goes back to normal.

I'm thinking of changing out sprocket sizes with the idea that maybe different ratio would help with the engine braking I currently have 17-34 set up.

Thanks for your time and sorry if this should be in a thread of its own I'm new here.

If it’s popping out the exhaust on deceleration I believe it’s too lean. Changing the drive ratio isn’t going to fix it. The throttle is full closed when this happens? Try opening the mixture screws a turn and see if that helps.

 

[thechickenman]

Its not a popping noise, its more of a loud gurgle is how I would explain it. Maybe its normal with high compression but its pretty loud when engine braking and really noticeable on a downhill. If I pull the clutch in the noise goes away which makes me think its something to do with the rpm changes on deceleration under load. Yes its when i completely lay off throttle

 

[jay760]

Are you running Air filters? If not this would cause the noise you are describing, there is nothing high compression about the Mike's xs kit, should be virtually the same as standard with a bit more go, unless you've made other changes as well