High Compression Help ?

[Biggles19]

Good afternoon,

I’m once again digging into the knowledge of this forum for advice,
So the bike set up if you have not seen previous posts is
750cc big-bore kit by Smedspeed

Standard XS650 head

Mikuni TM34 Flatside carbs with custom manifold by Smedspeed
Velocity stack air intakes by Steel Dragon Performance
Custom electronic ignition by Heiden Tuning
Dual 1 3/4" stainless steel exhaust pipes by John Campbell

So compression? With the kick start this bike is hella hard to kick (we have gone e start back on the bike) I’m just curious is there anything I should be checking set up wise that could help / worsen the amount of force needed to kick this ? I have 20 stone big lads who struggle to kick this thing over !

Many thanks again !

 

[XsTony]

Good afternoon,

I’m once again digging into the knowledge of this forum for advice,
So the bike set up if you have not seen previous posts is
750cc big-bore kit by Smedspeed

Standard XS650 head

Mikuni TM34 Flatside carbs with custom manifold by Smedspeed
Velocity stack air intakes by Steel Dragon Performance
Custom electronic ignition by Heiden Tuning
Dual 1 3/4" stainless steel exhaust pipes by John Campbell

So compression? With the kick start this bike is hella hard to kick (we have gone e start back on the bike) I’m just curious is there anything I should be checking set up wise that could help / worsen the amount of force needed to kick this ? I have 20 stone big lads who struggle to kick this thing over !

Many thanks again !

Hi Mate,
I have a 840 which is impossible to kick over, but I have fitted a smedspeed 4 brush starter motor and a lithium ion battery which turns it over no problem .
Tony

 

[Biggles19]

Hi Mate,
I have a 840 which is impossible to kick over, but I have fitted a smedspeed 4 brush starter motor and a lithium ion battery which turns it over no problem .
Tony

Hi Tony thanks for the reply the starter is working the dreaded clip is the main issue I’m having even after replacing it with a new one it’s only getting a few starts before I’m getting the grinding back, I’m not opposed to kick starting just as you said with yours there is some serious kick required, that’s if the wants to start easy

 

[jay760]

Start it like a big single, get it just over tdc then kick, but put all your weight on it don't think you can just kick it over

 

[JJames]

Just curious. What is the advertised compression ratio? How about compression psi.?

 

[XsTony]

Hi Tony thanks for the reply the starter is working the dreaded clip is the main issue I’m having even after replacing it with a new one it’s only getting a few starts before I’m getting the grinding back, I’m not opposed to kick starting just as you said with yours there is some serious kick required, that’s if the wants to start easy

If you do a search on here there will be a post about starter gear clip tension which must be at least 5lbs.
I have done this mod on both my 650‘s and it definitely works.
Tony

 

[Its been a long time]

Hi Tony thanks for the reply the starter is working the dreaded clip is the main issue I’m having even after replacing it with a new one it’s only getting a few starts before I’m getting the grinding back, I’m not opposed to kick starting just as you said with yours there is some serious kick required, that’s if the wants to start easy

I did the starter grinding fix yesterday. I tested the clip tension as removed and with a NoS Yamaha clip installed. There was no difference between the old and the new clip drag. I squeezed the new clip and got around 3kg tension versus about half that with the both old and new clips before squeezing. If I was doing this again, I would measure the spring drag with suspended weights rather than a scale. I think using weights to determine spring drag would be both easier to do and more accurate.

You might find this thread from yesterday useful -

https://www.xs650.com/threads/musings-on-clutch-overhaul.66566/post-844347

 

[Gary Jones]

Good afternoon,

I’m once again digging into the knowledge of this forum for advice,
So the bike set up if you have not seen previous posts is
750cc big-bore kit by Smedspeed

Standard XS650 head

Mikuni TM34 Flatside carbs with custom manifold by Smedspeed
Velocity stack air intakes by Steel Dragon Performance
Custom electronic ignition by Heiden Tuning
Dual 1 3/4" stainless steel exhaust pipes by John Campbell

So compression? With the kick start this bike is hella hard to kick (we have gone e start back on the bike) I’m just curious is there anything I should be checking set up wise that could help / worsen the amount of force needed to kick this ? I have 20 stone big lads who struggle to kick this thing over !

Many thanks again !

Do you have the timing set to advanced? I built a '71 xs650 blueprinted and balanced, and it was a bitch to start if the timing was too advanced. However, when it was correct it ran 127.42 mph / quarter mile. Lot of work went into this bird. I'd also check the cam timing, if you don't have a degreed cam wheel you may have to split hairs with cam crank and ignition to get a better start and performance you're looking for. Good luck.

 

[Biggles19]

Miss off she’s got a smedspeed rephrased cam I will take a look into your suggestions many thanks Gary

 

[arcticXS]

A higher primary ratio, would in fact also make for easier kicking a big bore/ high comp engine over tdc. Obviously, the engine would turn over slower. How that would affect starting I do not know.

 

[jay760]

Do you have the timing set to advanced? I built a '71 xs650 blueprinted and balanced, and it was a bitch to start if the timing was too advanced. However, when it was correct it ran 127.42 mph / quarter mile. Lot of work went into this bird. I'd also check the cam timing, if you don't have a degreed cam wheel you may have to split hairs with cam crank and ignition to get a better start and performance you're looking for. Good luck.

What we're your times?

 

[Ratranger]

Hi Mate,
I have a 840 which is impossible to kick over, but I have fitted a smedspeed 4 brush starter motor and a lithium ion battery which turns it over no problem .
Tony

Do you have any info on the 4 brush starter? It's no longer mentioned on the smedspeed site which means info is very slim.

 

[XsTony]

Send Rick an email, I bought mine last year when I built a 840 with a rephased crank.
Tony