piranha-bro2
Hero member
- Location
- Melbourne
Def not the way good SF should make you feel - no wonder the Jota won the comp for 'best ride to Breganze'!
750SF valve timing/advance and compression numbers
- Thread starter TeddyG
- Start date
I think I picked up one with the devil in it Quentin. Its been a long long road of continuous improvement, just to get it 'tolerable'. It's bloody confusing, all the performance related stuff checks out, but the bike is still a pile of slow, vibratory frustration.
• L & R cylinders hitting TDC together: Yep, bang on.
• Cam timing OK: Yep (and double checked by Sr. Oro after the cam flange separated on the way to Breganze last but one time).
• DMC ignition thrown on - spot on timing and correct advance. Twin outlet coil - nice fat spark.
• Endless experimental jetting changes. Including careful setting of cut away (weaker all-over helped a lot).
• Choke circuit doing it's thing properly.
• Carbs/stubs/isolator/had all smooth bored. No nasty steps.
• Wiring improvements (suspected bad ignition feed - dedicated relay fitted).
• Tappet adjusters improved to ensure true clearances being set (got rid of a bit of dishing).
• Exhaust internals checked for any nasty manufacturing mistakes.
• Compression OK and no unusual hisses when leakdown tests.
The engine always feels like it is fighting itself and just doesn't 'flow'.
When I read your comment about being able to hit twice the 50mph TeddyG is suffering from, I just giggle to myself, mine wouldn't get anywhere near the ton.
This mornings revelation, after the last ride out, suddenly... cannot get first gear. Was perfect when I put it away. No strange noises or change to clutch feel.
Maybe the solution is to give it the 'Full Paul Marx'....
(Sorry Paul - but at the moment if this one burnt, I would do a happy dance around the flames).
Oh, well, I'll wheel it into as corner and spend some time fettling the Jota....
• L & R cylinders hitting TDC together: Yep, bang on.
• Cam timing OK: Yep (and double checked by Sr. Oro after the cam flange separated on the way to Breganze last but one time).
• DMC ignition thrown on - spot on timing and correct advance. Twin outlet coil - nice fat spark.
• Endless experimental jetting changes. Including careful setting of cut away (weaker all-over helped a lot).
• Choke circuit doing it's thing properly.
• Carbs/stubs/isolator/had all smooth bored. No nasty steps.
• Wiring improvements (suspected bad ignition feed - dedicated relay fitted).
• Tappet adjusters improved to ensure true clearances being set (got rid of a bit of dishing).
• Exhaust internals checked for any nasty manufacturing mistakes.
• Compression OK and no unusual hisses when leakdown tests.
The engine always feels like it is fighting itself and just doesn't 'flow'.
When I read your comment about being able to hit twice the 50mph TeddyG is suffering from, I just giggle to myself, mine wouldn't get anywhere near the ton.
This mornings revelation, after the last ride out, suddenly... cannot get first gear. Was perfect when I put it away. No strange noises or change to clutch feel.
Maybe the solution is to give it the 'Full Paul Marx'....
(Sorry Paul - but at the moment if this one burnt, I would do a happy dance around the flames).
Oh, well, I'll wheel it into as corner and spend some time fettling the Jota....
Exmoor beast
Hero member
- Location
- Minehead,Somerset, ENGLAND OF COURSE
How long have you had this bike running badly? You’ve been to Italy twice running like a bag of crap?
Something seriously not right- something I have learnt is never rule out something an expert has checked- if it feels like it fighting itself it’s got to be the cam timing, crank phasing or odd pistons- something odd.
Try doing an MPG on it to see if has any efficiency. That at least might measure its performance beyond a feeling. Maybe a dyno run, I spent a good few months banging my head against a tooth out most dismissed. Phil Todd did a simple valve timing write-up for triples years ago that didn't rely on timing marks or TDC marks. My triple ran CV carbs with plastic slide back then, it melted those slides jamming them in place on a 4-day ride coming home on a trailer, and even then I couldn't convince the engine builder that there was something definitely wrong. It would start but ran like a gutless scooter.
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As the Dartmoor dodger points out, what about crank phasing, has it been pulled apart at some time?Happy with itself
The graceful dance of a couple on the ballroom floor, not 2 boxers belting the shit out of each other
And odd pistons has been seen before.
Paul
Exmoor beast
Hero member
- Location
- Minehead,Somerset, ENGLAND OF COURSE
The Dartmoor Dodgers-are in fact a netball team- I only played one game..they pulled me off at half time!
hooksey
Hero member
- Location
- Vic , Australia
Makes me wanna give netball a try..........The Dartmoor Dodgers-are in fact a netball team- I only played one game..they pulled me off at half time!
Clutch Drag Haggis..........
piranha-bro2
Hero member
- Location
- Melbourne
A free-flowing SF feels like a horse heading back to the stables - very willing!! I'm hearing your pain, Haggis. What model SF is it?
Over the years I've ridden SFs that I'd describe as 'lemons'. Good ones pull VERY hard to 7500 and a good one will do that in 5th. At the end of the day they are machines, nuts and bolts and metal and oil. If it were mine I'd just pull the motor and start from scratch - look closely at the pistons, bores, rods (are they straight?) ... check the crank for true. It sounds like it's so unrewarding to ride that there's little point until you can make it go the way it should.
Tippie
Hero member
- Location
- Dr?bak, Norway
What camshaft is in it? Might be worth trying a different one. The cam in the SF2 I have just put together has one exhaust lobe 10 degrees advanced from where it should be.
I remember that there were huge differences between new bikes back in mid 70s when I used to ride new Lav and BM up to the rego office in Melbourne. Some bikes of both marque were like I would be pretty disappointed if I bought, just felt tight and awkward in every way, others just felt fantastic straight out of the box. None felt like what you describe though. Your bike should be able to pull wheelies downhill in 3rd gear whilst downshifting!
I remember that there were huge differences between new bikes back in mid 70s when I used to ride new Lav and BM up to the rego office in Melbourne. Some bikes of both marque were like I would be pretty disappointed if I bought, just felt tight and awkward in every way, others just felt fantastic straight out of the box. None felt like what you describe though. Your bike should be able to pull wheelies downhill in 3rd gear whilst downshifting!
Uphill!
Exmoor beast
Hero member
- Location
- Minehead,Somerset, ENGLAND OF COURSE
K
I have had stretched cam chains on Kawasaki Gt750 where the cams are literally miles out and they go like ten bastards- obviously both cams massivesly retarded ( nearly a tooth out!) but still more or less in sync- rev to high heaven.
Thanks for all the suggestions and comments folks.
My SF is indeed now wheeled into a corner. Going back some years, it did come with an unknown bucket-full of issues, exposed only as I rode it and got to understand it, everything basically needed attention.
As I work though it, it does get better and better all the time, but no single fix has given it the correct performance. I have no idea what crank is in it. Cams are standard for an SF - soft tuned. Next job (after Breganze now - fiddling with Jota first), is to dig into the primary drive and see what is causing the drag. I suspect worn and warped plates.
Going back to TeddyG's intial post, the biggest thing holding my particular bike back was over-richness. I have gone quite a lot leaner [than std spec], but I'm now suffer ring-twitter about holed pistons
My SF is indeed now wheeled into a corner. Going back some years, it did come with an unknown bucket-full of issues, exposed only as I rode it and got to understand it, everything basically needed attention.
As I work though it, it does get better and better all the time, but no single fix has given it the correct performance. I have no idea what crank is in it. Cams are standard for an SF - soft tuned. Next job (after Breganze now - fiddling with Jota first), is to dig into the primary drive and see what is causing the drag. I suspect worn and warped plates.
Going back to TeddyG's intial post, the biggest thing holding my particular bike back was over-richness. I have gone quite a lot leaner [than std spec], but I'm now suffer ring-twitter about holed pistons
All my 750s, SFC included are running leaner and with hotter plugs. 5 to 10 points down on the idle jets.Thanks for all the suggestions and comments folks.
My SF is indeed now wheeled into a corner. Going back some years, it did come with an unknown bucket-full of issues, exposed only as I rode it and got to understand it, everything basically needed attention.
As I work though it, it does get better and better all the time, but no single fix has given it the correct performance. I have no idea what crank is in it. Cams are standard for an SF - soft tuned. Next job (after Breganze now - fiddling with Jota first), is to dig into the primary drive and see what is causing the drag. I suspect worn and warped plates.
Going back to TeddyG's intial post, the biggest thing holding my particular bike back was over-richness. I have gone quite a lot leaner [than std spec], but I'm now suffer ring-twitter about holed pistons
I learnt that Gijs van Dijk who isn't a novice was doing the same.
I think that if basic tuning and twiddling doesn't get a freshly bought bike going correctly, the engine needs taking to bits .
Paul
henrywillms
Hero member
- Location
- Canada
Teddy...frustrating situation. They are pretty simple bikes and no special skills or trickery or hidden secrets are normally needed to make one run right and keep it maintained. The experts as noted above have offered the right advice including likely something the previous owner may have done to cause this. I can only add that one option would be to have an expert....you are not too far from Wolfgang...to have a look at it....either in its current state or if you do pull the engine apart, to see what may not be "normal".
TeddyG
Hero member
- Location
- Portland Oregon
Thanks all,
It turns out that I mistakenly diagnosed a rich condition since the plugs were constantly fouling/engine bogging at throttle, but it was in fact a lean condition at the upper rev range. Scott Potter who previously worked on the engine, suggested engaging the enricher while riding at higher speeds, and the engine came to life. It came to me w/ 138 main jets, so I installed the base 140s, 55 pilots,270 atomizers/middle needle notch. Steve Allen at Bevel Heaven advised the richer atomizers, saying the enricher use indicated a lean condition. This combo gives me the best engine performance, and the B8 plugs are burning clean. It will now accelerate w/ no bogging. I use only ethanol free gas.
It turns out that I mistakenly diagnosed a rich condition since the plugs were constantly fouling/engine bogging at throttle, but it was in fact a lean condition at the upper rev range. Scott Potter who previously worked on the engine, suggested engaging the enricher while riding at higher speeds, and the engine came to life. It came to me w/ 138 main jets, so I installed the base 140s, 55 pilots,270 atomizers/middle needle notch. Steve Allen at Bevel Heaven advised the richer atomizers, saying the enricher use indicated a lean condition. This combo gives me the best engine performance, and the B8 plugs are burning clean. It will now accelerate w/ no bogging. I use only ethanol free gas.