880SFC Dyno results

OK, it's getting closer .................. one more jet change, and she'll be good to go. As it stands now, 65hp at 6,000RPM.
Sounds really nice, idles smooth and a bit rich on both main and pilot, new jets coming from Sydney.

Dyno guy, says on the road, it snatches a bit when pulling out of low revs.
I think I'll blame the pumpers for that. When it comes back, I'll disconnect them and see what happens.
 
chrisk said:
Dyno guy, says on the road, it snatches a bit when pulling out of low revs.
I think I'll blame the pumpers for that. When it comes back, I'll disconnect them and see what happens.
Click to expand...

Low revs = ?? Bit of a vague description, 'snatches' ... when the throttle is opened from the stops? Snatchy as the revs rise? When the throttle is open slightly? Wide?

I'm sure when you've done some k's yourself (Kays?  8)) you'll be able to give us a better pic. Gonna be a hoot for you to get on that thing, Chris!
 
Bike back in my hands, rode home and flat spot is between about 1500 & comes good about 2500rpm, on dyno it showed that at the flat spot it was as lean as! So, with that, I presume the cutouts are way too high.

The snatch he was talking about was a typical drive chain snatch as it misses and farts.

But fuck me, above 3000 revs and this thing boogies, and pulls like a steam train, for a bike that?s 46 years old.

From 2,500 to 6,000, the hp curve was ever increasing and smooth as a babies bum.

It going to be hard to take it easy for run in.

So, tomorrow I?ll pull the slides out and see what cutouts they are and ask you edumacated folk what you think I should go down to.
 
Last time I bought slides they were $80 each and that was 15 years ago.Have you tried raising the needles, highest position of the needle is richest etc.So that's the bottom notch.I remember new slides are slightly different to the old ones, don't remember the details so take care.Changing needle hights is a 10-minute job so easy to do.Also maybe try a touch of choke as you ride it to confirm its lean
 
Assume you are using Dellortos?
Have you optimised mixture screw settings/pilot jet size?
At those sort of revs it's still on pilot jets.
 
Grant said:
At those sort of revs it's still on pilot jets.
Click to expand...
Exactly. Nothing to be gained playing with needle settings if the fluffing is coming on low throttle positions. Sounds like the sort of behaviour you get when tootling at low revs with very small throttle openings.
I used 70 cutaways for years with my SF1 (which later served with my SFC motor) and thought it seemed pretty smooth until I tried a pair of carbs fitted with std SF2 50s. It felt heaps more refined.
Motor sounds fab Chris!
 
I take it you won't be goin down the corner shop on this bike CK !
Just keep rpm above 3k ;)
Like others have a play with pilot ,needle heights and mixture screws before muckin about with slides.
Don't poke a hole thru the back of that tank.... snds like a hoot  :D
 
Grant said:
Have you optimised mixture screw settings/pilot jet size?
At those sort of revs it's still on pilot jets.
Click to expand...

:o I just had a flash back: Dyno guy said he placed two long niffers up the pipe, up into each header, one pot was running way leaner than the other, so much so, there was almost one turn variance once evened out ............... With that, and the fact that it was really lean just off idle, in the "progression phase" where the flat spot is................
I bet there's an O ring missing or buggered! Will know in an hour or so!
 
I thought the idle jet and therefore the mixture screw had an effect all through the range and especially at idle and up to 1/8 of the throttle action. A missing O ring would change all the jetting? Cruising along an expressway at 100kph at 1/8 of throttle has you running on the idle jets,yes?
 
Vince said:
I thought the idle jet and therefore the mixture screw had an effect all through the range and especially at idle and up to 1/8 of the throttle action. A missing O ring would change all the jetting? Cruising along an expressway at 100kph at 1/8 of throttle has you running on the idle jets,yes?
Click to expand...

No, idle jets are just that. Just off idle brings in the secondary port, via vacuum, at just off idle until the needle takes affect, and then the main jets take over.

Here is the conundrum though.
Both O rings good, both springs same length. To get even mixtures at idle, dyno guy had to set mixture screws ...... wait for it....... l/h 3/4 turn from closed. R/h at 2.5 from closed.

WTF is wrong here?

Both slides at same height.

Choke plungers come to mind, but feel fine. And both cables seated, even if that were the case it?d show up at off idle as well.

Mixture at needle and main jet are fine.

I?m beginning to take Reds theory, through the fucking Dellorto?s in the bin. Be a shame, they are brand new!
 
My twin the same Chris..... although not as big a discrepancy, only 3/4 turn diff !

Quite possibly carb orifices/mixture screw taper a little different who knows.  :-\

 
Sounding curious and curiouser - might need a little butter  :P

Must be possible to track this down, Chris. Either one carb is getting too much fuel (eg choke plungers not closing) or one is being starved (eg blockage in the air or fuel galleries, air leak in manifold).

Pretty sure the uneven intervals in 270 cranks might affect idle as well - one side has to wait 450 before firing, the other 270, so the latter is moving quicker when it fires (= has more momentum) than the former. Only noticeable at idle.

But yours is actually spluttering, so I'd be looking for a prob. Have you put a strobe on the thing? Time to start eliminating possible causes ...  and ... just cos the carbs were new don't mean they are gonna be perfect!
 
chrisk said:
No, idle jets are just that. Just off idle brings in the secondary port, via vacuum, at just off idle until the needle takes affect, and then the main jets take over.
Click to expand...
Incorrect.
And may I politely suggest you read and try to comprehend what others are attempting to advise?  :-X

Please read the Dellorto 'guide to the choice, setting and use of tapered-needle carburettors'
take note of;
2.2 'Operating ranges. Scheme of phases while running'
3.5 'Progression system'
      fig 20 shows the location (2) of the 'progression hole'. This can be blocked and impacts the mixture when the slide starts to lift (transition period)

Otherwise, I can not add to what others have previously suggested.
And Dellorto carbs do work, so have fun  :D
 
chrisk said:
Here is the conundrum though.
Both O rings good, both springs same length. To get even mixtures at idle, dyno guy had to set mixture screws ...... wait for it....... l/h 3/4 turn from closed. R/h at 2.5 from closed.
WTF is wrong here?
Click to expand...

Ok.
Also read section 3.4 'Idle systems'  (dunno)

<edit: the guide should be sitting in your work email inbox>
 
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