building the fantasy carby 750 top-end

[brad black]

all the 800 heads would be the same.  apart from the guides.  i'd say the 7mm stems just lead to faster guide wear, but i'd not be overly concerned about either.  they can all break collets, possibly a combination of rpm and valve weight.  altho i have seen a 600 do it too.

you'll need some high comp pistons as the 800 chamber will be quite a bit bigger, it's basically the old 900 chamber.

but otherwise it'll be a good swap i'd say.  easier than getting them big valved and finding 900 cams.

probably just as easy to get an 800 motor and fit it tho.  you get a 6 speed that way.

[brad black]

to fit the 696 heads you'd need to fit the cylinders as well.  given the 696 is a shorter stroke, the rods appear to be the same (xx1A vs xx2A #) and the inlet ports appear to be in the same place the piston should be 2mm or so longer.  so you'd machine 2mm or so from the top of the 696 pistons as required to fit the chamber profile and increase your comp as well.  you'd need to get the valve reliefs deepened too i assume.  the manifolds should fit straight up.  you'd have to fabricate exhaust as required.

but there's a lot of assumptions there.

[carbmon]

all the 800 heads would be the same.  apart from the guides.  i'd say the 7mm stems just lead to faster guide wear, but i'd not be overly concerned about either.  they can all break collets, possibly a combination of rpm and valve weight.  altho i have seen a 600 do it too.

Cool, that opens the pool of parts a bit.

you'll need some high comp pistons as the 800 chamber will be quite a bit bigger, it's basically the old 900 chamber.

Higher compression pistons are a given for the project.  Would you suggest the “11:1” designed for the 750 or go up to the “12:1”, expecting the as-installed ratio to end up a lot lower than the 'as-stated' ratio with the bigger heads?

but otherwise it'll be a good swap i'd say.  easier than getting them big valved and finding 900 cams.

probably just as easy to get an 800 motor and fit it tho.  you get a 6 speed that way.

Understood.  Maybe very close to a cost-wash, too, considering that the high-comp pistons required for the head swap seem to be pretty rare on the used market. BTW, I assume that the sensor assy on the 695/800 H head can just be pulled and blocked for a carby installation?

to fit the 696 heads you'd need to fit the cylinders as well.  given the 696 is a shorter stroke, the rods appear to be the same (xx1A vs xx2A #) and the inlet ports appear to be in the same place the piston should be 2mm or so longer.  so you'd machine 2mm or so from the top of the 696 pistons as required to fit the chamber profile and increase your comp as well.  you'd need to get the valve reliefs deepened too i assume.  the manifolds should fit straight up.  you'd have to fabricate exhaust as required.

but there's a lot of assumptions there.

Yeah, the fair amount of machine work + lots of assumptions still to be proven make the 696 route a bit more of a challenge (and expense) than I'd personally want to undertake.

[Speeddog]

FYI, 696 heads have 20 tooth pulleys, where the 750's have 18 tooth.

So you would have to swap one way or the other....

[carbmon]

FYI, 696 heads have 20 tooth pulleys, where the 750's have 18 tooth.

So you would have to swap one way or the other....

So what's the tooth count on the bottom for each (sittin' here bored, drawing a sketch and thinking about cam timing)?  Just a mental diversion, definitely not a project I'd undertake.



Noticing the availability of complete engines compared to just heads on eBay ... I'm back with Brad's 'just swap-in an entire 800' comment, trying to think through the steps of the carb/timing tuning process with that engine wrapped in 39 FCR's  and an Ignitch unit instead of the FI system.

You know, simple questions like "given 39 FCR's setup for the stock 750, and a 'dumb' new Ignitech box" .... how do you set 'em up to just start the thing and get it to run good (and safe) enough for a start at tuning?

Yeah, if not already obvious, this is the clue that I'd be in way over my head on any of these projects (pardon the pun).  

[Speeddog]

The 696 has 20 on the drive pulley, 750 has 18.

All are 1:1 from the drive to the head.

Seeing as an 800 will pull nearly the same HP as a 900, I'd go with 41's.

[Duck-Stew]

800 motor swap tips:

Intake & exhaust manifold placement is the same so just swap the 750 parts on & go.
2005-6 800 motors have the wet-slipper clutch, 6-speed trans & 8mm valve stems (8mm have the good valve guides which hardly ever go soft)
You'll still have to deal w/the 10mm to 12mm engine mounting bolts, but that's minor.
You'll have to get the single timing pick-up to fire both ignition coils (Ignitech)

[carbmon]

All are 1:1 from the drive to the head.

Cool, much simpler that way.

Seeing as an 800 will pull nearly the same HP as a 900, I'd go with 41's.

Aha, clarity … I'd not thought of it that way.  I've got the 39's and I recall seeing something (I think on Brad's site) about him playing with 39's on a client's 900.

So, if one started by setting up the carbs as they would be for a similar HP motor, that might be a good ballpark to get things going?

800 motor swap tips:

Intake & exhaust manifold placement is the same so just swap the 750 parts on & go.
2005-6 800 motors have the wet-slipper clutch, 6-speed trans & 8mm valve stems (8mm have the good valve guides which hardly ever go soft)
You'll still have to deal w/the 10mm to 12mm engine mounting bolts, but that's minor.
You'll have to get the single timing pick-up to fire both ignition coils (Ignitech)

Thanks!  I knew about the 6-speed and someone here already clued me about the 8mm vs 7mm stem/guide issue but I wasn't aware of the slipper.  So just for clarification … are other/later years (800) with the wet clutch non-slipper?

Yeah, the bolt thing is a non-issue it seems, easy fix with careful overbore of the frame.

The Ignitech has provisions for the single pickup programming, so that shouldn't be a problem.

I still wonder about how to find a good initial timing curve for the Ignitech on the 800.  I wondered if the OEM 800 timing map is known/published and if replicating that as close as possible in the Ignitech would be a good starting point for a carby version (taking care to match the base advance)?  I understand that without a TPS/MAP (not going there!) the number of points available on the Ignitech map is somewhat limited so the timing 'curve' might not be as smooth as the OEM FI timing curve, but so it goes.

Just concerned about a starting point for all the stuff fuel delivery/ignition related from the standpoint of not wanting to melt/burn anything (other than fuel!) in the combustion chamber right out of the box.  “Optimizing” ( I know Brad doesn't like that term) could then follow.

I should ask directly … has anyone here done an 800FI to carby conversion?

[Duck-Stew]

2003-4 800's are wet-clutch 5 speeds.  

2007-8 800's are 6-speed, wet slipper clutch but have the 7mm valve stems.

Because of the similarities of the 900 and 800 combustion chamber, I'd start w/the 900 ignition map and go from there.  It'll likely be close (my guess).

You will likely need to adjust, but the 900 carb tuning would be a good start (since they're making roughly the same power).

[koko64]

DS
What's the stock compression ratio of the 800?

[Duck-Stew]

DS
What's the stock compression ratio of the 800?

IIRC: 10.8:1  (Could be 10.6:1...)

[brad black]

10.4, +/- 0.5.

i can't believe how many engines there are on usa ebay.  heaps of 620, but quite a few 800 and 900, etc.  and so many 1098.  see if you can jam one of them in.

if you're going to fit an 800 i'd just get a 900.  it's a stronger motor.

[Raux]

1198 motor in a Monster 1100 

[carbmon]

.....i can't believe how many engines there are on usa ebay.  heaps of 620, but quite a few 800 and 900, etc.  and so many 1098.  see if you can jam one of them in.

if you're going to fit an 800 i'd just get a 900.  it's a stronger motor.

LOL
750 head mods>800>900>1098+  in my former business we called that "project creep"  

I understand what you're saying about the 900, a well-proven easy swap, too.

Shoot me for sacrilege but I like the quiet of the wet clutch and the look of the engines without the external oil lines for my project's styling goals.

Always a matter of personal preference at the bottom line, ya know  

[brad black]

wet clutch i can understand.  you can always seal the cover on the dry clutch and run oil in it.  works well.

external oil lines are pre 98 only.  the air cooled only cylinders are 98 and 99 i think, i've had 2000 models apart that are oil cooled without external lines.

the fact you can run with much lighter clutch springs to reduce lever effort and you effectively have another gear plus it's all stronger is what makes the 900 motor attractive to me.  now that i've hotted up a 750 i'd not do it again, i don't see the point when the alternative is easy.  i only did mine because no one had ever asked me to do one.  for what it is it's a good result, nearly as powerful as an 800 with the basic inlet and exhaust mods.  which, when you say it like that, makes it sound like a waste of effort.

i've owned 4 (i think) 6 speed ducatis and the 5 speed is like the 6 speed without 6th.  the extra gear makes the engine so much more usable as an all rounder.

the small motor 6 speed has a narrower spread than the 900 box, but it's still better.