Another eng swap thread:(Edit: no longer considering EFI, upgrading 750 engine

[Duck-Stew]

Ferracci 11:1 drop-in 750 pistons and 695 heads on a 750 (same as late 800 heads w/7mm valves) run very, very well for a few $.

Done it twice.

Also, from my 15 years working on Ducati engines, the above is ALL I would ever do to a 750.  They're just not worth it beyond the above.

And a +1 to 900 heads not fitting onto small case motors (600, 620, 695, 750 & 800).

[LowercaseJake]

Ferracci 11:1 drop-in 750 pistons and 695 heads on a 750 (same as late 800 heads w/7mm valves) run very, very well for a few $.

Done it twice.

Also, from my 15 years working on Ducati engines, the above is ALL I would ever do to a 750.  They're just not worth it beyond the above.

And a +1 to 900 heads not fitting onto small case motors (600, 620, 695, 750 & 800).

What kind of gains in HP/Torque could I expect from those mods? Initially planned to put in a light FW and call it a day. Maybe try out those Mikuni TDMR although I think they'd be too big for a 750 much like FCR41s are too big. The Mikuni slide carbs are 300 dollars less, and I prefer slide carbs over vacuum.

Any other carbs that fit? Perhaps some of the Mikuni round slides?

[koko64]

Do the TDMR carbs come in 38mm or 39mm sizes? Stick with tandem down draught carbs to keep it simple. I take it that you will run stock manifolds. I've played with TM38s but they are separate side draught carbs and there is alot of mucking around involved. The TMs are cheap as chips but any savings would be lost in set up and dyno time. I guess you would have similar issues with VMs, etc. FCR39s would be great, but yeah very pricey nowdays.

[koko64]

https://www.google.com.au/url?sa=t&source=web&rct=j&url=https://m.ebay.com.au/itm/Mikuni-TDMR-40-flatslide-racing-carburetors-Ducati-750-900-SuperSport-SS-NEW-/192026282767&ved=0ahUKEwiFm_Sbm57XAhVDn5QKHVOvB7kQFghUMA8&usg=AOvVaw2Cu1Aov-nTUEa9QmPwM5vb

Wonder if they make smaller sizes?

[ducpainter]

https://www.classic-raceshop.com/mikuni-tmr-tdmr-carburetors

38's anyone?

[koko64]

I reckon 38mm is a good size. Worth emailing to get a twin set made up.  I expect cheaper at two carbs.

[Duck-Stew]

What kind of gains in HP/Torque could I expect from those mods? Initially planned to put in a light FW and call it a day. Maybe try out those Mikuni TDMR although I think they'd be too big for a 750 much like FCR41s are too big. The Mikuni slide carbs are 300 dollars less, and I prefer slide carbs over vacuum.

Any other carbs that fit? Perhaps some of the Mikuni round slides?

I never dyno'd either bike, but it felt *almost* as much as an 800.  Speeddog can attest, he rode the one...

[LowercaseJake]

Based on the info from you guys I'm going to pass on buying an 800 + EFI, when my 750 I already own can be made to perform about the same for less money. And like a glutton for punishment I'm leaning towards flatslides instead of EFI for the simplicity.

Interesting -  I've received responses from Kaemna, FranksMX!, and the company Ducpainter linked to. All 3 replied, 2/3 can get the 38's but they all seemed confused by why I'd want to buy them, and insist the TDMR40 is the correct choice.

Something else Ducpainter mentioned struck me - that even the FCR41's might be too big for a stock 900 engine. I think he's on to something....bigger carb, lower velocity they feed the motor at, which would explain poor throttle response and a lot of the people (inc myself) who were initially underwhelmed by the FCR's before lots of tuning. And I doubt 41's would ever be appropriate on a 750 for anything other than WOT at a track.

I know it's only a mm, but I wonder if the Mikuni flatslides perform significantly better at part throttle because of it. The info from Brad Black's website seem to support the notion that the smaller flatslides give better throttle response and torque when just cruising around.

So anyways the TDMR are available in 38mm but all the dealers seem adament about 40's being the right choice.

Lastly having tuned both vaccum and slide carbs, the latter is my preference by a mile. I'm even looking at

these: https://www.ebay.com/itm/Dellorto-PHM-NS1-ND1-38mm-PAIR-carburetors-Moto-Guzzi-Ducati-SS-4906-4907/172650522787?hash=item2832c5e8a3:g:8dAAAOSww9xZA~rW

What do you think, Koko? pretty sure these were OEM equipment on the early to mid 80's SS900 and 750? wonder if they'd bolt right up to my intakes?

[Duck-Stew]

They may bolt up.  I used to have some 40mm Dell-Ortos.  But, the Mikuni's will perform better as they're newer technology.

[Duck-Stew]

I guess the best way to describe how the high-comp/695-headed/750 rode is:  Like an 800 but more power 'up top' instead of torque and it suffered from the 5-speed trans.  Personally, it's my least favorite Ducati transmission that I've ever owned/ridden.

Hope that helps.

[LowercaseJake]

I guess the best way to describe how the high-comp/695-headed/750 rode is:  Like an 800 but more power 'up top' instead of torque and it suffered from the 5-speed trans.  Personally, it's my least favorite Ducati transmission that I've ever owned/ridden.

Hope that helps.

I am def going to miss that 6th gear. But I do like a wet clutch.

Looking at my old set of 38mm Mikuni's....they are shot to $hit. Float bowl gaskets need replaced and the slides are sticky. I "know a guy" who sells these BRAND NEW for $250, complete with fuel hoses, pre-jetted for USA M600's. Was originally going to buy the Factory Pro ti kit but I may be better served just getting the new in box ones. I seem to remember the main jet being the only thing required when going to pods/open airbox; Stew, if I order an assortment of larger jets from my local Carb Parts Warehouse (GREAT company) which sizes do you recommend? I seem to remember way back when, I bought the FP kit when removing my airbox lid, used the largest jet provided, and it ran great everywhere. I just don't remember what size it was.

Altho 250 here, 20 bucks there, all to have the vaccum Mikunis I don't enjoy fiddling with, those 40mm TDMR's sure are becoming tempting. Especially since I'll be upgrading the 750 heads and adding Ferraci pistons.

750 gets bagged on but personally I loved that engine for commuting and cruising.

[koko64]

Based on the info from you guys I'm going to pass on buying an 800 + EFI, when my 750 I already own can be made to perform about the same for less money. And like a glutton for punishment I'm leaning towards flatslides instead of EFI for the simplicity.

Interesting -  I've received responses from Kaemna, FranksMX!, and the company Ducpainter linked to. All 3 replied, 2/3 can get the 38's but they all seemed confused by why I'd want to buy them, and insist the TDMR40 is the correct choice.

Something else Ducpainter mentioned struck me - that even the FCR41's might be too big for a stock 900 engine. I think he's on to something....bigger carb, lower velocity they feed the motor at, which would explain poor throttle response and a lot of the people (inc myself) who were initially underwhelmed by the FCR's before lots of tuning. And I doubt 41's would ever be appropriate on a 750 for anything other than WOT at a track.

I know it's only a mm, but I wonder if the Mikuni flatslides perform significantly better at part throttle because of it. The info from Brad Black's website seem to support the notion that the smaller flatslides give better throttle response and torque when just cruising around.

So anyways the TDMR are available in 38mm but all the dealers seem adament about 40's being the right choice.

Lastly having tuned both vaccum and slide carbs, the latter is my preference by a mile. I'm even looking at

these: https://www.ebay.com/itm/Dellorto-PHM-NS1-ND1-38mm-PAIR-carburetors-Moto-Guzzi-Ducati-SS-4906-4907/172650522787?hash=item2832c5e8a3:g:8dAAAOSww9xZA~rW

What do you think, Koko? pretty sure these were OEM equipment on the early to mid 80's SS900 and 750? wonder if they'd bolt right up to my intakes?

If you are committed to the short stroke motors and want to build a hot 750 or 800, then definately go for the 38mm flatsldes and keep that air velocity up. Stick to your guns and dont let them sell you 40s. Tell them your tuner is working to a specific motor combination or recipe. If the 38s belong to the next body size down in the product range, the margin on resale may be less than the 40s.

In the Delorto catalogue there are new flatslide carbs (wickedly expensive), which shows the march of technology.  Round slides have friction, strong return springs and more chance of vacuum lock at large throttle openings.
If I wanted an 800 with efi or six gears I would spruce up my 750, sell it and buy an M800 or S2R. If a 5 speed gearbox doesn't bother you then hot up your 750.

[LowercaseJake]

Koko, I just committed to a set of FCR39's. Got a helluva deal and just couldn't bear the thought of those CV Mikunis on my bike. I actually already flipped em for $150, woohoo! Also the Mikuni 38's would've required I buy a used throttle and cables (ditching my fancy Domino quick turn) a choke assembly, carb sync tools etc. In the end I wouldn't have saved much.

Since he's a Keihin dealer and building these himself, I need to give him a baseline for slide position, jets etc. The baseline for 39's seems to be identical to 41's and I see no distinction between 750 or 900, not on Sudcos website, CCW's FCR FAQ, etc. I find that odd.

Since the 695/800 head swap is a future project I was thinking I'd keep the needle clip position, fuel and air screw settings the same and asking for a leaner slow fuel jet and richer main jet. Maybe a 55 slow jet and a 160 main jet, since I have a free flowing exhaust and open airbox. Just need the bike to run decent.

BTW, according to him, Keihin is discontinuing banked 39's in the near future. Not sure how true that is but he's a no BS guy.

[LowercaseJake]

Oh, and apparently the TDMR 38's aren't available in a banked config that fits 750/900 manifolds. At least according to FranksMX.

[ducpainter]

Oh, and apparently the TDMR 38's aren't available in a banked config that fits 750/900 manifolds. At least according to FranksMX.

I'm not saying it isn't true, but the stock carbs on Monsters are BDST 38's. The spacing on the manifolds isn't foreign to Mikuni.