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V7iii Carby conversion

Discussion in 'V7/V85/V9 Chat & Tech' started by Dinsdale Piranha, Sep 9, 2020.

  1. Dinsdale Piranha

    Dinsdale Piranha Cruisin' Guzzisti GT Contributor

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    I have a V7iii Special - my first fuel injected bike. Had enough of FI tor now! I need something to tinker with. Just wondering if anyone here, or anyone you know has done a carby retro-fit on a fuel injected V7.

    I'm assuming that the existing ignition timing pick-up would be suitable to feed a signal into any garden variety CDI box.

    Carby-wise I'd be looking at a pair of Mikuni TM33 or perhaps TM36 flat slide pumpers. They come in quite a range of venturi sizes, but alas, not with accel pumps. The hardest part (for me) would be fabricating a mirror pair of intake manifolds.

    I've fitted different carbies to already carburettored bikes in the past, but never a retro-fit onto a FI engine. The Mikuni TMxx series are outstanding units, and quit easy to set up and tune. The Keihin FCR series are also excellent performance pumper carbies, but much more fiddly to get set up nicely.

    Any help/suggestions/ideas would be well appreciated.
     
  2. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    I would say just leave the V7III alone and by a bike that has carbs if you want to tinker. Just get an old Brit bike and you will be turning wrenches all the time.
     
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  3. Dinsdale Piranha

    Dinsdale Piranha Cruisin' Guzzisti GT Contributor

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    Nice thought - but a non-starter. It's not my desire to be turning spanners all the time. Besides with an old Pommish bike it wouldn't be turning spanners all the time, it'd be mopping up oil all the the time.

    At this stage I'm seeking out the various pitfalls which I haven't seen - a feasibility study so to speak . The FI on the V7 is just a very basic electric carby, with no user tunable possibilities. I'm not talking about Todd tuning, which is already applied. Looking at power, torque and fuel economy, I reckon there are worthwhile gains to be had on all 3 parameters using high end carbies. Many pre-FI Guzzis 750s have considerably higher output, and that with quite ancient, small Dell'Ortos without accelerator pumps.
     
  4. DeadEye

    DeadEye High Miler

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    See if you can find bits from a XR600/650R giant dual carbed Single Cylinder pig.
    Rejet them, adapters for the intakes, and Bob’s you’re uncle !

    Google - XR600R intake and you’ll get places that make custom intakes.
     
  5. GuzziMoto

    GuzziMoto GT Reference GT Contributor

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    You aren't going to get more power, torque, or fuel economy by switching to carbs. You will likely give up some of that, though. You may gain some by things like porting and / or cams, but you could do that with FI as well.
    That said, if you really want to go that way, I would think it is do-able.
     
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  6. vagrant

    vagrant High Miler GT Contributor

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    I say this with all due respect. You need to drink more and think less!
     
  7. Dinsdale Piranha

    Dinsdale Piranha Cruisin' Guzzisti GT Contributor

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    OK, so how come the older (carburetted) models put out so much more? I do realize that the older, higher powered 750 models are all big block engines, and that the power drop came with the newer small block engines. The power wasn't improved with the application of FI either. And not appreciably improved with a full engine redesign (cf Hemi Heads).
    1975 "S" 62hp
    1975 "S3" 70 hp
    1971 "V7" 70 hp
    1973 "V7 Sport" 70 hp
    I think these are all 30mm Dell'Orto PHBH model carbies too. Old, basic (agricultural) and non-pumper.

    So, I guess the question is: What is it about the small block engines that prevents them from producing anything near the output of the 45+ year old big block engines? The big blocks are more over-square, but overall, just older technology. Do the big block 750s have Herron Heads, Hemi Heads?

    Any'ow, for now it's all speculation/feasibility. Apart from anything else, being "old school", I'd much rather a bike or car with far fewer electronics and more that I can fix, service and tune. I know carbies!

    Btw, one other thing I'd need to take into account is the dash. There are several fine options out there though: Acewell, Koso, TrailTech and sure more.

    I find the discussion interesting, so please, some more ideas.
     
  8. Dinsdale Piranha

    Dinsdale Piranha Cruisin' Guzzisti GT Contributor

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    Hard to do - I don't drink at all :).
     
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  9. vagrant

    vagrant High Miler GT Contributor

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    all those numbers were pulled out of some engineer's ass to make him look good in front of the boss. I'm sure real dyno numbers are quite different.
     
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  10. Dinsdale Piranha

    Dinsdale Piranha Cruisin' Guzzisti GT Contributor

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    https://www.motorcyclespecs.co.za/index.htm
     
  11. GTM®

    GTM® Administrator Staff Member GT di Razza Pura

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    Easy, those are crankshaft numbers, not rear wheel. My 1100-2V California motor made 72 rwhp with intake and exhaust mods. Modern engines are fighting emissions restrictions. High 50's (V7) and low 60's from the small block motor (V85TT) is impressive.
    We have a good friend (JB Weld) that carb'ed his California motors, and they do get better gas mileage (hence pollute more), but I'd bet anything they don't put down as good of numbers. The big struggle for the newer single throttle body/ECU V7/9 would be the ECU for timing control, especially with the "wet" alternators.
     
  12. dale decrescenzo

    dale decrescenzo Tuned and Synch'ed

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    assumptions: my'18 V7 is a wet alternator, "wet" alternator is residing in an oil bath area...
    questions: why would the "wet" alt have an effect on horse power ?, is the ECU timing control not programmable?
     
  13. DeadEye

    DeadEye High Miler

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    Everything Sploshing around in a liquid slows down ?
    ( It that the Idea behind dry Sump engines ? - asking )

    How much parasitic loss in the bikes drive train - generally they add/subtract 15% - 20% for a car Dyno's numbers ?
    200 at the wheels = 230/240 at the crank
     
  14. GTM®

    GTM® Administrator Staff Member GT di Razza Pura

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    You have to read the question asked at the top and topic of this thread.
     
  15. DeadEye

    DeadEye High Miler

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    Come come now you don't believe everything you read on the Internet ??? :rofl:
     
  16. Dinsdale Piranha

    Dinsdale Piranha Cruisin' Guzzisti GT Contributor

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    All the numbers quoted for the series iii are crankshaft numbers too. I am comparing apples with apples where numbers are concerned.

    DeadEye, Vagrant, give me a better set of more verifiable numbers and I'll use them - you might be right, so give me a source. Until then, carburetted big block engines from 45+ years ago produce considerably more power than modernized small block engines with FI.

    How can this be?

    Todd, I know that when you produce power/torque figures that they're rear wheel figures. Pretty much all manufacturers (MG included) quote crankshaft figures, so that's all I have to run with. I'm also well aware that the shaft drive soaks a lot more power than a chain, hence crankshaft numbers are better for comparison purposes.

    Somehow we've taken this topic off track, into some kind of adversarial contest. I was just soliciting ideas.
     
  17. DeadEye

    DeadEye High Miler

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    Dinsdale, it is pretty odd that we can’t reconcile how the performance number seem to be going backwards as we “Advance”

    You may remember in the seventies how automobile performance number went from between 200 - 300Hp to mid - low 100’s because off emission regulations , unleaded fuel and net vs. gross Hp values

    This article explains a lot of the why. (If they can be trusted to no be just making up @#$& )
    https://ateupwithmotor.com/terms-technology-definitions/gross-versus-net-horsepower/

    Don

    PS: When it comes to any “discussion” that is not solely based on one source of hard facts - it’s guaranteed to go off the rails. We can’t have a argument about what a inch is, ( except that the length of what you use to measure it will be affected by temperature :rolleyes: ) but we can argue about what a Gallon is. :devil:
     
    Last edited: Sep 11, 2020
  18. GTM®

    GTM® Administrator Staff Member GT di Razza Pura

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    Simple. The small block heron head started out as a 350cc econo-commuter. The big blocks were over-built hemi-head mills. More robust and designed to make power.

    Understood, but plenty of dyno numbers out there these days for RWHP. I should have my new dyno any day now, so I'll be able to start logging some serious data to post soon.
     
  19. dale decrescenzo

    dale decrescenzo Tuned and Synch'ed

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    just grab you a nice horizontal weber and make a manifold to fit. Single cable pull and no sync required.
    ( good carb beats FI any time )
     

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  20. Moto-Uno

    Moto-Uno Cruisin' Guzzisti

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    Those quoted numbers for HP are pure unadulterated crap . Like a few others here I have had the privilege of working at a shop with
    a dyno. I ran my Le Mans2 for over 18 times and ended up with a true 70.2 rear wheel HP . That bike ran 40mm Dellortos , Bub large diameter headers , 89mm High comp Wiseco pistons , twin plugged heads and a Mega Cycle 620 cam . It took removing the baffles
    and air filter to get to that number . This was done in Ottawa , Ontario that is less than 600 feet above sea level . That same motorcycle
    would walk away from other Le Mans 2 bike in a highway roll on . And that was 10 hp less than they advertised stock! I had to gear down
    at least twice to beat an RD 350 Yamaha in a highway roll on when the bike was totally stock :( . That's my rant and I still have the Dyno
    charts to prove it . Peter
     

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