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Thread: MB100 development

  1. #1
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    MB100 development

    Just getting back into bucket racing.

    Had the MB100 dynotuned in prepartion for the Battle of the Buckets at Ruapuna on 15 Oct 11. Results (shown below) were mixed.

    Click image for larger version. 

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    Positives from the session on the dyno were:
    1. The bike is no longer in grave danger of seizing because it was running way, way, too lean.
    2. I actually know where its making power and can now ride it accordingly.

    Negatives:
    1. Bike is making less power than expected and is quite peaky. Peak power is also being made quite low at around 9200rpm. Exhaust seems to be the culprit on this.
    2. Carb seems to be too large for the bike. Diagnosed from:
    No power increase with a jetting increase.
    Jetting also can't be increased as carb won't flow enough air. Raising the needle to flow more air (to allow bigger jet) just causes bogging issues.
    Unable to reduce the jetting size without compromising the fuel/air ratio and placing the engine at risk

    What I don't have is an objective point of view of what can reasonably be expected from this motor and where I should start to try and improve it. I've heard figures of upto 30hp being bandied around, but would be happy with a little more than what I'm getting over a much broader rev range.

    Bike is running a Mikuni carb that's been machined out to 27mm and what looks like a home made exhaust system with a can of unknown origin.
    Hilleye

    If it doesn't bring a tear to your eye, add a little more fully synth 2T to the mix.

  2. #2
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    Quote Originally Posted by Hilleye View Post
    Just getting back into bucket racing.

    Had the MB100 dynotuned in prepartion for the Battle of the Buckets at Ruapuna on 15 Oct 11. Results (shown below) were mixed.

    Click image for larger version. 

Name:	001b.gif 
Views:	177 
Size:	45.2 KB 
ID:	247520.

    Positives from the session on the dyno were:
    1. The bike is no longer in grave danger of seizing because it was running way, way, too lean.
    2. I actually know where its making power and can now ride it accordingly.

    Negatives:
    1. Bike is making less power than expected and is quite peaky. Peak power is also being made quite low at around 9200rpm. Exhaust seems to be the culprit on this.
    2. Carb seems to be too large for the bike. Diagnosed from:
    No power increase with a jetting increase.
    Jetting also can't be increased as carb won't flow enough air. Raising the needle to flow more air (to allow bigger jet) just causes bogging issues.
    Unable to reduce the jetting size without compromising the fuel/air ratio and placing the engine at risk

    What I don't have is an objective point of view of what can reasonably be expected from this motor and where I should start to try and improve it. I've heard figures of upto 30hp being bandied around, but would be happy with a little more than what I'm getting over a much broader rev range.

    Bike is running a Mikuni carb that's been machined out to 27mm and what looks like a home made exhaust system with a can of unknown origin.
    Have a word wiyh "speedpro". He has the 30hp MB. He also built a 20hp motor for a guy with a nice spread of power

  3. #3
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    OK, from reading that quickly It looks as though you may have a few miss-understandings about some fundamental concepts in engine tuning.

    I suggest if you want to get ever reasonably serious about it you should read the ESE works tuner thread, In there are heaps of links and information. Especially valuable are the links to books by A. Graham Bell and Gordon Jennings.

    They won't tell you everything you need to know but they are a good start and the thread should help heaps with your understanding of different aspects of engine tuning.
    Heinz Varieties

  4. #4
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    12th February 2004 - 10:29
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    MB100s are REALLY good engines. You don't mention porting. The transfers can be left alone initially. It's hard to describe but you want to increase the exhaust port area above the level of the transfer ports. On the intake try and find a 4-petal Yamaha reed block and rubber carb mount. With a bit of filing and an extra pair of holes just above the bottom pair they bolt on quite tidily. The single piston-controlled intake port needs an extra port added each side though you can get good results just filling in the intake so flow is directed through a slightly enlarged single port. 28mm is a good carb size and a better carb would be a later model keihin. If you go for a bit of compression you will want to change the ignition system. Aim for about 13 to 15:1 depending on fuel you use. A good pipe is essential. An MB engine should rev to 13,000rpm with no worries and run to over 14,000rpm when needed.

    A few things you've said are a bit hard to understand. Be very careful when tuning the motor on a bigger track if you are unsure of how it all works. It's real easy to put a hole in a piston. You should expect 20+hp without too many worries. Pete Sales at Total Motorcycles near Palmerston North does a very nice basic port setup for reasonable money. He could spin the head as well for a nice combustion chamber.
    Try and score a MB50 6-speed gearbox, they drop straight in and are worth tracking down.

  5. #5
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    Everyone is going to have an Idea on it but BEWARE some ideas will be given to you from people who are themselves confident they are knowledgeable but in fact are a wee bit less informed than they realise. (Speedpro Isn't one of those).


    Having said that I will add my opinion which Isn't the most authoritive - by far.

    I have an MB100 that is almost standard but I've done a few things to, I would look into the reed block before the carb, although you could probably go up from 27 mll to about 20 - 32 for a rouandslide or 28-30 for a flatslide. Bigger is OK later, but that seems about ballpark for a lower tune motor.

    The reed block.

    Common mod is to use an RD350 reedblock and manifold, it had 4 petals and is alot bigger, It also has a lift profile that isn't as severe, as the MB one. Should be able to find these bits for cheap or free as they are often discarded from RD's in favour of RZ units.
    I saw a large gain in performance when I was still running the completely standard engine with just a pipe when I changed to fibre reeds, I don't know the dyno figures but it added considerably more usable rev range up top. (Cheers to F5 Dave for that advice)
    The bend on the standard stops is real severe and Speedpro mentioned they could be re-bent to give the same sort of lift with a less severe bend. Look at other more performance based reed blocks to get an idea. The holes need to be slotted or re-drilled to allow that.

    The pipe.
    Pipe is all important.
    It is important it matches the engine.
    My pipe is close to the ESE 18hp build, It works OK on a kart track on standard porting but if you are running at Ruapuna you may need more outright power. You want to start by measuring the pipe you have. A bit of string and/or flexible wire will help.

    Hopefully that adds positively to the pile of advice you are likely to get.

    Above all remember to think, learn, take notes, change one thing at a time, Think some more, read, learn, think, read, think, learn...etc
    Heinz Varieties

  6. #6
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    Speedpro is on the money.

    Now I look at the graph...

    That isn't that bad really as a start point, I'm racing OK with less than that now. (Kart track though)

    EDIT: Ah, Nope, now I see, was looking at the figures on the wrong side, 14 is a bit sadder than 17. I think mine has about 14.
    Heinz Varieties

  7. #7
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    Quote Originally Posted by Hilleye View Post
    What I don't have is an objective point of view of what can reasonably be expected from this motor and where I should start to try and improve it. I've heard figures of upto 30hp being bandied around, but would be happy with a little more than what I'm getting over a much broader rev range.
    After 5 years of development Speedpro has a 30hp MB100 with about 4,500 rpm power spread, posts of the graph and details are on his #6 thread, but 20ish is possibly more realistic to start with. The MB100 is a very good engine.

    The ESE thread also has a lot of info, best to scan through the pictures (there are more than 2,000) using the Thread Tools option to find interesting posts and each 10th page starting at page 80 has a collection of interesting bits making it easy to find good stuff. The ESE guys use GP125 engines but a lot of the 2-stroke stuff is pretty applicable to any stroker.

    Goodluck

  8. #8
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    Sorry should have mentioned that it already has the six speed box and read valve with rubber inlet conversion.

    Indications on potential are good though.
    Hilleye

    If it doesn't bring a tear to your eye, add a little more fully synth 2T to the mix.

  9. #9
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    Quote Originally Posted by Hilleye View Post
    Sorry should have mentioned that it already has the six speed box and read valve with rubber inlet conversion.

    Indications on potential are good though.
    It looks Like I will be divesting my portfolio of MB and H100 parts inc 2 complete engines and probably 2 extra 6 speeds soon if anyone is interested.plus some random 50 shit. The TZR250 carb (Parallel twin carb) fits nice on the manifold too.with a little sleeve to fill in the gap.CR ignitions fit too.Also try and stick with genuine Honda parts for the internals where you can.
    I would quite like to see someone do the air cooled 125 with one to be honest.


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  10. #10
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    Quote Originally Posted by Hilleye View Post
    Sorry should have mentioned that it already has the six speed box and read valve with rubber inlet conversion.

    Indications on potential are good though.
    Is the exhaust port still as original?

    You should see a good gain on these just by grinding to ease the bumpy bit where they transition from the steel liner to the aluminium outer part.

    Be very careful about making it bigger though, You don't want to get it wrong.

    Also make sure the bits that the ring touches stay as a nice working surface for the ring.
    Heinz Varieties

  11. #11
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    The carb on your bike is a TZR2501kt, on a TZR250 it flows enough air for 25hp so that probably isnt the problem. Before you bought it I think it tangled a ring in the exhaust, the old rebore guy declared it rooted, but I think it was tidied up and put back on. you may be better off starting over with a new barrell.
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  12. #12
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    Ah, the truth comes out.

    Anyone got a spare MB100 barrel they want to sell?
    Hilleye

    If it doesn't bring a tear to your eye, add a little more fully synth 2T to the mix.

  13. #13
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    Quote Originally Posted by Hilleye View Post
    Ah, the truth comes out.

    Anyone got a spare MB100 barrel they want to sell?
    Buy all Husabergs stuff, that'll give you spares for the rest of your life
    "If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough power."


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  14. #14
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    Quote Originally Posted by speedpro View Post
    Pete Sales at Total Motorcycles near Palmerston North does a very nice basic port setup for reasonable money. He could spin the head as well for a nice combustion chamber.
    . . .
    & talking of chambers he's made the odd MB100 expansion chamber as well if you want a decent set up with little risk.

    Have to be careful when making a reed setup not to put the carb on too much of an angle. This is easy to upset using a conventional carb saddly such as the very nice flatslide keihin Mike suggests. That 1KT carb should flow well enough for the time being & is angled down ok combined with an old Yam reedblock & inlet rubber should put the carb on a decent angle. I did have problems with a KR250 carb which uses the same casting as the TZR carb that only manifested on long tracks where it ran out of fuel just after the main straight on 'Puna B track springs to mind. if this happens come back & I'll tell you how to fix it, but the TZR carb is probably better.
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  15. #15
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    For long circuits an ignition which doesn't have the high rev retard is mandatory. Not so important for kart tracks which favour mid range.

    An alternative to increasing inlet port area is to put ports in the rear skirt of the piston giving 360 deg timing regulated by the reeds. Works to lengthen small end life but shortens piston life...swings and roundabouts. Very good power though....

    Motorcycle exhausts - Zorsts - do a good MB100 chamber.

    Air cooled 125...done that, goes well.

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