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lingeringstin... |
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lingeringstin... Trackday Trickster
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stevo as b4 |
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stevo as b4 World Chat Champion
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lingeringstin... |
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lingeringstin... Trackday Trickster
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Teflon-Mike |
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Teflon-Mike tl;dr
Joined: 01 Jun 2010 Karma :
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Posted: 01:23 - 24 Jun 2017 Post subject: |
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Onthis egie, I suspect you are over thinking it, and givig it FAR too much credit to cofound!
The inlet manifold is mai restrction on sigle carb set-ups; doesn't seem to make much odds whether you drop a 24 or 26mm keihi on them.
Twins do liberate a tad more throttle response, but probably no more power.
Air-Boxes DO work, ad on the T-carb set-ups o the benly egine there is a long 'snorle' on the carb goig into the carb mouth to offer a good amount of air-correction ad smooth flow out before it gits the jets.. they DO make a difference, they DONT add restriction...
Open carbs and pod filters DO...
Lacking an flow smoothig before ar eters the carb, adnd pullng air i any direction aroud the corner of the carb mouth, that can actually offer a constrction to reduce flow, and turbulance over the jets that hasn't had a chance to settle ot before it passes over them, screweing some of the metering finesse.
Pod filters... offer no correctio; still drag air from all directions, and make it tur eve tighter into the carb-mouth, and often more so NLY lettig air enter fro the side, so have to make tight 90 degree turn to get into the carb, and in incredibly small volume and distance infront f the carb-mouth.... just about as 'bad' as you can make thigs really....
YET.. little benly engie is so low tued and so tolerant on the most part, even a pod filter doesn't seem to screw them up THAT bad! ____________________ My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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lingeringstin... |
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lingeringstin... Trackday Trickster
Joined: 01 May 2014 Karma :
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Posted: 16:26 - 25 Jun 2017 Post subject: crab |
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The situation I have here is very little room to fit a carb since I'm determined to shoehorn it onto my MZ frame. I am still running around with an MZ engine at the moment and won't really have time to offer things up to see how they fit until the actual day (or few) when I take off the MZ engine, sharpen my hammer, fit a new blade to my hacksaw and fire up the welder.
My TS250 MZ frame is the shortest one they made and I'm running 16" wheels and no shocks so it's really low to the ground. At the moment you can scrape the exhaust round a roundabout if you're not careful and stub your toe on the tarmac going round a corner if your foot is under the shift lever, but I've gotten used to it. Basically it's a rather dinky little bike that scuttles around at car door handle level and it's going to be a squeeze to fit the Benly clone engine onto it but I think it will be a lot of fun in the end. Like a slightly overgrown pitbike.
I've only roughly measured things for engine mounts and the quadbike exhaust I'm using. This has to be a VERY BUDGET engine swap done in as little time as possible. Naturally there are complications already like where to fit a starter button and general rewiring to do, and the rear wheel will have to be reversed so the rear brake has to be redesigned, and many other little niggles. I've cobbled together some modified MZ engine mounts for the back and I'm going to weld a Benly front engine mount to a bit of box section and bolt that to the MZ frame just behind the headstock for the front mounting point. I'll probably cobble up a head mount after everything else but that will be easy.
The biggest carb problem is that the MZ frame is a weird curvy pipe spine design that slopes down at the back and it looks like there won't be enough room to fit the Honda Rebel inlet I've got so I need to dodge the carb sideways using the quadbike inlets or something.
My nice budget idea at the moment is to hang the carb out at a 90 degree angle using some bits of plastic pipe for garden ponds. The picture below shows it all in bits but when it's all squoze together in place it actually fits together really well.
The main problem is the 28mm carb. I'm thinking it will be too much for that engine, so I was thinking of buying a smaller size that can fit into the rubber booty thing. There's a few to choose from in a sort of 22-24 range and they aren't very expensive.
Obviously massive performance isn't what my bike's made for but it does need to at least run OK. I don't think the sideways carb setup will greatly affect things. Seen similar done to four cylinder bikes and it seemed to work fine.
https://s3.postimg.org/6cgchkdxv/image.jpg
https://s3.postimg.org/ke0vofgkz/image.jpg
https://s7.postimg.org/oueszf4sr/image.jpg
https://s7.postimg.org/im7yb27yz/image.jpg
https://s14.postimg.org/8tzcb8kox/image.jpg
AND if I had to I could use two more of those 90 degree elbows plumbed in off the manifold rubbers and drop the whole thing down by another two or three inches. It would mean the fuel mixture being drawn a long way, uphill and around the corner but I don't think that would make much difference really. It would actually lower the carb location down to about the same level as the current one on the MZ engine but I don't want to do that unless I have to. But if I need the room it's a possibility.
By the way, where do the footpegs on a Benly go? Do they bolt to those extra lugholes on the bottom of the engine, and are all the 125/185/200/250 ones basically the same? It would be great if I could fit Benly footrests and side stand. |
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Triton Thrasher |
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Triton Thrasher Could Be A Chat Bot
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lingeringstin... |
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lingeringstin... Trackday Trickster
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stevo as b4 |
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stevo as b4 World Chat Champion
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lingeringstin... |
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lingeringstin... Trackday Trickster
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lingeringstin... Trackday Trickster
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lingeringstin... |
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lingeringstin... Trackday Trickster
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jjdugen |
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jjdugen World Chat Champion
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Posted: 00:09 - 28 Jun 2017 Post subject: |
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Oh boy..... The big manufacturers spend fortunes on flow benches to optimise gas flow, you want to do it with some B+Q plumbers supplies? Yes! I like your dedication!
My 'dabbles' mainly on a 60's CB72 would suggest....
Anything that you want to rev above 7000rpm (and increase power, not just noise), requires the SHORTEST inlet tract you can fit. A longer tract, as you have designed, will give better low, medium rev range performance.
I can tell you that, on the CB72, the head was adapted from the C72, a single carb design. this meant that, as I recall, the LH cylinders inlet tract had an offset towards the middle of the block. Whatever, it meant that this was the cylinder that constantly nipped up when used in extremis. Sorted by up jetting that cylinder carb over the RH cyls carb.
You do not have that luxury on a single carb setup, but, then again, you have an asmatic wheezer at best. I don't think, TBH, you will notice any difference, its in such a low state of tune it would probably run off a Wal Phillips 'injector'. ____________________ The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi? |
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Teflon-Mike |
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Teflon-Mike tl;dr
Joined: 01 Jun 2010 Karma :
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Posted: 02:12 - 28 Jun 2017 Post subject: |
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Looking at the instalation tightness you have, I dont really thk that makig up a manifold to do little to help and use what little available space you have is necesserily the best way to go.
Think that comes to my mind, is your 1+1/4 SU.. in the petrol tank, V-Max styleee... manifolded down either side of the frame spine, for shortest inlet tract, and 'even' flow to either pot.. 1&1/4 SU is sized for what, a 30-40bhp mini engine? It's probably not far off for the 'demand' of a 20bhp twin. Mounted over the egne, in the tank-area, you could make t quite a tidy instalation, and use the tank, as a fairly decent sizd still-air box.. all good stuff, to my mind.
What did they use on 2CV's? A small Solex Down Draft with accelerator pump might do quite nicely.. actually, one of the twin-choke 'progressive' that has tiny primary barel, might be rather useful; small primary may be big enogh on it's own.. but second barrel could give some useful added oomph if motor sucks hard enough... I'd probably probe that notion a bit further.
Petrol is easy to find space for, it will flow into whatever shape you make a tank to fit anywhere on the bike, and you could, back to the SU carb, use Mini's SU electric lift pump to keep the float bowl topped up, if you cant get a gravity feed.
As to the rest of the installatin, the grosely lowerd stance of the MZ frame and almost diagonal path of the spine, I think is likely to make stuff 'tight'; Benly motor's ot that long but it s fairly tall, and inconveniently tall at the back, where the rear face is almost vertical, compared to the MZ's nice little radius.....
Getting the motor n the frame, nicely lined up and hanging something like, I think should be the top priority here. May mean some post fit faff, choppng the exhaust to fit to suit, and waving carb and bits of hose about to find best place for it; but, that muddle in the middle behind existing pegs? What is that, a cetre stand?
Likely that having got the motor something like located, earlier suggestion of using the Benly peg mounts or similar bolted under the engie, could add to the issue of ground clerance, and from what I see i pics, I am wondering whether some sort of general up and tidy up, extending the sold-struts maybe 1/2" to bring the swing-arm level, and gain a bit more under cariage clerance for taller motor, may be in ordr, and then, choppng CB125 rearsets, and or AJS Raptor forward controls, and going full chop high-way pegs, to get them infront of the motor and up out the way of the under-carriage, might not be the best way to tackle that issue...
But, tis your baby... that's 'just' the sort of ideas prompted by pics...
I'm sure you could get the B&Q leggo fit pipes to work... just don't thnk it's likely to be the overall easiest of most effective ways about, or best way to use the space you probably dont have to mess....
I was looking at CB125 inlet flanges and trying to work out f yu could make use of earlier T-Shock stubs that angle cabs out fro the ceter line, or fit mono-shock TD flanges that angle them 'in', upside down or crossed side to side, to angle them out, to make better use of space, with twin-carbs..but I couldn't find any handy! (and ISTR that they aren't quite symmetrical to allow such re-orientation') BUT, other notion to my engineering aesthetic is again to go 'up' rather than back or 'out', and crack out the lumi-weld to re-angle a Twin-Carb set up.. which again, if you went high-way pegs might make a bit more room for them without knocking knees guzi style!
Census here, though does seem to be that you are not chasig the fattest pig, messing wth the leggo pipe work from B&Q, and probably making more problems with it than you solve... ____________________ My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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lingeringstin... |
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lingeringstin... Trackday Trickster
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Posted: 14:43 - 28 Jun 2017 Post subject: piggy |
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I’ve measured things and the Benly clone engine is near as dammit only about as tall as the MZ one but the whole engine is shorter from front to back, which is nice. That gives me some wriggle room to shift the engine about a bit. If you look at the pics above you’ll see how close the MZ exhaust pipe is to the C90 mudguard but it works. The Benly clone with the high level quadbike exhaust would be more out of the way. I’ve already got the quadbike exhaust. It’s a two into one that will run round the righthand side and exit just under my top box by way of a VW tail pipe or two. Easy and cheap and will work fine.
I would love to use the 1 1/4“ SU if I could because I’ve had a lot of success messing about with them. I am a huge fan of the no jets design and the easy access fuel bowl. I used the bigger inch and a half carb for years before going to the smaller one about a year ago.
Unfortunately they just don’t like to work very well on my modified piston ported two stroke where there was a bit of a blowback in the inlet before the piston fully closes off the port so the SU piston bounces up and down alarmingly when you’re not just fully blatting it down the road. Consequently if you were stuck at low speed anywhere the carb would quickly begin flooding the engine as the carb’s piston bounced up and down like mad. No form of damper oil or not or spring could stop it fluttering badly. It’s just an inherent issue with my bastardized MZ engine. Wouldn ‘t be a problem with a four stroke.
But on the MZ engineI could never quite get it to work right so I converted the SU to cable pull by drilling a tiny hole in the tube bit where the needle inserts so I could run a cable up the tube and out the top, but on the smaller one I connected the cable to the skirt of the slide as you can see in the pictures. I had to drill some air holes in the top of the damper pot to let the air out when you pull the slide up and had to take out the butterfly at the front of the carb and stop up the spindle holes with bolts.
After all that it just worked like a big Amal only better. With 300 different needles to choose from and an adjustable jet tube it could be tweaked very well and I was getting some amazing performance and mileage out of that design. The problem with SU now is that they’re expensively “vintage” and rather big. I would love to use a non-adulterated SU but I’ll have to do that later. It will take some crafty inlet manifold design. But yes I do hope to use it at some point. For now though I’m going to bodge on the 28mm KOSO and hope for the best. I think it’ll work for now, at least enough to get me going.
I got the footpeg gubbins for a 185 Benly which appear to perfectly bolt to the bottom of the 250 engine I’ve got. The problem is that the footpegs come out at pretty much the same point as my MZ ones and I find that location a bit uncomfortable so I’m designing some footpegs to mount right on the end of the swingarm bolt. I’ll still keep the Benly thing bolted to the bottom of the engine for the side stand arrangement but I’ll cut off the footpeg bits. I’ve never liked that idiotic MZ side stand on the rear axle. The Benly stand will be much better.
I never liked the MZ footpeg placement and years ago when the nbike was more normal and I was a courier I would use the rear footpegs to rest my feet on for motorways. That was OK but I did used to wish there was some manner of halfway point footpeg placement, which is exactly where the swingarm bolt is. I just never got round to doing anything about it until now since there’s going to be major surgery to fit the new engine.
I’m having bolt holes tapped into the ends of a spare swingarm bolt and will use that for footpeg attachment with some clever use of welder, old gudgeon pins and Yamaha rear monoshock parts. I’ll be using a YBR125 brake pedal when I switch the wheel around for the engine swap. I already have one and it fits beautifully in the mockup I did with a bunch of disk magnets. I’m getting something like a CB125 gear lever and linkage for the other side. Should work fine. All that crap where the MZ pegs mount in front of the center stand can just get hacksawed off.
https://s10.postimg.org/j723heusp/image.jpg
https://s15.postimg.org/iw92ys6bf/image.jpg
https://s10.postimg.org/s3exu6y1l/image.jpg
In the above photo you can also see the current brake rod shite and the center stand held up with a spring going to the old rear footpeg mount. All that shit could go if necessary.
I’ll be making some new struts about an inch or two longer for the rear at some point after the engine swap is done. The GS750 forks I’m using stick up a good couple of inches out of the top yoke so there’s room to raise the bike for a bit more ground clearance. |
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Old Thread Alert!
The last post was made 6 years, 304 days ago. Instead of replying here, would creating a new thread be more useful? |
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