ok, i got the reed valve gt250 engine running fine. anyway, to the point where it will start first kick every time. now what, thinks me? i saw this monoshock swingarm off a yam yzf125r and liked the looks of it. first fit i'm very pleased with, but there's a lot of fabbing between now and the finished product. why do i keep doing this to myself? ;D
cheers, gil.
first fit:
(https://i.postimg.cc/h40qhWTT/reedbuildx58.jpg) (https://postimg.cc/nMMWwWdh)
Man what the heck did your yz's look like over there, your working with parts we didn't get again I bet. I stalled on a project so cutting and taking on another
FZ125, maybe?
sorry kids, typo :bang: it should actually say: swingarm from a yamaha yzf 125r or yzf r125, whichever you prefer. it's coming on anyway. when i make some decent progress, apart from measuring and mocking up, i'll post a couple of photo's 8)
cheers, gil.
long way and a long time. all welded up and works properly. just trying to get the chain run dead on now, then hopefully the rear end will be finished ;D
cheers, gil.
p.s. more info on the build when my new shed heater gets here. too bloody cold to type :eek:
rear shock mount:
(https://i.postimg.cc/ZKt8TWnx/reedbuildx73.jpg) (https://postimg.cc/vDhghHW4)
im not sure if you are going to, but id add a gusset per side.
:twocents:
hi mark, sorry i thought i'd answered this. obviously not :eek: across the back of the plate is another square crossmember, welded right above the shock mount. it's welded right across the plate, top and bottom, as well as welded to the diagonal frame tubes. plus the diagonal tubes sit under the top frame tubes, so they won't go anywhere. tbh, i think it's well over engineered, and anyway, it's now at the powdercoaters having a nice bright red put on it, so too late 8)
cheers, gil.
ha. sweet! should be fine, im known for way over engineering stuff. love it.
looking forward to seeing the frame in a red. :clap:
wait no longer. finally got the red and chrome bits back this morning. just got to wait a couple of days for the black bits. chrome powdercoating looks much better in the flesh, it looks like nickel plating. very pleased 8)
cheers, gil.
red and chrome bits:
(https://i.postimg.cc/ZnnwntQj/reedbuildz2.jpg) (https://postimages.org/)
very nice.
the wheel do look really, really good
Those look really good! :clap:
and so it begins again :burnout: just wish the temperature would rise a bit 8)
cheers, gil.
we've started:
(https://i.postimg.cc/4xGtMF02/reedbuildz8.jpg) (https://postimg.cc/xcscNgnL)
getting there. sorry i haven't got the time to commentate on everything i've done to the old girl, but as you can see, i've been busy. working on the rear brake atm, after spending several days getting the chain run right. excuse the mess. when this is finished i'll have a tidy up - promise 8)
cheers, gil.
reed valve gt250:
(https://i.postimg.cc/xdfjB96s/reedbuildz19.jpg) (https://postimages.org/)
with rear wheel:
(https://i.postimg.cc/xTGMVfqJ/reedbuildz21.jpg) (https://postimages.org/)
Quick note, gussets are usually placed on the 'side' of the tubes, so as not to cause a stress riser, two cents.
Cheers, 50gary
That rear sprocket (sorry, chainwheel) looks big, Gil; are you going to trail ride that bad boy?
sorry gary, never understood any of that :eek:
wade, there is a reason for the 46 tooth rear sprocket. when i was messing about with the rear spring height, the dogbones angles and all the rest of it, i had a problem with the chain dragging across the top front of the swingarm - a lot. so i swapped the 41 tooth sprocket for a 46 tooth, to lift the chain up and away from the top of the swingarm - which it did. i then made some 25mm longer dogbones [or bananas as i call them, cus that's what they're shaped like], and fitted them, which lifted the chain even higher. then of course i realised that the rear shock was bottomed out, or is it topped out? as it had no weight on it. if it was compressed then the chain would lift anyway. so where i am atm is 46 tooth rear sprocket, long bananas and the chain not dragging. where i want to be is fitting the rear tyre, weight on the monoshock and see how far off the swingarm the chain is. THEN i'm going to try the 41 tooth sprocket, which will put me on gt250 gearing, and if the chain is still clearing easily i've got a 39 tooth to fit. btw, i had to mill a 3mm deep circle out of the back of the sprocket where it bolts to the wheel, as it stuck too far out to get the chain run right. still loads to do before i'm happy with it 8)
cheers, gil.
been there. the lightweight chain drags pushing it around, but with me on bike its way off. it can be frustrating but f-it. had same issue with grom and LT250 motor,, but again, with arider on no issues. Looks great. :cheerleader:
thanks mark, that gives me some hope all will turn out right eventually. the original yzf125 was a smaller chain and sprocket size, so i got a [i think] something daft like a 410 suzuki front sprocket [520 chain instead of gt250 525] with 15 teeth. the rear sprocket is actually off a rg250, as it was the only one that was a 520 chain and the 8mm mounting holes were 100mm apart. BUT, there were only 4 holes. so, 2 of them were right and i drilled very carefully another 4. hey, if it was easy everybody could do it and then it would be boring. oh yes, the original 520 chain i bought dragged on the frame. that was a hd chain, so i bought a standard type and that was fine. people make me laugh when they say how easy just to do something. they don't know the half of it. at the end of the day, it's great fun and i'm enjoying it. i'd enjoy it even more in a warm workshop instead of a cold, draughty shed, but suppose i can't have everything 8)
cheers, gil.
p.s. all the cross tubes i added make a triangle and unless they actually collapse in the middle there is no way they can push up, which is where the rear shock would be pushing them. all around that area is engineered like the eiffel tower and if it cracks or splits because there are no gusset plates i'll report it with one of these: :bang:
pinched a good fuel tank and sidepanels off one of my half built projects and fitted them just to see what it would look like. a tad too much red methinks 8)
cheers, gil.
reed valve gt250:
(https://i.postimg.cc/4yGFYxRH/reedbuildz31.jpg) (https://postimages.org/)
lines look great. id go silver with black pinstriping. dump the special badge. remides me of king/queen seat GS's
silver with black pinstriping? hmm, sort of like the old nortons et al? tbh i always preferred the black with gold pinstriping. whatever, the fuel tank and sidepanels are not staying red 8)
cheers, gil.
p.s. i thought you'd like the 'special' badge mark, as it's actually off a yamaha :cheesy:
not much different from the last photo, but shortened battery box and both stands going to the powdercoater in the morning. fuel tank off to be blasted and hopefully won't need much more than a thin coating of filler, rub down, high build primer, then sprayed. suppose it depends how many stone chips there are on it. up to now there's at least a dozen :cheesy:
cheers, gil.
reedy:
(https://i.postimg.cc/kGJT06v3/reedbuildz48.jpg) (https://postimages.org/)
final bodywork colour. oiltank side done, just the fuel tank to do :wave:
cheers, gil.
reedy gt250:
(https://i.postimg.cc/m28MnpXk/reedbuildz63.jpg) (https://postimages.org/)
Best part is when you take it out and somebody comes up to you and says' MY buddy had one JUST like that in the 80s!'. really? "yeah.exact same" :dawg:
Looking good. :clap:
thanks mark, but i can always come back with 'oh really, a 2018 arse end fitted in the 80's' :burnout:
anyway, people can say what they like. i built it for me, tight budget, in a shed and i love it. never actually built a reed valve engine from scratch. never even owned a monoshock bike, never mind built one - apart from the project before, the ham kob, and that was monoshock when i got it - so i'm pretty damned chuffed [english odd word, meaning very pleased] with it. in fact, chuffed to bits :laugh:
here's to the next project, whatever that is :guinness:
cheers, gil.
got the old bird running something like, with jet sizes suggested - on here i think - for a reed valve 250 with spannies on. i put #25 pilot jets in it and 130 main jets [standard are #30 and 112.5]. above 3500 it was fine, sounded crisp and revved lovely. below that with the choke on or off, the foam filters on or off it bogged. it was awful. so i had a trip over to see ron - of fahron fame - who only lives about 10 miles away and had a word with him, telling him my woes. his advice was try turning the pilot air screws out. from fully in, 2 turns out. wow, what a difference that one alteration made, it will now tick over. BUT, why is one side getting hotter than the other? apparently it's the choke on the left side that causes it, it makes it run slightly richer, so come down one size on the main jet, just on the left hand side and try that. the bloke's a genius. the engine runs lovely from tickover. don't want to rev the hell out of it until the engine is run in, but up to 4500 it's crisp and sounds gorgeous with these spannies on it. in fact it sounds like a tz250 - honestly :celebrate:
cheers, gil.
p.s. once the paintwork is done, i'll see what she rides like.
In theory, if the choke is only on one side and the other is linked to it, then mixtures "should" be the same but in reality, it might favor the choke side.
That said, when the choke is OFF, there should be no difference.
What I have found a few times on a variety of different bikes with VM Mikunis is that the enricher plunger goes hard and fails to seal properly. That allows it to run as if the choke were partly on.
Check the choke plunger - they are cheap to replace and if you have the air screws at 2.0 turns, try going down one size on pilot jets. With reed valves there will be less reversion in the inlets, so the motor will need to be jetted slightly leaner than the same set up on a piston port number.
thanks for the reply teazer, i shall stash all that in what's left of my memory bank. when i was talking to mr fahron about the reed valve bike i actually asked him about coming down a size on the pilot jets and he told me not to bother, and use the adjustment on the pilot air screw as it covers a far bigger range than the pilot jet. agreed on the carb choke though, even though ron reckoned that even when new, with the choke off mikuni's always ran slightly rich on the left side. perhaps that's why suzuki fitted a size smaller jet on the left than the right on the 250a? you might not find that in any book, but it's true. so to reiterate, while it's running right i'm going to leave it alone until it's road tested. on the bench it's not quite the same :haw:
cheers, gil.
No worries mate. Is Ron still doing the Fahron thing? He knows his stuff for sure.
But while I'm here I have to inform you that the correct color for tanks on a red framed bike is bright metallic silver like a decent Triton or a small Dream 50 sports things from Mr H.
That's you told so I am sure it will be corrected immediately, if not sooner.
You could do the tins in white like http://pinkpossum.com/td3/index.htm and that would look appropriate for a fast two stroke twin.
Don't mess about lad. Get on with it..... :whistle:
thanks mate :wink: doesn't show very well, but the sidepanels are actually grey metallic, as the fuel tank will be. i've used this combo before and they go well together. wait until the gloss black ramair covers get back from the powdercoaters and see who that bugs :vroom:
cheers, gil.
p.s. when i nipped in to see ron he was just finishing a tz750 engine for an outfit off. the place is stacked with 2 stroke bits and he's working 7 days a week - even at his age, he's no spring chicken - so yes, fahron is still going :love:
still prepping the fuel tank at the mo, i've been at it for well over a week. somebody said to me to wait until i've got the high build primer on and then i'll see all the dents - magnified. they weren't wrong. even little tiny dents i couldn't even feel with my fingers are now showing up here there and everywhere. i think i'm over the hill with it now though. as far as i know i've just done the last 2 dents. rub them flat tomorrow and start with the high build again. did i mention i hate prepping for paint? give me an engine and gearbox to build any day of the week :haw:
cheers, gil.
p.s. yes, i am too tight to get it done professionally, and anyway, this is supposed to be a shed build :like:
I just did a tank for a different bike (no 2t content). I have a nice solid tank full of filler, and a rusty tank full of holes but no filler. Painted them both, I will never do this again!
My point is I feel your pain! The kicker is are we ever satisfied with the result?
Wow. Buzkill. Just when I was getting brave.
I think I have decided to find a pro and save myself from disappointment.
How come everybody who gets a professional has to have it redone at least once?
I'm already worried about chipping the paint. Maybe it should be left raw and clearcoated. I understand patina now...
IR8D8R
after getting sick and tired of will she/won't she start, dependent on the weather, the government of the congo or the price of eider duck eggs, i decided i'd had enough. a few years ago i had the same problem with a newly rebuilt rg250 powervalve engine, which turned out to be the chokes not working properly in the flatslide carbs. so i decided to build myself a pair of butterfly type chokes. after i fitted them the rg engine fired and ran first kick every time. got bored with it, took the engine out of the modified gt250 frame and stashed it for another day. butterfly chokes doing nothing, so why not fit them to the gt250 reed engine? what did i have to lose? scratted round for some clips - trust me, new mikalor clips the right size on order - and put some old wide jubilee clips on. normal choke off, butterflies closed and she fires and runs first kick every time. couple of photo's of the butterfly chokes fitted and the inside of one of them. just need a good clean, new mikalor clips fitting and bob's your uncle.
cheers, gil.
butterfly chokes:
(https://i.postimg.cc/13bVtQfk/reedbuildz95.jpg) (https://postimg.cc/XrcYHtKL)
choke closed:
(https://i.postimg.cc/V6C0yL1G/reedbuildz96.jpg) (https://postimages.org/)
choke open:
(https://i.postimg.cc/mkVbJ0cp/reedbuildz97.jpg) (https://postimages.org/)
I can see how running with a non-stock airbox would almost require such a setup to give sufficient restriction for starting. A good mod for pods users.
That is an interesting solution for sure. A butterfly choke will reduce airflow by 5-20%, so I hope they are larger than the carb bore.
But the fact that they work and regular enrichment circuits don't is more interesting. It suggests that the enriching circuits are not doing what they are supposed to do and that suggests a lack of air velocity through the carb. With that sort of choke, the pressure differential between the intake side of the carb and atmospheric will be substantial and consequently fuel will be dragged through every jet.
Makes me wonder if it needs softer reed petals that open further at very low engine speed. In theory, two stage reeds would be perfect as long as the small reeds petals are thinner or are "softer" ie they bend with much less force. I wonder what they came from and if there are more suitable reeds available.
thanks teazer, informative as ever :like: a few answers then: carbs are gt250a 28mm bore. i.d. of chokes is 38mm. thought i'd posted this already, but obviously forgot, i fitted some new dual stage reed petals, made over here in england by a reputable company. the top petals are very flexible, the bottom ones are a lot stiffer. after the problems i had with the rg250 engine, which turned out to be the chokes/enricher circuits not working properly and this engine showing the same symptoms, i decided to fit the butterflies, as they worked perfectly on the rg250 engine. and touch wood they are working well on the gt250 reed engine. i fitted the new reeds and tried them before fitting the butterflies, but it was the same as the standard ypvs reeds i had on originally, i.e sometimes it would start perfectly first kick and other times it just wouldn't start at all, until i took the plugs out, put my hand over the carb inlet, turned the engine over by hand a few times until my hand started getting wet. then replaced the plugs and airfilter and she'd kick up first kick :love eyes:
cheers, gil.
this is the dual stage reed petal kit i bought and fitted :Clown:
cheers, gil.
petal kit:
https://www.ebay.co.uk/itm/362743199636?hash=item54752df794:g:awwAAOSwIr5dbXjG
it shouldn't matter. the slide is behind the enricher circuit which should supply plenty of vacuum to pull it up IF the slide is down far enough. Me, id drill out the starter jet a few thou and will work just fine. however, that's a neat solution.
I mean, if i can get a 350 to start on enricheners with v force reeds and 36mm carbs.... yours should work just fine.
the one problem with this set-up is the quarter turn knob for the butterflies sits inside the left sidepanel. on the rgt it sat outside. anyway, i decided to buy a 12v push-pull type solenoid, get a brass bracket brazed on the butterflies shaft and go from there. i decided to repurpose the headlamp flasher button. press it and the chokes close. let go and the chokes open again. well that's the plan, wish me luck :wave:
cheers, gil.
unfortunately mark, mine are the old type mikuni vm28's. they only have one line for starting, and that's the pilot jet. i don't have the other line - or bypass hole as some people call it - which sits between the slide and the engine intake manifold, where there is vacuum to suck fuel up and start the engine. the hole from the pilot jet sits inside the slide, towards the front [engine side]. with the bypass hole it would probably start a damned site easier. if you've got mr bell's bible anywhere to hand, look at pictures 5.1 and 5.2 in the carb section, and you'll see what i mean. mine are the one illustrated in 5.2. anyway, thanks for help and suggestions, always appreciated, and i'm still enjoying what i'm doing :Clown:
cheers, gil.
i've got her running well. not as well as i'd like as i think she's still running a bit rich. that could all be sorted after a phone call to ron at fahron who's put me onto a bloke about 20 miles away with a dyno. plus, he only does 2 strokes. so hopefully i'll find out what meagre bhp she's kicking out and he'll sort my jetting out for me as well. i replaced the long bananas on the rear shocker with shorter ones to lift the rear end up, which meant i had to extend both stands. all done now, apart from having the stands powdercoated. anyway, photo is as she sits now - hopefully nearly finished. new project in the pipeline, after buying a 2019 gsx-r125 rear end for a start :thumbs:
cheers, gil.
reed valve monoshock gt250:
(https://i.postimg.cc/ncPQjzbJ/reedbuildq6.jpg) (https://postimages.org/)
so cool, i like it a lot. curious to see the numbers on this. :toot:
Hats off to ya Gil, she's a beaut!
Quote from: m in sc on August 18, 2021, 12:07:41 PM
it shouldn't matter. the slide is behind the enricher circuit which should supply plenty of vacuum to pull it up IF the slide is down far enough. Me, id drill out the starter jet a few thou and will work just fine. however, that's a neat solution.
I mean, if i can get a 350 to start on enricheners with v force reeds and 36mm carbs.... yours should work just fine.
AGree.
I kick start our drag bike which has TZ750 cylinders with Blaster reeds and 34mm carbs. Are you 110% sure that the tiny starter jet in the float bowl is clear? They are only 0.6mm diameter and block easily.
i've tried 3 lots of refurbed and sonic cleaned carbs c/w new jets and all set up the same - but the bike is just the same every time. which is why i put the butterfly chokes on. next time the carbs come off will be when the bike is on the dyno and exhaust analiser and i'm changing jets - probably. while it's running right i'm leaving it be. of course i really ought to get a spare set of carbs drilled, so i could try them without the butterflies :like:
cheers, gil.
p.s. drilling the carbs for the diagonal bypass hole. i should have made it clearer.
If those carbs have choke (starter) jets in the float bowl, I can tell you that they don't always open up after a long hot soak in the ultrasonic cleaner. I have had a few Mikuni carbs that had to be mechanically cleaned out with wire.
Good idea to add that bypass hole.
What I do after I clean carb bodies is to grab a can of WD40 and blow it through one drilling and repeat on the other carb(s). That way I can see if the same passage flows more or less the same amount on all carbs and then I move to the next drilling. Rinse and repeat.
The starter jet is a PIA because it's pressed in and not replaceable and it sits at the bottom of a well where garbage accumulates.
As I said above, I tend to use WD40 because it's less toxic than spraying half a can of carb cleaner around the workshop.
if it wont clear out, take the pressed jet out. my old s2 had a carb like that, i just yanked it out.