OzVMX Forum
Clubroom => Tech Talk => Topic started by: twinrock on March 31, 2018, 09:59:42 pm
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Hey looking for some guidance in improving bottom end power and response.
The bike is a dt200r but with a twist..it has a blaster 240cc big bore air cooled top end married to the crank case inducted bottom end boyessen dual reeds 30mm lectron carb and wr200 fmf pipe. Off throttle is quite flat and slow tight stuff gives the clutch hand quite a work out. The mid and top end is opposite comming on hard with light switch delivery.. which makes it hard work.. im happy to move the power in favor of the bottom end .any mods you can suggest would be great to try..was even thinkkng of a early honda style exhaust pv set up..lol
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Without knowing all the porting details all I can suggest is to lengthen the header pipe to increase to the tune length of the pipe. Try 100mm if you can make it fit. A bit more timing advance might help if it's not already on the edge. Also try lowering the barrel and spacing the head up the same amount to bring back the port timing.
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try leaning the needle 1 clip and see if this smooths the hit. does it feel like its dragging a bit before the top end rush? it may be a little rich on the bottom. you could try dropping the pilot jet 1 unit as well as get the airscrew out to 1.5 turns.
check the float level is right as well.
packing the muffler with steel wool instead of glass can also give more bottom end.
with the mods to the bike, its hard to make any simple suggestions without going "mechanical"as sleepy suggested.
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thicker head gasket, place weight on the flywheel,
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Smaller carby?
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When you say off the bottom is quite flat, I would start with jetting and changing ignition timing if you can. Its good to make sure what you have is correct before trying different carbs and pipes etc. I got a bike a lot better first with jetting etc and then I added to the header pipe.
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Thanks guys.. it will be difficult to lengthen the header pipe. I have advanced the timing by adjusting timing plate.
As far as the carb goes its a lectron which has a metering rod..not jets as such..i have noticed these carbs seem to loose bottom end response dispite claiming the opposite. I will try a different carb .i have heard of lifting the cylinder thicker bace gasket.?.the bike has almost 170psi compression . I had not heard of steel wool in muffler before..any one used reed spacers to increase bottom end
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A thicker base gasket, or head gasket will do the opposite to what you want.
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Yeah i have just been researching base gasket thickness.. now i think about it makes perfect sence..it does feel like a porting or pipe issue..maybe i can run a thinner bace gasket to lower the exhaust port ill check the head squish to make sure i have enough tollerance..also with that kind of compression should i be running as high octane as possible..would that make much difference thanks again
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Thinner base gasket will only make a marginal difference as you will only change the port timing by a small amount. Increasing the CR will help the bottom end to a point but without knowing were the squish and and ratio are now I can't comment but can say that the octane of the fuel will not change the power in a low compression engine, octane is only the resistance to knock and has nothing to do with the calorific value of the fuel.
It is possible to machine the bottom of the barrel to reduce the port timing but a thicker head gasket or re-machined head is needed to get squish and CR back to were it should be.
Pity you can't lengthen the pipe as it would make the biggest difference, sure you can't add a bigger radius bend and push it sideways and then re-join.
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Sounds like you've mixed and matched a little to much.....
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Im not real smart, but a dt200 is never gunna have a lot of bottom end. If you ride a lotta tight stuff, lower the gearing....
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Yeah..but mixing and matching is what i enjoy..i ride with a mate who has a basically stock dt..its much easier to ride in the very slow tight stuff..due to the power valves..but after 1/4 throttle my bike runs away easily..its also feels considerably lighter..less top heavy to be more specific as it has no radiators plumbing fluids and protective frames and guards..so pros and cons.. my idea behind the engine was a nice simple smooth air cooled engine with oil injection With fun power..thanks for your help it has given me some direction
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Put a D slide PWK carby on it. 28/30/32. Will be night and day over the Lectron.
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My idea, good or bad. Tune it with the pipe. Bit of a story but had an IT400 motor in a DT250 mono frame & someone had over ported it to 192 degrees on the exhaust. Was useless--ok at idle up to 1/4 then flat till 3/4 then it went mad. Was 'so' bad i add 100mm to the header & being my lucky day it totaly fixed it. But changing tact a bit on my AG100 grasshopper [assgroper] they have a good cylinder to modify but come with a tiny 20 or 22mm carb [same outside diameter as a 28. In my wisdom i fitted a 28mm. Went good up top but lost its sharp bottom end. So maybe two different ideas to think about. Cheers. ps, like what ya doing though. Mix N Match--fun times.
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Yeah i had a d slide 30mm befor the lectron on the water cooled top end..i did notice the drop in bottom end when swapped.. but was keen to try the lectron as i ride at different elevations all the time.. i think ill go back..as for the pipe i lookedat it today..just dont think ill get 100mm in there
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Not saying 100mm is the magic number but can you make some sort of loose extension to fit between the pipe and cylinder just to experiment before welding anything in place. Just move the whole pipe forward on it's mounts a bit to try. Easy sitting here pushing buttons lol.
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I think I'm with Momus here, I'd grab a $50 PWK carb, I just fitted a PWK to my bike, I can't believe how it rips from the bottom-end over my round-slide. I don't have any experience with a Lectron.
On my KDX400 I extended the header pipe 40mm as the bike was all top-end but 40mm was too much, it lost all the top-end, I'm going to cut 20mm out.
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Well today i remembered i had a pipe i made up for a dt200L which worked very well. Comparing the 2 pipes it is longer in the header.this motor shares the same bottom end as the blaster..not crank case inducted . I would asume port timing would be closer between these 2 motors. Im going to cut it and fit it to the dt200r/ blaster big bore motor..and go from there..thanks again guys
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sounds like you have plenty to go on with! just do one thing at a time and test, also start with the easy stuff ie head gasket throw another one in if it don't work no real time or money waste, on that note pretty much most low down pulling engines are a low comp motor, smaller carby is a good idea, and yes the exhaust is a important tunning device, we had a junior in sidecars who could not come to terms with the pokey little 2 stoke so we fitted a reducer washer on the end of the muffler as he got used to it we drilled out the washer, at the end removed the reducer, funny thing is 12 months later they win the state titles/champion ship on the same bike