inlet 38mm
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@calum yeah I’d agree mate, even when I fitted and setup my 32mm I wasn’t all that convinced it made a huge difference, and massively reduced mpg haha. But ofcourse the benefits come with the other changes that were made, but if I’m honest the standard carb on these bikes is a cracker when it’s setup right.
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I’ve fitted a 34mm carb to a standard inlet, I put the inlet in the oven for 20 mins and used a thin smear of Castrol Grease, worked a treat!
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@calum
mhm I'm not particularly sure if a 38mm is too excessive, but as soon as I mount it I'll try it and I'll let you know -
@DylanDT219 the ports aren't the problem with the Athena kit. They aren't great but they aren't the problem. I will be writing a blog on this in the fullness of time, along with how you fix the Athena barrel and what it is like afterwards. But it's all in development now.
In short, it's the port timings not the port windows that are the problem.
Take the head off, or look up the exhaust port and rotate the crankshaft 360 degrees to see what I mean. It should be obvious.
Also bigger is not always better. The engine produces a finjte amount of vacuum pressure. A bigger carb reaults in losses of this oreasure. Loss of pressure results in loss of soeed which will negatively impact your performance. Don't go too big. Don't go too small. There is a middle ground. 34 is probably a little on the big side. 32mm is pretty sweet.
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look maybe because here we have a different mechanics thought but put a 38mm on a 170cc athena which also has some design problems I don't see a problem in doing so, I repeat my dtr with the 170cc athena, carb of the 30mm, firebox + fmf and not it is not even 100 km / h. I prepared the cylinder together with a friend of mine who knows enough and we also prepared the engine block along with everything a zeltronic control unit, reed valve v-force 4 will also be added. I think a 32mm with all these things is underdeveloped for the components it will mount
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Right, okay cool. I am just trying to help.
I have been around these bikes for 13 years. I have seen how they tune. I have ran Athena 170 with 38mm carb and rode it daily. I linked a video of that bike on a flyby.
I am trying to give you my experience. Out of all the modifications I have done, the best I have got out of my bike is a ported 3mb with altered squish 32mm carb, underslung pipe and zeel.
It's not the carb as to why you can't do over 100
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@calum
go easy I'm not saying you don't know anything about it but here it works differently, especially because I live in Switzerland and here. engine blocks of the dt are different from all the rest of the world such as the 4BL there has never been here etc. etc. my engine block is 3ME and since you have worked a lot on this type of bike you will also know this and you will also know that they are blocked , for sure the carburettor is not the problem but it can help a lot -
@dylandt219 Calum’s right I’m afraid, carburettor is not the issue..
I’ve played around with the ignition timing through Ignitech DCCDIP2 aswell as carburettor and all sorts on my DT through the years. I recommend you work through what you’ve done and find the actual issue or limitation that’s holding the bike back, as even the standard 28mm can quite easily produce numbers on a mild ported 170 kit. If you’ve been messing with your timing through the zeeltronic put it back to a base map, fresh spark plug and check the spark is good, these units have had issues in the past and it’s not unknown for them to be duff out the factory. I would be more inclined to suggest an exhaust issue or timing related/spark problem than anything else, or if you’re still using the servo powered YPVS make sure you’ve not got it running backwards!
The carburettor should not be an issue unless you have jetted it absolutely wrong, but I think if that was the case you’d be having terrible running conditions all the time. -
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@glynn123
no I understood that the problem is not the carburetor but I repeat it is one thing that helps the motorcycle to do some numbers for sure, mine has been blocked at the level of the control unit in fact as I repeat I will command the zeltronic -
@DylanDT219 I'll just clarify this one more time.
It's not the size of the carb as the reason why you can't do 100KMH. A stock DTR will do that no problems.
The problem lies elsewhere.
As I initially said, 38mm can be attained on the stock inlet manifold if you enlarge the size of the inlet manifold.
I used a drill attachment called a "Hole Saw". It was a crude method that worked.
Whilst YES it can be done, you won't net gains from a bigger carb. Bigger is not always better.
I won't say anymore on it now.
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@calum The first people with a 170 kit lifted the cylinder 3mm, hence the terrible torque curve..but from then on the myth that the 170 kit needed 'port adjustment' was set in stone...(while it benefits from porting, lifting the whole lot 3mm is a bad idea) The Athena 170 cylinder is exactly the same casting as the 125, but bored out more and the pv is spaced further away from the bore. double check the pv cable setting. On mine with the pulley lined up with the mark, it was only about 3/4 open. Only when I looked up the port did I spot why it felt so flat initially! Exhaust port width limit is 73% of the bore diameter with good rings (measured straight across). So 56mm bore is 41mm and the 65mm bore can be opened up to 47mm. Although in the interests of safety I've stuck with 45mm for now (70%), same as the standard RD350. Most people reported a good increase in bottom end grunt but no real gain at peak hp. It turns out this is mainly due to the cylinder casting being the same as their 125cc cylinder, so it has 125cc sized ports. I opened them up to 170cc sized ports by widening the exhaust 5mm, and lifting the transfers about 1mm.
Initially the 170 kit felt awful, until I double checked the pv setting and found the spool must have a different end for DT's, as even with the pulley lined up, it was about 3mm closed. Once that was reset, it flew... Mick Abbey said 30mm best carb
for ported 170 so fitted 30mm Koso-Pwk. -
@theportingmaster At bottom dead centre, the exhaust port is still covered by the piston. The same goes for the transfers too.
https://www.youtube.com/watch?v=e6dc-5hFH5w
Lifting the barrel up so the exhaust/transfer ports are actually exposed will allow the engine to reach its full potential.
Not to mention the actual transfer ports aren't fantastic.
Here's my DT 125 R 3MB00P Barrel
vs the Athena 170
For fun let's compare that against a bog standard Aprilia RS 125 barrel
The DT just isn't a fast bike. But a "Performance" barrel that covers the transfer ports and exhaust port at bottom dead centre isn't helping matters.
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@dylandt219 asking for advice and replying in the way you have is childish and just makes you look like a tool mate, if you clearly don’t understand what you are doing I think the best advice anyone can give you now is take the bike to a mechanic. Everyone here is trying to be helpful but it’s clear you’ve already chosen the route you want to go down, so why even ask?
You can take the advice or alternatively spend £200+ on a big carb and have an even bigger steaming pile of shite that still goes 100km/h, you’ll learn either way -
So what I consider the "Holy Bible" for two stroke tuning
Graham Bell's Two Stroke Performance Tuning. I've read it cover to cover, is a real eye opener.Some of the things just seem quite obvious now, but the part about carb size was really interesting.
