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Project 2-Stroke Honda Grom

Discussion in 'Other Projects - Other Bikes (non 250's)' started by Duggs63, Dec 3, 2016.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    You cannot use silicone with fuel, it expands way too much. If you have a silicone hose lined with NBR or FKM then that would work.
     
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  2. Duggs63

    Duggs63 Well-Known Member

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    Good point. I'm not sure what the inner coating is but the plan is to get one fabbed out of ally.
     
  3. minimac

    minimac Active Member Premium Member Contributing Member

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    Still waiting for the end result!
     
  4. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Me too.
     
  5. Duggs63

    Duggs63 Well-Known Member

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    Hey guys.

    Apologies for the delay. I have a few projects on the go and the Grom was put on the back-burner a little bit. Mainly due to the issues I have come up against.

    We got it going and revving through to redline, which turned out to be that the factory NSR150 Main Jet was wayyyy to big, or rather we shortened the NSR exhaust too much to make fit it under the bike so I suspect the pressure wave was reaching the exhaust port well before it was supposed effecting power delivery.

    There is still something funny going on, because when we fitted the stock exhaust (which hung out the side of the bike like a truck exhaust) and refitted the stock main jet, it still wouldn't go to redline. The only reasons I can think of for this is the silicone intake is sucking closed and/or the stock CDI is cooked and the timing is out - Interested to hear your thoughts.

    I then refitted the smaller MJ (with the stock exhaust) and we threw it on the Dyno and it was getting closer to the power it should be making... and then the clutch started slipping.

    48360863_218528999038011_1069314747804942336_n.jpg

    47680453_1106041589550760_3830471277336854528_n.jpg
    That is still almost a 300% gain over the original Grom engine.

    The plan now is to fabricate a dirt bike style exhaust with an bend in-front of the motor to get the extra length. Something like this:
    85947357.jpg
    The issue here is measuring the chordal area of the NSR exhaust ports as they are quite a complex shape. That and the tools and materials needed to fab up something like this.

    Its never easy...
     
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    Last edited: Dec 10, 2018
  6. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Don't worry about trying to use the NSR main jet, use what ever the engine needs.
    You are a long way from standard, no airbox, aftermarket (modified) pipe, etc so the standard jetting will mean nothing. That about 100mm you took out of the pipe will effect it to some degree, how much don't know, but I would concentrate on getting the jetting right to suit what you've got.
     
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  7. ShaneP

    ShaneP Well-Known Member Premium Member Contributing Member

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    The dirt bike exhaust is tricky to package, pushing into the radiator and front wheel. But, they can be cut at their joins, rotated and rewelded. However, what do you want from it? The longer expansion chamber might help with low-down torque, but can cut the top-end power. The total pipe length is also a consideration, or at least the muffler length. Remember TYGA built the pipe for a reason, usually maximum power. As for the port area, I'd just use the port-pipe diameter for area, seeing as that is where you're working from.

    I've been doing a 2-stroke swap, but mine is a dirt bike engine in a road frame. In my case, the exhaust is unmodified, just fitting in. But the intake is going to be my issue: it'll mess with tuning and performance, too. Getting very close to complete, so I'm excited!!

    Sorry I was much specific help, some more details would benefit. Good luck. Also, someone on Facebook (Australian Smokers group) has done this conversion, they might help you out
     
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