Modification issues

Izzyrolls

New Member
May 29, 2019
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I bought some dirt bike parts and wanted to try them on my bike for more power. I had to cut up and weld my pipe in a very peculiar way due to the space I had available. I’m wondering if the pipe is simply too big, not enough header length, or if the way I got it welded makes the bike practically impossible to start. I also had to make a custom intake manifold for a carb that came with the parts and also because of the space I have available with my frame. I’m not sure if I have to rejet the carb for my bike or if the crease in my current manifold setup is what’s holding me back. I believe the carb is 16mm from when I measured it with a measuring tape, the taper on the slide is the same size as the NT. Last this is that I threw 2 or 3 base gaskets because at BDC the piston wasn’t flush and at TDC the transfer wasn’t fully open so maybe it’s timing for all I know.
 

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Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Los Angeles, CA.
First... The header length is very important for proper timing of the pipe. (also, the pipe needs to be from a engine roughly 80cc)... If these aren't correct?, you're probably better off not even having the pipe. :(

Second... REMOVE THOSE EXTRA BASE GASKETS!!!!

Third... That kink in the intake will definitely cause problems, (but shouldn't keep it from starting).
I would try to shorten the intake as much as possible.

Fourth... It looks like that carb has a choke?? Make sure it's off!

Hope this helps. :)
 

Izzyrolls

New Member
May 29, 2019
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The pipe’s origin is unknown, I thought about using a pipe calculator and keeping the belly and baffle the same and see what it would give me for the header and diffuser. I’m conscientious of the choke but I was concerned maybe if I should get a jet kit. The bike ran once after peddling my balls off letting the choke off although it never ran after. It felt like it would die anywhere near idle or low speed.
 

bairdco

a guy who makes cool bikes
Aug 18, 2009
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living the dream in southern california
THIS is the perfect example of why you modify one thing at a time...

I think, (and by "think," I'd put money on it,) you main problem is the intake.

First, it looks like the carb is lower than the intake port. So despite the fuel mixture having to navigate all the twists, turns, and steps, it has to go uphill.

After trying to start it, if you pull your spark plug and it's dry, you know it's not getting any fuel.

That intake is a mess. You want a smooth flow of atomized fuel. You've got a set up that has potential for leaks everywhere.

I would fix that before touching anything else. And here's why.

Even if your pipe's not tuned, it'll still run.

If you haven't touched the timing, it's probably correct. If you start messing with that, you'll just make bigger problems.

The bike should still run if your jetting is wrong. Like crap, but it'll run.

Take the base gaskets out and just use one. Once you get it running decent you can experiment with that.
 
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Izzyrolls

New Member
May 29, 2019
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It’s been **** but it’s together, I ended up soldering brass tubes to an intake I cut down but I really don’t know how long that will last. I’m considering adding a layer of jb weld over what I soldered for good measure. I got rid of all but the original gaskets. So I start my engine up with throttle body cleaner and she runs but only at WOT and if I went anywhere near idle it would die and I would have to start the bike again by peddling like a mfr while throttling to keep the engine going until I didn’t have to peddle. Thinking about back pressure, I end up putting this silencer that slips on to my exhaust and my bike was able to start without me having to peddle but it didn’t like to to idle. The bike was able to sustain the whole ride but i didn’t go fast to where I felt tears in my eye so I know it hasn’t gained power. The spark plug looks tan to me but it want to adjust the c clip to see where I can get any sort of gain. The pipe is prolly the culprit to my lower speed but I’m going to modify it over these next few days and see where I can take this motor. I upgraded my cdi and magneto, im wondering if getting a porter cylinder with bigger transfers will help me get bigger power along with a good head that gives me a better compression
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bairdco

a guy who makes cool bikes
Aug 18, 2009
6,549
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living the dream in southern california
If it's only running at WOT, it's still probably an airleak. It's sucking air in and that makes it rev up.

While it's running, spray some carb cleaner around every solder joint, where the carb connects, and at the intake gasket area.

If it sputters and dies, it's leaking.
 

Izzyrolls

New Member
May 29, 2019
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So I got my bike back up to 24 mph, I would say it would hit max 27 28 before when I had a super banana pipe and now I’m only using the stock for the time being but the super banana really did bring some torque to the bike. I hear all the time of people doing 40 and i can’t imagine that a better pipe alone is going to get me 15 more mph. I still want to use the pipe I fabricated because the super banana doesn’t seem too small compared to it and I would imagine it would be in the mz65 ballpark. I’ve been thinking of using 3/4 or 1” ID conduit as a header between 6 and 14 inches somewhere. Finding a diffuser to fit may be difficult but ive been thinking of asking this place nearby that I know mass produced cones... if not then it’s back to the banana pipe and I’ll still have to recreate a header and fabricate it back up. Only other mods I can think would be balancing the crank and upping my compression. I’ve cut a skirt on the piston intake but I can imagine things can be done to better the timing to where I need it to be
 

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