12 mm stock Minarelli intake ->14 mm!

Matt Scout The Scouting Dcon /

So this Sunday I was seriously emasculated on the ride. Even the STOCK peds were showing me up. Granted I'm hauling the equivalent of two average riders, but I would think the performance gap would be smaller than it was, having a 14.12, 12 intake and expansion exhaust.

So I am taking two approaches. I want to get new rings. The current ones might be okay, but I have no idea what the history is on them, so I figure better to replace and just get it over with. The other approach is to bore out my intake and ports.

I grabbed my 12 mm intake and took some measurements, to make sure I would have enough material to bore it out to 14. I couldn't get my hands on a true 14 mm bit, but a 9/16 bit reads as 14.2 mm on a caliper, and I figured that was close enough. I put the intake in a vice and used a cordless drill (explaination below, please don't flame me) and went _SLOWLY_ , ~100-200 rpms. I went through a progression of bits, slowly boring on up to the size I would finish with. I would be taking too large a bite with using the finishing bit right away, might lose control of the drill or ruin the intake.

I like the results of my handiwork. The resulting interior is a little rough from using a handheld drill, which should help with atomization. I tried clamping it in a drill press, but I just couldn't get it to sit securely. I know this sort of thing can only be done with intakes that have straight runs like stock Minarelli intakes, but it gives you an idea of how to do it if you are as bold (and cheap) as I am.

Re: 12 mm stock Minarelli intake ->14 mm!

Good work Matt!

i love DIY intake bores.

Re: 12 mm stock Minarelli intake ->14 mm!

Matt Scout The Scouting Dcon /

The next step is boring out the jug, which I plan to do tomorrow. I'm a little nervous about that. I read Smitty's guide about porting...it's like if you even THINK about porting while standing next to your jug it will instantly turn into a boat anchor via your brain waves.

Re: 12 mm stock Minarelli intake ->14 mm!

i have a spare, you can have it.

Re: 12 mm stock Minarelli intake ->14 mm!

Matt Scout The Scouting Dcon /

Hey, thanks! I'll cross my fingers, hopefully I won't have to take you up on your offer. I know Smitty was just trying to discourage the less-than-adept-with-tools among riders from doing it themselves, but it still makes me cautious.

Re: 12 mm stock Minarelli intake ->14 mm!

Same thing on drilling out the inlet in the cylinder. Go very slow. Stop before the bit gets to the actual opening in the cylinder wall. If you drill through into the cylinder port itself you can upset the port timing. It is OK to widen the inlet port a little but don't raise the top. After you get close, use a dremel to smooth up the transition.

You will lose acceleration but gain some top end.

Re: 12 mm stock Minarelli intake ->14 mm!

Matt Scout The Scouting Dcon /

Nuts, I'm looking for more low end grunt to get my happy butt up a hill. Will this give an increase in rpms? I might change the front sprocket down to a 10 from an 11, but I don't want a decrease in speed to go with it.

Re: 12 mm stock Minarelli intake ->14 mm!

mill the head, thats cheap.

Re: 12 mm stock Minarelli intake ->14 mm!

Matt Scout The Scouting Dcon /

I can do that. I heard you can go down 1 mm to get 11:1 instead of 8:1 compression. I figured a compromise, go .5 mill down to start and see how well it runs.

And I JUST filled up my tank with 87 octane.

Re: 12 mm stock Minarelli intake ->14 mm!

NO WAY silverfox, this guy will not loose any low end. the 12mm intake is pure restriction on a v1 engine.

Hey buddy, i do this same exact thing to every minarelli i work on. make the intake 14, then open up the cylender to match it.

You will totally gain low end AND top speed. money back garunteed. milling the head on a minarelli is difficult due to the lip around the edge of the bore.

you were on the right track with boring out your intake. KEEP GOING!

Re: 12 mm stock Minarelli intake ->14 mm!

Matt Scout The Scouting Dcon /

Okay, here's my plan. Tomorrow I will bore the intake port out to 14 mm, it was what I planned to do. If I screw it up, I can get another one from Peter I will also take the jug to 1977 and talk to the folks there, see if they can hone it for me so I can break the rings in properly.

Y'know, as much work as it turns out to be, it's a lot of fun doing mod work!

Re: 12 mm stock Minarelli intake ->14 mm!

Matt Scout The Scouting Dcon /

Just bored the intake and I figured I would match the exhaust while I was at it. I came within ~1 mm of going into the actual port face in the cylinder wall on the intake! Good thing I took it slow and watched what I was doing. I like the way the exhaust is shaping up. I didn't realize how much difference there was between the old and new until I compared gaskets. That might have been a cause of my problem too. I should have it all back together and running by Friday, so we'll see what all this stuff will do to the poor little Snark.

Re: 12 mm stock Minarelli intake ->14 mm!

I can agree with Zach.

But I would take things one step at a time.

Things to accomplish in the following order:

Drill out the carb

Drill out the inlet manifold

Drill out the inlet port but not the window in the cylinder wall

Raise the compression

Lastly, play with the cylinder porting windows.

Minarellis can fly, but they are still single speed. In gearing you have to find a happy spot that will give you some acceleration but yet a decent top speed.

My handiwork

Matt Scout The Scouting Dcon /

Talk about cutting her close!

That light grey half moon shape in the inlet side is as close as I could get with the drill before encountering the port window. I estimate it to be about 1 mm, so good enough for me.

My matching job on the exhaust side. Used a die grinder and like always, went slow. It's matched up pretty good, it was horrible mis-match before and I didn't realize it. Definitely should see a marked improvement.

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