searching for a bit more speed ...

since a puch won the bbq4 race ... i'm looking for a bit more speed out of my minarelli. i won't make the changes now, but i'm looking for tips on how to do this.

here's what i have so far:

- polini performance exhaust

- dellorto 15.15 carburetor w/ #53 jet

- standard bore piston and cylinder

- 10 tooth sprocket

i think an 11 tooth (or more) would defintely give me more speed, right? i currently go a bit under 35mph. so another 5mph should put me over the top. i don't want a speed kit (in fact, they're banned from our moped army races, we have to have 50cc or less).

do you think changing to a smaller or bigger jet would make a difference? i haven't had a chance to test different jets out yet, but if anyone has a suggestion, let me know.

if any of you can think of anything else to do ... please let me know. maybe a larger manifold? i don't want to sacrifice too much bottom end, however. i'm open to all suggestions. thanks.

Re: searching for a bit more speed ...

port and polish.

daveb

Re: searching for a bit more speed ...

Hi,Miguel! I don't know if you saw my post a while back,but my minnarelli was starving for air.Make sure you're getting enough,because I gained 4mph and after I drill another hole in the air box I think I'll be approaching 38 mph! But don't do anything to your airbox that you can't reverse.In order to test for problems,I pulled the inserts(2 of them in mine)and when I saw an improvement,I drilled an extra hole.BYE!

Re: searching for a bit more speed ...

Reeperette /

With Don..Modify the Airbox.

Also, Sprocket is a good idea.

Advance the ignition timing.

Try a #51 Jet.

On the "Out there" front...Have it bored 0.5mm over and get an overbore piston and rings (if such are available)

-Ree

Re: searching for a bit more speed ...

well, i don't want to do anything w/ piston. but i'll try the smaller jet. and i'll try the modification on the airbox. what about the airbox cover that's just round and has no "box". would that be even better?

i don't want to drill anything. i'd like a bit more speed. but gaining another 2mph at the risk of wrecking a cylinder or something just isn't worth it to me.

i know the sprocket will give me more top end. but i don't want to loose to much acceleration. so i'm looking for easy mods that can let me keep some bottom end.

thanks for the suggestions.

Re: searching for a bit more speed ...

Oi,

Three things that you can do for sure.

1. Send the cylinder to a dirt bike shop and have an extra transfer port added and enlarge the current ones. A good experienced race tech. can do this no problem (I've had it and seen it done many times).

2. Get the flywheel lightened at the same shop (Flywheel being the one in the crankcase - there are two flywheels in the bike).

3. Get the other flywheel lightened (the one with the cooling fins that fits over the stator). Either replace it with a fiberglass one (do they make these for mopeds?) or turn it down smaller diameter wise. Tootaloo!

Re: searching for a bit more speed ...

Don, how do you pull the inserts and still be able to get them back in???

Re: searching for a bit more speed ...

Ron Brown /

Miguel,

As you noticed, my Motobecanes do ok. All I have done with them is to increase air flow by increasing the size of the air filter, then reduce the main jet size as much as I could without leaning out too much. I have also made sure the ignition timing is correct.

I don't know what your air box looks like, but I cut out 2 sides of mine, then used 2 squares of "UNI" filter foam, slit along all 4 edges, to fill the holes.

I know when my peds max out, they are spitting gas/oil back out of the carbs. I assume this is because the stock exhaust back pressure is causing reverse flow through the cylinder when the ports are open. I would expect your exhaust to reduce or eliminate this problem. The only other non invasive mod I can think of to increase your top end would be a velocity stack on the carburetor. I don't know if your air box would allow this, but maybe you could run without the air box just for the race. The principle behind the velocity stack is that the air mass in the stack is accellerated during the intake stroke and as intake vacuum declines, the inertia of the intake air, traveling at high speed, continues to stuff mixture into the crankcase, giving a slight "supercharging" effect.

I am not radical enough to try this but if you want to, I'm sure that someone here could come up with some approximate dimensions.

The only other ways to prep for the race are a complete tune up, including de-carbonizing the cylinder and cleaning the exhaust, check and lube all your bearings, run hard tires and make sure your brakes are not binding.

Oh, streched out horizontal, wearing only bathing trunks worke for Rolee Freigh (sp) at Bonneville when he broke the production motorcycle speed record. :-)

Ron

Re: searching for a bit more speed ...

in 1956 (or whatever)... Rollie Free.

we were doing a bit of that this last winter on ice (cept the near naked part)

Hey Ron... the VJMC doesn't have a message board do they?

I've never been a part of one of those e-mail groups... which is better?

I would think a message board is better.. rather than clogging up your email inbox.

Re: searching for a bit more speed ...

Ron Brown /

Fred,

I've never tried an email list either, forums just seem easier to use and brouse. I thought about joining the VJMC once but never got around to it. They do seem to have a lot of people who know a lot of good stuff.

Ron

Re: searching for a bit more speed ...

i'll try the bigger airbox. mine is rather small. i'll try various jets also and see which works best. also a larger manifold. thanks for the ideas. i'll keep the more radical ones on hold for now. i'll get back w/ you all later when i try some of these out and see what does what. too bad i'm leaving the country for two months. not much of a chance to experiment. but i plan to be deadly at the next race. i want to move up a few slots from 6th ... we'll see.

Re: searching for a bit more speed ...

Hi,to ` No One' in particular! Pun intended. Well,I can't speak for all air boxes,just three that I've modified on my own bikes,and the plugs are actually not plugs but tubes which can be popped out and that leaves a much bigger hole.You can pop them right back into place if need be,but I haven't had to do that yet.Sorry if I confused you when I mistakenly said `plug' when I should have said something else.I just never make a modification that I can't reverse unless I'm awful sure it's gonna' be a permanent one.BYE!

Re: searching for a bit more speed ...

hey a smaller sprocket in the rear end will give you better top end i don't know if there's one that mathches up with your's but it's worth a shot.re- jetting the carb is never a bad idea and the advice you got to port and polish is alway's a winner

Re: searching for a bit more speed ...

ok .. still all good advice. but what exactly is port and polish? and would someone w/ moderate mechanical skills (ie me) be able to do it?

but so far i think better/bigger airbox and smaller jet are the winners. i think my manifold's as good as it's gonna get.

Re: searching for a bit more speed ...

Matt Wilson /

Does anyone know where different sized carb jets can be purchased and a fair price for them

Matt

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