derestricting a moby

is there any way to make my moby go a bit faster. downhill is great 35-almost 40. uphill is tougher-20-25. flat speed about 30-32

what is derestricting? is it 1. possible 2. worth it 3. good for the ped?

thanks!

Re: derestricting a moby

People use larger carbs made by Dellorto, thats the most common. Exhaust can be de restrcited a bit, but I dont think theres much of a point UNLESS you also run a larger carb.

If you are very mechanically inclined, porting costs virtually nothing but drill/dremel bits and time, and yields fantastic results.

With a 2 stroke, the best bolt on is expansion exhausts, but for a Moby, expect some custom work and a near $200 price tag for that, not to mention probably having to figure a way to get one out of Europe.

Theres every performance part you can imagine in Europe, but nothing incredibly cheap or easy to get.

If not just for performance though, the Dellorto is recommended as it is considered more reliable, more tunable, and easier to work with than a stock Gurtner. I use one, I like it.

Re: derestricting a moby

like chris suggests, go for a dellorto sha15.15.

and also open up the stock exhaust a bit.

it wont hurt the engine to be able to breathe a little easier.

Re: derestricting a moby

porting a 15mm carb and an exhaust pipe if u really want to, also the speeds u posted are typical fast moby speeds, and u should be proud u have a quicker moby.

Re: derestricting a moby

How do you open the stock exhaust to make it breathe easier? Drill holes in it?

Re: derestricting a moby

I have a dremel tool and consider myself somewhat proficient with it. Can porting be done just by holding the dremel free-hand (no drill press attachment or other aids)? Also, what kind of bit do you need to open up the ports?

Thanks for the info!

Re: derestricting a moby

Yes porting can be done free hand, but try to make it look nice. Any bit for grinding metal, probably a rough sandpaper bit to start with, down to finer ones to finish it off nice and smooth.

Also, carbs can be ported. So a 12mm Gurtner can be ported up to 13 or 14mm.

Really, the first thing anyone should do to their bikes is called blue printing, which means making everything as it was designed to be, as the manufacturing process has a lot of errors. It includes cleaning up rough edges etc. So you will probably find some of those in your engine, clean them up a little, and you will have a feel for how the metal grinds away.

Re: derestricting a moby

If you take the end of your exhaust off and look down into it, you will see one large hole and 2 small holes way down inside. I believe the small ones are the main source of restriction, so those should be drilled larger. I will do a few simple math equations tonight and figure out what size you want those to be.

The large hole is what the tube inserts into. Some have cut this tube shorter, essentially bypassing those 2 holes. That will work as well but will probably be louder than by drilling the 2 holes larger.

BTW, this is all theory, I havent actually done this, but I think it is a sound idea. But, these should de-restrict the muffler and still keep it sounding good.

Again, I wouldnt do too much to the exhaust unless I was running a larger carb. On 2 strokes you can easily have too little back pressure and get worse performance.

Re: derestricting a moby

Ignore everything ChrisP says, as a general rule. Anything he tells that's true is just parrot speach of what someone else said.

There are good articles in the wiki about motobecane specific porting, repair and carb-modification.

Re: derestricting a moby

TREATED

Re: derestricting a moby

I'm getting a 15.15 for my moby, can I use the 15mm intake and not change anything else? (such as exhaust)

Re: derestricting a moby

"The large hole is what the tube inserts into. Some have cut this tube shorter, essentially bypassing those 2 holes. That will work as well but will probably be louder than by drilling the 2 holes larger."

i cut the tube shorter...and my moby is cutting out now. but my moby is stock...hopefully a carb upgrade will fix it...or i'm just going to weld that pipe back on somehow :(

Re: derestricting a moby

what do you mean by cutting out?

Re: derestricting a moby

Stfu. I never heard one person ever mention anything about drilling those 2 holes larger. I took a long look at my exhaust, figured where the gas flows, and figured out where the restrictions were.

I only heard of one person cutting the tube shorter, so the fact that I mention it is not parrot speech it is simply another logical way to de restrict it.

Look Bret get off my back. I dont know what your problem is but all I am doing is helping people. Go take a look at the inside of a Moby muffler and you will see everything I say makes perfect sense.

Re: derestricting a moby

What 15mm intake? A stock Moby is considered a 14 or 13.5. So in essence you will have a 15.14 carb, essentially a 14mm carb.

Anyway, people on here all the time say they run this carb and a stock exhaust. Personally I tried it once and it didnt work, but Im sure its something minor I over looked.

I run a 70cc motor and 15.15 carb on the 14mm intake. The stock exhaust was really restrictive, it was about 4mph slower than using a de-restricted VLX exhaust. Due to stripped exhaust threads, I now have to run with no gasket, which means less back pressure, and it is running almost as good as with the de-restricted VLX exhaust. But I do not actually recommend running with no gasket, the exhaust wobbles, exhaust leaks around the port, and sound is actually pretty nice but certainly not quiet.

Re: derestricting a moby

hahaha ohh boy. are you sure its a 70 cc?

Re: derestricting a moby

"what do you mean by cutting out?" cobalt60

check the wack ms paint skillz!!!

Re: derestricting a moby

sorry

1187830732_moby_exhaust_cap.jpg

Re: derestricting a moby

pat, i heard chrisP has an autistic kit

whoops, i mean autisa.

Re: derestricting a moby

i heard he was taking it to the salt flats.

Re: derestricting a moby

oh damn sorry for being a dunce..."cutting out" i mean like i'll be on the throttle steady and it'll just start to die. at wot it'll go then skip a couple of times then cut out and die.

Re: derestricting a moby

Yes Im sure.

Re: derestricting a moby

Slander

Re: derestricting a moby

i'm gonna say this for the last time:

NOTHING YOU DO TO A STOCK MOBY EXHAUST AFFECTS PERFORMANCE AT ALL!!!

quote me if u want

unless u stuff it with shit and clog it up, then it will slow u down. u can run no exhaust and will see no gain or fall in performance.

believe me i have tried, all the stupid sudgested tricks to stock moby pipes, non do shit.

the only derestricting u can do is to take the airbox off the stock gurtner. also boring out a gurtner is not possable due to the intricite design and the way the difusser works, u also can't get jets for gurtners so boring it out is not worth it, since uy'd have to drill jets too.

Re: derestricting a moby

Dan Adams said he bored out a 12mm Gurtner to I think 13.5mm and he was happy with the results.

As for stock exhaust mods, did you ever try drilling those 2 holes slightly larger? And were you running a larger carb at the time?

Re: derestricting a moby

its not worth your time, just buy a bigger carb!!!!

Re: derestricting a moby

kind of in addition to this topic: I got a 15mm intake from quarterkick.com (pretty nice, btw) for my motobecane 50v. I have a 15.15 dellorto in the mail. My problem is that the opening on the end of the intake manifold (rectangular, where it meets the intake port) is significantly larger than the intake port on the cylinder. This is noob question, but am I supposed to dremel the cylinder port out to match it up with the size on the intake manifold? Can I get away without doing this? I'm reasonably skilled with a dremel, but am still reluctant to start grinding on/near my cylinder. I can do it if I must. Thanks,

-Steve

Re: derestricting a moby

No, you can't get a Gurtner jet but there is a way of adapting an adjustable one from a Tecumseh lawnmower carb to fit, a friend of mine did it with the one on his 50M since it came without the jet. I need to look up some details, I wrote it down and passed it on to someone once. The main hangup with these carbs is the venturi size, there isn't a whole lot that you can remove and still have it work with air leaks getting past the throttle slide, maybe 2-4mm or so.

Re: derestricting a moby

comment about the 15mm intake from quarterkick.com

by Mike

Date Added: 08/14/2007

Nice alternative to the stock curved intake. The casting is decent, but slight modifications are required to make this intake fit. (The top of the intake rubs on the fins of the cylinder so a little material must be removed.) A Dellorto SHA 15:15 carb fits neatly on this intake.

Re: derestricting a moby

Not sure what you're telling me. I've read that on the site. Got it today and after 5 mins with a dremel it fit right on. Negligible work, worth it cause I think it's easier to deal with the shorty then the long curly intake. But now should I match up the intake port to the intake manifold, or can I get by without it? Thanks,

-Steve

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