Malaguti Phantom F12 70cc tuning

Hi guys, new to scooters, although i have 2 zxr 400's and a yamaha fzr 1000 exup-r so i know my bikes

Ive just bought a malaguti phantom with a 70cc kit to use as a project for next year, but the bike bogs with anything more than half throttle.

Ive not pulled the carb yet, but as far as the seller knows (and it looks like it), its the standard carb.

My question is this, has anyone matched a carb diameter (i see 17.5/19/21mm for sale) and main jet for the 70cc kit for this (or a similar) bike...to give me a decent starting point?

Bike is running a non-standard can and non-standard air filter.

Im completely new to 2 strokes...at least they are cheaper than big bikes for parts

Cheers guys!

 

I think as standard they run a 17.5 mm dellorto, but i could be wrong.
With a 70 kit on it, aftermarket pipe, and filter, the carb main jet needs to go up at least 5 points from standard, quite possibly a lot more. I would hazzard a guess at more likely 12 to 15 points up.
Best bet is to have a look at the main jet size, then go to donotlink p-stop, buy a jet pack and have a play with re-jetting. Take care though not to make it too lean, keep an eye on the colour of the spark plug, too lean equals a popped piston in time.
If you wanted to change the carb completely, go for a 21mm and appropriate filter. One that will keep the rain out because sports/open filters can cause problems in heavy weather.

 

cheers, ill pull the engine this weekend and measure the venturi diameter, i think the standard jet is around a 78, ill buy a series of jets and go from there. ill post anything i find up here.

 

Easier to measure the carb slide.
You can always create a new thread in the scooter projects section, we all love a good build.

 

build thread might have to wait a while, ive only just finished a full engine rebuild on the fzr 1000...

 

Yeah, they're ok for about a 1/4 mile.
What you had to do to it?
Ride a modded zzr1100 myself as my everyday bike

 

Carb will be a 17.5mm dellorto and 'banner001'.. 78 standard jet? Wayyy to high standard jet will be 56-58 if its never been messed with, and i'd agree with steve, with open air filters its recommended you go 10 sizes straight up on the jet because if the increase in air, and for the pipe and bore a couple of sizes so i'd say you need to up jet atleast 12 sizes providing the carb has never been messed with

 

when you say 10 sizes, do you mean go from (for example) a 55 to a 65, or do you mean go up 10 jet sizes (i.e. 55->58 is 1 size) which would mean 55 goes up to a 80 main?

im guessing the latter.

the fzr needed all new gaskets, seals, o-rings, barrel hone and 4 new sets of piston rings, all new main and big end shell bearings, 12 inlet valves de-lipping, all 20 valves lapping in, new camchain and valve clearances doing...plus ive given it a damn good clean, had the engine painted, cleaned out the carbs and made 1 good set from the 2 i had lying about...its got some pull, just needs running in now, it passed its MOT, just waiting for my mate to dig out the V5 and i can tax it then

 

No I mean literally 10 sizes, so yeah like 55-58, 80 sounds about right for your setup if not slightly higher

 

thanks bud...ill buy a main jet pack and possibly look at getting a bigger carb, payday is coming up...

 

Now that's a proper engine overhaul. I take it you mean to keep it for a while then?

 

yeah, its my 135bhp baby gonna fighter it as it was in a right state when i bought it. one of the zxr400's is my mint commuter bike, the other is my 66bhp lightened track bike.

the fzr has cost my ~£1400 including purchase price to get it to its current level...im expecting to pay another £2k to get it sorted how i want...next job is custom aluminium subframe to fir race R6 tail plastics, lithium battery and repositioning/centralising some of the electrics along with fitting a tube-type fuel sender to the tank.

 

ok bike "as standard" had 73 main, 19mm dellorto carb, 70cc kit with race can and pod filter with needle on the 2nd clip (from top)...wouldnt rev past half throttle but did 60kph.

changed to 85 main, and raised the needle to clip 3 (from top), got the bike to idle without needing to blip the throttle, same problem but will only go to 40kph.

95 main - wouldnt even move once you touched the throttle.

so ill see if i can make the 73 main feel any better with adjustments to the needle jet to see if if feels like it wants to go richer or leaner...then ill jet from there.

am concerned that it wont go more than half throttle though...

 

Leave the needle on the middle clip for now, it idles so that's a good start.
Put an 80 main jet in if you have one
Turn the air mix screw all the way in then out 1 1/2 turns
If it still bogs at half throttle, could be that it is getting too much air so try restricting the filter some more. If that works then you have a massive jump in main to deal with.

If it is still the same, or worse, then start to work from the bottom up.
Put the smallest size main jet in that you have; something like a 60.
Air screw at 1 1/2 turns out
Then work your way up, jet size by jet size,
It sounds like it is either getting too much air, or, too much fuel.
Re-jetting is a pain in the arse, time consuming, and a headache, especially if you don't have the full range of jets available to you, both up and down from what you have now.

As a general rule, if you keep the standard carb , but change the pipe, you would jet about 2 to 3 sizes up. Add an open filter, and you could jump another 5 to 8 sizes.
So, if you have a 19mm carb and 70cc kit, they would seem to be compatible 'as standard':
Lets take it that the carb, 'as standard', had a 56 main jet size.
Add the pipe, need to go to a 60 main jet as it lets the fumes out quicker, so reducing the back pressure.
Add an open filter as well, would start at a 68 main and see what happens.

 

yeah most of my main jets start at 95, ill pop down one of the garages here and see what/if he is selling individual jets, if not ill buy a few sets of ebay.

didnt have an 80 main jet in the jets box last night, just the 85 which made it worse than with the 73...looks like im jet hunting

 

if its the aircooled 1 it has a 12mm gurtner carb standard

 

it is the AC one, by "as standard" i ment how i bought the bike. now i know what jets were in it ill get a selection and try all combinations.

 

its been a while, managed to get it running right with 4.8g rollers and a massive 110 main jet...

 

Thought you'd left us for another forum
So a 70 kit, 19mm carb, race pipe, pod filter, 110 main....................gonna drink the go juice, but thats not an issue, keep an eye on the colour of the plug, it might be a bit rich with the 110, but see how it goes.

 

im using it to commute at the moment so i can check it all over, looks like its doing 60mpg...which is not bad for whats bolted to it, everything works except the clock...ill have to see if its faulty, or a wiring error.

garage is starting to get a bit full-up now
its fairly happy sitting at ~56mph (on the dash - about 52mph on GPS), but i dont think it has enough power for a gear-up kit, and im not sure how much i wanna spend on it