Author Topic: 3MA Mongrel  (Read 568 times)

drunkn munky

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3MA Mongrel
« on: February 09, 2019, 01:37:42 AM »
I bought this little mongrel 3ma just before xmas as a mostly finished project that had been left standing for a few years, it’s a 3ma5 with a 3ma1 front end and 32mm carbs, 3ma4 crank, pistons, barrels, heads and cdi. Apparently it ran a few years back but not well so first job was to get the carbs off and see what’s what, inside we have

270 mains
6L2-63 (3ma1) needles on the top clip
Q4 needle jets

VAJ system had been removed and a fixed air jet setup in place, no airbox snorkels and exhaust rings removed.

Carbs were also full of oil to the point it was leaking out the overflow  so they’ve had a good clean and after a few discussions decided to get the bike back to a standard setup. Was offered a VAJ system so took that and found some airbox snorkels, fitted 200 mains and put it all back together eager to get it started.

Kicked it over but nothing, didn’t even remotely sound like it wanted to go, cracked the drain open on the carbs, full with fuel, was getting a good spark so kept kicking for a good ten minutes but no so carbs off again, yes I’d refitted the rad!!!!

Jets out again, carb cleaner, compressed air and refitted this time leaving off the airbox and rad. Couple of and kicks and boom she crackles into life, one happy camper. Airbox and rad back on and she starts with ease using choke, picks up from idle nicely and revs cleanly although took it no higher than 5k. As it starts to warm up I turn the choke off and I can hear straight away it didn’t like it, needs coaxing off idle and feels very flat unless giving it a good blip and it’s getting worse the warmer it gets to the point it will die if left to idle, oddly though putting the choke back on improves things.

Obviously it needs work but it runs so I’m happy enough, now off to read various threads on running issues and see if I can improve on things tomorrow but here’s some pics of her....

drunkn munky

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Re: 3MA Mongrel
« Reply #1 on: February 09, 2019, 02:55:40 PM »
Started from cold again this morning with choke and all is fine until you turn the choke off, revs drop as they should but bike sounds very flat and needs careful throttle input from idle to prevent it from stalling, airbox is becoming a pain to remove now so going to mod the airbox before going any further, is it 63mm hose thats needed? and does it need jubilee clips to prevent air leaks as all i can find is pics without clips fitted.

The bottom of the airbox seems to have collected a reasonable amount of 2 stroke oil, does this indicate the oil pump is faulty and letting oil pass when not in use or supplying too much oil?

I also need to fit some paddock stand bobbins but am i missing something from where they fit on the swignarm as all i have is a large hole??
« Last Edit: February 09, 2019, 03:06:06 PM by drunkn munky »

chubba

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Re: 3MA Mongrel
« Reply #2 on: February 09, 2019, 04:24:10 PM »
Mines got jubilee clips on the hoses , have you had the pilot jets out when I removed mine nearly every one of the small holes were blocked even after a week upside down soaked in carb cleaner, I've been lucky so far with fueling but split manifold rubbers are common issus

Louis

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Re: 3MA Mongrel
« Reply #3 on: February 09, 2019, 04:39:21 PM »
Hello,

From what I read think your 3MA is running like it should, I know that sounds doubtful with the described symptoms.

The problem now these days is that the 3MA is lift on a platform they not belong
Terms as ultra rare, unique, special, only 500 made, etc are words many times used with a sell of a 3MA.
Prices are sky high, and disappointment is something that lurks around the corner

From a technical point a few, they are great.
Carbs at the frond, exhaust as straight as possible at the back a real race replica from the TZ racer. (from memory the TZ's at around 88)

But from a road riding point a few they are not that good.
The fueling problem was and still is, the biggest problem the 3MA has.
You have to be a real 3MA enthousiast to live with this and work your way around it when driving :)


What you can do with your bike to see if its running like it should, try the following.
1) When you use the choke its only use for starting the bike, when it runs try to close it as soon as possible (it will fill up your crankcase in no time)
2) Ones its running keep it running on throttle (not on choke) let it slowly climb in RPM and not stop at 5000rpm let it climb till +/-8000rpm or higher.
3) when you can hit 8000rpm or higher this will be good enough to ride it trough the street
4) Warning you will not make friends when you ride through the street, as it will smoke like nothing else, but try in second gear to let it accelerate to 8000rpm
5) ones that is going all right you can let it pull till +/-11.0000rpm (most off the fuel in the crank cases will be gone then) it will feal crisp again.
6) check the throttle response now if its like it should, ones the crank cases s clean it should kick out those rpm's without any problem

Same is for riding a 3MA (with a fixed airjet)
1) Don't drive to long behind a slow riding car, let your bike slow down more shift down and accelerate so your clear out the crank cases
2) try not to ride to long in low rpm's (it will fill up again)

Its a play bike, ride it in the higher RPM's and she will go like a dream (-P)

Good luck
King off all twostrokes ''TZR250 3MA''

mellorp

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Re: 3MA Mongrel
« Reply #4 on: February 09, 2019, 05:43:14 PM »
As Louis says, they bog for fun off idle, fill the cases and do not like to run slow. When you 1st set off it will feel dreadful until it clears. At this point, they run really well, until you slow down again and the cases start to fill up. You get oil and fuel leaking/over flowing when not on full chat. Bit of a disaster really !!!!! The reed cage spacer kit helps a bit.

You can mess with the pilot jets (a bit bigger) and air screws to make things a bit better, however that does make it a bit richer throughout the range.

Running without snorkels makes things even worse.

They are all like that mate  :-)
Mellion say If it ain't broke thrash it until it breaks

drunkn munky

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Re: 3MA Mongrel
« Reply #5 on: February 09, 2019, 07:03:29 PM »
Im starting to realise what everyone means now when they say these things bog down, it did cross my mind a number of times whilst running it up that this is how they are as when rev'd hard it feels crisp and sounds mint although i do feel mine needs a little work, or compromise to get the idle a touch more stable. i've not set the floats yet or played with the air screws and hoping the reed cage spacers will improves things.

I did plan on using the 3MA as a road bike but i think thats not the best idea ive had and it will be more suited to track use, i'll upset the neighbours for a bit with a few test runs first though and get it setup the best i can.

drunkn munky

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Re: 3MA Mongrel
« Reply #6 on: February 09, 2019, 07:05:43 PM »
Can anyone confirm this cad drawing is the correct measurements for the 3ma reed cage spacer

mellorp

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Re: 3MA Mongrel
« Reply #7 on: February 09, 2019, 08:02:17 PM »
Mellion say If it ain't broke thrash it until it breaks

drunkn munky

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Re: 3MA Mongrel
« Reply #8 on: February 10, 2019, 04:52:01 PM »
Here a video taken today from cold, used the choke to start but immediately took it off and kept it going on the throttle. Very slightly better but still flat low down which I’m finding hard to believe it’s bogging from overfueling as the engine note improves when choke is applied(not shown in this video), my pilot jets look to have 15 stamped on them and air screws set at 2.5 turns out.
Revs do seem to hang though so maybe I’ve a air leak that’s not helping matters, the lower airbox doesn’t feel like it’s high enough to fit as it should to the top air box so maybe it’s here, if I push down on the top airbox it makes a good fit but springs back up when I let go so possibly the top box isn’t fitted right.
I’m also thinking my inlet rubbers are past there best as it’s impossible to seat the carbs by hand, I have to use a jack between the front wheel and carbs to push them in to position, these could be old and perished.

Lots to check but it’s all progress

https://youtu.be/mFusYHUmHog
« Last Edit: February 10, 2019, 06:19:39 PM by drunkn munky »

Louis

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Re: 3MA Mongrel
« Reply #9 on: February 10, 2019, 07:26:12 PM »
Don't worry to much about throttle response, Its a 3MA it does not react like a RS250, RGV250, 3XV etc even a TZR 2MA does react better on throttle response.

You need to ride it first to make sure the cases are clean :)

Here a example of me with a bid to large mains, you can hear it clearly its choking on it self in the lower rpm.
But ones you let her climb in rpm to clears the crank cases its gone it she is crisp again. (-P)
https://www.youtube.com/watch?v=auYHJbNsYkU

King off all twostrokes ''TZR250 3MA''

paul8899

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Re: 3MA Mongrel
« Reply #10 on: February 10, 2019, 08:20:33 PM »
What size air jet are you using and have you tried it with the air screws screwed in ?

Might be worth taping over half the snorkel holes on the airbox to see what happens.

drunkn munky

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Re: 3MA Mongrel
« Reply #11 on: February 10, 2019, 09:04:55 PM »
No i haven't adjusted the air screws from anything but 2.5 turns i will experiment with them once ive got the parts the cut the airbox as i cant face draining the cooling system again, I need to order a few more parts to make it road worthy then i can MOT it and give it a proper test on the road, as louis says i dont think im going to gain anything trying to set it up without riding it.
« Last Edit: February 10, 2019, 10:18:27 PM by drunkn munky »

mellorp

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Re: 3MA Mongrel
« Reply #12 on: February 10, 2019, 09:58:49 PM »
Once given a run and warmed up they pick up quite well
https://www.youtube.com/watch?v=Se00GdJ3whQ
https://www.youtube.com/watch?v=nfix0NnBEt8 (That's Paul Lee on his 350 N1)
Mellion say If it ain't broke thrash it until it breaks

drunkn munky

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Re: 3MA Mongrel
« Reply #13 on: February 10, 2019, 11:18:30 PM »
They sound mint when on song  (-P)

Louis

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Re: 3MA Mongrel
« Reply #14 on: February 11, 2019, 12:04:27 AM »
They certainly do :)
https://www.youtube.com/watch?v=zLf6nTaL_Qw

One tip, start large on the mains when you want to drive it like a GP machine.
They don't need much to brake down ::)
https://www.youtube.com/watch?v=r_tpCbfCCXE
« Last Edit: February 11, 2019, 12:08:09 AM by Louis »
King off all twostrokes ''TZR250 3MA''