MV 125 trl Carb Question - MVAgusta.net
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post #1 of 12 (permalink) Old 03-02-2011, 04:03 PM Thread Starter
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MV 125 trl Carb Question

Hi everyone

Does anyone know which groove the clip on the carb needle is standard for a 1957 MV125TRL?

My plug keeps oiling up.

Any ideas?

Thanks
Keith
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post #2 of 12 (permalink) Old 03-02-2011, 05:50 PM
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Hi Keith.

Groove #2 is standard.

Make sure your float height is OK and that the needle valve is seating and the float not punctured.

You might find that your needle and/or needle jet is worn. With old carbs this is very common and it can be amazing what a few new parts can do.

Does it tick over OK? If not you may have the idle mixture set a bit rich. I think the screw should be out about 1 1/2 to 2 turns.

Hope this helps.

Dorian.
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post #3 of 12 (permalink) Old 03-03-2011, 01:50 PM Thread Starter
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Thanks for the reply.

I have installed all new jets, screws, and needle.

I will check the float and set the idle mixture screw as recomended.

Keith
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post #4 of 12 (permalink) Old 03-04-2011, 07:54 AM
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:: Dell'Orto Carb Settings

Keith,

I had a lot of trouble initially with the Dell'Orto MA16b on my bike. You can obtain some new parts through Dell'Orto here in the UK - even for older carbs! New bodies are harder to come by, especially since these were common on classic scooters of the period so you're competing for old carbs with the scooter crowd as well.

I've gathered a fair bit of info on the MA16b (if that's what you have) and you're welcome to it. One other thing to check for is that the float weight is correct. Should be 6.5 grammes. A second-hand carb I came by had a 7.5 gram float in it! Needle should be a D8.

If none of this helps you should consider the possibility that the crab has a hairline fracture somewhere. This happened to one I had. No amount of tuning, cleaning/fixing re-jetting &c worked. I tried a new slide, new needle, new jets..... everything to no avail.

Of course, choke is OFF when in the full UP position.

Here's a link to the appropriate documents in my gallery:





Wow! There's a LOT more availability now then there was last time I looked!

http://www.dellorto.com/merchandise/...rtsectionID=30

For parts contact:

Matt Cooper
eurocarb ltd.
256 Kentwood Hill
Tilehurst
Reading, UK
RG31 6DR
Tel +44 (0)118 943 1180
Fax +44 (0)118 943 1190
[email protected]
www.dellorto.com


Good luck!

Last edited by Sheriffof0; 03-04-2011 at 08:05 AM.
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post #5 of 12 (permalink) Old 02-19-2012, 05:42 AM
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Hi, I just bought a 125TR from 1954. The bike starts with no problem and runs perfect at idle but always stalls at low speed.

It must be the carb (MA16B) but I'm not sure how to make adjustments. Can someone help?

Thanks! Charles
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post #6 of 12 (permalink) Old 02-20-2012, 06:52 AM
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If the carb is running rich despite correct mixture adjustment I would suggest adjusting the slide needle to the lowest setting. i.e. there are three grooves on the needle. Make sure the clip is settled into the BOTTOM one. You will need to slightly recalibrate the air-fuel screw accordingly.

What's the plug looking like? Oily/dirty: too rich; brown/powdery white; could be too lean. Somewhere in the middle like a golden pancake.... Goldilocks zone.

Check the jets for blockage. Try not to poke wire through the holes as this can sometimes enlarge them unless you're quite careful in your choice.

Where you at Little Red Devil, I have an almost identical bike I suspect so may be able to help after several years of steep-learning curves.

If you look at earlier entries in this post you will have seen the DellOrto documents and the link to UK Eurocarb who are very good with parts. Keep your eyes peeled for MA16b carbs for sale on eBay - they do come up but are rare and can be quite pricey. The correct slides are very hard to come by. Should be a 55 in the TR but I have a 50 and have to adjust accordingly.

As Dorian hinted above, it's amazing what a few small carb adjustments can do to performance. I replaced the slide spring a month or so back and the difference was remarkable. Just comparing the new spring to the old one showed how compressed it had become over time.

So..... check you have a 55 slide, D8 needle, a 6.5g float, a 260B pulveriser, a 65 main jet and a 35 min jet. If so, you're starting out with all the proper kit for the MA16. If the slide is badly worn you can consider replacing it with a slightly larger or smaller one (+ or - 5) but will have to tune out the difference on the slide needle and the air/fuel mixture screw.

Eurocarb can provide relpacements for just about every bit of the MA16b except the body, 55 slide and a few other bits and bobs. the good news is that these carbs were being used on Vespas and Lambrettas of the same period so whilst that means you're in competition with the scooter crew, they're not as rare and expensive to maintain and replace as many of the bigger carbs.

Any Qs. ask away....
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post #7 of 12 (permalink) Old 02-20-2012, 07:07 AM
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Wow! You're in luck.....

If you need MA16b parts - even those that cannot be had from Eurocarb, this seller in Italy has pretty much everything you'rte going to need and it appears to be NOS.

I have just bought a very rare 55 slide from him. I've not seen new ones available ANYWHERE in 4 years of looking. Smoke 'em while you've got 'em gents.....

http://www.ebay.it/sch/cpom7169/m.ht....c0.m270.l1313
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post #8 of 12 (permalink) Old 02-20-2012, 09:07 AM
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Hi, thanks for the quick feedback Sherif! I cleaned everthing on the carb except I can't find the min jet! (sorry I haven't played with carbs in a while!) how do you get to it?
The only setting difference is the float which is a 7.5 g instead of 6 g but I wonder how this can affect my problem... Basically the engine runs perfect at idle then after I put it in gear, as soon as there is a resistance against the back wheel it stalls. If I run it on the central stand then it's ok.
Cheers,
Charles
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post #9 of 12 (permalink) Old 02-20-2012, 10:11 AM
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Hmmmmm..... sounds like your clutch *may* be the problem.

How long have you had the bike, have you been able to ride it before now? What was the performance like when you rode it before?

This sounds very much like the symptoms I was having when my clutch plates were replaced and I had a worn/incorrectly sized bronze clutch bush.

It will be interesting to see what other folk diagnose.

You might try running it on the stand, in gear at high revs and braking/changing through the gears in case the clutch is stuck a bit but that's just my two-cents worth.
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post #10 of 12 (permalink) Old 02-20-2012, 10:14 AM
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Oh, BTW, the mini jet is inside the lower part of the barrel, screwed into the wall at an angle. If you remove the pulveriser and the maxi jet you'll see it. To remove it you need a small electrician-sized screwdriver. Take a little bot of care cos it's small and easy to lose if you don't do it on a controlled surface. Also don't over-tighten when you replace it. Just hand-tight is fine. a little soak in petrol and compressed air through the hole if it's blocked - overwise some VERY thin wire.
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