Montesa Mh 349 Questons

[jools]

Hi! I recently got a Mont MH 349 - 1985, stunning condition, however I have had a go on it and found that its possibly running way too rich, it's fluffy and with a bit of white smoke. It has the Standard Amal Carb on it, however I do have a Mikuni for it.

A few questions;

1. Would it be possible for someone to confirm what jets should be in the amal carb? *EDIT* the jets in my Amal Carb are pilot ~ 30; Main ~ 145; Slide ~ 35; Needle ~ ? (was in the middle setting of 3)

2. I got the bike with the Mikuni carb on it, it tick over and revs out with this carb on it, but when its under load - ie. just setting off in 1st gear - it starts to die, like fuel starvation. Are these carbs, if correctly set up supposed to be better than the Amal? *EDIT* Jets in the mikuni are pilot ~ 35; Main ~ 130 (do have a 135 & 140 in the kit; slide ~ 2.5.

3. What fuel mixture is correct for these? I believe its 100ml to 5 litres of petrol?

4. Finally, the corrct amount of gear box oil amount? What type works best?

It has a standard airfilter in it which is perfect. There are no restrictions on the air side. The engine sounds sweet so I know it hasn't been thrashed! If anybody could help me with this it would be much appreciated!

Thanks for now!

Edited July 4, 2010 by Jools

[jimbo349]

The 2 stroke oil if mineral should be 25:1 4%

Gearbox is 300mils of 90 weight

Clutch as manual should be 10w30 but most people use 10 weight or ATF 300 mil again

the jets for the amal I will check tomorrow as my manual in on my desk at work.

[woody]

With the Amal, make sure you're not running with the choke on. The lever works the oppostite way around to the conventional way - down is choke off, up is choke on. Easy to get wrong if you're not used to them and I've seen it done - someone rejetting their carb as it was running too rich but they were running with the choke on.

Yes, a Mikuni is better than an Amal but if the Amal is in good nick the bike will run perfectly, the difference with a Mikuni will be minor. Mikunis are a nightmare to jet due to the infinite combinations of needle / needle jet pairings and there is no base setting from which to start from. With the Amal you will be able to find the right jet specs from somewhere so at least you'll know if your jets are correct. I'd only swap from the Amal if I was sure it was worn in some way.

Gearbox, you can use a modern light gear oil such as Silkolene Light. For the clutch, David Taylor recommends Morris Lubricants Golden Film SAE 20 following advice from Kevin Breedon racing. Dave's son Rob has been riding a MH349 for quite a while which they have pretty well sorted and have found that this oil gives the best performance from the clutch. Or you can just use ATF as mentioned before.

Synthetic 2-stroke can be used at the ratio you suggest, 50:1

[jools]

Thank you both for your helpful feedback!

jimbo349 - If you could comfirm the jets for me that would be excellent!

woody - Yes I understand the Amal carbs are pretty good. I realized the choke position is different, as this was the first thought that occured to me. The carb is in fine nick. I dont think the bike has had a lot of use! Thanks for the tip aswell with the clutch oil.

I just wanted to confirm the correct jetting before I start going a bit deeper into other things! I checked the plug and it seemed near enough perfect colour.

Thanks again!

[jimbo349]

Ok Amal carb as per MH359 manual

Make;Amal

type;L-2627/216

diffuser diameter;27

Main jet;145

Low speed jet;20

Gas valve;no.4

sprayer;107

position needle; 2a (2B1)

Looks like the low speed jet could be the problem.

James

[tayld]

Hi there,

The standard Amal set-up as quoted by James has given us good results.

There is also a 35 cold start jet screwed into a pocket in the float bowl. The pilot and cold start jets are identical apart from the metering hole size, there is a chance the 20 pilot jet is hiding in the float bowl. The fit of the slide in the carburettor body will affect the carburetion at the bottom end to quite a degree, if it is badly worn the bike will tend to run weak at the bottom end.

The number 4 slide does seem to be the best for the MH349, we have tried other slides and had poorer performance.

When setting the air screw aim for the maximum engine speed +/- 1/4 of a turn on the air screw to suit the rider rather than an actual number of turns out. Details of tuning Amal carbs are still available from Amal themselves as a download.

Before making major adjustments to the carburettor first check the ignition timing, air filter and be wary of leaking crankshaft seals.

If the exhaust has lost the packing from the rear box or leaks from the joints carburetion will also suffer.

We use the standard Motoplat points ignition with an external condenser mounted next to the coil. The ignition is set manually to 3,0 mm BTDC then checked with a strobe light, fine adjustment to the timing being made on the points gap (within the limits marked on the flywheel). The spark plug is a basic NGK BP5ES.

The air filters can suffer over time, we have had some old filters which have turned to dust on handling them. The filter is not expensive to replace. The filters we use are from In-Motion, treated in original Twin-Air blue filter oil. This oil seems to work well and does not run to the bottom of the vertically mounted filter over time.

When changing the crankshaft seals we have stuck with the genuine Montesa seals (Part no. 0099-2540SDE).

In the petrol we use Castrol TTS mixed at 40:1. The original carburettor settings were based on conventional mineral 2T oil mixed at 25:1 or contemporary synthetic oil mixed at 33:1. Using a modern oil at 50:1 or more will have a tendency to richen the overall mixture.

The MH349 used in the traditional trials series had its original main bearings replaced at Christmas but is still on the original 1984 piston as far as we know.

Hope this helps.

[jools]

Hi Thanks for your replies!

jimbo349 - Thanks very much for looking up the jet sizes for me, very helpful!

Tayld - You have given me a lot to go on! I did a search on this site yesterday for 349 topics and couldn't find anything. Today I found most of the topics you have replied to by doing a search through google.... Strange! all helpful stuff, Thank you very much for your advice!

I will double check the correct jetting. I have ditched the Mikuni carb in favour of the Amal to keep things simple. I have a feeling it is getting too much air. Will get to the bottom of it!

Thanks for now.....!