Sherpa Model 80 Engine And Amal Concentric Mk 1

[triple_x]

Hi

I an running out of patience with the Amal Concentric.

To explain the background on my ground up rebuild my target was to get the bike original in all things.

To this end I purchased a new Concentric Mk 1. It is Jetted correctly runs realy well when the engine is warm and then always starts first time.

However when cold it is B**** and needs 20 - 30 kicks to get going. It tickles up with fuel over flowing so there is no fuel shortage.

Sammy Miller, James @ JHS racing have told me I am wasting my time as the cold staring design is poor, and to get a Mikuni or DelOrto, well ok that may be the route.

But surely Bultaco would not have put up with this problem when they sold new bikes.

All seals, bearings, gaskets are new and from the airfilter through to the barrel is airtight and the Exhaust is totally new, also I use an Elextrex world CDI ignition and the timing is correct, the plug is as recommended by Dave Renham.

Do I just give up and go the Mikuni or Dellotro or am I missing something.

As an aside my Anglian over the two years of use (66 - 68) always started.

Comment would be appreciated.

Regards

Martin

[myson]

I am rebuilding M-80 and before I stripped it down I rebuilt the Mk1 concentric and it started 1st or 2nd kick from cold. This was with a knackered piston and worn bore no air filter and an old plug. Something must be causing problem like poor jetting,blocked idle jet pulling air at cranks poor spark or timing. worth doing search on this forum for poor cold starting and see what comes up. Mine would only start after a 50 yard push before carb rebuild!

[woody]

There is nothing wrong with the cold starting of an original Amal as fitted to the bikes back in the 70s. They started 1st kick no problem after flooding with the tickler. They still will if the carb is in good order.

These new Amals however..... General opnion is that they aren't as good as the originals, airways aren't cast properly, may be blocked with swarf. I have a new one for my '72 Bultaco and I can barely start it from cold. I have to blow down the tank breather, hold the tickler down and kick it all at the same time to get it started. Once it is it won't pull properly. Something is wrong somewhere but I gave up and fitted an OKO.

Amal are still a going concern, although no longer located at the original premises down the road from me in Birmingham, they relocated somewhere else and are owned by Burlen Fuel Systems. I recently read an article they put in Old Bike Mart to protect their name as it appears that there has been misuse and copying of the Amal trademark and products. I took this to mean that someone else has been manufacturing carb parts and actual carburettors and selling them as genuine Amal products. Consequently, some of the Amal products we buy may not be genuine Amal which may explain why there are problems with these carbs.

If it is genuine Amal, it will come with a guarnatee label inside the lid of the box signed by the supplier confirming the part is genuine Amal. If it doesn't have the label, it isn't genuine. It may be worth contacting Amal, telling them where you got the carb and they can confirm whether it is a genuine article or not.

[bultaco49]

Hi

I recently fited a new Burlen/Amal concentric Mk1 to my model 49. To start in this cold weather requires flooding and the engine is reluctant to rev until warm. It does start after no more than three kicks though. I stripped the carb prior to fitting and found no problems with jetting, airways or build. The carb comes in a blue white box with genuine Amal markings and the guarantee under the lid as Woody describes. They also supply a handy guide and setting up chart.

As your engine is similar to my late model49 the spec for my carb is -

Amal concentric mk1 627/303a

main 160

N/jet 106

Pilot 20

Slide no.3

The big problem with Amals has always been wear to the slide (which is the reason I renewed my carb). and the ease with which over tighteneing the flange can distort the flange and body. The new carb comes with an O ring recessed into the flange face so the nyloc nuts only have to be nipped up. When I am happy with the slide size I will replace with a bronze slide which is supposed to slow the wear rate to the carb body.

I know some of you are reading this and thinking why not fit a modern carb but I'm a bit old fashioned about such things and in fact a properly set up Amal suits a model 49 or 80 fine.

Hope the above is helpful Martin and you get your bike set up.

[feetupfun]

I have a couple of Bultacos with the Mk1 AMAL (M49 Sherpa T and M138 Alpina). Both are the original carby that came with the bike. I find that tickling with the bike upright does not get enough fuel into the motor but leaning the bike over a bit while tickling so that the tickler side of the bike is the higher side raises the fuel a little bit higher in the float bowl, causing more to run into the motor and these bikes will start on kick 1 or 2 from cold. Not so if I don't lean them over while tickling.

Both bikes run fine in normal use with the MK1 AMAL carby.

[triple_x]

Thank you all for your help.

This afternoon i stripped the carb down and could not find any evidence of blocked jets.

Have not yet had a chance to get it started (make the bed, polish the shoes, empty the dishwasher and cook the dinner) It was valentines day!!!

I bought the carb from Bultaco UK it came in a white box with proper Amal logos.

Unfortunately i threw the box away, just trying to keep the garage tidy.

James @JHS has said that it is not getting enough fuel to cold start. On all his vintage rebuilds he uses the MK 2 concentric even though they are not original, one can at least start them.

I will get it all back together Monday evening and advise.

Thank you all for your time. A problem shared is a problem halved.

Have good week, oh by the way I have booked a days training with Steve Saunders next Saturday to see if @ 61 I can still hack it feet up.

Kind regards

Martin

[swooshdave]

Thank you all for your help.

This afternoon i stripped the carb down and could not find any evidence of blocked jets.

Have not yet had a chance to get it started (make the bed, polish the shoes, empty the dishwasher and cook the dinner) It was valentines day!!!

I bought the carb from Bultaco UK it came in a white box with proper Amal logos.

Unfortunately i threw the box away, just trying to keep the garage tidy.

James @JHS has said that it is not getting enough fuel to cold start. On all his vintage rebuilds he uses the MK 2 concentric even though they are not original, one can at least start them.

I will get it all back together Monday evening and advise.

Thank you all for your time. A problem shared is a problem halved.

Have good week, oh by the way I have booked a days training with Steve Saunders next Saturday to see if @ 61 I can still hack it feet up.

Kind regards

Martin

Post your jets.

I have a M49 with a sleeved original Amal and it's a couple kicks cold or else the pilot jet is clogged.

Also what spark plug are you using?

[fsb]

I find that tickling with the bike upright does not get enough fuel into the motor but leaning the bike over a bit while tickling so that the tickler side of the bike is the higher side raises the fuel a little bit higher in the float bowl, causing more to run into the motor and these bikes will start on kick 1 or 2 from cold. Not so if I don't lean them over while tickling.

Both bikes run fine in normal use with the MK1 AMAL carby.

Exactly the same thing I've found out too and I also lean the bike sidewards with the tickler hole upwards.

Martin: Does the spark plug gets wet when you try to start it or is it still dry? If it's dry it definitely is a carby problem...

bye, Felix

[triple_x]

Hi

First of all thank you all, for your help and advice.

The jetting is correct 20, 106 and 160 slide is to spec.

Monday I stripped tha carb down, yet again and none of the jets were blocked!

So i got my magnifying glass out and looked at the bores in the carb and all appeared clean.

I then blew compressed air through, took the pilot screw out and found a piece of alloy swarf in the hole removed it replaced the carb and it started third kick and has done since. It is still a bit weak until warm but other than that is sweet.

One other point the CDi unit had to be set at 10deg BTDC just under 1.5mm BTDC. Apparently this is to make starting easier it then advances to 23deg or 3mm BTDC when the engine is running this is to provide a better spread of power.

Appreciate all of your comments.

Regards

Martin

Edited February 17, 2010 by Triple_X

[swooshdave]

One other point the CDi unit had to be set at 10deg BTDC just under 1.5mm BTDC. Apparently this is to make starting easier it then advances to 23deg or 3mm BTDC when the engine is running this is to provide a better spread of power.

CDi? Really, what kind?

[triple_x]

The supplier was www.elextrexworld.co.uk. kit STK-154

Very simple to fit just line up to the centre line of stator plate screw (2 o'clock) with the centre line mark on stator plate, then the difficult part check with a strobe.

Have just got back from a training course with Steve Saunders, absolutely excellent day. I cannot recommemend it highly enough.

The whole day gave me a real buzz. I did it because my last trial was the Perce Simon 1973 and I thought i may be rusty.

I truth I think I was more than rusty.

Anyway back to the bike. With the full Kit Campeon Exhaust the bike just would not pick up under load from from low down.

Steve suggested that I remove the rear triangle box ( I could not remember any of the works bikes using it ) it immediately improved 100%.

It is not perfect but it is a lot better.

But I was pleased for a ground up rebuild to run without (Exhaust excluded) problems for 5 hours and ride through at least 40 section.

Boy am I out of condition, my legs were totally shot by the end of the afternoon.

Regards

Martin

[rcgods]

My M91 Sherpa is the same. With the triangle box on the rear it was hard to start and was "fluffy" on throttle. Removed it, all is well.

[triple_x]

Interesting and comforting that another owner has the same issues with the Kit Campeon rear box.

Is there a solution apart from ditching it or using it solely for display?

My thoughts are to change to tube diameters to match the exit tube from the middle box.

My son is putting a boroscope in the box Monday to see exactly what the internal layout is.

I suspect it is just two tubes (1 in, 1 out) with two diagonal baffle plates.

Any advice would be welcome as currently the bike is a tad loud.

Martin

[bultaco49]

Hi - If you look at my 'Kit' model 49 on page 6 of the tc garage I have fitted the Sammy Miller mid box and a banana tailpipe. This solves the difficulties involved with repacking the mid box and the less then efficient triangular box. The Miller box (still available from Sammy Miller Products) is pop riveted together and is very easy to repack. Banana tail pipes come up from time to time on ebay.

I dismantled the triangular box on my Alpina (which is as you speculate - tube in, two baffles, tube out) fitted a perforated tube and packed the rest of the box with fiberglass. I don't trial the Alpina any more but it works fine for road use.

When I removed the box from the bike, it weighed as much as a brick - which is pretty much what I found it to be full of when dismantled. Baked mud and carbon!

Tim