Bultaco Mk11 Frontera 214 38mm Amal carburettor

[PeterC]

I had some time to myself on the weekend. Re mounted the fuel tank which was sealed with POR15, put the fuel taps in and thought why not try the 38mm Amal to see if it still leaks. The float needle (new Viton tipped didn't seal in its seat. I recently secured a well used 38mm Concentric MK2 which had been on "Alky" and had the fuel inputs hogged out to increase fuel flow.
Most importantly what it did have was a solid brass float needle seat (rather than the pressed brass one), so I switched float bowls.

Lo and behold flooding problems solved. turned on fuel - (both taps) filled the tank (to check it wasn't leaking anymore, choked it and second kick and away she went.

Voila

Some things take persistence which means the Mikuni has been put away whilst I check jetting for the Amal.

Does anyone have their own jetting specs for the Amal? - 38mm MK2 on MK11 250 reed valve Frontera

[southnztim]

Not sure if you have this or not, but the following are listed in the Mk 11 owners manual for the 38mm amal mk2. Main jet 430, Needle jet 109, Needle 2F1 pos 3, slide 2.5, Pilot jet 30. Might be somewhere to start. Saying that, be wary as it states the same jets for the 370 which is a mile too lean!

[matcho mick]

geezas,pretty serious numbers there,apart from i don't know what a 2F1 needle is,& 30 pilot sounds tad lean,even for reed valved bully,109 nj's up there bigtime?,

[PeterC]

Thanks for the jetting specs SouthNZtim. They are always a starting point. You don't perhaps have the specs for the 370 MK11 Do you?

[southnztim]

Sorry about the delay Peter. Tied up over the break. My 370 MK11 runs a twin plug head and reed valve. Amal 40mm MK2 carb. Main jet 490, needle jet 112, needle 2F1, slide 3, pilot jet 30. It idles and runs clean and hard right through. Plugs are a nice tan colour. Cheers

[PeterC]

Thanks for that Southnztim.

My 370 MK11 Model 215 (work in progress) doesn't have a carburettor at present, but does have twin plug head and reed valve> I will continue to search for a 40mm Amal and work on an alternative solution

[southnztim]

Forgot to add. That's running on avgas at 20:1 oil ratio. Might be hard to find a good Mk2 40mm carb. They don't make them anymore. I was lucky and came across a NOS body. 38mm carb was used on all except for the American market from what I understand. Stand to be corrected on that though

[PeterC]

Thanks for adding the oil ratio and fuel type. Are you running "Bean Oil? I have been using 25 to 1 (bean Oil) with 98 Octane in the 214 (250). Many years ago ran Castrol R30 at 20:1 with "Super" leaded which was the recommendation.

[southnztim]

No. Just using Castrol TTS. The R30 wouldn't mix with avgas unless acetone was added so I went with the TTS. Mixes easily and keeps between meetings.

[PeterC]

Have secured a 40mm amal carby whick looks new will post results when fitted to the 215

[Hoony]

What Year is Mk11, is that the last one ?

[southnztim]

Mk 11 production was 77-78, then they did a Mk12 in 79. Proto type Mk 15, but that never went to the production line