Hitchcocks Forum

I have just finished the mounting of our host tuned cylinder head on my 500cc cast iron. It is eqiupped with an Amal MK2 30 mm carb with a velocity stack. The exhaust is rather free flowing.

This set up and the old cylinder head gave a nice ride on the rich side. I have not yet had a ride with the new head, but on the first start up (fairly easy to start the first time) I experienced the bike would not idle as with the old head.

Question is: does any of you guys with tuned heads had to re-jet after installing the tuned cylinder head?

Any advice/input is more than welcome.

All the best
Jacob

Forgot to mention the carb set up: pilot jet 25, main jet 200, needle jet 105, needle 2A1 in middle groove, air vent 3.5, throttle slide 3, cold start plunger pilot jet 50.
Jacob

It sounds about right , I ported my head myself and took the inlet to 32mm with a free flow exhaust and larger valves , my MK2 concentric carb is 220 main , 106 n/jet , 25 pilot , 3 slide . Mine is rather hard to start without a kick with a rubber glove over the air filter to suck more fuel in ready for the starting kick , the engine will not start at all with the choke lever but this is Australia and it's pretty hot right now . I am still fine tuning the tick over but with the performance camshafts and 535 piston I dont have many in this country to compair notes with , the dust here means I have to have the conical filter .

Hi Phil

It's good to hear about carb experience similar to mine from so far away. I'm not done with the fine tuning yet. My previous setting was just like yours, but with the stock head, 30 mm carb and 500 cc (still stock cams). Starting with the cold start plunger is also impossible for me. I have to try your trick with a hand partly covering the air inlet. Or maybe fit a smaller size air vent.

Denmark is at times a very wet country, and never a very hot place. This means we don't suffer from dust problems in relation to carbs and air filters, so I can run the Enfield with just the velocity stack. This is new to me, so I have to ajust for that as well when fine tuning. Before that I had the S & B conical filter. Some severe back fire burned away whatever filter material the filter had between the metal net, meaning total free air flow, but with a terrible flow pattern creating too little vacuum.

Compared to India (and Australia?) our riding conditions are colder. And this affects the jetting to the rich side some how. Anyway this coming weekend will be the time for some test riding if it's not too cold or raining. At this time of year the riding season is more or less over, but I have to try out my new tuned head before winter.

all the best
Jacob

Phil, conical filter won't keep much dust out and that fine dust is the bigest killer of motors. We look at the weather map, Darwin never under 30C

Hi Phil. Do you really have to cover the intake to the air filter to get your bike to start in that nice warm, dry Australian climate. Strewth mate. I am surprised. In the UK, where it is usually cold, wet and windy then a degree of choke may be necessary, but on a nice warm day, and during most of the summer period I do not need to richen the mixture on any of my bikes to get them to start. In the cold old winter the choke on my Amal carbs is more than sufficient. Some of mine have an air filter and some do not but it makes no diference. The same applies on the Honda CB500. Is you motor running on the weak side on the slow running jets I wonder?

I ported it right out to the near limit , the choke wont even get the carb wet and if switched on when the engine splutters it will cut out dead for the 2 mins needed to get the engine running sweet , somethings wrong to have to kick it over with a glove but thats the only working choke at the moment . I might try the 45 pilot jet I bought but that would not get the plug wet on first try , the choke would not be an issue with a more ajustable float setting , less vac = higher float hight .

Phil, I had a bad vacuum too with the conical filter on. This is why I changed for the velocity stack. It did improve on both starting and running. All filtermaterial burned away in the conocal filter because of severe kick backs when starting. So it made no difference with the filter on and a lot of good sense to mount a velocity stack. Now I only have kick backs on rare occasions and a much better air flow.


My initial start up problems with the tuned head is also solved. I had to lower the needle one notch and raise the throttle slide. There is still some fine tuning to be done for the very open and almost closed slide positions.


Now I just have one question left before the end of the season: How many km to ride before I re-torque the head bolts?


happy trails
Jacob

Gents,

No wish to teach you to suck eggs etc but are you opening the throttle as you attempt your starting? MK2's fuel enrichners need the throttle shut to work.

Just a thought.

Paul.

Paulk, when starting my Bullet it simply doesn't get enough fuel if I do not twist the throttle just a little. It might be the reason for the cold start plunger not to work, but at the same time not twisting the throttle and only using the the cold start plunger it will not start either.

Long time ago I had a Bonneville (Amal mk1). It would only start with a twist. Maybe it's Amal working this way or maybe it's me? Most important thing is that the bike starts and it does. I'm in the process of some fine tuning of the carb and will give the fuel enricher a second chance.

all the best
Jacob