FH - update

 The FH has been the go-to bike recently, and it is shaking down again after it's 500 mile service. I'm getting on top of the carburation helped by Hitchcock's (or Amal's?) guide to tuning the Mk1 Concentric, and now that I have it ticking over with a #30 pilot jet and the pilot air screw 1/4 turn out, I might go to a #25!

It's flying along and looks great:

Notice that the rear wheel is nicely off the ground in these pictures!

The only problem is - it's still burning oil in little puffs on start-up or when taking off from a stop, not constantly. The head is going to have to come off again to inspect the guides which is a shame, because the leaks are cured...

FH - carburation

 For the record, at the 500 mile service I have changed the carburetter slide on the FH for one with a #4 cutaway.

A #3 1/2 was previously fitted, and the plugs were quite dark.

It's still got a size 30 pilot jet, and for the record, the pilot air screw is about one quarter of a turn out. Perhaps I'll go to a size 25 pilot jet? 

Charlie's Shed - Concentric carburettor

 Since yesterday when I managed to accidentally drill out the pilot air screw thread on the 928, I've been thinking about how to approach carburetion on the FH. I fitted the Monobloc, which is a bit worn particularly around the mixing chamber cap screw and I realised that I would need to alter the cable lengths to use it. 

Some more thought had me realise that I could repair the damage to the 928 and have a better solution for my non-standard Huntmaster more quickly than messing about with a Monobloc. 

The first thing I did was to tap out the new pilot circuit access ports. The one in the inlet taps out to M5, but the one opposite the pilot air screw is a bit more tricky in that it's too big to tap to M6 and the wall thickness is too small to tap to M8 - but it is perfect for M7. Try buying an M7 grub screw! However, I do have M7 by 1.0 taps and dies by some streak of good fortune and I have tapped that hole M7. 

I drilled out the pilot air screw thread with I think a 4.5 mm drill. I tried tapping it M5 but I guess the hole was not clean enough for that and I had to go to M6. 

The next go/no-go job was to determine whether I could make a successful pilot air screw with a larger thread. I grabbed a bit of 10 mm brass rod:

That turned out ok. It seals most of the pilot air port (you can see the witness mark) but I suspect the thread is bottoming out somewhere. Blowing past it is quite difficult, so it will probably be ok. I replaced the tired O ring.

The next job is to seal the opposite port. I made a plug, but unfortunately the cheapo M7 die I have had for years just won't cut and is now in the bin.

A couple of days later, equipped with a new M7 die I made a new plug:

This seals the cleaning port nicely:

Now we can put it back on and road test it.

FH - Monobloc Carburetter

 I've been toying with the idea of fitting an original carburetter to the FH for a while, and finally bought on on eBay - I actually ended up with two, having bought one, it turning out to be not as described and the seller not wanting it back. That was a 389; I also have the correct 376/12.

Having messed up the 928 by not paying attention (more of that later) I fitted the 376:

It's not in too bad shape. The mixing chamber cap retaining ring is a bit loose, and of course the slide is a bit worn but otherwise it's sound. It's more or less to spec - I can easily modify the #3 slide to a #3 1/2 with a file; I have a close-enough main jet. The 928 that was fitted had a 260 and was obviously 28mm - that's about 1 1/8" which suited the 'Road Rocket' specification to which the engine is built. 

	Monobloc 1	Huntmaster	Road Rocket	Monobloc 2
Part Number	376/12	376/12	376/36	389/12
Size:	1 1/16”	1 1/16"	1 1/8"	1 3/16”
Main Jet:	260	240	290	300
Pilot Jet:	25	25	35	30
Needle Jet:	106	106	106	106
Position:	3	3	3	3
Slide:	3	3 1/2	3 1/2	3

The plan is to see how this goes before we do anything else - it should give me a better base to get the carburation right. Unfortunately I will have to make the throttle cable shorter and the choke cable longer to make this work...

'Do anything else' could mean buying a 928 Premier; it could mean buying a new Monobloc.

And the 928 that came with the bike? It wasn't the Premier, so it had the built in idle jet. I wanted to change the pilot jet size and to be able to clean the idle circuit so I drilled out both the plugs that seal off the idle drillings, re-tapped one M5 and was considering tapping the other one M7, and making a special plug - unfortunately I took my eye off the ball, and thinking if I put the plug further down I could put an M5 plug in that side as well - and drilled out the pilot air screw thread. One useless 928 body, for which you can't get a spare.

FH - test ride

 I took the Huntmaster out on a nice little test ride today, 25 miles around North Norfolk to buy samosas from a nice family run department store in Holt.

It went beautifully - no problems other than the usual sweating from the base gasket! I think we also have to admit that the number two exhaust guide is probably leaking - probably too much clearance. There's wet oil at the silencer.

It's idling very nicely - I stopped to reduce the speed at one point, and to take a few pictures, and the idle is certainly more reliable than it was.

FH - pilot circuit

 No pictures, but this afternoon I've drilled out the fixed size 20 pilot jet in the Huntmaster's MK1 Concentric carburettor.

It's now got a size 30 pilot fitted, which reflects the size 35 specified for the BSA Road Rocket (fitted with a Monobloc) and the fact that Concentrics are supposed to run richer than Monoblocs...

Time for a road test.

FH - getting there

 A few minutes in the workshop moves the project on a little bit: the speedo drive locating pin has arrived from the AOMCC gearbox man:

It fits in this hole:

A look at the carburetter reveals that the float chamber gasket is actually there, but that the drip shield is a little distorted and a bit loose, which probably caused the spitting back. The main issue, staring us in the face (and highlighting the perils of long-term projects) is that the carburetter needle is still in the box of bits!

The engine idles now.

By the way, I have changed the 210 main jet to a 260:

A couple more problems are revealed - the inlet rocker oil banjo is loose, and the magneto earth button doesn’t work. The inlet banjo is an easy spanner job; the cutout requires a bit more investigation.

FH - a little more progress, and a big step...

 Well there's been a little bit more progress today. First off, I've finished the second of the finned exhaust clamp bolts:

Secondly I've been talking to people in the club about tyre sizes and whether I can get my desired tyre (Avon RoadRiders) in the size that I want. Having a look at the distance between the tyre and the chain guard reveals around 3/8" to 1/2" but also that this tyre, an Avon SM Mk11, is actually a 325-19. The front tyre, a Dunlop TT100 by the way is a 90/90-19 or 3.60-19. They are both from the 1980's.

I am hoping to buy Avon RoadRider tyres but unfortunately they are not available in the right sizes for this bike. The options appear to be to use a 100/90-19 for the rear (Avon's recommended replacement for a 350-19) and a 325-19 (original size) or a 90/90-19 for the front.

The next bit of progress is very small - it's just a P clip for the front brake cable. I've attempted to adjust both brakes but right now the front tyre is in the wheel clamp.

Lastly and very quietly and secretly I have hooked up the temporary fuel tank to the carburettor and started the bike. Unfortunately it will only start using Easy start, but at least it starts and runs. There may be some problem with the fuel supply or with the float bowl. It runs and returns oil and it runs nice and quietly so now I know that I have the HT leads the right way round, and the oil system is working properly, and the valve timing is correct and the ignition timing is more or less correct though it does spit back through the carburettor.

I think we'll have to wait 'til Monday to have another chance at it, but sleeping on it and looking at some of my pictures suggests that the float bowl gasket is missing. This will give you an air leak in the pilot fuelling circuit...

FH - various jobs

 There's lots of little jobs around the bike to be getting on with. This one is the dynamo cork gasket which I bought from eBay. It was a little big and needed 3/8" taking out of the circumference.

That's the dynamo chain in place. I had one with a split link which I think is unusual - but I think that this is the original chain. I replaced it with an endless one from Draganfly. It's very difficult to tension because whilst you can turn the dynamo to tension the chain, as soon as you do up the clamp it pulls the dynamo back into the crankcase and loosens the chain again...

These are the clamps for the head steady. I've fitted them in place with some leather shim between the clamp and the frame to protect the paint. I'll leave these here for the moment until I have made the new studs for the rock box, and then I can fit the head steadies.

I bought all the cables as universal types from Draganfly. When I unwrapped them I was pleased to find the air and throttle cables were complete with their nipples fixed in place at both ends. Whilst the throttle cable fits ok, the choke inner cable is much too long so I will have to move the nipple.

These two pictures show the routing that I have adopted for the clutch cable. I've shortened the outer to suit this routing, and when the gearbox is back together I will fit the nipple.

I've made up two gaskets for the carburettor and the heat shield. 

Perhaps inevitably, the throttle stop is missing from the twist grip. As soon as you slacken the cable these loose stops fall out and can be easily lost. I'll make one on the lathe later - perhaps two, one for the toolbox as a spare.

FH - carburetter

 If any of you recall this post from last year, you'll know that the Huntmaster kit arrived with an Amal 928 Concentric carburetter:

Now that we are getting around to fitting the cylinder head, we'll need to sort out the jetting for this carburetter. A plea to the AOMCC forum revealed that revered Huntmaster rider Steve's FH is fitted with a 626 Concentric with a 200 main jet and a 3 1/2 slide with the needle clip in the middle position.

The difference between a 928 and a 626 is the body size - the 900 series is the larger. The 600 Series comes in 22mm, 24mm, 26mm and 27mm bore sizes and the 900 Series in 28mm, 30mm, and 32mm bore sizes. Presumably a 626 has a 26 mm throat and a 928 has a 28 mm throat; for the record, 28 mm is just over 1 3/32".

As you'll know from this post, this FH is built to Cyclone spec, more or less equivalent to a Road Rocket. Later Road Rockets use a 1 1/8" Monobloc; earlier ones use a 1 1/16" 10TT9 with a 340 main jet, so this 928 should be there or thereabouts but jetting it might be fun. We learned from the forum that Concentrics run about 10% richer than Monoblocs, so we should fit 10% smaller jets and a slide one size smaller.

Standard fitting for the 1958 FH is a 376/12 Monobloc, which is 1 1/16" throat diameter. Jetting is as follows:

• Size: 1 1/16"
• Main Jet: 240
• Pilot Jet: 25
• Needle Jet: 106
• Needle Position: 3
• Slide: 3 1/2
• The carb parts list indicates it uses ferrule 6/132A, which means it doesn't have cable adjusters.

Standard fitting for the 1958 Road Rocket is a 376/36 Monobloc, which is 1 1/8" throat diameter. Jetting is as follows:

• Size: 1 1/8"
• Main Jet: 290
• Pilot Jet: 35
• Needle Jet: 106
• Needle Position: 3
• Slide: 3 1/2

The kit 928 R300 is set up like this:

• Size: 28 mm or 1 3/32"
• Main Jet: 210 (I've got a 260 to replace this)
• Pilot Jet: None, drilling only; apparently 0.0016 (equivalent to size 20) but I understand these can be drilled out and a jet fitted
• Needle Jet: 106
• Needle Position: 3
• Slide: 3 1/2
• It hasn't got any cable adjusters.

Apparently you can fit a pilot jet in the threaded port shown here, on the right & under the bell mouth:

There's an excellent page on the Amal website that tells you all you need to know. It's here, and it revealed that the needle I have is the correct one for a 4 stroke 600/900 series carburetter:

FH Dry Build - Carburetter

 Some while back, actually in this post, I outlined the trial fit of the carburetter and the fact that the shiny new bell mouth didn't fit very well - as you see here:

Having checked the threads for damage I concluded that the undercut on the carburetter body wasn't deep enough, and/or that the last thread was not cut fully to depth since the new bell mouth did not want to screw fully on. 

I noticed that the horrible plastic one had a short length where the thread was relieved, and not wishing to set the carburetter up on a face plate and recut both the thread and the undercut, I put the bell mouth in the three jaw chuck very lightly to avoid distorting it:

I relieved the thread with some very light cuts for a few millimetres - the bell mouth fits perfectly now:

FH Dry Build - Carburetter

The FH kit arrived all those years ago with a brand new Amal Mk1 Concentric, a 928 and a carburetter that I have no experience with whatever, but I am not going to delve into that now. Today I am only concerned with mounting it to the head.

The standard carburetter for the FH is a Monobloc, retained with two 3/4" hexagon bolts with 5/16" CEI threads. All well and good, but the concentric has a rather large tickler button which prevents you getting the bolts in...

No matter, I can make a couple of studs on the lathe. These will be 5/16" CEI both ends, about 1 1/16" long with about 3/16" plain in the middle. Here they are, part way through manufacture:

I bought a new alloy bell mouth, which is very nice. The rubber fits neatly inside it:

The next problem is that either the carb thread or the bell mouth thread is not to size, or is damaged. This is as far as it will screw on:

FH Dry Build - Barrel and Head

After completing the primary case installation, I moved on to the head and barrel. This was pretty straightforward, and I retained the head and barrel in place with a couple of bolts each, though the threads will need cleaning up when I rebuild the engine.

The main purpose of this step is to establish fixing points for the exhaust, carburetter and head steadies. The head steadies fit to two of the downward facing rocker box studs and its clear that the existing ones are fretted quite badly and will need replacing.

Secondly, the kit of parts I bought all those years ago included a brand new Amal Concentric Mk1 928 carburetter so it will be interesting to see how that performs - it will be a new experience for me. The FH was intended to have two bolts holding the carburetter in place, but unfortunately the large tickler fitted to the 928 prevents one of the bolts going in - it will need a couple of studs making up or I could use the 5/16" CEI x 1 1/16" stud specified by Ariel for the iron head singles under part number 0183.