Are there different pilot jets for monoblocs?

[highboy_coupe]

Hi, starting to feel like I post too many questions on here...

I found that the monobloc that came in my box of bits for my '65 B40 was from an Ariel Hunter, still a 376 but a 376/8.
The pilot was mangled beyond belief and the bike never ran on it unless on wide open throttle.

So I found a 376/253 body on eBay for cheap and ultrasonically cleaned it, and bought some new jets.

I bought a 376/076-20 from Amal,  and it is a different shape to the jet that came out the old 376/8, that one has a short thread and a very long jet tube, whereas the new Amal jet has a longer threaded section and a finer point. Both marked with 20.

I guess either things have changed, or the 376/8 had the wrong jet in it.  I would have continued to use the 376/8 body but the newslide rattled about quite a bit in it, so I thought better of it.

[rhyatt]

If you can go onto the BURLEN site, the Amal people.
You have options of looking via carb or by bike.
Loads of help from them over the phone , I've rung them in the past, helpful lot

[bikerbob]

I have an Amal catologue which states that the correct carb for your year is 376/280  1/16" bore  Main Jet 376/100-190  pilot jet 376/076-20  Needle jet 376/072-105 needle position 3
Throttle valve 376/0603 Repair kit RKC/376  Major repair kit  RKC/376MS Special Details Plastic air tube. All this is from an original Amal catologue. The carb you have is for a B40 1962 but all the info is the same for the 1962-66 models so the carbs are identical in there specs.

[DAVE BRADY]

Hi,

Don't forget that now matter how many new bits you put in an old carb the internal air and fuel passageways can still be quite worn.  By the time you have bought all the replaceable parts you are not far off anew carb which will give the best outcome.

Dave.

[highboy_coupe]

Thanks is for the info, looks like I at least have the correct pilot now, the main is a 200 but then it's a +40 9:1 piston so I think that will be ok. I have the 190 as well to put back if not.

I bought the pilot from Burlen, based off the correct carb for the bike!

If after all this cleaning and rebuilding it still doesn't work, I may just buy a new one, the Keihin copy that is currently on there works well, but I can't tune out the massive backfires on the overrun!

Out of interest, the 376/8 that was on the bike looks a slightly better design, it has more strengthened areas at angles and where things screw into the body...  If the slide bore hadn't have been worn, are all 376 bodies (dependent on bore size) the same?

[rhyatt]

Backfires on the overnight are often an indication of an air leak between the exhaust pipe and the head or somewhere along the line.
Try resealing that pipe to head joint , I use silicone bathroom sealer

[highboy_coupe]

That is a very good point, I used Holt's firegum but I can see that it has expanded and cracked a fair bit in not very much time at all, so much for trying to use the correct product!

[rhyatt]

Smear the silicone around the 1st inch of pipe and inside the port.
Push them in and it'll do the job.

[DAVE BRADY]

Hi,

Wurth do a high temperature silicon sealer for wood burning stoves. 

Dave.

[Derek996]

High temperature silicon exhaust sealants are available from motor factors.

[Mike40M]

I use high temperature silicone with good effect. But also used ordinary bathroom silicone when out of hi temp. Also worked.
On the B40WD had to make a new mount to get the pipe a snug fit into the head.

[highboy_coupe]

Great, got my engine back together, put the monobloc on and..... Leaks, lots of leaks. I should have tested it off the bike!!

Ah well, looks like it's mainly the float chamber and the main jet housing.. so back to the bench with that particular carb.  Incidentally, although the fuel was dripping out, the bike was nowhere near starting, not even a cough. Bear in mind it starts second kick with a crappy Chinese carb on it.
I want to go back to the Amal for originality and to make sure the mixture is correct, but that didn't sound like it was going to start at all!

[DAVE BRADY]

Hi,

Amal do a service kit for the monobloc with lots of bits in it.  They are available from Feked as well.

Dave.

[highboy_coupe]

Thanks Dave, yes I have one on order!
It already has new jets, a needle and a slide.

[highboy_coupe]

Things not looking great, got it to start with the monobloc, but was tedious and took a long time. Everything scrupulously clean or new, and it seems to like a high idle, but only fires every other time, and is uneven.
I guess that means the carb body is knackered?  It revs up really nicely, and no pops or bangs on the overrun.