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.
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
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.
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.
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?
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
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!
Smear the silicone around the 1st inch of pipe and inside the port.
Push them in and it'll do the job.
Hi,
Wurth do a high temperature silicon sealer for wood burning stoves.
Dave.
High temperature silicon exhaust sealants are available from motor factors.
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.
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!
Hi,
Amal do a service kit for the monobloc with lots of bits in it. They are available from Feked as well.
Dave.
Thanks Dave, yes I have one on order!
It already has new jets, a needle and a slide.
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.
Hi,
This sounds typical of primary circuit wear. The tiny air and fuel passageways get eroded over time and cannot be really repaired. No matter how many new bits you fit only the middle and top end can realistically be restored but even then a new slide in a badly worn body will not give optimum results.
I would imagine that a new carb. body with all your new bits fitted will solve any issues and you will get the best from your bike.
Dave.
Thanks Dave, I agree... I'll start saving my pennies! Unless anyone has a nearly new Monobloc lying around?!
I guess the ultrasonic cleaning would make things worse in this case, as it's removing material and potentially widening any passages.
Hi,
Although ultrasonic cleaning is very good I suspect that even that will not necessarily clean these passage ways. Once you have the carb sorted you will trouble free riding and the more miles you do the cheaper per miles your new carb body will be.
Dave.
Oh the saga continues... Put the grotty and suspect 376/8 through the cleaner because why the hell not, and with all the bits swapped onto that body, it starts and idles quite nicely. It does leak from the main jet cover in spite of a new gasket kit from Burlen.
It is much harder to start with the monobloc though, the choke is blocked off but I heard they don't do much anyway.
I can live with the hard starting if "they all do that sir".. as long as it runs nicely out and about and doesn't stall!🤔
The key thing to have an easy starting motor is to get the slow running mixture set perfectly.
Set the throttle stop for a brisker than normal tickover, then adjust the mixture for a peak in rpm.
Reduce the throttle stop to lower the revs back down and repeat the mixture tune again.
When all is OK reduce the throttle stop for the tickover speed you require, competition bikes have to reduce to zero, for safety purposes, and many VMCC members like to reduce to rediculesly low rpm, which I think is just showmanship and not sound engineering.
Hi,
Don't forget that the slower the tick over the less the oil flow and pressure so a slow tick over could lead to unnecessary wear especially if pain bearings are involved.
Dave.
From what you have said, I believe the solution to your starting problems will be a new carburettor.
In the meantime, regarding the leak, I have found modern fibre washers to be quite useless. Even if softened in acetone, they soon harden up again and leak.
I assume they arrive here on a Container Ship.
Perhaps you might try a Dowty washer, or maybe make a washer out of thickish gasket paper?
It may be that the float bowl lid is buckled, they can be bent back into shape.
You can get new old stock Monobloc float bowl covers/lids from Autocycle Engineering on ebay/
https://www.ebay.co.uk/itm/265318850347?epid=645125204&hash=item3dc63c5f2b:g:jBkAAOSwdwhgXcwJ
Thanks for the input, yes I made my own double thick gasket and it is now sealing nicely. I can get it to start quite well on the second "live" kick after a few priming kicks with the fuel on.
It will idle fine once warm, bit then after a while it will stall, especially at junctions!
I guess clutch drag may not help in first with the clutch pulled in at a junction.
It's strange that idle is more likely to die when fully warmed up!
Yes the answer is probably a new carb, but I'm a sucker for punishment!
There is different sizes for monobloc pilot jets. The most used are 20. 25. 30.
Thanks indie, it's that the one that came in the carb was a different shape, it was marked 20 bit the threaded part was shorter than the one I got from Burlen
The most common used size is a 25. 20 is weaker and 30 is richer.