Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Inlet valve B44

I accidentally acquired a B44 cylinder head (as you do!) that has already had an oversize inlet valve fitted, 1.6" head. The port has been enlarged and smoothed out, although the job was only half done, and it looks like they used a rasp to do it! I am sure it will polish just fine.
Here is the thing...….. what are the downsides of fitting it to my bike? 40 thou overbore, JE slipper piston, Vape ignition, new carb.

Saying hello to the exhaust valve or piston.Check with clay on piston dome.

See This old post for some info on using a bigger inlet valve on a B44. Looks like 1.600 is about as big as you can go and consider some before/after tests to see how much of an improvement is made.

I'm considering a similar upgrade on my B44 so keep us posted.

Ok, thanks for the advice, I omitted to say it is a square barrel motor, so from the inferences it should be a fairly simple task. Any "improvements" I get will only be "measured" by feel. Although I now actually have a shed to work in, I am the original "shade tree mechanic". The bike was built in the shade of a mango tree, flow measurements are a tad beyond my facilities!

I did the same on my son's B44 a couple of years ago. I used an A65 intake valve along with the A65 retainer and keepers. As I understand it it is a common mod and it really woke the B44 up! no problems with clearances.

So in the spirit of "keep us posted" as requested by Gunner.

After "fixing" the no compression problem that didn't exist I took the bike for a run.

Well it was not exactly asleep before I put on the head with the larger valve and ported inlet, but to quote D.W.R. it certainly has "woke up"! Not that much different up to 1/4 throttle but after that WOW!. Still tuning the carb settings which are quite different to the old standard head.

Very responsive and eager to go faster, worth the grief the process has caused (see my recent post on B44 Cylinder head).

I'm gonna kill myself on this thing.

Hi Dave, thanks for the update, sounds like it was worthwhile, so will certainly be on my list of future upgrades on my B44. By the way, what size carb are you using?

I recently stuck a pair of a65 valves (+caps and collets) in a b44 because the originals were clapped and
it runs well. I used 'em 'cos i had 'em rather than looking for performance etc.

Don't even think about polishing the port, it will flow better if it has a rough finish.

Gunner, …….. just using the regular Premier edition AMAL 930, jetted up as I brought it for a American spec B441 VS. The adjustments on the pilot circuit were a bit different with the mixture screw a good half turn out (richer?).

Andy …… I started to clean up the port a bit but my boredom threshold is quite low so it is still not what you might call shiny. why will rough give better flow??

Since I got the pilot system better tuned the bike feels like it has a rocket in its arse at all throttle settings, why did BSA not do this way back when?

Screw out for pilot equals leaner, the taper point meters air. The pilot jet is a fixed orifice, the pilot air screw controls how much air is bled through.

Yeah thanks for clearing up richer or weaker. I knew it was the opposite to what you would think, but then I thought that because I knew it to be the opposite to what you would think, and I thought that turning out makes it weaker, then the opposite of that would be richer (or leaner?) What ever, …… turned it till the bike ran better!

As far as why did BSA not do this mod? to be fair, they actually did, and a few others, then realized they could squeeze another 60cc or so out of the bore, called it the B50!

Leaner = weaker

This screw is critical to starting, pickup and fuel economy.
Set for max idle speed, then screw in 1/8th of one whole turn. Or through 45 degrees.
Another way is to screw out til revs rise then begin to fall and mark opposite screw slot with a sharpie, then screw in till revs again rise then begin to fall, mark new spot, set screw half way between marks.


On a sister subject

There are extended throttle stop screws available that are easy to adjust for cold starts , these are very handy for starting a stone cold single, screw in a 1/2 turn to slightly lift the slide, dont touch the throttle , kick, broom.
reset when warmed up.

Yep I was looking at those screws, Lowbrow Customs do a set, throttle and pilot screw, in brass that look real nice, and of course AMAL do a throttle screw alone for 1/10th price.

Probably will get the AMAL one as if I have the pilot as well I will spend far too much time fiddling. I got it "just right" then proceeded to mess it up just giving it a little tweek.
Never really have a "stone cold" start here and very rarely even need to tickle the carb, but it does like the tickover a tad high to start well, a little higher than I like to hear.