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MikeJ
MikeJ
San Mateo, CA USA
Posts: 32
Joined: March 2017
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Thread Like Summary
Allan G, BobV07662, gavin eisler
Total Likes: 6
Original Post (Thread Starter)
#825814 10/06/2020 7:57 PM
by Michael Veary
Michael Veary
I have a problem with my AMAL 930 fitted to my 535cc Royal Enfield Bullet.

Let me give the background:

The bike, a 2001 model, has a 535cc aluminium barrel and piston big bore kit (200074C) supplied by Hitchcocks Motorcycles. It is superb. It was fitted with a VM28 jetted nicely. The bike is running superbly; it starts from cold 1st kick, warms up and runs perfectly, never misses a beat and idles smoothly. So, why, you may wonder, did I decide to replace the VM28 with the AMAL 930? I’m beginning to ask myself the same question…

Anyway, on to the problem. As stated above, after swapping the VM28 out and the AMAL 930 in, it still runs fantastically, starts easily and goes like the proverbial solids off a polished 304 (or maybe 316) shovel BUT, and it is a big but, every single time I pull up at a junction it cuts out. So, flip out the kick start, one kick it starts immediately and it idles beautifully. Off we go, riding wonderfully until the very next junction. It cuts out. Flip out kick starter, one kick it starts immediately and it idles beautifully. Off we go… repeat ad nauseum.

I have read, manifold times, John Healey’s excellent guide to tuning the AMAL, various other tuning bibles, all the threads I can find on this and other boards but, sadly, albeit some describe similar problems none offer a solution to this exact problem so, I am asking before what precious little hair I have left falls out in desperation, has anyone got any idea what on earth could be wrong?

Like I’ve said, otherwise the engine is perfect, ignition spot on, valves exactly set, and it’s a complete dream otherwise, easy to start, goes like the clappers etc. etc. but at every junction it cuts out. Starts immediately the next kick and idles beautifully.

All help most gratefully received (by my hair, too).

Thanks in advance,

Michael.
Liked Replies
#825878 Oct 7th a 06:59 AM
by Mark Z
Mark Z
One more test if you will; this one must be done where there are no other vehicles present, and you can drop speed safely without braking. Do precisely that; as you're tooling along, just pull in the clutch and let go the throttle, but don't brake. If the engine doesn't die in that case, your problem may be electrical.

Here's where I'm going with this, and if you can positively attribute the problem to the carburetor change, then I'm all wet, but: This bike has battery-coil electronic ignition, right? If the battery is weak, dropping to idle and at the same time applying the brake(s) and thus powering the stop light may cause the battery voltage to momentarily dip below the threshold required by the ignition module to function. Running without the headlight on would accomplish the same test, but I'm guessing you cannot turn off the lights on that bike. It's a long shot, but I encountered this problem on my A65 with electronic ignition (and a bad battery).

Again, if the problem can be truly isolated to the carburetor change, or if the engine does die when you suddenly drop to idle without braking, then the oversized carb may be presenting an air velocity problem at low rpms. I've experienced this problem too on my A65 with oversized carbs, but it was not severe enough to kill the engine. The symptom could be more severe on a big single though. If this is the problem, it may be alleviated with a smaller throttle slide cutaway.
1 member likes this
#826073 Oct 9th a 07:56 PM
by kevin
kevin
Originally Posted by Allan G
Kevin if your reading this, with your cyclo-bolt. have a try of this also, it may also fix your carb issue.

all the passages in that BSA were clear. i'm simply not sure what the issue was with this, but it seems to be fixed now. a new needle jet is going in anyway just because two arrived in the post today.

i attribute my problems to BSA voodoo.
1 member likes this
#826057 Oct 9th a 04:22 PM
by John Healy
John Healy
Quote
BUT, and it is a big but, every single time I pull up at a junction it cuts out

This is similar to a problem that plagued the Triumph Daytona when first fitted to the bike in 1967. The cure was to move the pilot jet from the body (as used with the two stroke version of the MKI) up in the body nearer the transfer ports.

On the over run the increased level of vacuum in the intake port draws all of the fuel from the transfer port after the idle jet leaving no fuel to support idle.

We did some early testing with the Premiers on the Daytona and experienced similar problems. At best we were only able it to get it "pretty good" when we ran out of time with the bike.

In reality the fuel level has never been a problem. The variation in acceptable fuel with the original white plastic float was .170" to .240" below the top edge of the bowl. Further any "perfect" fuel level is effected daily by the barometric pressure. So often you are chasing your tail when searching for that "perfect" float bowl level.
1 member likes this
#826265 Oct 12th a 02:18 AM
by htown
htown
My experience with the stay up floats on six bikes now is that they need to be parallel with and slightly proud of the top of the float bowl when the needle is seated. If you set them up this way the fuel level will be very close to the .21" below the top of the bowl recommended by Amal. I always check the fuel level once I have the carbs on the bike just to be sure. If you try to set the front of the stay up float .08 below the lip of the bowl like the plastic float the fuel level is too low and you will likely have idle issues or at least I did. If you get the stayup a bit too high you will soon know it as the needle won't shut off the fuel flow. If that happens just adjust it down a hair and you should be good.
1 member likes this
#826516 Oct 13th a 10:42 PM
by John Healy
John Healy
Andy I think you might look at this statement a bit closer.
The VM and the Amal MKII were the work of Barry Johnston of IMI Amal.

It is not true that the VM has more choices of needles. If you look at a chart of VM needles you will find that they are listed by the Venturi size and there are typically only about 5 for a given VM Venturi size. The MKII has about the same number. Don't be sucked in by that big needle and needle jet chart. Look closer at what fits what and see that the list shrinks quickly.

When you start measuring the needles and needle jets you will find that while the actual dimension vary a few thousandths of an inch between the VM and MKII, the orifice they create is extremely close. A lot of pre-jetting can be done comparing what works on one with what is available on the other.

The typical VM uses an Amal 4/042 main jet. You will find that for a given Venturi size approximately same size main jet will work for either the VM or MKII on a given motorcycle.

It isn't a happenchance that the Amal's MKII starting system is the same as the VM and share about the same range of jets and needles. The MKII also includes air corrector jets.

I wish I could read Japanese as there is an article in a Japanese motorcycle magazine about Barry Johnston and his relationship with Mikuni. It came out about 20 years ago. Maybe one of our Japanese members know about this article.
1 member likes this
#826705 Oct 15th a 06:31 PM
by Dibnah
Dibnah
smile

I had intended to replace my rice rocket this year with even faster rice rocket; however, the temptation of buying a Brit single cylinder mainly based on the challenge of kickstarting the thing is gaining favour.
1 member likes this
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