850 Mk3 Set up with 230 main Amal jets?

Hi Everbody,
Situation:
Just got a 75 Mk3 ( after having a MK3 in 1982) and have been sorting it out. Engine is great. K&N filter, Peashooters and no crosspipe headers. Replaced sloppy Amal 932s with Wassell EVO carbs. Wassells set up for 260, 106, 3-1/2 , pilot 17 --typical MK3 etc. Bike would dry soot plugs in 10 miles. Tried twisting all the screws . No joy.
Finally looked inside the old worn out 932s and found 230 jets. Everything else MK3.
Put 230 jets into Wassells--and bingo, clean plugs. I will try 240 and 250 jets just to see how they do.

Question: Does anybody know of 230 jets working well in 850 MK3?
Thanks a bunch,
Kara

230 was fitted for the black cap silencers, for peashooters they will be too small, on my mk2a I use 260's but it will vary with your local petrol etc.

The manual says to use 230 Amal main jets but that is with stock exhaust system and airbox.
BTW the main jets control 3/4 to full throttle and have no real effect below that use , so I'm not sure what is really happening . Perhaps something else changed when you put them in.

Main jets should only operate above 3/4 throttle. If you are not fanging the bike, the plugs should probably not soot. Try lowering the needles until you get the cough when you ride the bike and then raise them one notch. You should be able to ride it, changing up and down through the gears without getting a cough or a miss. But if your needles are one notch too high, your bike will be sluggish and you will soot the plugs. If the mains are too rich, it really doesn't matter too much unless you are riding the bike at full steam. Then it will go marginally slower, but it won't burn a valve or a piston.

My friend had a very similar problem with his MK3, that turned out to be age related!

His age, not the bike He kept forgetting to back the choke off

Regards

Esme

acotrel said:

Main jets should only operate above 3/4 throttle. If you are not fanging the bike, the plugs should probably not soot. Try lowering the needles until you get the cough when you ride the bike and then raise them one notch. You should be able to ride it, changing up and down through the gears without getting a cough or a miss. But if your needles are one notch too high, your bike will be sluggish and you will soot the plugs. If the mains are too rich, it really doesn't matter too much unless you are riding the bike at full steam. Then it will go marginally slower, but it won't burn a valve or a piston.

Click to expand...

Hi Acotrel,
Thank you. I think I will run it a bit this morning with both new Wassells and prove that it is not sooting. Then I can put the 260s back in and see if it soots up. If it does, then I can raise the needles one notch. They are in the mid position.
Sincerely,
Kara

Raising the needles makes it richer, so it will soot even more.

I think you mean to lower the needles (by fitting the clip in a higher grove).

Have you checked the air screws?

Hi Everybody,
I put the 260 mains back in and did not change a thing. The mixture screws were left at 1-1/2 turns . The bike went from idling smoothly and running decently, to running rough and backfiring and not being something I even wanted to try and tune. It is now my direct experience that going from 230 main jet to 260 main jet makes a big difference at idle. I suspect the 230s may be a tad lean, and I have some 240s coming in which I will try next .
Sincerely,
kara

Hello

Ich have also an MK3

The right size of the main jet is so dependent on the Air-Filter and Exhaust.

I have a stock Air-Filter and balanced peashooter exhausts.

At the Air Filter
FOAM SEAL - AIR BOX part-no: 06.4174
had even an influence on the setting of the carburator

In my case 240 or 250 are a good choose.

Regards Marcel

Changing the main jets should not affect the idle. Perhaps you have flooding ?

acotrel said:

Changing the main jets should not affect the idle. Perhaps you have flooding ?

Click to expand...

You did not listen. Main jets changes will make no difference.
Change out all rubber , gaskets, float needles and old floats.
I drive MK III stone stock black cap crossover exhaust and air filter.

Torontonian said:

You did not listen. Main jets changes will make no difference.
Change out all rubber , gaskets, float needles and old floats.
I drive MK III stone stock black cap crossover exhaust and air filter.

Click to expand...

Directed to the poster , apologies.

Are the main jets from the same source, this does not seem right.

Well, it’s also my experience that main jets DO effect idle and other low running circuits.

And, I think Amal know this, that is why Amal tuning guides tell us to get the main jet correct FIRST before tuning any of the other circuits.

If you end up metering off the main jets when you should be metering off the needles and needle jets, you will end up in a bind - the mains might be too lean. In some situations it is necessary to recess the needle jets so the tips of the needles are still captured at full throttle and then metre lower down by lowering the needles, so that at full throttle the metering is done by the main jets and not the needles and needle jets. As long as the main jets are at least slightly too rich, you are safe. At full throttle you can run out of vacuum and get detonation. Detonation and piston/valve burning does not usually occur at mid-openings of the throttle - as you wind it on, the jetting is usually rich enough, however as lean as you can without getting the cough is good.
The mains should be set by plug readings. Getting the mid-range right is more difficult, but if the mains are not slightly over-rich when you set the mid-range, you end up getting the mid-range wrong (over-rich so the bike accelerates slower).
My brother runs Kawasaki triple two strokes on methanol and we have almost come to blows over this stuff. If he gets it wrong, there is big money involved. Doing plug chops to set the mains is often un-necessary. If the mains are slightly over rich, very few bikes run slower because of it, unless they are on huge race circuits.

I notice you've said the pilot screws are 1 1/2 turns out.
Does this mean you've set them as per the manual, or have you tweaked them for optimal running?
My MkIIA with a very similar setup to yours still ran fine on the original Amal 932s but they weren't badly worn, and my pilot screws were barely a full turn out once tweaked for optimal running.
I don't disagree with Eddie regarding the effect of the main jets, but if the pilot circuit is out it will have a significant effect.
The pilot circuit also plugs up for fun...

With pilot screws, if they are a fuel control - I simply wind them in with closed throttle until the motor misses then back off. I cannot imagine how changing the main jets affects the low running or idle. The main jets simply do not operate at those throttle positions. The main jets work at full throttle to compensate for loss of vacuum.

I agree 100% with Fast Eddie, go read the tuning brochure that comes with any new AMAL carb, the reason why they [AMAL] tell you to tune from main jet down is that main jet size DOES have a marked affect on all other settings, these are the folk who designed and manufacture the things, they should know what they are talking about. Possibly the reason why you chaps from the US have a bit of an issue dealing with these critters, is the popularity of Mikuni,s and Mikuni conversions over there, which are tuned from the bottom [idle-circuit] up, which works a treat on them but does not work/ apply to AMALS.

One thing to check is that the pilot jets are screwed fully home
if these are loose fuel passes around the jet and you will always get a rich mixture signal at idle / slow running
check this first it may be a simple fix

I left the main jet out completely once on my B44 when I was tuning it, there was no difference at all compared to running with a main jet until I opened the throttle over 3/4. You do get to know what 8 stroking is when you do open the throttle more than 3/4.