Runs well, plugs foul....

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dynodave said:
It has been a while since I read Rowley's write up, but I excruciatingly dissected what he offered and his final conclusions. I have thought a lot about what: 1. balance pipes do to the low RPM breathing and the "open header'' effect and the resultant mixture/fuel requirement, then 2. How will the stepped spray tube affect the whole range of flow, to give the richer mixture at the lower RPM and throttle setting. 3. why then the 3-1/2 cutaway is necessary to start to lean it out after the open header effect fades. 4. the leaner taper of the 4 groove needle to hold back the final 260 main jet.
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Then you certainly misunderstood what I said.
As Bob Rowley states below, the fitting of stepped spray tubes was required in order to pass a roll-on acceleration test when mutes were fitted (as mutes were normally included in the crates and fitted by the dealer if local noise regulations required) therefore, it appears all bikes had to comply regardless of whether mutes were eventually fitted or not.

The test did not, however, fail when mutes were NOT fitted as Bob R says "...this was fine without the mutes fitted,.." so = no mutes-no problem.

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"A new acceleration test was introduced for USA and from memory the test was 40 mph snap open throttle in top gear, this was fine without the mutes fitted, but with the mutes
( small disk fitted to the end of the exhaust silencer ) , this caused a [????] the muted condition, no matter what you say our suggest the final cure was to install a cut away spray tube, this allowed a much smaller main jet to be used this in turn stopped the eight stroking when trying to pass the USA acceleration test, think 40 to 60 mph in a certain time.

It is not difficult to see how this worked, FOR THE MUTED CONDITION

Most times with the mutes fitted we would snap at the 1/4 mile point at 30 and 40 mph and be doing the same speed, 30 or 40 mph at the timing lights, after 1/4 mile, of course you could feather the throttle back and judicially pick up speed and improve, but the idea was that a person when accelerating passed a long vehicle could not be expected to intervene and should expect a solid reliable acceleration.

You may not be aware that AMAL did not set up the Carburettors for the trade, BSA, TRIUMPH, NORTON but development worked closely with Amal, and the responsibility for final sign off and payment was down to the Test and Development department of each of the firms, as Deputy group test rider under Bob Mann's we carried such responsibility.

It's quite wrong to suggest that we would have changed or introduced things for no good reason.

One final thing that would vindicate the modification was the fact that we had over 150 bikes held up and not allowed in California test Authority and after the modification they and all subsequent Norton's passed straight in.

I am not sure if Alan Lines? of Amal is still alive but he would no doubt give you chapter and verse on how and why the cutaway spray tube was beneficial to the MUTED CONDITION.

One day I may find my notes on this mod but in the meanwhile could I ask you to at least give some benefit of the doubt, the cutaway spray tube was a category 'A' modification for all machines that required Mutes.

Regards

Bob Rowley "
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The passing test seems to be written a bit confusing. Is this what he's claiming?
You are driving down the road 4th gear 30-40 mph (1500/2000RPM), then snap open the throttle (all the way) and have only 1/4 mile to gain 20MPH up to 60MPH. This would simulate a 1/4 mile pass?

Their original test results would cause 8 stroking (super rich?) and would not get up and go??? and only way to accelerate is you close the throttle? Which is not allowed by the test rules?
I don't believe it!
I can see a failure to pick up (minimal) fuel at all (almost complete loss of vacuum at fuel pick up), and would sporadically keep running while coasting. This would be lean fade out, bogging, not 8 stroking rich.

Muting would restrict the air flow through the whole system and make it even harder to get the engine to pick up/atomize fuel/air due to the mute flow restriction. If it can't go out, it can't get in ... A richer spray tube would give a little shot more of fuel and make a few HP to push the air out of the mute and go down the road for the 1/4 mile roll-on up to 60.
 
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The ability to whack the throttle open, might be the reason some bikes have pumper carbs. My experience has been, that if the carbs are jetted for best performance, you usually need to feed the throttle on - in one strong steady squirt if you want max acceleration. If you do that with a properly jetted motor, the effect is probably better than you get with pumper carbs unless the pumps are very well controlled in the amount of fuel they deliver. The problem is the loss of vacuum which is caused by large throttle openings combined with low revs. It causes the mixture to be too lean, so the motor simply gasps.
There is also another problem which can occur. Sometimes the mixture is fully controlled by the needles, so the main jets never operate. If you do plug chops to set the mains, when you fit a bigger main, you should get a change in the plugs. If you don't, it might be necessary to recess the needle jets and meter lower down, so the tip of the needle always remains trapped and does not hang-up the slide.
 
To go back to:

dynodave said:
I see this as 6 pages of failing to acknowledge the effect that balance pipes have on breathing.
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When I bought my 850 Mk3 it had non-standard 932 carbs with flat top spray tubes, 2-ID needles, 3.0 slides, separate pipes and peashooters.
Later, a balanced system was fitted (after one pipe fractured) which made no apparent difference to performance or carburation so I'm sceptical that the difference between separate and balanced pipes has all that much effect on breathing.
 
ludwig said:
"..IMO " ?

Not good enough . Proove it ..
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Rowley/Norton/Amal They don't give proof either!
Did individual pipe 750 pass the "overtake/passing test" yet fail with mutes?

As I've said on occasion the 32mm 750 carb (configuration) can wholesale be swapped with the balance carb setup since it is rich enough across the band. I base this on the balance pipe set up being lean and usually idle warm up benefit from the choke use. The balance pipe setup is noticeably leanish in comparison.
The 750 conventional set up is very often stripped of the chokes (not that I recommend it).
I'm pretty confident an exhaust analyzer would show a difference at the low rpm balance pipe operation. That would of course have to take into account the exhaust note level.
Balance pipe has been used and proven for decades in nascar and in my own dual exhaust truck from 73 until 94 for 160,000 miles. New it got 8mpg (dealer said I would never see 10MPG) I got it up to just under 16mpg. I believe balance pipe physics is not a myth...
It's only science and instrument measurements will ultimately tell the truth. That has been my whole life career's work and sometime even now in retirement.
 
o0norton0o said:
I have a bunch of comments on different things on this thread so far:

*First, your initial post said you had "3 position needles", and now you seem to be saying you have "4 groove position needles". That strikes me as something to check on as the possible problem (maybe, swap the old needles and needle jets for the new ones to see if that cures your problem)

I did swap out three groove for four groove looking for more finite adjustment options...have switched back to 3 groove.

*regarding the float height comments, Slightly lower fuel levels in the bowl due to float height wont make your bike's plugs look too rich, which was your original problem. Lowering the bowl's fuel level height might make you run out of fuel at WOT, but won't make your bike's plugs richer looking... so I wouldn't chase float height adjustment, unless you know the fuel level is too high.

Engine was bogging in search of fuel. I once again reset the float height with the tru-floats, (not the fixed position white nylon ones I originally installed) raising them an RCH more and alleviated any fuel starvation.
Understood regarding fuel height/plug fouling.

*Your discription of adjusting the air screw on your first post seems to indicate that you might think that the air screw adjustment is significant throughout the full range of throttle. It's greatest influence is at idle and the lower register of throttle. Set the air screw with the technique posted below and if you get a good idle and good transition to your lower rpms, then you're air screw is 'set'. Here's my technique to set it up.

-Start the bike, set the idle stop screw somewhere near 1000 rpms. Go back and forth from side to side to get an even sounding cadence for the cylinders.

-Turn the air screw in until the bike starts to run rough, noting the screw position. Then turn it outward until it runs rough again and note that position. Return the screw position to the midpoint of those 2 position. Now do the same to the other side.

-Return to the original side air screw. While the bike is running, and you have the screw driver on the air screw, gently lift and lower the throttle as you turn the screw in and out very small amounts to see if you can smooth out the transition from "idle jet only" running to the beginning of the needle jet/needles influence being added in. It's very subtle to find the smoothest transition point position. Do the same to the other side... (If you want, you can repeat this last process again to micro adjust each side)

Good technique which is really close to what I ended up doing. I am now just barely tweaking the air screw looking for a reliable setting.

*At this point, you've set the air idle screw, So any other changes you need to make to the bike's carburation in higher RPM ranges are not related to the air idle screw position, and the variables you're left with are cutaway size, needle size, needle jet size, and main jet size.


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*Hotter plugs seemed to help your idle, but now you're claiming that moving the needle up (clip down) has made the plugs look lean and bogged down sooner... If anything, moving the needle up should make the mixture RICHER, so that wouldn't account for leaner looking plugs.

........ If I couldn't get past 4500 rpms, with new hotter plugs and readjusted float levels then I'd suspect that maybe I have the wrong cut away size, wrong needles, wrong needle jets, or wrong mains. The stock recommended settings are the best place to start. Then make adjustments to one thing at a time only, then retest to see where your at.

The cuts on the new slides match to original...l did research that before purchase.

Couldn't get past 4500 due to fuel starvation, float bowl too low level too low.

In the past, I had 240 mains on my commando and could never get past 85 mph. It was like there was a wall at 85. I changed to 220's and zoomed right up to 100mph. Sure enough the 220's were the recommended size for my set up. If I was you, I'd start with all the recommended settings and make adjustments to components based on what RPM range seems off.

This is just my $.02 so feel free to ignore it...
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Thanks for taking the time to share your experience on my carb issue
If I ask the question I never ignore an answer whether I like it or not.

I finally got my carburetion quirks figured out.

It was a combination of components/settings adding up to my fouled plugs.

Danno advised I change from fixed nylon bowls to adjustable bowls, and how to adjust, good change.

I attained a clearer insight as to how important float bowl adjustment can be.

I switched back to the 3 groove needles from the four groove...
and here is where I was getting ambushed. The circlips supplied for holding the 4 groove needles in place were slipping up past their seated position and getting hung up on the spring. I was never getting an accurate setting because the damn things kept moving within the slide and needle jet.
So sometimes they would hang up during a run and sometimes would drop back down into proper position. Now, I should have more carefully inspected these when I installed them, but I trusted the vendor who advertised they were applicable to 932's.

I figured this out after a day of frustration by pulling the bowls and then the jets while in place on the engine...and saw that the needles were not equal length.

Once again I pulled the slides and this time I found a needle/circlip hung up on the internal slide spring.

So as o0norton0o, Acotrel and others recommended I returned to all the original "book" settings I had started out with including a return to original the 3 groove needles with the circlips mounted in the #2 groove position.

I have properly set floats, properly adjusted needles and air screws and am running a hotter plug.

Now, after some tweaking of idle adjustment and air screw the engine starts on the first or second kick, idles wonderfully and was still pulling strong in excess of 90 MPH. I got caught too. The police officer let me go. He also rides a motorcycle.

Thanks guys for letting me in on what you have learned and sharing it.
Now I have go figure out how to keep the chain guard from rubbing the chain.
 
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baz said:
Wow this post is getting way off track !!
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Unbeknown to you (I guess) except for acotrel blab on pumper carbs, that will not advance the amal carb 74 850 with balance pipes solution.
How the nonstandard amal jetting will affect the more or less standard balance pipe 850 does seem relevant.
Feel free to add something useful.
 
most of this is very confusing. first is how you describe the needle ID. both 4 ring and 2 ring needles have 3 adjustment grooves. second you NEVER said which spray tubes are in your carbs as this is what dictates which needles are to be used. the problem you had with the needles not staying put on the clip sounds like junk aftermarket parts and i dont see how the needle was getting hung up on the spring.

Lineslinger said:
I switched back to the 3 groove needles from the four groove...
and here is where I was getting ambushed. The circlips supplied for holding the 4 groove needles in place were slipping up past their seated position and getting hung up on the spring. I was never getting an accurate setting because the damn things kept moving within the slide and needle jet.
So sometimes they would hang up during a run and sometimes would drop back down into proper position. Now, I should have more carefully inspected these when I installed them, but I trusted the vendor who advertised they were applicable to 932's.
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Hey Great! Your persistence paid off. FYI, the circlip getting caught in the spring rather than getting seated below the spring does happen sometimes upon reassembling the carb bodies. I've done it myself before.
 
Lineslinger
Well done!
I have also seen the problem.
Runs well, plugs foul....
If it occurs again I have a couple of suggestions for prevention.
Norton Owners Club supply a clip which greatly reduces the likelihood of the clip getting caught by the spring.
Runs well, plugs foul....
It is difficult to fit compared with the standard one as it has the throttle cable passing through it. I found it took 4 hands to fit!
Runs well, plugs foul....
Also a shim can be made to fit between the standard clip and the spring. I'll try and dig out the details. [edit - M10x16mm 0.5mm thick shim washer. ID opened up with Dremel to 12mm] This means there is a circular face above the standard clip and below the spring so no chance of 'catching'.
I was struggling to match this problem to the symptoms but this is a known problem - maybe wider than generally thought!
Andy
 
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Great use of foglights Lineslinger to make your way through all of this and arrive at a solution. I got so twisted that I forgot what the issue was in the first place.
So much experience bouncing around is confusing and difficult to collate.

I've got those. They weren't a great pleasure, but did work.
 
bill said:
most of this is very confusing. first is how you describe the needle ID. both 4 ring and 2 ring needles have 3 adjustment grooves. second you NEVER said which spray tubes are in your carbs as this is what dictates which needles are to be used. the problem you had with the needles not staying put on the clip sounds like junk aftermarket parts and i dont see how the needle was getting hung up on the spring.
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In regards to needle hang up please see the photos posted by DevonNorton.
I made the jet and needle purchase from a reliable supplier I used throughout my restoration. If you want to tell them about your “junk aftermarket” opinion I can PM their contact info to you.
Sometimes $#)t happens.
I did my best in trying to explain issues via the written word...very often two people can both read the same sentence and come away with two entirely different understandings of its intent.
I assumed that when I made note in the beginning of this novel “Standard Amal 932’s” that would be explanation enough in regards spray tubes.
Hope this helps.
 
yes please PM me the supplier you used as i have never had that problem. as to standard 932s there is NO STANDARD 932. the 72 750 combat and 73 750 had 32s with a flat spray tube. than we have the 850 with 32s and the cutaway spray tube. it sure makes hard to diagnose with incomplete info.
you still have not confirmed what needles you have as to 4 ring or 2 ring NOT groove.

Lineslinger said:
I made the jet and needle purchase from a reliable supplier I used throughout my restoration. If you want to tell them about your “junk aftermarket” opinion I can PM their contact info to you.
Sometimes $#)t happens.

I assumed that when I made note in the beginning of this novel “Standard Amal 932’s” that would be explanation enough in regards spray tubes.
Hope this helps.
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Good fortune with it and log some riding time. I believe you've earned some stress free miles.
 
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With your carb issue solved you might try going back to the original plugs and see what if anything happens. Running a hotter plug is probably something to avoid if possible.
 
Glad that you got it sorted. Wish that I'd read of your issue earlier as I had the exact same problem a few years back. Between the new stay up floats being too high and switching over to the 4 position needles and faulty too small retaining clip, my sweet running 850 became a testy beast. All is good now
 
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