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Carb setting help #745594
08/15/18 2:01 pm
08/15/18 2:01 pm
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Clarkston, MI
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redmosquito1 Offline OP
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Got my 67 A65L back together and running, it’s not smoking so far but it does have a heavy stumble when accelerating under load.

Hoping someone can help me get a base setting for the carbs.

I’m running megaphone pipes, short velocity stacks and .060 over bore. Any tips or setting recommendation for my carbs to to work from?

Thanks

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Re: Carb setting help [Re: redmosquito1] #745602
08/15/18 2:47 pm
08/15/18 2:47 pm
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West Virginia, United States
Beach Offline

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Set it according to manual. Thinking 1 1/2 on mixture


Bill
1974 Norton Commando
1966 Lightning
1965 Lightning Rocket
1966 Norton Atlas
1967 Norton Atlas
1948 Panhead
Re: Carb setting help [Re: redmosquito1] #745606
08/15/18 3:43 pm
08/15/18 3:43 pm
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argyll. scotland, uk
gavin eisler Offline
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More info needed, what throttle position does the stumble occur, , if it spits back on opening it needs less cutaway, past 1/4 to 1/2 its more likely to be needle position.
Easy stuff to play with , needle position, try weaker/ lower needle, Megaphone- itis is a thing , try googling it. Sometimes means a weaker middrange is needed.

Last edited by gavin eisler; 08/15/18 3:46 pm.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Carb setting help [Re: redmosquito1] #745651
08/16/18 12:46 am
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Clarkston, MI
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redmosquito1 Offline OP
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It was happening running about 40mph in 2nd gear so 1/4 to 3/4 throttle maybe. I wasn’t paying a ton of attention to throttle position at the time though. It took about 2 miles to start doing it, would that indicate it was running lean? And when first started it was running richer because the float bowl were over filled from tickling the carbs?

I forgot to mention these are 388/689 monoblocs.

Re: Carb setting help [Re: redmosquito1] #745653
08/16/18 1:13 am
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Clarkston, MI
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redmosquito1 Offline OP
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Not megaphones, the pipes are Dunstall replica reverse cone mufflers. I guess these might be megaphones, I dont know.

Re: Carb setting help [Re: redmosquito1] #745654
08/16/18 1:16 am
08/16/18 1:16 am
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argyll. scotland, uk
gavin eisler Offline
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If it gets worse as it warms up it suggests richness, try lowering the needles, this will help in the mid range, if they are old carbs then fit new Needle jets, these do wear and have a richening effect as the hole opens up. Have a look at the plugs, if very sooty then defo too rich at the mo.
Put some masking tape on your throttle barrel , put a mark on your throttle twist grip, mark the masking tape at o, 1/4 1/2 / 3/4. make sure you can see your marks easily.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Carb setting help [Re: redmosquito1] #745657
08/16/18 1:22 am
08/16/18 1:22 am
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argyll. scotland, uk
gavin eisler Offline
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I had them once , they are megas , might need a size or two bigger main jet. What settings are your carbs at the moment?.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Carb setting help [Re: gavin eisler] #745658
08/16/18 1:48 am
08/16/18 1:48 am
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Clarkston, MI
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redmosquito1 Offline OP
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I dont know I have to go out and check. I think I set them to the manual a couple of years back, but the bike never ran right on account of having .040 over pistons in .060 cylinder bores m. I can’t remember if I messed with the settings or not so I’m going to set everything to factory spec and ride it again.

Re: Carb setting help [Re: redmosquito1] #745667
08/16/18 4:24 am
08/16/18 4:24 am
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Clarkston, MI
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redmosquito1 Offline OP
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I am running a #3 slide, air valve was 2 turns out, jets and all replaceable parts are brand new from AMAL, needle was on 3rd notch. I lowered the needle to the 2nd notch and turned the air screw 1 1/2 turns out from seated. I fired the bike up, with it on the center stand the bike stumbles off of idle now but revs past smooth all the way up once it gets past the stumble. I didn't get to ride it as its pretty late, and tomorrow its calling for rain all day so wont get to do load testing until Friday at best.

It's been a while, but are there new slides available for the 689 carb? I havent looked in a few years but they were impossible to find back then. If not, would stock pea shooters work better for me? I just got these pipes cheap and they look cool, not that the peashooters don't look cool.

Re: Carb setting help [Re: redmosquito1] #745683
08/16/18 9:01 am
08/16/18 9:01 am
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argyll. scotland, uk
gavin eisler Offline
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AMAL , Burlen are remanufacturing Mono blocs, so I would think new slides are available.

The pilot air screws should be adjusted for max idle speed when the motor is fully warmed up after a decent run, Once set lower the throttle stops to give a normal idle.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Carb setting help [Re: redmosquito1] #745705
08/16/18 12:28 pm
08/16/18 12:28 pm
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Rotherham - S. Yorkshire
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If these are definately replica dunstalls, have a look at either welding some of the outlet tubes up, or Weld a nut in the centre hole and make some discs that have varous holes or hole sizes in... Sounds like too little back pressure. I sourced some original dunstalls for mine.... Far better than the repo's... I have another (albeit) battered original set, and the outlet holes are smaller still.

But the problem itself won't be properly rectified with carburation alone. it'll run better but you will be constantly up and down the box, improving the back pressure will give the bike more torque.

HTH


beerchug
Re: Carb setting help [Re: redmosquito1] #745878
08/17/18 10:51 pm
08/17/18 10:51 pm
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Sydney Australia
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double ditto on the tuneable Dunstals.
Ran them for decades and it did make a big difference to the power characteristics of the bike.
To a large extent they got replaced with the rat traps which were really popular with the in line 4 riders.
The replicas did not have a nut in the middle tube but you could weld one into it, but the baffle usually gave up in a few years.
[Linked Image]
This is a stainless replica made by Overlander Equipment downhere in OZ fitted to the 71 A 65L
Looks like it ran best with 3 outlets open


Bike Beesa
Trevor
Re: Carb setting help [Re: redmosquito1] #745880
08/17/18 11:05 pm
08/17/18 11:05 pm
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Clarkston, MI
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redmosquito1 Offline OP
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It seems the tubes are steel in these replicas since they’re magnetic, I think I’ll pick up a bolt and weld it into the center tube and make a baffle to bolt in. I’m going to head out later tonight to see if it runs better after I lowered the needle 1 notch, waiting on the rain to clear up first.

Re: Carb setting help [Re: redmosquito1] #745908
08/18/18 6:39 am
08/18/18 6:39 am
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Clarkston, MI
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redmosquito1 Offline OP
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Took it out for a short ride tonight, it seemed to run much better until wot where it would spit and slug a little bit. I'm guessing I need to get a larger main jet? Digging through my random bag of parts I did find a 300 main jet, probably to big but it leads me to believe it was running a 300 main jet back in the 70s when it was last on the road before I acquired it. I think I may order a 280, 290, and 300 main jets and try them out. Or if I install a baffle of some sort will the stock jetting work?

It was far from a successful ride, the screws holding my tach into the cup fell out so the face was bouncing around. The screws holding the gauge bracket backed out so that was bouncing around. The tank moved around and thankfully didn't do any damage but I hate taking that thing off and trying to get the rubber spacers in the right spot. Also found out my head light is in need of adjustment and one of the gauge lights burnt out. Anyone know of a non Lucas bulb that fits thats readily available at big box auto stores or batteries plus bulbs? And finally when I first turned on the fuel and when I stopped for fuel I had a nice spurt of fuel coming from my ticklers, luckily a light rap on the float bowls stopped that.

On a positive note I was able to find the tach screws and rubber thingies, unfortunately it took forever to uncrimp the ring but I was able to get it off with out breaking it or the glass. I was also able to dig up the old style of floats that didn't have any leaks, they have the brass pivot and dont get stuck on the screw boss like the new style. And bet of all no major leaks when I came back, I'm taking all of this as a win.

Re: Carb setting help [Re: redmosquito1] #746130
08/20/18 5:40 am
08/20/18 5:40 am
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NickL Online content
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The gauge lights are b9s's as i remember. get a couple of led ones off eBay.
If you block a hole or two in the exhaust you probably wont need the bigger main jet.


Lamas are bigger than frogs.
No room for sanity here.
Re: Carb setting help [Re: redmosquito1] #746131
08/20/18 5:44 am
08/20/18 5:44 am
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The gauge lights are b9s's as i remember. get a couple of led ones off eBay.
If you block a hole or two in the exhaust you probably wont need the bigger main jet.


Lamas are bigger than frogs.
No room for sanity here.
Re: Carb setting help [Re: redmosquito1] #746155
08/20/18 1:21 pm
08/20/18 1:21 pm
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Clarkston, MI
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redmosquito1 Offline OP
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Went for ride the other night and when I got home she wouldn’t idle. I’ve only been able to get her to run for a few seconds before it dies, if I rev it beyond 2000rpm it will stay running but close the throttle and she dies. After it dies it just shoots flames out of the carbs or backfires out of the exhaust, but usually a from the carb. I’m lost as to why since it’s never had issues starting 1st kick even with pistons that were .020 under the bore.

Any thoughts on why this is happening now after a good ride where it ran great? Stock jetting, needle on 2 notch, valve clearance is spot on at .008” in and .010” ex, reset the pazon pick up plate to the starting spot so it’s timed correctly and I have good compression. I’ve tried the air screw at anywhere from 1 turn out to 2 turns out. Only decent change was older plastic floats with a brass pivot, went to those because they don’t get stuck on the bottom of the float bowl allowing a stream of gas to flow from the tickler.

Re: Carb setting help [Re: redmosquito1] #746158
08/20/18 1:28 pm
08/20/18 1:28 pm
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Central Ohio
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PFribley Offline
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Intake air leak!!!

Re: Carb setting help [Re: redmosquito1] #746166
08/20/18 2:00 pm
08/20/18 2:00 pm
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Clarkston, MI
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redmosquito1 Offline OP
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I’ll check that when I get home, but I don’t see how that’s possible. Just to be sure I’m right, it’s paper gasket, isolator block thingy, rubber oring and carb? Brand new paper gasket and oring were used and the nuts are nylock nuts. But maybe I had a gasket fail or that hose between the 2 carbs is cracked.

Re: Carb setting help [Re: redmosquito1] #746169
08/20/18 2:53 pm
08/20/18 2:53 pm
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Central Virginia
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Originally Posted by redmosquito1
I’ll check that when I get home, but I don’t see how that’s possible. Just to be sure I’m right, it’s paper gasket, isolator block thingy, rubber oring and carb? Brand new paper gasket and oring were used and the nuts are nylock nuts. But maybe I had a gasket fail or that hose between the 2 carbs is cracked.



Just going by the "last thing you changed" philosophy, I'd recheck the float to make sure that the "older plastic float" you installed didn't get shocked by having to go back into service again, or that a piece of muck didn't interfere with the float needle or pivot ... ?

Lannis


I stopped believing for a little while this morning. Journey is really going to be upset.
Re: Carb setting help [Re: redmosquito1] #746193
08/20/18 7:55 pm
08/20/18 7:55 pm
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argyll. scotland, uk
gavin eisler Offline
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Or the pilot jets are blocked.Always suspect them firs.t they are the smallest holes and are the first to block if there is rubbish in your fuel. These are also what keep your motor running with a shut throttle , so if it needs blipped to keep it going they are out of whack.

The next steps are essential to get a clean running twin carb set up, monos or concs makes no difference , principles are the same,

Are your carbs synched correctly?, this means warming the engine completely with a decent run, at least 6 miles.
Fit a clamp to the balance pipe, if a clamp doesnt work , temporarily block the balance pipe by pulling one side and plugging the end of the pipe and the stub ( do this balance pipe stuff first with a cold motor , then set off), Remove one plug . and clip it to the head, start the motor on one , raise the idle a bit so its stable, then adjust idle mixture screw for max idle speed, lower idle with throttle stop to around 900 rpms, repeat same for other side.
Put both plugs in ,start up, idle will be too high now, drop each throttle stop screw an equal amount so idle is steady as desired,

Thats the idle set. This is the correct setting for your idle mix, not anywhere between one turn and two turns open but precisely set to give optimum running with a warmed up engine. Make a note of where the idle mix screws end up, mark the body to line up with the screw slot, screw in counting whole turns ( 360 degree is a whole turn ) and fractions of a turn, they should end up somewhere between 3/4 and 1 3/4 out. Reset to as tuned, once you know the setting, If they end up out of this range less than 3/4 means you need a bigger pilot jet, more than 1 3/4 means you need a smaller pilot jet.

Now synchronise the throttle cables ( motor OFF0 , look in the inlets , put a finger on one slide , watch the other slide, and with your 3rd hand slowly open the throttle, if one slide lags behind the other take up slack on the lagging side cable, rinse and repeat until happy. Alternatively fit a balancer across the balance pipe tappings for this part, results are similar , the balancer is maybe a bit more accurate.
Ride off with your new smooth , clean running motor.

I do all this at the side of a quiet road, well away from neighbors. The run home allows you to appreciate the improved running.
Tools needed , plug spanner, screwdriver for mixture screws.

Once cold . later Reconnect/ unclamp the balance pipe , ( the balance pipe helps accommodate slight variations in carb balance and is a good thing for a smoother easier starting bike)

If you dont have chokes fitted , you will need to tickle when cold, and the motor may take a mile or so to clean/warm up.
Once warm it should pick up cleanly with no fluffng after trailing the throttle on a downhill section ( for me , thats when I know things are right).

half of this depends on everything else/ timing/ etc being correct, the rest of it is down to the quality of your throttle cables, If you have to cut your own cable outers to get the right fitted length make extra sure the outer ends are ground square and there are no springy coils anywhere to mess with the synch. And dont grease the throttle drum,( I used to, big mistake, now it gets a thorough clean and light oil only.), Bicycle shops have very nice teflon lined outer, with inners to suit, I use the local pushbike shop for throttle cable bits, just buy the throttle barrel nipples/ferrules in., cycle inner cable comes with a nipple that will work at the carb ends.

Last edited by gavin eisler; 08/21/18 9:20 am.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Carb setting help [Re: redmosquito1] #746264
08/21/18 5:01 am
08/21/18 5:01 am
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Clarkston, MI
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redmosquito1 Offline OP
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So removed the old style floats, did some light sanding on the new style floats and some clearancing of the screw boss and now the new floats sit on the bottom stop boss and don't stick. Fuel pissing out the tickler problem solved.

Still not running. I had fuel flowing out of the pilot jets when I removed the cap so I didn't go any further, but since it isn't running tomorrow they'll come out and get looked over, maybe replaced if I have another set (probably not, will order some though.) The plugs are wet with fuel so I know fuel is going into the cylinder.

I have spark, I have compression, I have fuel, valve clearances are correct, timing is set per Pazons initial settings, carbs are tight with new gaskets and orings.

I don't know what else could be causing this, next step is to pull the pilot jets and look them over and then set the needle back to 3rd slot and see if that does the trick. It was running so good took, this damn bike is driving me crazy!

Re: Carb setting help [Re: redmosquito1] #746265
08/21/18 5:02 am
08/21/18 5:02 am
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Clarkston, MI
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redmosquito1 Offline OP
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Thanks Gavin, I'm glad you write is in this thread so I can find it easily. Once I get it running good I'll balance the carbs per your instructions.

Re: Carb setting help [Re: redmosquito1] #746350
08/21/18 10:17 pm
08/21/18 10:17 pm
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You shouldn't have fuel flowing out of the pilot jet. That screw meters air, not fuel.

Is your float level(s) correct?


Ginge
Re: Carb setting help [Re: redmosquito1] #746367
08/22/18 12:10 am
08/22/18 12:10 am
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Isle of Wight, UK
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It's sometimes difficult to know whether your description of symptoms applies to a run before or after the changes you are making. It would make diagnosis easier if you could describe the state of things first, then followed by how it performed. An ordered sequence of change and effect makes problem solving more efficient.

Presumably the bores and pistons are new now? Not just new +60 pistons in the old +60 bores?

When problems seem to come out of the blue, running EI, the 1st thing to check is charging/battery/voltage control.

I think the carbs are 389 Monoblocs? all spares for which are readily available.

On these carbs, removing the pilot jet cap will allow petrol to pour out, as the jet takes petrol from the cap.

It sounds like the " it just shoots flames out of the carbs or backfires out of the exhaust, but usually a from the carb" happens since you reset the Pazon to initial setting?
If so, this setting is only very approximate, and I'd suggest returning it towards where it was when it was running in a usable way.

Gavin's advice on setting up the carbs is valid, except I'd always synchronise 1st, then the idling setting.

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