New Amals Replace Mikuni - What a difference!

Well I just finished installing a pair of Amal Premium carbs, switching out the single Mikuni the previous owner had added. I have to admit my only reason for doing this at the time was to return the bike to a stock appearance. . . but after riding it, I couldn't be happier with the performance. In fact, I couldn't believe the difference! I guess it makes sense. . . two carbs are able to move more fuel/air than one, but I really didn't expect the difference to be this noticeable.

The installation was pretty easy. I had to weld my ignition switch tab back onto the air filter back plate, as the previous owner had cut it off when he relocated it after removing the old spam-can. I replaced both petcocks and added the stock fuel lines, which look pretty sweet. I also had to re-plumb my XS-650 PCV valve, and my oil tank catch bottle in the battery box, as the hoses were in the way of the new air filter. In fact, I think installing the air filter was the hardest part of the job . . . Holy cow! You guys must never change your air filter. What a royal pain getting that front plate and the carb boots in place! This is one aspect of the Mikuni conversion I'm going to miss. Maybe someone has a tip on how to make this easier.

Anyway, if you're like me and you've never run anything but the single Mikuni, do yourself a favor and go back to Amal (preferably, new Amal Premiers). The bike starts first or second kick, idles smooth after just a couple of minutes of warmup, and runs like a bat out of hell!

If you just have to have a Mikuni, PM me. I'll make you a deal on my old setup.

I don't bother trying to fit that ham can back on with the carbs in the way, I just take the time to put the carbs on after the ham can. To me it's worth the bother.

Dave

DogT said:

I don't bother trying to fit that ham can back on with the carbs in the way, I just take the time to put the carbs on after the ham can. To me it's worth the bother.

Dave

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So let me see if I've got this right. You pull the carbs to change your air filter. Really? Probably wouldn't be any more difficult than what I went through!

Yes, but how often do I change the air filter? Not much. Even once a year, it's a 2 hour job at most, even taking the tank off. And I don't throw tools across the next county or get blood all over the gearbox. Of course having the S exhaust doesn't help me much. It looks so easy in the 'Riders Handbook' but I've never been able to do it. I just make a project out of it.

No doubt about it, to keep em mostly factory is a manhood will power task tester so a badge to wear proudly of the time stolen from rest of life. If really filtering matters in your conditions the factory paper element is as good as it gets low restriction wise too. Got a nice hit again viewing the new proper dual rounded shapes and tidy fuel hose instal, yum. Play with the float level to get near 1.5 pilot turns out best idle and diddle the needle height and might get a bit more pleasure from pleasure time tasks.

I have non Premier Amals, that I have tuned with all the good bits from Burlen and even set up the fuel levels with a home made manometer. And I agree they can run very nicely on good Amals. Maybe not the 40 year old originals. And air cleaner removal is best done in my opinion by removing the carbs from the mainfolds. I would not be surprised if that was the intended way. All you end up doing otherwise is scratching everything. On 850 mk11's the silver part of the air cleaner has water trap attached, so it really is only possible to remove with carbs out.
Get yourself a carb balancer, manometer type off ebay or such like, and you can really keep the big humming.
Cheers Richard

Just be alert to the rubber pleat decay as that can bypass filter and lead to blow by oil mess. I found if I trim one pleat off its a better fit under less stress and proneness to crack open. Still not happy with ways to seal boots around carbs, hose clamps, zip ties or tape. Its possible to do filter with carbs on but as I've learned & as stockie2 pointed out, seeming short cuts with Commando usually disappoint and. If ya look close at rallys ya can tell by R forearm size whose twisting two throttle springs instead of one : )

stockie2 said:

I have non Premier Amals, that I have tuned with all the good bits from Burlen and even set up the fuel levels with a home made manometer. And I agree they can run very nicely on good Amals. Maybe not the 40 year old originals. And air cleaner removal is best done in my opinion by removing the carbs from the mainfolds. I would not be surprised if that was the intended way. All you end up doing otherwise is scratching everything. On 850 mk11's the silver part of the air cleaner has water trap attached, so it really is only possible to remove with carbs out.
Get yourself a carb balancer, manometer type off ebay or such like, and you can really keep the big humming.
Cheers Richard

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Richard - Can you post more info and maybe a pic of how you use the manometer to balance your carbs?

And a general question about 'reserve' gas supply comes to mind.
Is a 'reserve' built into the Norton tank somehow (I thought the right side channeled it differently), or is it a function of how the petcock is built?

t

"Holy cow! You guys must never change your air filter. What a royal pain getting that front plate and the carb boots in place! This is one aspect of the Mikuni conversion I'm going to miss. Maybe someone has a tip on how to make this easier.
"

It helps to put some small cuts on your wrist and forearm before starting. I have found that getting that out of the way first pre-conditions your mind for the job and makes it much easier!

OK, seriously…I believe, though I can't say this for sure, that the variations in factory tolerances/assembly make some bikes easier than others as far as filter changes. I change my filter in maybe 15 minutes if that. The primary "clearance" issue is the distance between the carb bell and the air filter's rear plate. A secondary concern is the flexibility of the rubber boots. The more clearance and the more flexible the boots, the "easier" it is.

There are various techniques that people seem to use. What works fine for me is to initially just unbolt the bolts and remove the filter/screen by pushing the front cover forward and rotating it and working it out - which is not too hard. HOWEVER, going back together is the fun part. I remove the front cover/boots and then place the filter/screen/front cover in place and loosely bolt it in (bolts finger-tight). THen I compress the boot and work it into position between the plate/carb bells. A little silicone grease on the plate-end of the boots, where the groove is that rides in the plate itself, makes this pretty easy. The boot will initially have the carb-end much further onto the carb than its final position. If there is any difficulty in working the grooved end of the boot into the plate, a small screwdriver will help. Anyway, that's how I do it and it really takes very little time.

Be sure the rubber boots are supple/not cracked. Get new ones if needed. I have never needed to use any sort of clamp to hold the boots onto the carbs. But every bike has it's own "thing." I f I needed clamps I'd use black zip -ties.

The Reserve function is handled by the petcocks. The Running petcock has a stand pipe a couple of inches long so that when it can no longer feed gasoline you must open the Reserve petcock which has no standpipe. You can remove them and check that all is well.
Jaydee

mike996 said:

. . .THen I compress the boot and work it into position between the plate/carb bells. A little silicone grease on the plate-end of the boots, where the groove is that rides in the plate itself, makes this pretty easy.

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Short of removing the carbs, this may be the easiest way to go about it. My boots are new, so maybe a bit stiff. As far as removing the carb, in my case, I don't think I can just removing them from the manifold, as I don't think I have enough room to clear the studs. Probably best to detach from the head. Well, at least I don't have to worry about that for awhile.

I did use the drill bit trick to do the initial setup and then tweaked it with the TwinMax. They were pretty darn close, but ran even better once I disconnected the TwinMax and re-attached the balance tube. I left the pilot screw at 1.5 turns and haven't changed it. It's running so good I almost hate to mess with it. Some of you experts could probably get a little more out of it. Any hints here?

Regarding a water trap on the silver part of the spam-can. . . Not sure what you mean here. If mine had that, it's been removed. Can you describe?

-John

Re reserve fuel…

It may depend on the tank - for example on the fastback tank having the long/short standpipe is useless and causes you to loose fuel capacity. Not sure if that is true with the roadster/interstate tank.

The reason this occurs is that once the fuel drops below a certain level, there is no communication between the "halves" of the tank. So if you have a standpipe tube on one side, you PERMANENTLY lose all the fuel on that side of the tank that lies below the top of the pipe. So, on a fastback tank, to be able to use all the fuel, you need petcocks with NO pipe on both sides. You use all the fuel on one side and then turn on the tap and use all the fuel that remains in the other side - the "reserve" - about 3 quarts on my tank. That way, you access to all the fuel in the tank. If you use a standard petcock with the standpipe on the normal side, you are losing approx 3 guards of fuel.

Again, that's with a fastback tank.

Like Mike996 I also don't bother with a stand pipe in either of the petcocks and although mine is a roadster tank and less gas is isolated by the center divide what is left after a stand pipe sucks wind is just sitting there. I do not believe it naturally sloshes over to be used and I sure am not going to lean my bike over and shake it to get the last dregs out when with just regular petcocks one can get all the gas all the time. A tank holds what a tank hold having a reserve does not get you extra gas. Also I really don't service my air filter all that much either. When you think about it a car engine has the same clean air needs as a Norton and will go 25,000-30,000 mi or more in year round conditions our Norton's will never see. A stock Norton filter is of pretty good size for a twin cyl engine too so routinely changing it seasonally or after a couple, three thousand miles is, I think a waist of time and money. But the feel-good factor may out weigh all of my arguments, and as always, "it's your bike".

Here is the air filter removal instructions that I scanned from my Riders Manual.


Commando Air Filter Instructions

The best I can figure is that you are supposed to remove the front air filter plate but they are not very clear in their description however, the 850 Commandos originally have baffle plates welded in the front air filter plate. I cannot imagine how you could possibly remove the air filter element without removing the plate first. I like how the picture shows just ONE HAND gently removing the air filter element like nothing could be easier!

On my Norton I fabricated a battery tray so that the rear air filter plate sits farther back than originally designed. Then I modified the top bracket by making it two pieces so I can easily unbolt it and allowing me to move the top of the plate back a little bit. Now I can remove the filter out the right side without removing the front plate. I also used Mylar tape on the frame tube to prevent the paint from being gouged.

As for my Norton Interstate I have been experiencing fuel starvation way before running out of fuel. I don't know if it is because the stand pipe is so long or the fuel is staying on the opposite side of the tank. There are fuel taps available that are push on/push off variety and they also have a little lever on them for reserve. I was thinking maybe a couple of those on my Interstate tank might be the way to go. They are supposedly good quality, made in England parts.

It helps to put some small cuts on your wrist and forearm before starting. I have found that getting that out of the way first pre-conditions your mind for the job and makes it much easier!

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this is outstanding advice

Hehe filter screen handling is a task of a 1000 cuts and snags. The manual drawers were either ignorant or laughing their behinds off on the decades of newbie's trying to pass the teethy springy screen under the Ign. switch side, ugh. Its kind of cheating to modify air box placement but congrates on improving the system. City going pavement only cycles likely can go years w/o the filter bother only needing attendance about as often as the booties decay. I like the looks of the air box and think Norton did a good job of placement and shape for the filter and flow function and not at all annoyed by the sucking sounds of nailing it. This subject also fits well in the most disliked feature or task thread.

I've wondered about how well just the boot pressure alone would seal in my Trixie and last few 1000 miles were run that way as boots seemed to fit more square on throats with a pleat removed, which I only did to remove the crack I found till new ones ordered, which I'll slice off ahead of time. I'm resealing Trixie so will peek at 7000 mile old paper element to see if dust getting past it and how caked it is or not. With the oiled k/n air box element or the cutie pie stuffed k/n fitler of a mono Mickie carb I found grit and fiber layer with fine dust in the manifold. Ugh. Put extra layer of UNI filter foam over em till going back to factory set up. Gave the foam to Wes to cover his Mickie k/n semi flitering crap magnet.

As far as the reserve issue, mine came with no standpipe on either EW petcock and the F/G Roadster tank. The tank is separated at the center, so either side will serve as reserve, as long as it's turned off. But there was a decal indicating 'Reserve'. I'm not sure if it came with petcocks that way originally or not, I got the bike with 4K on the clock and it looked like it had been used a bit hard but after 13K the crank and journals looked fine despite no filter.

Dave
69S

The other thing I have found is to screw on the metal locating rings for the boots with the flange facing forward, it seems somewhat counter- intuitive but gives a few mm extra clearance and every bit helps in this tight environment.

For all the work and effort, I'd pull the amals straight off and put the Mikuni back on again. I have spent so much time in the past trying to keep amals in sync I never want to go there again. The only time it seems the amals are synchronised is with throttle wide open. I experience no performance loss with the mikuni, except a few mph at top end. I don't care about this. I'm not racing.
It starts, idles nicely and needs no adjustment and no tuning.

Good luck boys, I am afraid I am converted!

phil yates said:

For all the work and effort, I'd pull the amals straight off and put the Mikuni back on again. I have spent so much time in the past trying to keep amals in sync I never want to go there again. The only time it seems the amals are synchronised is with throttle wide open. I experience no performance loss with the mikuni, except a few mph at top end. I don't care about this. I'm not racing.
It starts, idles nicely and needs no adjustment and no tuning.

Good luck boys, I am afraid I am converted!

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Hi, welcome to the board. Can you say "oil thread"? :lol: