Variations within the 930 Amal Concentrics - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 11 (permalink) Old 03-28-2019, 12:28 AM Thread Starter
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Variations within the 930 Amal Concentrics

My original Carbs (930 Concentrics) Have a 2 1/2 Cutaway on the slides............a 220 Main Jet .........and 106 Needle Jet exactly to specs

My New Carbs .............................Have a #3 Cutaway on the slides...............a 190 Main..............and a 106 Needle Jet but the diameter of the area where the Needle

sits is a larger diameter as well as a heavier needle.

Should I put my old Jets into the new carbs as well as the needle from the old carbs? The old slides are definitely worn so do I need to order new slides with the correct cutaway?

Last edited by Stopngo; 03-28-2019 at 12:32 AM.
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post #2 of 11 (permalink) Old 03-28-2019, 04:58 AM
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Your new carbs are correct. My new replacements had a 200 main jet recommended by the supplier for ethanol added fuel. Works very well set up like that.

Now,where did that bit fall off ?
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post #3 of 11 (permalink) Old 03-28-2019, 09:54 AM Thread Starter
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Thank you for that. Still a bit confused. You say you have a 200 so I wonder why would my 190 be correct?
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post #4 of 11 (permalink) Old 03-28-2019, 10:30 AM Thread Starter
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Ok...... Maybe I'm over thinking things here.
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post #5 of 11 (permalink) Old 03-28-2019, 03:06 PM
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Hi Stopngo, Exactly what carbs did you get? Amal premier?

The sellers often sell a "universal" slide/jetted carb. They generally list the slide/jets in the spec sheet on their web page. So carb may or may not be best for your needs as sold.

On paper this should be simple but often it's not. Variations in fuel can have dramatic effects. I don't feel you are overthinking this. Worn slides will make bike do odd things just a trace off idle & rolling on throttle on slow curves & the like. Can cause spontaneous stalling at lower speeds also. Also will need to have idle higher than normal to keep motor from stalling.

The new Amal castings compared to 1969 & 1973 castings are different in many ways even though at a glance the same. The floor drillings for idle/transfer holes are different sizes. Not sure what you mean by larger diameter of where needle jet sits matters. I find the mixture between the old carbs & new premier to be same with same size needle jets. Changing needle jets gives the expected changes. I find changing slides & main jets give the expected changes as well. Read the notes below about air filters though.

The old needles often wear a flat spot and can score on the side that contacts needle jet. Also the needle jet wears oval from the needle contact. This wear especially on needle gives a rich spot in mixture. Generally around 1/8 throttle where we mostly ride. Needles are only 1 size, but there can be .0005" variations in straight portion diameter. .0005 will effect mixture as the clearances are so small.

I find with premiers they tend to come with a larger (removable) idle jet. This is correct & needed. The changes in the new design seems to require that.

Float level is very different on new carb as well. It will be higher than float bowl gasket surface & parallel with the surface. Sounds way too high, but is correct. Only an actual test of fuel level will confirm you true level, but I've found 3 recent premiers this was correct.

If I was doing the carbs, I'd leave new .106 needle jet in place. I'd put clip on bottom groove of needle. I'd leave #3 slides. I'd install 200 main jet from old carb. Mixture screw base setting 1.5 turns out.

This should allow easy starting & decent running for road test to warm motor & begin tuning.

I find for 10% ethanol fuel in California 5% richer across the board for mixture seems desirable.

Your exhaust & air filters make a large difference. I find the original type air filters with "fabric & wire gauze" made in UK work best as they are exactly like originals. I find the paper type Emgo tends to fit loose in housing & even with spacers made to fill the gap, then can modify the mixture. This upsets the entire tuning. I found it impossible to get a prefect tune with these. Ordering the original type, the tuning now made sense & changes to jets/slides gave the expected results.

Before carb tuning valve adjustment, timing must be correct. This is a given. Compression must be good meaning no leaking valves or horrible rings. As long as valve sealing is good, some ring wear & oil consumption doesn't seem to make a huge difference. Any valve leakage will make tuning impossible.

Tuning is a time consuming process. Plug readings can vary greatly depending on fuel. California fuel will look pretty much the same unless really rich or really lean. The ivory for lean, black for rich. A good mixture general looks a little rich with my fuel.

For tuning start with a road test say 65 mph up a moderate hill (if possible the hill). Motor fully warmed. Roll on full throttle & hold it. If motor misfires like ah ah ah, then runs normal backing off ah ah ah again rolling full throttle back on the main jet is too large. Reduce 1 size & try again. I always start rich & work down after 8 stroking. I leave the size where 8 stroking is 100% gone. Lean is harder to tell. Motor will gain very slight power when backing off throttle very slightly. Again I struggle with lean even after many attempts to feel this.

Rich & lean at lower speeds like 25 mph are a little harder & often takes some trial & error. Lean is harder to tell. Rich though backing off throttle to zero & coasting down in 2nd or 3rd if jerky & blah blah blah is probably too rich. Needle jet too large.

Remember needle is straight for a long ways so clip position doesn't matter until you get to taper. Many don't seem to understand this. Before the taper slide is important. Then taper/slide work together for a ways, finally 100% main jet.

Here's a link to tuning guide. Mark your grip! That's the only way to know what part of carb is in operation. The only way!

The link looks wrong, but is correct. Print the tuning pages & take with you on road tests. You'll soon see how it all works.

https://www.princeton.edu/ssp/65-cub...albritbike.pdf

Take your time & good luck.
Don
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post #6 of 11 (permalink) Old 03-28-2019, 07:08 PM
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Originally,they had 190 jets when petrol had no ethanol. The 200 jet compensates for the rubbish petrol in the UK. I still have to use a premium petrol with a higher octane rating.

Now,where did that bit fall off ?
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post #7 of 11 (permalink) Old 03-28-2019, 10:46 PM Thread Starter
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Quote:
Originally Posted by rambo View Post
Originally,they had 190 jets when petrol had no ethanol. The 200 jet compensates for the rubbish petrol in the UK. I still have to use a premium petrol with a higher octane rating.

Originally was when? My original 68 Bonnie had a 220 Main as I stated.So our gas (petrol to be politically correct) would appear to be megga rubbish....no?

And thank you TR7R for the substantial info. I will digest it as soon as I can and will get back.
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post #8 of 11 (permalink) Old 03-29-2019, 05:55 AM Thread Starter
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As for Amal Premier carbs or not am not sure because they were replaced by a repair facility in 2007 but if drain plugs under the bowls are an indicator then yes. Back into it when I return from vacation.
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post #9 of 11 (permalink) Old 03-29-2019, 06:37 AM
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Hi,

Quote:
Originally Posted by Stopngo View Post
As for Amal Premier carbs or not am not sure because they were replaced by a repair facility in 2007 but if drain plugs under the bowls are an indicator then yes.


The quickest external indicator of an Amal Premier is another slotted screw opposite the horizontal air screw? This is the removeable pilot jet. Standard Mk.1's have a cast cone opposite the air screw, because bodies are not cast handed. The cone is for starting the pilot drilling, the body was/is 'handed' when the pilot air and fuel passage was/is drilled nearly all the way through from one side, the fixed pilot jet was/is installed through the drilling, then the air screw.

However, 'ordinary' Mk.1's can have been modified either with the cone drilled and tapped for a plug screw - so the fixed pilot jet is more accessible for inspection and cleaning - or for the later removeable pilot jet.

Hth.

Regards,

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post #10 of 11 (permalink) Old 03-29-2019, 07:52 PM
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Hi Stopngo, New in 2007, I don't know what you'd have. So far as I know the only way to tell for sure is to unscrew the plug opposite the mixture screw.

I find this kind of confusing. Seeing a plug on the opposite side doesn't mean it's a Premiere. The latest non premiere has a removable plug, but it's just a plug, not an idle jet! Removing the plug allows easier cleaning of the pressed in bush type jet, but again it's not a jet. To me the heads look the same. I have friend that has these on his Bonnie. I've personally had the plugs out & cleaned the idle passage, which had metal chip in it from new. However some new non premier I've seen in photos have what looks like a mixture screw head in the opposite side, so I don't know what production is what. Why some x head & others slot head.

The pressed in idle jet is also known as the idle bushing.

I couldn't seem to locate the photos of my Premier internals. They got lost in another file. The removable idle jet size can be identified by the number of rings machined on the sliver end. In this link the jet has 1 ring. I find Amal is sending out carbs with 3 rings on jet. Making it part #622/502-19. From my experience this most closely replicates the old pressed in bush. The old bush ID is about .0165". The 3 ring jet is about .019" ID. There are 5 sizes of removable idle jets with the largest ID being #5. I've only personally seen #3s though.

Here is link to a photo of removeable idle jet:

https://www.ebay.com/itm/Amal-Premie...cAAOSwzaJX8dv9

I took photo of removable jet head for my '73 Tiger. This is a right carburetor if it was on a Bonnie.

I took a photo of the idle circuit with pressed in jet on an original Concentric that was kept on counter of Rabers so you could see how the passages were arraigned & how hard it is to clean the idle passage.

I've never had an idle jet passage I couldn't clear, but some have been a real fight. Start by cleaning well with carb cleaner & blow out all passages well to dry. Soak an hour in white vinegar, but force vinegar into the idle passage using a soda straw. Suck up some vinegar & blow it into the idle passage from float bowl side ( the bottom) so it goes forwards towards the idle jet. Keep carb completely submerged in vinegar the entire time while using the straw so all air is forced out. Wait 1 hr. Then flush with hot water.

Then plugging the rear air port at carb inlet & the floor ports ( the 2 little holes) at the same time blow compressed air into the mixture screw hole. Then blow air into the fuel suction hole at carb bottom. The air should pass freely both ways & keep cleaning until all white crust or hardened deposits come free. Use straw of carb cleaner spray can & blow carb cleaner to & fro until clean spray comes out of both floor holes & the air holes & the mixture screw hole. However... in stubborn cases, it can seem clean, but deposits might flake off later. I had to do my carb 3 times until finally it was good. Meaning it ran good a week or so then clogged again. Did that 2 times.

After that stayed clean forever, but longest bike has sat since was 3 months. If used regularly I find our 10% ethanol fuel keeps carb squeaky clean.

The middle photo that shows the fuel passage from float bowl. It is seen on bottom right. That is the idle fuel supply. Fuel is sucked up from bottom of float bowl, up into idle passage. So you can see you have a 90 deg turn at each end of idle passage which makes it so hard to clean. On a left had carb on Bonnie this passage is drilled on the opposite side.

(Just in case... on very early concentrics & some 2 stroke concentrics the idle jet was screwed into this drilling on bottom, but didn't work well so they moved it to the current location)

The passage in float bowl itself can clog also, so be sure to clean it.

According to Amal starting in May 1986 the float level should be above bowl surface & parallel with surface as current production is.

As was correctly stated, if compression is good, valve adjustment good, timing good, all that is left is carb slide sync & clogged fuel passages. You already verified chock slides are fully up.
Don
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Last edited by TR7RVMan; 03-29-2019 at 08:14 PM. Reason: added sentences
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