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MK II Amal warm up #453653 09/09/12 6:19 pm
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Woodsie Offline OP
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On my 79 bonnie with MK II amals, the bike starts fine with the choke on but it takes several miles before I can shut the choke off. I can ride off with the choke on and it runs fine but after a few miles it starts to run rough but it'll die at an idle with the choke off so I have to keep running with the choke on and running rough. Eventually I can shut the choke off. What do you think is going on, or is this normal. My understanding is that the choke allows more fuel through and the "warming up" process is the actual engine warming up to give a better combustion environment. So is my problem even a carb issue????

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Re: MK II Amal warm up [Re: Woodsie] #453713 09/09/12 11:06 pm
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Woodsie Offline OP
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I don't know how the internals of the choke work but, it does have a plunger. You push down on the lever which lifts the plunger on each carb. I call this the choke on. The choke off is the normal running position with the plunger down.

Re: MK II Amal warm up [Re: Woodsie] #453719 09/09/12 11:35 pm
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DavidP Offline
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Yes, the 'choke' is really an enrichment jet for the idle circuit. Sounds like your idle circuit is partially blocked. Remove the pilot jet and spray cleaner into the hole. You should see a stream out the small holes in the carb throat.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: MK II Amal warm up [Re: Woodsie] #453721 09/10/12 12:00 am
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desco Online Happy
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If your carbs are like mine you've got it back wards. Pull the air cleaners off and look inside the carbs.With the key off twist the throttle full on. If can see anything hanging down that's the choke. It should be retracted up into the carb body while running.


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
Re: MK II Amal warm up [Re: Woodsie] #453727 09/10/12 12:21 am
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DavidP Offline
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Your carbs are MkI, with a choke slide. MkIIs use an enrichment jet. The plunger uncovers this jet when the lever pulls it up.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: MK II Amal warm up [Re: Woodsie] #453731 09/10/12 12:37 am
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Woodsie Offline OP
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I'm positive that these are Mk2. I am looking at my parts book, it calls them Mk 2 Concentric. It shows what they call the "cold start plunger assy" with the pilot air screw below it. I'm going to take DavidP's suggestion of removing this screw and spraying carb cleaner into it.

Re: MK II Amal warm up [Re: DavidP] #453732 09/10/12 12:37 am
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desco Online Happy
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Thanks, I know nothing of Mark IIs. I hate to confuse the guy.


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
Re: MK II Amal warm up [Re: Woodsie] #453735 09/10/12 12:59 am
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Woodsie Offline OP
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Desco, I appreciate that people will go to the trouble to give input, so thanks. I should probably not call it a choke. I think "choke" comes from car carbs that have the butterfly flap in them. I don't know if any motorcycle carbs have that feature. I will probable continue to call it a choke, for lack of knowing what else to call it. Cold start lever, air enrichment lever. Most people would probably say "you mean the choke"

Re: MK II Amal warm up [Re: Woodsie] #453736 09/10/12 1:01 am
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John Healy Offline
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Without going on, it sound to me that the enrichener is doing what it was designed to do. You might try a smaller enrichener jet. The typical 1979 Triumph comes with a 50 jet. They usually work better with a 35.

For the enrichener to work when the engine is cold the throttle must be closed! When you raise the slide manifold vacuum drops and there is less fuel drawn through the enrichener, but still enough to keep a cold engine running. Once the engine warms all that extra fuel vaporizes and the engine starts to run real rich. Automobiles use a mechanical (bimetal spring) or a computer what you must do by hand. Slowly lean out the mixture as the engine warms and the heavy molecules start to vaporize.

The bulk of the gasoline is made up of "heavy" molecules that will not vaporize into a useable fuel until it comes into contact with an engine that has not come up to operating temperature. Thus a small amount of light molecules, that will vaporize at ambient temperature, is included in the gasoline. It is these light molecules that the engine runs on until the engine warms. Because there is so little of the light molecules in the fuel that will vaporize when the engine is cold you need to flood the engine with the fuel unit there is enough of the light molecules to support combustion.


Re: MK II Amal warm up [Re: Woodsie] #453739 09/10/12 1:22 am
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Rather than riding with the enricheners on you should keep the revs up to 1500 rpm by working the throttle. USe the enrichers to get the bike started and rev it a few times to get it up to 2k rpm then pull the lever up. You might get a little stumble but keep the bike running by not allowing the throttle to close fully. You are risking fouling your plugs if you ride with the enricheners on.

Scott

Re: MK II Amal warm up [Re: Woodsie] #453750 09/10/12 2:12 am
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DavidP Offline
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Originally Posted by woodsie
It shows what they call the "cold start plunger assy" with the pilot air screw below it. I'm going to take DavidP's suggestion of removing this screw and spraying carb cleaner into it.

That's not the jet I meant. That one seems to be working just fine.
The jet to which I referred screws into the bottom of the carb body inside the float chamber. Pilot jet, idle jet, whatever you call it, the passage behind that is your main idle circuit.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: MK II Amal warm up [Re: Woodsie] #453751 09/10/12 2:19 am
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John Healy Offline
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David, the MKII doesn't seem to suffer blocked pilots anywhere as often as the MKI with the pressed pilot. Woodsie, spraying cleaner through the pilot jet to resize it is an effort of futility.


Re: MK II Amal warm up [Re: Woodsie] #453759 09/10/12 3:24 am
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KADUTZ Offline
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britcycle.com has a good item on AMAL MK2 carbs in their Tech Help Files.
Also I assume you are runnning a Champion N5 plug or its equalivent if you have stock US EPA jetting.


1970 T120RT
1978 T140V
Re: MK II Amal warm up [Re: Woodsie] #453760 09/10/12 3:27 am
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bonneville15 Offline
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woodsie:
Use sea foam aditive in the fuel. It really helps clean the carbs without take them apart. The rubber mounted carbs are Mk II. I had a 79 Bonni Special.
William


ASE Automotive Master Tech.
Never regret anything in your life because at one point, that was what you wished for.
Always tell the truth, even if your voice shakes.
1977 T140V
Re: MK II Amal warm up [Re: Woodsie] #454044 09/12/12 2:45 am
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Woodsie Offline OP
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I have put some sea foam in the tank and taken it for a spin. It seems to be idling much better. Opening up the carbs this winter is on my list. I am going to look into the sizes of the jets and needles etc. Turning the enricheners off sooner and keeping the rpm's up worked as well. I have always tried to keep the rpm's down after first starting the bike, but 1500/2000 didn't seem too bad. All is well in T140 land again

Re: MK II Amal warm up [Re: Woodsie] #454052 09/12/12 4:10 am
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DavidP Offline
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Good news, woodsie.
BTW: Do these later Bonnies still have the balance tube between the intakes? If so, be sure to inspect/replace this often. Even a tiny leak there will drive you nuts.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: MK II Amal warm up [Re: DavidP] #454128 09/12/12 6:10 pm
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htown Offline
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This sounds about par for my bike with MarkII's. Enricher lever down to start with no throttle opening. Up after about ten seconds. Have to keep blipping the engine to keep it from stalling. Shift into first carefully at the bottom of a blip. After a few minutes riding the engine will settle into a good idle. If you have the idle set to keep the cold engine running it will be too high when it is warmed up. Just something I have learned to live with.
My bike also tends to flood pretty easily with the enrichers on. If it doesn't start after two or three kicks, its best to lift the lever up and open the throttle about 3/4. Usually roars to life then.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2018 Kawasaki Z900RS


Everything will be alright in the end. If its not alright, its not the end.
Re: MK II Amal warm up [Re: Woodsie] #454847 09/18/12 5:09 pm
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tomterrific Offline
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I tried the #35 enrichener jet but it was still too rich to warm or ride with the 'choke' on. I used the original #25 idle jets in the enrichener and that's about right.

I found my MK II Amals easy to plug up (or partially block) an idle jet with a speck of dirt. The quick fix that worked every time was to pull out the mixture screw and stick the little hose from a can of carb cleaner inside. A quick spray and the dirt gets blasted back to the float bowl. Wear eye protection as some spray comes back out. My Triumph isn't the only bike I've used this back flush trick with. It works so well that I have made up a little spray tube with a wrap of teflon tape and a little o-ring to secure it. This plugs the mixture screw hole a bit for a better blast.

Tom

Last edited by tomterrific; 10/01/12 4:27 pm.

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