Very rich carbs on a 71.

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Feb 8, 2019
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Fired up the 750 and like always it only took 2 kicks. Idle seemed just a lil low so I turned the slide stops in 1/8 turn. Bike is warming up so I blip the throttle and the motor falls on it's face. Black sooty exhaust at anything above off idle, sooted up the plugs as I tried to bring the rpm's up. It kept coughing and back firing with black sooty exhaust. Plugs sooted up again. Fresh plugs and 1 kick and she sits there idling smoothly but you try to give it some throttle and nothing but soot and coughing. I dropped the bowls last yr and sprayed them clean and sprayed up into the jets with carb cleaner as winter storage prep. It's bone stock except for an old Boyer?? ignition with stock coils. I'm using BPR7ES plugs with solid core wire and non resistor caps. Anyone help point me in the right direction? Plugged jet???
Thanks all,
Mike
 
As a guess - float sticking. I have had a problem with the bowl gasket being cut a little larger then needed, and it hanging up the float
 
Check the last thing you effed with.
Solvent clean spray to store is not fail safe.
Was Sta-Bil used?
It's always the last thing, ain't it? I had two 4 cyl bikes both being recently fixed up, with the full carb rebuild treatment. Both acquired bad manners around the same time, carb wise. I had filled both from the same fuel can which I had recently filled. That only dawned on me after pulling carbs on one, then the other. I put some 'Heet' additive in and both were cured. Both were bucking and snorting and would not take throttle, it was horrid.
 
Check floats and more importantly fuel level in bowls. There is a simple clear tube on a a spigot through a spare plastic bowl drain cap method to assess level alongside the bowl to carb flange (check Amal site for spec on fuel level...not the float level).

I've had some symptoms like your when giving the beans...stumble, misfires etc. Turned out to be worn/ovaled out needle jet and also once an unthreading main jet.
 
If in storage always wise to drain the tank and put in fresh fuel no matter what you use, modern fuels are not the same as the old leaded fuels of old.
 
Thanks all.
I put some Sta-bil in a full tank of E free fuel. It still has the fiberglasss tank (it does have a purple coating inside) so I'm leary about additives & ethanol. I'll dump it and try some fresh fuel & pull the bowls and check the floats again. I lowered the floats a lil' bit last yr because the bike would sit and load up at a stop light and surge a bit at idle.... It cured that and ran great, but it has sat 9+ months till today. (moving sucks)
 
Float bowl level and or sticking can be a huge influence in how it runs.
Yes, moving does suck, a lot.
 
Easy for me to $ay but $ooner or later buy a new steel or aluminum tank .

Also what is the mileage on the carbs
?
If high consider buying new. The needles ,needle jets , float needles,floats and eventually the slides and bodies all wear out from violent vibrations to them .
Well that just co$t you a bit .Or not .
 
Generally it's the last thing you did so before you dig deeper. With reference to adjusting the tick over. Did you turn the air screws in 1/8 turn by mistake?
 
When I had a similar problem, it turned out to be the air filter element. I had washed the bike and the filter element had got soaked. Maybe remove the inlet rubbers and give it a run?
 
UPDATE=
Thanks all for the suggestions on my problems. I tracked it it down to a broke choke cable.... that made the chokes to be "on". I rarely if ever use the chokes but the cable is original and must have broke last yr when I had pulled the carbs for major rebuild/cleaning. I now have a stack of sooted plugs to clean now lol.
 
When I read the first few posts on this topic, it immediately sounded as though the chokes might be stuck open. I don't think it can happen with Mk2 Amals or Mikunis where there are no cables. On early Amals there use to be a thing inside the slide with was used to obstruct the slide cutaway for cold starts.
 
Mk2 Amals do not have a 'choke' as such, they have a cold start jet which is closed off by a rubber tipped, spring loaded 'plunger'. When the rubber tip wears, the jet isnt closed off properly and and the mixture gets to be very rich.

The 'plunger' may be operated by a lever mechanism on the carb body, or cables to a lever on the handlebars.


I have the Mk2 carbs on my T140, they work nicely.
 
UPDATE=
Thanks all for the suggestions on my problems. I tracked it it down to a broke choke cable.... that made the chokes to be "on". I rarely if ever use the chokes but the cable is original and must have broke last yr when I had pulled the carbs for major rebuild/cleaning. I now have a stack of sooted plugs to clean now lol.
Rabbit,
If you rarely if ever use your (choke),why not get rid of it and the cables involved? I took mine off many years ago and just installed the Amal plugs that fit the top cap. I don’t know where in the US you are located but I have never had a cold-starting issue with them removed Just my 2 cents
Mike
 
The problem with carbs which are jetted too rich, is the motor will still run OK. - And if you do not fang the bike, you do not detect the loss of performance. The choke which does not seal when in the off postion, is not easily detected.
 
The problem with carbs which are jetted too rich, is the motor will still run OK. - And if you do not fang the bike, you do not detect the loss of performance. The choke which does not seal when in the off postion, is not easily detected.

The problem had already been identified as a broken choke cable even before your previous post.
 
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