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Carbs suck?

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Tony G View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony G Quote  Post ReplyReply Direct Link To This Post Topic: Carbs suck?
    Posted: 14 Sep 2020 at 15:13
So I've the old air filter housing out, and found a 1989 filter wedged in place. new one ordered.
Cleaned carbs, found plenty of grot and blown out filters.
   Fittered plunger style chokes. Started up out of curiosity, still dose not like choke so would point to rich mixture.Left hand carb ( when sitting on bike ) sucks plenty of air, at idle but stalls if I put the choke on. Right hand carb sucks very little air at idle and the choke makes no differance. 
  when the left hand plug cap is pulled the engine nearly stalls but the right hand plug makes no differance. both carbs suck air when revved. Any ideas 
I'll get their soon
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Post Options Post Options   Thanks (0) Thanks(0)   Quote c13pep Quote  Post ReplyReply Direct Link To This Post Posted: 14 Sep 2020 at 16:30
Had exactly the same on the Monza and only cured by replacing both plugs but am replacing the caps as well 

CHRIS 
you can`t have any fun in a straight line

Monza

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Tony G View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony G Quote  Post ReplyReply Direct Link To This Post Posted: 14 Sep 2020 at 17:53
Thanks Chris ,I'll at those to my list SmileSmile
I'll get their soon
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chrispy View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chrispy Quote  Post ReplyReply Direct Link To This Post Posted: 14 Sep 2020 at 19:00
My bike starts quite well ,
I have noticed that you require next to no choke on these bikes starting from clap cold,
If I touch any choke it will stop the engine .I have only used choke a couple of times when bike has been stood for a week or so ,even then I only need choke for a second or two.
have you adjusted the cable free play so both carbs slides are moving together from lifting off the idle stops ,it can be done with carb balancer gauges, or if you have the filter off try the peg trick by putting half a wooden peg resting on the carb slide sticking out of the end of the carb,then as you twist the throttle you can see the pegs start moving, they should obviously move in unison,great visual aid for getting the carb slides in balance.

Cheers
Chris
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richard Hyatt Quote  Post ReplyReply Direct Link To This Post Posted: 14 Sep 2020 at 19:05
If the left plug cap removal makes no difference than something is not right on that cylinder.
Can you swop the plug cap and plug to the other side , then run it and see if youve 3xported the fault to that side
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Tony G View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony G Quote  Post ReplyReply Direct Link To This Post Posted: 14 Sep 2020 at 19:08
I did a quick visual look with the carbs of the bike. The right hand carb dose slide befor the left. 
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Tony G View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony G Quote  Post ReplyReply Direct Link To This Post Posted: 14 Sep 2020 at 19:22
I was toying with that idea I' do that the next few days 
  Thanks all
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 14 Sep 2020 at 20:30
Well you do need to synchronise the carbs first. Both should open or close at exactly the same moment. Adjust the cables until they do, then see if it's improved.
Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote AdrianW Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 2020 at 10:26
Tony,
As Brian says you need to synchonise the carbs first.. With mine I replaced the cables (I do this on any bike new to me) and adjusted them until I could hear them both "plop" down together. You probably need the air cleaner / pods out of the way to hear this properly.

I had already refurbished the carbs at this point (new needles, needle jets & float needles) and was lucky enough to borrow a vacuum carb sync tool to finish the job.
Tickover is a bit high when hot but the plugs are a lovely colour and it runs well - one of the few success stories with my bike so far......

Cheers,
Adrian
Bristol UK
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 2020 at 10:28
It probably goes without saying but if they're that far out make sure you wind the throttle stop screws right out before doing as Adrian says. Obviously this means it won't idle but at least your cables will be properly synchronised.Then when you do a proper synchronisation using carbtune or whatever you can tweak the cables to suit.
Ian
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Tony G View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony G Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 2020 at 10:45
Thanks for all the helpful info. I'll check in the next few days and report my findings.
I'll get their soon
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iceni Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 2020 at 12:22
Not wishing to hijack the thread, I’d be chuffed if I could revert from EFI to a carb on the little Benelli!

Edited by iceni - 15 Sep 2020 at 12:32
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 2020 at 12:29
Anything is possible I've been told.

My response is usually "Try striking a match on a jelly".
Brian.

Better 5 minutes late in this world than years early in the next.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote i24 Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 2020 at 17:45
Originally posted by chrispy chrispy wrote:

have you adjusted the cable free play so both carbs slides are moving together from lifting off the idle stops ,it can be done with carb balancer gauges, or if you have the filter off try the peg trick by putting half a wooden peg resting on the carb slide sticking out of the end of the carb,then as you twist the throttle you can see the pegs start moving, they should obviously move in unison,great visual aid for getting the carb slides in balance.
Cheers
Chris


My procedure for this:

  • Take off both carbs, and adjust the idle adjust screws until both slides are exactly the same gap from closed. Use a 1mm drill bit as a feeler gauge. Also set the idle mixture screws the same (2 turns out).
  • Connect the throttle cables, while the carbs are still loose. Balance the carbs on top of the frame so you look into them and see both slides at the same time.
  • Adjust the cables to both slides start to move at exactly the same time when you twist the throttle. Also set the free play in the cables to about 1mm - but exactly the same on both carbs.
  • Then reassemble them onto bike.
  • Start the bike and make small adjustments as as necessary. But make sure that you turn the screws and adjusters by exactly the same amount on each carb.
If the carbs are clean and working properly, the bike should run nicely! Replacing worn or damaged throttle cables is a good investment.

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Tony G View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony G Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 2020 at 19:16
Brilliant advise. Thanks.
   EFI to carbs, I had a similer thought with a car I had. and another thought at one time convert from petrol to diesel. I did'nt get round to the efi which is theoretically doable but probably not as efficient?
   As for petrol to diesel, I sold the petrol and bought a diesel.
once more thanks for advice
I'll get their soon
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