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skeptical old git
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Discussion Starter · #1 ·
Something strange has happened to my AT. Suddenly.

Starting it from cold, it has always insisted on full choke (won't idle on part choke for more than 4-5 seconds, ever) until it's warm enough (minute or two in winter, 15-20 seconds on a hot day) to idle with no choke at all.

It still demands full choke to start with, except now I can't get it to idle properly without choke until it is really warm (like, 3-miles-down-the-road warm). Increasingly the idle speed fixed the problem, but then when properly warm it would "tick" over at 2000-2500rpm. Embarassing at the lights...

Now we have an uneasy truce with a fast (1500rpm) warm tickover, but only just ticking over at about 7-800rpm when cold without choke. Obviously not right.

Riding the bike, it accelerates fine. Holding steady speeds I have noticed something that's hard to put my finger on - for a fraction of a second it's as if about to lose power (like running onto reserve), but only a fraction of a second and then it's fine. It's borderline noticeable and could be a hefty dose of paranoia - when you expect trouble you tend to notice stuff that isn't there (like if you run onto reserve on the motorway and 30 miles later you see a "Services 20" sign;-)

I've done nothing to the bike except filling the tank with Shell unleaded and fitting the crash bars and hand guards. The tankful of Shell is the only plausible contender there! Seems unlikely, and in any case a refill at my regular garage hasn't rectified it.

Things like pinched fuel lines, dodgy vacuum fuel taps etc. can cause fuel starvation, but that ought to get me when riding fast, not cause tickover problems?

Any ideas for what I could check out?
 

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I had a similar problem when I mistook the idling jet screw for the carb balancing screw. :shock: The idling jets need to be screwed in all the way and then out for 2 3/4 turns for a '[email protected] the idling jets are the screws on the underside of the carbs towards the out side.
 

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Senior Consulting Member
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icenian said:
Something strange has happened to my AT. Suddenly.
And it must be catching. Mine's doing similar Icenian and I've noticed that at tickover it feels like one cylinder only fires occasionally, getting more frequent as the revs rise :(

I once had a Z650 that did the same thing, that turned out to be a blocked idle jet so I think I'll start there on the AT if it doesn't cure itself (some chance :wink:)
 

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skeptical old git
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Discussion Starter · #4 ·
Oops, sorry to have passed it on!

I've been away for a while so haven't been riding the AT. I've now noticed that there is a flat spot at around 3000rpm. If I have the revs at just the wrong spot, it will actually lose speed on a steady throttle. In normal town riding (about 30mph) this seems to affect me intermittently.

Not sure what would affect cold idling and also running at ~3000rpm though. I know virtually nowt about carbs, but it won't be using the idle jets at 3000rpm under load will it?

Did once have slightly lacklustre low rev performance from a VFR750. I was recommended a fuel additive (erm, reddex???) poured straight into the air intakes! The entire street was engulfed in thick smoke for several minutes (long enough put the bike in the garage and then hide before anyone came out to see where the smoke had come from!) Then I took the bike out, and the first time I opened the throttle (end of 30 limit about 100 yards down the road) I laid down a smoke screen for about 200 yards.

It worked - but considering the side effects, I don't think I want to go down that route again!

The fact that it is only at certain rpm, and the bike accelerates fine and holds high revs and high speed, make me think it's not electrical and not blocked fuel line/vacuum tap type problem causing restricted fuel flow. Think it has to be carbs...
 

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I guess the only thing you can do is go through the ignition and fuel systems methodically to identify and fix the problem. I've had varying success' with Reddex over the years (apparently you can use diesel to do the same job) I've found it of no help if a jet or passage is actually blocked, but it does seem to loosen those carbon deposits when it does get through :wink:

Happily mine seems to have sorted itself without any action on my part :D
 
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