Stumbling idle and hanging revs

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Wrongun
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Posts: 17
Joined: Mon Sep 26, 2022 8:49 am

Stumbling idle and hanging revs

Post by Wrongun »

Does anyone know what the causes of this can be?
The throttle cable and mechanism are fine, the butterflies are good, the injectors appear to be working fine, all four cylinders reach the same temperature together, the intake boots and plenum to throttle bodies boots are good - there's no difference in revs while spraying carb cleaner around these places.
It has new plugs, ht leads and spark plug caps.
I've checked the tps, the air temp sensor and engine temp sensor and all are within range as per manual. There are no codes being emitted from the control unit.
I should probably try balancing the throttle bodies but I'm pretty sure I'd make it worse with the idle as rough as it is.
Could it be down to the tps being out of adjustment? Can I adjust the tps before balancing throttle bodies? And if the problem is not the tps will adjusting it make the issue worse?
The bike rides fine otherwise and pulls really well once off idle.

Apologies for the long post and questions and possibly repeating myself.

Cheers
rangeroy
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Location: Yorkshire.England

Re: Stumbling idle and hanging revs

Post by rangeroy »

Tank return valve sticking a little maybe?
Wrongun
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Joined: Mon Sep 26, 2022 8:49 am

Re: Stumbling idle and hanging revs

Post by Wrongun »

Forgot to say it's got a brand new return valve in the tank.
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750turboguy
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Re: Stumbling idle and hanging revs

Post by 750turboguy »

This is so common. EVERYONE always goes for the big ticket items like TPS, Injectors, etc...when its almost always something small.

I post this alll the time... These bikes are going on 40 years old now.

Check ALL of these...

1) EVERY vacuum hose and EVERY connection where EVERY hose bends and connects on to something. Look for cracks or crackling
2) How old are the spark plugs and caps? REPLACE THEM!
3) Check electrical connections throughout the entire bike. Unplug all the connectors and spray electrical contact cleaner on all the pins
4) The rubber manifolds on BOTH side of the throttle bodies. Big job but REPLACE THEM
5) There is a ground wire connection to the frame right around or above the clutch cover. Undo it, scrap the paint from around it. Shine up the spade lug and reattach
6) There is another ground wire connection under the tank near the coils. Do the same thing with that one.
7) Have you replaced the fuel filter?. If the engine is starving it will sputter
8) How old is the battery? I don't care if the bike starts, These bikes eat lead acid batteries for dinner. A bad or week cell can cause intermittent ignition problems and sputtering. If the battery is 3 or 4 years old, put in a new one. AND DONT GET A GEL battery. Stay with lead acid.
9) If the throttle bodies need syncing you can hear it at idle. The idle is not smooth and engine sounds like its chugging. Usually this smooths out as you increase the revs.
10) The ignition coils....they are 40 years old now. REPLACE THEM.

Hope this helps.
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