Oscillating idle

[warren3200gt]

Having trouble trying to pin down and remedy the cause of an oscillating idle issue.
Firstly it should be said its a mix mash of parts build. Z1000J2 with gpz1100 top end. Vm 26 SS bored to 29.5mm. Runs perfectly for low down grunt with stock 900 jets and needle. Great plug colour. Colour tuned to good colour. Stock J ignition/ignitor/coils. Kill switch and stand override switch work perfectly.
Symptoms, at idle the rpm oscillates from 1k to 1.2k and back again over a period of 5 seconds climbing up then 5 seconds descending down and just continually repeats. It not erratic its consistent.
It's not the end of the world annoying just a little irksome that I can't dial it out.
Kinda thinking because of its consistency it's electrical supply to the coils but not yet checked to see if voltage oscillates with revs.
Open to other ideas before getting back at it tomorrow.

[gray]

I think you're describing a symptom called " hunting" . the engine is trying to find its comfort spot but keeps overcorrecting. Cant remember what is a symptom of - slightly too rich or too weak mixture at idle. I await the opinion of others

[warren3200gt]

Hi Gray, it's not hunting. It's far to rhythmic for that. Due to it being so rhythmic I'm pretty certain the cause is electrical, maybe I need to check the voltage to coil input to see if it oscillates with the revs. I'm also going to drop the plug gaps from 32 to 28 just to give the 40 year old components an easier time.
Let's see what difference, if any, it makes.

[Al]

Clutching at straws; if its the regulator part of the reg/rec, switching on and off, you might be able to trip it up temporarily by switching on all the lights. If its a resistor in the IC Igniter (my favourite thing to hate) you might be able to accelerate it by heating it whilst running, with a hair dryer. I know a lot of us dont have hair dryers so a paint strip gun may work instead.
If someone has accidentally plugged the ignition into the flasher relay,.....well, i'll let you decide.
Issues with the tacho feed are a monotonously repetitive theme for me. If my tacho starts going wonky i know i have a bad coil connection. Its to do with how i laid out the wiring on mine which is not standard. The tacho takes its feed from one coil only. Useful test maybe to plug it into the other one!!
AL

[Al]

J tank 'fuel filler caps' like to vacuum up. Its a weird design of matrix venting through a convoluted pathway which gets blocked. Can try opening the cap and putting the tap on prime.
AL

[warren3200gt]

J tank 'fuel filler caps' like to vacuum up. Its a weird design of matrix venting through a convoluted pathway which gets blocked. Can try opening the cap and putting the tap on prime.
AL

I've tried with the cap open and no difference. It's got an inline fuel tap fitted with the carb vac capped so for all intent and purposes its either on or off.

[warren3200gt]

Okay, embareeeeeeessssed I'm blaming Jack
Whipped the plugs out to regap down to 28, or so I thought!
Don't ask me how but they were all around 10. Surprised they didn't coke up immediately on choke.
RE gap to 28, fired up and almost steady idle!!!

[Mathh]

I am a bit confused now.. When you say 28 do you mean 2.8mm or 0.28mm?

[zed1015]

I am a bit confused now.. When you say 28 do you mean 2.8mm or 0.28mm?

28 thousandths of an inch.
Around 0.7mm .

[warren3200gt]

28 thou (0.7mm)

[Mathh]

Ah! Thanks!