Hi Guys,

I have a problem...

I bought the bike from a dodgy guy and spent a bit of time fixing it up. I topped up the gas with 98, new air filter, cush drive, airtemp mod, co adjust from 10 upwards to 20 then 30. I was having trouble with stalling at low rpm so I cranked the idle speed. I think that's when I started getting trouble. I thought it was a bad battery as went flat trying to get it started. It charges up quickly but drops way down when cranking.

I've done the accelerator mod, adjusted the idle throttle and tps, installed a new tps even but still getting preignition at around 10-30% throttle.

I've also put an iridium plug in but it's one increment colder.

What can I do to troubleshoot?

My thought is that as I've adjusted the idle and then back to the tps several times, the relationship between the two is off and I need to go back to setting up the throttle plate/cable correctly then do the TPS, then do the idle adjust. The idle screw is set to max right now and it's taking a few twists of the throttle to get it started along with a bit of cranking, about 3 sec.

Could someone tell me how to set up the throttle vs the TPS?

Just so I'm clear, I call it preignition because it sounds like it's coming back up the intake so I'm assuming the inlet valve is open and preigniting.

After it pops, there is no subsequent firing of that stroke.

Cheers,

Matt

Just loosened the idle right back, adjusted the slack in the throttle cable. Checked the TPS and with the idle backed right off it was at 20. Now set 17 and I'll go grab a new battery

Sorry, but I'm not too clear by your description of preignition? Preignition, you would notice as a pinking, knocking or diesely sort of sound from the top end under load. Are you saying it is backfiring through the intake/air box?

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That's right, backfiring through the intake. What do you think could be the reason?

Just a side question: when setting the CO value, it sounds like a solenoid in the air box is energized...what's that about?

Cheers!

Matt

Right, I understand now.

Firstly, there is something quite amiss if your idle adjustment screw is set to its maximum to get the bike to idle and start. I think this is indicating other problems and you’re just trying to compensate for them with the idle speed?

You can set the TPS, but ideally you set it after you have got the engine idling correctly. The procedure is to set the idle first then loosen the screws on the TPS body so as it can be turned in its slots and rotate the TPS until 0.63 – 0.73V is detected yellow and blue/black wires in the back of the connector. Tighten the screws when the voltage is within spec. All this assumes a good TPS is fitted (which you say has been replaced).

However, as I mentioned, you really need to have a stable and correct idle speed first (1400-1500 rpm) – which you haven’t got. This, along with the backfiring through the intake, leads me to think that your valve adjustment is not within specification – probably the intakes valves are set too tight and are not closing fully after the intake stroke has completed? This may cause a small amount of fuel/air mix to be forced the wrong way through the intake and would explain the troublesome idle, hard-starting and backfiring.
You also need to have the CO set to somewhere around 10-15. (It’s not exact, but roughly what it should be for your year of bike). Also check the throttle angle is between 15 and 20 in the diagnostic mode. If that is way out then you’ll have problems.

Before going any further though I would take the tank off and check the cold valve clearances. Then go back to setting the idle, TPS etc. You can also check the valve/cam timing while you’re at it which, if not right, will cause similar symptoms.

It is also worth carefully checking for intake vacuum leaks as well as these can have serious effects on idle and slow running. The rubber intake hose on older bikes is notorious for perishing and leaking vacuum.

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