Suzuki GS850G crash damage

Q: My bike was involved in a crash and came down on the right hand (timing cover) side. All the electronic ignition pick-ups have been replaced by a previous owner with parts from a GS1000. I am not sure whether the black box was also replaced to match. The bike starts fine, but will not rev-out on the road. It is fine when sitting on the centrestand. Top speed currently is between 30 to 40 mph, depending on hills! So my questions are:

1) I would like to check the timing. I am used to setting timing on two-strokes with a dial gauge, so would like to start again and make my own timing marks and then check the timing with a strobe light. Why is it, when I look at the manual that the firing mark appears after the TDC mark?

The manual states at 1500 revs it should be 17 degrees BTDC and 37 degrees above 2350. If it is before TDC, then surely the Firing mark should be before the TDC mark? Am I going nuts?

2) To use a dial gauge, what would the 17 and 37 degrees translate to in mm? Again, can I just find TDC for number one cylinder, and turn the engine backwards to find the correct position to mark?

There does not appear to be an ATU (Automatic Timing Unit) fitted, which is correct for the G model, but if it has been swopped over for a GS1000 electronic ignition, along with the black box, this may explain the poor running? I can check this with a strobe light.

3) Brakes: The left hand caliper bleed nipple was very tight. I found out the reason why, it was to stop it leaking brake fluid. If I tighten it up using a ‘moderate’ amount of force it will carry on leaking through the centre hole when you apply the brake (I am not going to try ‘excessive force’!) I have never had this problem before and have bled quite a few cars and bikes in the last six months. I have replaced the bleed nipple, but this has made no difference. Any ideas?

Peter Wells

A: I would not bother thinking about ignition timing using a dial gauge. You could work it out if you really wanted, but to do that you would need to know the effective length of the conods. Then you could either create a scale drawing and measure the piston displacement at 17° and 37° BTDC, or work it out mathematically by trigonometry. As I do not have a GS850 conrod to hand I cannot do it for you I am afraid! If you really want to check the timing from first principles, then you would be better using a timing disc. I shall be covering what is required in a future Workshop article.

The Suzuki GS series shared ignition components, so using a system from a GS1000 on a GS850 should be OK. The mystery to me is that this must mean that the bikes from 550 to 1100 share the same timing points which I just mentioned, and this apparently works OK. However, it is not possible to mix & match components of different ages as there were three different systems. Up to and including 1979 models, they used old-fashioned contact breakers and ignition coils, with the timing advance taken care of by an almost equally old-fashioned mechanical unit using centrifugal weights, known to Suzuki as a Governor (because it looks like one rather than is one). For the 1980 and 1981 models that system was replaced by an electronic one using the combination of a couple of coils called the signal generator and an ignitor which carried out the function of the points but more reliably, and needing less maintenance. The ignition coils were changed to suit the new system. However, the mechanical auto-advance principle was retained, though using a revised unit. Finally, for the 1982 models onwards all that was replaced by a different system which had a different signal generator and ignitor. The auto-advance was taken care of electronically by the new ignitor, so the auto-advance unit was replaced by a plain rotor – a much better system.

Yours must be the latest system and this is confirmed by your saying that there is no auto-advance unit visible. One characteristic of the new system is that it is not necessary to check the ignition timing as no adjustment is possible: the plate holding the signal generator has plain circular holes rather than slots. So what is wrong with your timing? The first thought that occurred to me was that possibly someone might have got hold of the earlier ignitor which does not have the electronic uto-advance, but this is impossible as the later ignitor has four terminals for the signal generator connection, and not only that the terminals are ¼” flat blades, rather than round pins.

I think you are right about checking the ignition timing from first principles, so stay tuned and, as I say, I shall show you how to do it soon.

For your brake nipple problem, if you have replaced the nipple with a new one but still have the leak, then it must be caused by corrosion or other damage to the seating area at the bottom of the hole. It is tempting to try to correct it using a drill, but the question is: is the angle of the cone the same as an ordinary twist drill (118°). I do not know I am afraid (though it would have made life easier in the factory if it were), so you will have to measure it on your new nipple and possibly grind a special drill to suit.