First it doesn't, then it does, then it dosen't

[350matt]

As the thread title suggests a mate of mine is having a few probs with his std griff 500, we were trying to set it up on the rollers today and the first couple of runs were quite poor ( 220ish @ flywheel) with a very erratic torque curve not at all smooth.
After some small tweaking of fuel and spark timing the power was still poor (230ish)but not as bad, then next two runs suddenly running splendidly 260ish power with a smooth torque curve then after lunch the low power was back with erratic delivery, I should point out it's not misfiring, despite the power being up and down it does run fine with no stumble or dropping cylinders, overheating etc. I very much suspect fuelling and therefore ECU issues has anyone else had expierience of this? we tried cleaning the ECU contacts to no avail, where does the Griff take its engine speed from as there's no crank sensor.

Matt

[griffter]

350matt said:

where does the Griff take its engine speed from as there's no crank sensor. Matt

Off the LT wire from the ignition amplifier / coil AFAIK.

[rfisher]

You're welcome to try this;

www.pistonheads.com/sales/54383.htm

[350matt]

If it was cam timing, then how do you explain the 260ish it was pulling on the middle curves? and it then reverted back to 220ish after lunch?

Test results were all fine no fault with the kit, which is why I suspect ECU or similar

Matt

[NicBowman]

If it was fueling, you should see the CO go up and down. Did you check the basics such as condition of the HT, etc before starting the run?

[GreenV8S]

Could be the mechanical advance sticking? Was the ignition timing about right? Assume you were monitoring wideband so any mixture related problems would have shown up.

[griffdude]

350matt said:

260ish it was pulling on the middle curves? and it then reverted back to 220ish after lunch? Test results were all fine no fault with the kit, which is why I suspect ECU or similar

Too much in the pub at lunch???
Howard

[walking hormone]

griffdude said:

Too much in the pub at lunch??? Howard

surely 260 at the end of the first test session and 360 by the end of the pub session?

[v8 racing]

Matt if its any help i have just had a very similar problem on the dyno, i built an engine that would normally make 300 bhp but after running it in only made 220 and this was on a carb out of interest, no misfire's fuelling was perfect just pants on the bhp, anyway cut a long story short it was the dizzy or something inside it? i plonked another dizzy in and it instantly made 302 bhp, i tried to find the problem with the old dizzy but just doesnt seem like there was anything wrong?? advance was great no sticky bobweights etc...... anyway the customer now has a 300bhp and the bin men have a dizzy!!!