I've been trying to check the timing on my engine as I failed SVA on emissions. I'm having real trouble getting the gun to pickup from cyl 1, I can get a pickup on all the other cylinders and number 1 will pick up if I pull the lead slightly out of the dizzy cap so that I can see it sparking - although engine note is not different so I think it is still firing when plugged all the way in. Cylinder 1 exhast header does seem a lot cooler than the rest though so I'm a bit confused.

If I clip it on to number 6 (180 degrees out from no 1) the I can see the timing at idle is around 4 degrees btdc when it should be about 8-10.

Any suggestions what might be up?

plug gap?

weak lead? plug gap closed ?

Have take the spark plug out examine it and checked the gap.? --- also take another plug or two out to compare it with.

Also what type of igniton system have you got ? --- the RV 8 was fitted at least 6 different systems from the factory not counting the after market stuff.

The timing being a few degrees out is no big deal and won't have any effect on a single cylinder.

Could also be that No1 spark plug is just plain duff/tracking out, OR the lead is duff(earthing out) near the cylinder.
Swap the plug with another cylinder ( the fault will move to the other cylinder) or just stay put, then its a fault in the lead most likely.

Right, thanks for the advice so far, I pulled all the plugs and they were all a bit sooty so I cleaned them up, the gaps were all ok at 0.8mm. I measured all the leads and they all came out about 9K ohms, so no real difference between them. Put everything back together and still had the same issue, swapped plugs 1 and 3 no better, swapped leads 1 and 3 still no better, adjusted the timing using cyl 6 and engine seemed to run better but still no pickup on cyl 1!

Unfortunately I have the rubbish rv8 ignition system (opus??) but I can't really afford to replace it right now.

Think I will try new leads and cap for now and check the mixture on the carb. And when I can I will properly sort the ignition system. Anyone know if the default mixture on a weber/edelbrock 500 is too rich for a 3.5? I can't imagine it would be but I'm not an expert on these things.

Thanks
Dan

If changing the plugs and the lead has made no difference and you have a good spark at no 1 plug then it might be worth checking the compressions to start with. RV8 lumps can suffer with severe camshaft wear as well which can cause interesting running problems . To check remove the rocker covers and watch the rockers when engine is turned over , all valves should open by the same amount. If everything appears to be OK then look for air leaks on the inlet manifold especially around the port for no1 . Spray around suspect joints with WD40 , if there is an air leak the the engine will suck the WD40 in and run smoother for a second or two

Re jetting of the Edelbrock carb - you need to read this

http://how-to-build-a-pilgrim-sumo.wikidot.com/fueling-system


This might also be helpful

http://how-to-build-a-pilgrim-sumo.wikidot.com/useful-articles-by-membe rs


The OPUS system (no external amp and ballast resistor) really isn't that bad providing that it is all working properly - the downsiode is that it can develop hard to spot intermittent faults when old.

you might get more advice on the problem with No 1 cylinder from these guys
V8 Forum

I am with rusty nuts on this --- check over the valve gear then do a compression test or better still a cylinder leak down test.

[Edited on 28/2/09 by britishtrident]

Thanks for the links, the one on carb tuning is exactly what I need to sort my carb. I think I will have one more go trying to work out what is special about cyl 1 and will rotate the dizzy cap to see if it is that contact. And then I'll just replace the cap and leads cos I really should any way.

Thanks a lot
Dan