My next engine WILL be a Chevy, or a Ford, or ......

[Paul B]

Having recently spent some £500 on a new Weber 500, a new Edelbrock manifold, a used-but-good dizzy and coil pack and a carb rejetting kit from RPI, I STILL have this annoying misfire at idle on my Rover 3.5 motor!!!!!!!

I have now swapped ALL the bits of ignition and carburetion system out. The used dizzy dropped straight in and ran like it belonged there, and I did the 'performance mod' on the new coil and amplifier pack, cutting out all but the actual amp, and fitted it, http://www.v-8.org.uk/forum/viewtopic.php?t=78

And it STILL has this fart/misfire at idle.

I know it is not exactly the end of the world, but it just bugs me that it doesn't run as smooth as an eight should do. All I can think of that's left is either worn v/v guides or a cracked head. Can worn guides be diagnosed merely by pushing the valve stem sideways while the head is still assembled, or is it not an accurate method?

Anything I may have missed that could cause the misfire? I don't think it's on one particular cylinder and seems to move from bank to bank occasionally.

[racer]

And it STILL has this fart/misfire at idle.

I know it is not exactly the end of the world, but it just bugs me that it doesn't run as smooth as an eight should do.
Anything I may have missed that could cause the misfire?

I have found, over much time and frustration, that all Lucas distributors made for this engine are iffy, deliver a spark that matches that and they get worse over time. Problem is we never know that until we move elsewhere. We take the poor stock spark as a given

95% of the time any firing issues are cured when you put in a decent system from any other source. The Mallory Unilite is inexpensive and always works. (Though I am not thrilled with their Dual Point.)

If complete precision is wanted, a crank trigger is the way to go and if you are looking for a great burn low down..you will be surprised at what a £30 Buick dizzy can do delivering a fat MSD 6AL spark.

The only time I tried a "amplifier pack" with a 35DM8, the stutter got worse.

racer

[Paul B]

And it STILL has this fart/misfire at idle.

I know it is not exactly the end of the world, but it just bugs me that it doesn't run as smooth as an eight should do.
Anything I may have missed that could cause the misfire?

I have found, over much time and frustration, that all Lucas distributors made for this engine are iffy, deliver a spark that matches that and they get worse over time. Problem is we never know that until we move elsewhere. We take the poor stock spark as a given....

.....The only time I tried a "amplifier pack" with a 35DM8, the stutter got worse.

racer

Yes, I've heard that before somewhere; regular sparks dropped at low revs, but surely the company would have done something about it if they knew about it? Hmm, maybe not, hence the reason we don't have Rover any more, or a British car industry. Joe Lucas 'Prince of Darkness' didn't get his name for no good reason

The amp pack is the original, just trimmed a few wires off. Hope I got the correct ones, though it seems to run as 'well' as it did before I changed it out.

[IanT]

I feel for you Paul, I've been following your problems here and on the NSRA forum - might even have chipped in with a suggestion or two. I have a RV8 with a slightly rough idle but I wouldn't call it a misfire, the engine just 'rocks' a bit every few seconds.. gradually sorting out timing has helped, a 1" carb spacer helped a bit I think, new plugs, wires, etc..

Have you tried testing with a vacuum gauge? Check out this page to see what a bit of old-fashioned vac gauge reading can tell you about your engine without tearing it apart..

http://www.centuryperformance.com/vacuum.asp

[Paul B]

I feel for you Paul, I've been following your problems here and on the NSRA forum - might even have chipped in with a suggestion or two. I have a RV8 with a slightly rough idle but I wouldn't call it a misfire, the engine just 'rocks' a bit every few seconds.. gradually sorting out timing has helped, a 1" carb spacer helped a bit I think, new plugs, wires, etc..

Have you tried testing with a vacuum gauge? Check out this page to see what a bit of old-fashioned vac gauge reading can tell you about your engine without tearing it apart..

http://www.centuryperformance.com/vacuum.asp

I put a vacuum gauge on it several times, and it pulls 20" of vacuum at idle. I'll check your link to see what it actually means.

I think my 'misfire' might not be as bad as I once thought, as I have a stiff engine 'bar' to stop the motor moving on its mounts, so that may transmit the 'rock' enough to make it feel bad. I may actually disconnect it temporarily and see how things feel then.

A plastic heatproof carb spacer will be a good investment, as the carb gets too hot to touch sometimes, with manifold heat working its way up.

[Robrover]

I suppose you've tried swapping the step up springs around in the carb?

Seems though this may be more ignition related. I run an early Lucas SD1 dissy (Opus) with a modified advance curve and Lumenition coupled to an MSD 6A amp and Blaster 2 coil. Even with a cam and big valve heads it idles smooth down to 600 rpm when warm.

Worth checking the connections on all your plug/coil leads at both ends, use a genuine Lucas rotor and dissy cap, and route the leads separately so there's no chance of cross firing.

[Paul B]

I suppose you've tried swapping the step up springs around in the carb?

Seems though this may be more ignition related. I run an early Lucas SD1 dissy (Opus) with a modified advance curve and Lumenition coupled to an MSD 6A amp and Blaster 2 coil. Even with a cam and big valve heads it idles smooth down to 600 rpm when warm.

Worth checking the connections on all your plug/coil leads at both ends, use a genuine Lucas rotor and dissy cap, and route the leads separately so there's no chance of cross firing.

This is a new carb Rob, just fitted, still misfires like it did with the old setup. I've had two new sets of plug wires, a couple of dizzy caps, another dizzy, not new, but it works, another coil, amplifier etc. Plug leads have been routed several different ways. Some days it seems okay, some days plays up a lot, I'll sort it, eventually......

I'm going to relocate the amplifier box, modify it, as I'm not sure if it is getting the good earth it apparently needs. That'll be annoying if it is as simple as that!