Mis-fire when hot.

[haggis]

Hi guys, Sat on the side of the road! thought I’d solved my misfire, stripped my carbs, rebuilt them, new needles etc, tuned it and it run like never before, smooth and just fantastic, ( I mean the best it’s ever been) have done a couple of decent drives in it and all fine, but now the dreaded mis fire is back. so ticks over lovely, drives for about 30 mins with no issues, then slowly the misfire comes, until you just can’t drive it. So, along with carbs, new coil, fuel line moved to bulk head, Revotec fan, cold air box and feed to carbs, tappets are spot on, Now the only thing I’ve not touched is the dizzy, I’m running a 22D Lucas on a HC vitesse engine in my Gt6 mk1, ( I know it’s sounded like a mongrel) it does have some wear, ie the shaft moves about 5-10’ in both directions, but I wanted to check if. 
a, if the 22D( tr6) Is ok for this engine, ie advance etc. 
b, if the wear I mention could cause a misfire

c, if I should just get a 123 dizzy for it. 
 

again your help and comments are always welcomed and appreciated. 
 

thanks

hag . 

[NonMember]

(a) The 22D is the one with no vacuum advance, yes? You probably want a 25D. It shouldn't cause major issues but the vac advance gives better economy and probably better heat control

(b) If you're on points, even a tiny bit of play in the shaft can cause problems.

(c) Are you using a mechanical tacho? I don't think the 123 is available with the drive

[Ian Foster]

Hag

If on points, it might well be the condenser.

Replace with a know good one or source a replacement from a reputable supplier/specialist eg. Distributor Doctor.

Ian

[haggis]

Hi guys, electronic ignition ( the lumenition one)  and there is vacuum advance on 22D, with mech tacho. But I’m happy to convert the tacho if necessary for a 123. It’s a definite ‘pop & bang’ mis-fire, cooled it down and just managed to get home. 😅 

[NonMember]

OK, must be the 23D that doesn't have vacuum. It was fitted to some versions of the PI engine.

Pop and bang is suggestive of more than weak spark or bad plugs - those give definite stuttering but no pops or bangs, usually. If you're getting lurch-pop-bang then I wonder whether there's a loose or broken wire somewhere. That would, of course, be one benefit of an electronic tacho, that it will show when the LT side signal disappears. But a 123 won't fix a broken wire unless it's somewhere inside the 22D that you're removing.

[Pete Lewis]

spindle wear can occur on lucas and delco all need a squirt of oil down inside to lube the top bush now and then,

any wear gives the spindle to float and that makes the points gap uncontrolled and misfires abound, if youre on lumenition or any other leccy unit this 

is less affected and accommodates  more slop than mechanical points so its less of a problem.

does your rotor arm have rivet in its sweep plate ???

whatever the dizzy spec it should work in a basic maybe not utopia manner for much of the range of operation

its unusual for ignition problems to develop you either go or you dont   bad connections can introduce high resistance but what have you thats hot and wont work but does work when cold 

    you may be barking up the wrong tree ,   

it hasnt got a sealed non vented fuel filler cap ??

or a fuel line sucking air ?????   

or a pump not delivering the volume to run ???

 

[Waynebaby]

Haggis,

You mention you have a Lumenition ignition system. I had similar symptoms on my GT6 which eventually turned out to be a faulty Lumenition power unit. I swapped this for a new one and haven't had the problem since. The only issue is that a new power unit is pretty pricey, so you'd probably want to rule out everything else before going down that route.

Wayne

[thescrapman]

Do not assume that because you have changed the coil that isn't the fault, I had a Herald dumped on me that had only ever managed about 300yds in the year it had been back on the road, only when I fitted a old coil did I think finally prove the 3 new ones were all duff.

And the duffers were branded ones.

[Pete Lewis]

and add in the crap spark plug problems we now face  .  what are you using ??

and never ignore the disturbance of the fuel system and the breeding rubber slivers blocking the needle valve 

Pete

[haggis]

So thanks everyone for your replies, not sure where to start with reply but here goes,

it’s a magnetronic ignition from lumenition, so no power unit on this one. From the club shop, all fits inside the dizzy. 

the 22D I have has a vacuum advance which is fully working. I sucked it to see. 

standard Gt6 mk1 rear petrol cap, so assuming has a vent, but will check. 

running facet pump and malpassi fuel regulator, not seen any bubbles in filters or glass bowl so assuming no fuel air leak. 

spark plugs are BP5ES NGK, I think, but will need to pull one out to check as they could be BPR’s, in which case, I’m guessing I need to change them? What’s wrong with the R plugs? 

could be the pesky rubber slivers, tried to be so careful with them, filed pipes and everything. But have changed for ethanol pipes with the carb refurb. 

The coil was just warm when I broke down the other day, so don’t think it’s overheating, but will swap it out and maybe put the points back on and double check ignition wiring throughout. 

I’ll let you know what I discover. 
 

thanks

hag 

 

 

 

 

[Pete Lewis]

some say R plugs make no difference , my experience is they give problems  to me the resistive suppression corks up our weeny 22kv Ht  fine on a modern with 32Kv+ 

but any car ive twiddled over the years have solved poor running by replacing them , but now you can add the problems of ngk not being glazed and excess fuel contaminates and the plug conks out

there s no hope   maybe the cars got a virus   ha !!!

Pete

[haggis]

Hello again, Thanks for all your helpful comments. so I’m now looking into the coil wiring with my electronic ignition.  I have a 12v coil which reads 1.5ohms. There are two wires on the positive terminal one red from the dizzy and one white from the ignition. This white wire goes to the main fuse board and then onto the ignition. I can’t find any ballast anywhere but I believe it can be hidden in the system? Should I replace this wire ‘like for like’ ignition to fuse board to coil? If I do a separate feed, what fuse rating should I use? 
I’m assuming I may have a ballasted ignition wire causing my misfire problems?  Or would it not work completely? 
sorry lots of questions, there’s lots of coil wire posts on here already but they just don’t seem to make sense to my tiny brain. 
 

thanks again hag 
 

 

[Pete Lewis]

Hag,

a 1,5 ohm coil is for  6V ballasted system 

you should have a 3 ohm if there is no ballast resistor/ dropper wire etc ( most dropper wired are a dirty white/pink trace  switch to coil +ve)

the dizzy black goes to the coil -ve  make sure the coil polarity is ok ...but................

as you have a  straight white is normally a non ballasted 12v feed  needs a 3 ohm coil

you  have doubled the HT and doubled  the current requirement   by using a 1.5ohm coil  and things like rotors and dizzy caps wont take it for long and the doubled amperage may have cooked the leccy unit ????

Pete

[haggis]

Thanks Pete for the swift reply.  I’ve double checked my coil with a different meter and it’s 3ohm. The white wire is 12v so assuming that is all correct, because I’ve also assumed if it was shown no 6v it would mean I’ve got a ballast resistor hidden somewhere. 
So just double checking, my coil should be a non-ballasted 12v, 3ohm coil? Or should it be ballasted? 
still confused 

Thanks Hag 

 

thanks 

hag

[Pete Lewis]

12v  3 ohm is fine 

 white is 12v    fine 

so its not your problem  !!!!

should you have a ballasted system the points must be closed to energise the coil if left open circuit you will get 12v showing 

and a ballast system has a wire from the solenoid yellow with black trace  to the coil this gives the 6v coil a 12v boost when cranking 

 

Pete

[haggis]

Thanks again Pete, it’s a magnetronic ignition, the one that fits inside the dizzy, so no points. Does that mean ballast not required? 
 

thanks hag 

[Pete Lewis]

i dont think a ballast is ever required  its to aid starts on a cold day with a poor battery state   ( a plonker recovery system)

as you dont have a ballast dont worry about it 

 

[Pete Lewis]

did you check the  coil polarity is correct    white to coil +ve  ???

[haggis]

The white is connected to the positive of the coil, I haven’t done a polarity test as such as I thought that was for coils not marked with a + or -? Mine has clear markings? 
thanks hag. 

[Pete Lewis]

good thats another ..its not that then   ha !!!

i asked a check as the coil can do real silly things when reversed , in the run stop cool run stop get out kick something run ....stop    

Pete

[haggis]

Thanks Pete, ok that all seems fine, gonna try replacing the magnetronic with points next. I did have some coil/heat problems early on when I fitted the electronic ignition, just wondering if I’ve caused a problem with the unit. 
 

thanks again. Hag 

[Pete Lewis]

going back to points will need the timing checking again

pete

[haggis]

Hi all, so I decided to take it to work today, loaded tools in the boot, hoping for it to misfire and stop to check as many things as possible to determine cause ( well it was a nice day and I was not in a rush) it performed well until about 30 mins into the journey, then started to misbehave as expected, now it was hot today 24.5’ I managed to keep it going by keeping the revs below 2000rpm and accelerating softly and it kept going for some time until I got home. This evening in the cool night air I took it out for an extended drive, no problem at all, behaved perfectly, so I’m figuring this is definitely heat related. I’m using a Revotec fan on a Ali rad, with the fan coming on at 92’, I’m going to try it out with fan coming on a lot earlier and see if this makes a difference or I do have the original fan I could fit, just wondering on the general view on fans? Original or electric, what’s best? 
 

thanks hag 

[Pete Lewis]

 +1  for mechanical fan keeps a air flow all the time , and at +30 mph the ram of air reduces the horses to drive it 

Pete

 

[Bfg]

On 27/05/2020 at 21:25, haggis said:

it performed well until about 30 mins into the journey, then started to misbehave as expected

This is a common issue on the old Sunbeam motorcycles I'm an enthusiast of.   And on those bikes it's because the coil is failing or has been swapped for a modern one ..which because it is smaller - overheats.  Particularly the case as the coil (on the Sunbeam) is situated within a dry electrical box with no through-ventilation.  If you stop and let the bike coil cool down for half an hour then you can ride on again ..but it will falter after another 20 minutes or so, depending on ambient air temperature.  In cool evening air the darn thing is fine.  The vehicle's wiring is fine and the coil itself also checks out fine ..on the bench, because it's cool.

Anyway to test the theory for free on your car - simply try moving its coil (temporarily) to somewhere where the air flow is steady and cool.  If you're not driving in the rain, or off road rallying - there are usually plenty of options. 

Hope that helps, Pete.