missfire when cold

Post by **winger300** » Sat Apr 17, 2004 11:38 pm

I'm having a bit of trouble with missfires/backfires when the engine is cold.

It mostly happens at low revs at load, i thought at first it was due to a lean mixture, but i've checked it using my colourtune, and its ok. After 5 mins of driving its then fine.

It started giving me trouble when i change the HS4 carb for the HIF38. Could something else be causing this though?

Post by **Chris Morley** » Sun Apr 18, 2004 2:41 am

Condensation in the dizzy cap? I had this with a Citroen AX (split in the dizzy).

Post by **Cam** » Sun Apr 18, 2004 5:00 am

If it's carb related then the choke might not be coming on properly (or at all).

You say this has only happned when you changed carbs. Change back and see if it disappears, if so then I bet it's the choke.

If the colourtune reads 'ok' do you mean blue or yellow when cold??

Post by **racer** » Sun Apr 18, 2004 8:45 am

Have you got all the joints bolted up tight ,not drawing in air? I had this on another car,but found it dissapeared when hot ,because everything expanded to seal the joints (oo er !)

Post by **winger300** » Sun Apr 18, 2004 10:03 am

thanks for the replies, yes everything is done up tight, the choke does come on, or at least the revs rise to fast idle ok.

The colourtune shows yellow when cold, and when the engine is warm i set the mix using the pin lifting method.

Thanks for the replies, i'll give everything a check over this afternoon

Post by **winger300** » Mon Apr 19, 2004 12:55 pm

changing back to the HS4 fixed the problem.

The problem i think was due to me using the HS4 insualtor block wih the HIF38, therefore only using two manifold studs. Maybe it caused an air leak which was only noticable when cold, but either closed up or went unoticed when the engine had warmed up.

When i bought the HIF38 on ebay it looked like the previous owner hadn't used any insulator block, and had just bolted it straight to the manifold. Is this ok to do this?

Post by **racer** » Mon Apr 19, 2004 1:07 pm

Funny you should mention that........ When I got my hs4 ,Ithought it may work without the insulator ,but ended up making one from 2 pieces 6mm thick plastic ,and a gasket between . Had no probs.The studs have to be spaced with washers under the nuts if you don't use one ,I believe.

Post by **Cam** » Mon Apr 19, 2004 1:43 pm

If there is a scrap-yard near you, then go and get a spacer for the HIF38 from a 1.0 Metro (should be a few about).

Post by **Kevin** » Tue Apr 20, 2004 8:20 am

changing back to the HS4 fixed the problem.

Winger / Racer what air filter housing did you use with the carb.

Post by **winger300** » Tue Apr 20, 2004 10:30 am

i used a K&N cone filter

Post by **Kevin** » Tue Apr 20, 2004 11:45 am

Does that not make it a bit noisy/rorty

Post by **Cam** » Tue Apr 20, 2004 11:52 am

Yes it does, but we like that!

Post by **racer** » Tue Apr 20, 2004 12:51 pm

Kevin,I used a k&n cone,but previous to that used a midget pancake filter

Post by **Kevin** » Tue Apr 20, 2004 6:04 pm

Thanks for that guys, when I get back from holiday I intend to use an HS4 and see if the original air filter unit can be altered to fit, Iwill let you know what happens (sucess or failure)

Post by **winger300** » Sat May 29, 2004 10:53 am

seems as though the missfires haven't gone away.

For about a minute from startup it always misses and backfires when under a light load, if i cain it, then its fine.

I changed the dizzy cap, checked all the leads and changed the plugs. It always needs some choke to start from cold, even on a warm day, could this be a sign to something? or is this normal with an alloy inlet manifold?

The mixture is set correct with colourtune, so im thinking its the ignition. the coil perhaps?

The other thing is that when changing the engine i remember having difficulty putting the dizzy back in, and it would only fit one way, meaning we had to swap the leads around on the cap to get the correct firing order. What effect will this have?

Any ideas?

Post by **rayofleamington** » Sun May 30, 2004 12:17 am

winger300,
Yours sounds identical to mine

I thought it had gone when I changed the points and condenser (I'd already swapped over plugs points leads cap and rotor arm). After 10 days it came back with a vengence yet no missfire after 5 mins / when hot.
I have a few other things to play with yet as it is down on power (any more than half throttle reduces the power

)

If you managed to set the timing OK then it is unlikely to be anything to do with the Dizzy. Moving the leads to the next position is likely to be caused by one (or both

) of the engines having the dizzy drive in the wrong position, however if you can still set the timing correctly it doesn't make any influence - The thing to watch with odd angles of the dizzy is that you didn't mix up the opening and closing of the points and set the timing using the wrong side.

Post by **winger300** » Sun May 30, 2004 10:33 pm

one thing i have noticed is there seams to be a little oil fouling on cylinder 3's spark plug. Its always a little blacker than the other plugs which are usually the correct tan colour. The car is using about a pint of oil every 500miles. Perhaps the plug cannot spark properly until the oil is burnt away?

Perhaps one of those sports coils would provide a stronger spark and sort it out.

Post by **Kevin** » Mon May 31, 2004 10:48 pm

Just a thought guys but your symptons sound a bit like mine at the moment with my different engine but mine has a duff dizzy vacuum unit due to be replaced have you checked yours are fully working ?, mine has been set with an analyiser so basic timing and mixture at tickover are fine.

Post by **winger300** » Mon May 31, 2004 11:10 pm

thats a good question, the whole vacuum unit at the dizzy is a bit wobbly, but why would it be ok once warm?

Post by **Kevin** » Mon May 31, 2004 11:37 pm

but why would it be ok once warm?

Cant answer that by mine runs better when warm.