popping/misfire?/couching

Post by **cadetchris** » Fri Sep 18, 2009 12:58 pm

since i got the car back on the road, the engine has developed a habit of popping whilst at any cruising speed. when i have the choke hard out, it is as sweet as a nut, when the choke is in and when i am maintaining a steady speed, it pops and couchs and misfires, until i pull the choke out or accelerate.
i have wondered if its the mixture, but after windeing the mixture screw right in (the one underneith the cars, its big, brass and has the jet going through the middle of it)
and driving it for abit, adjusting the carb, driving abit more and then adjusting the carb, this seems to of done nothing to solve the problem.
does anyone have any ideas what the cause could be and a solution.

Post by **bmcecosse** » Fri Sep 18, 2009 1:29 pm

Winding the nut 'IN' will weaken the mixture - sound like it needs richening - which means winding the nut down! But could be other problems - low fuel level in the bowl etc - but does seem mixture related since choke sorts it!

Post by **cadetchris** » Fri Sep 18, 2009 2:53 pm

ah, i thought out was weakening, my mistake. ill go wind it in as far as it will go and have a fettle with it. hopefully it should be sorted

Post by **mike.perry** » Fri Sep 18, 2009 3:00 pm

Set the mixture nut 2 turns down, mark one flat with tipex and adjust up or down a flat at a time to get the smoothest tickover.
If that does not work then you have other problems.

Post by **cadetchris** » Fri Sep 18, 2009 3:48 pm

sorted. turned the nut up and then down 2 turns, was still abit rough, so turned it down another full turn. runs as sweet as a nut now, though i discovered that the exhust is blowing, which will make it sound alot better

Post by **cadetchris** » Sat Sep 19, 2009 8:14 pm

ok, no so sorted. it still coughs and pops all the time. have adjusted the carb again and that didnt make a blind bit of difference. also i ckecked the timimg, which was ok, so i am officially stumped to what it could be

Post by **bmcecosse** » Sat Sep 19, 2009 8:59 pm

So - it goes from 'sweet as a nut' to 'no so sorted' overnight ?? Strange! maybe you need to look at the condition of the carb/manifold gaskets etc etc. And - the blowing exhaust will mess it up - so sort that out first!

Post by **cadetchris** » Sat Sep 19, 2009 11:15 pm

allow me to shed some light in this, yesterday after fiddling with carb and running it through the village 5 times, it ran fantastically with no complaints.
however today it ran like a bag of nuts in a washing machine with a constant mis/backfire.
i think it ran good yesterday because the engine had warmed up, and today it was cold on both occassions, hence the bad performance.
i have sorted the exhaust, but still it has this persistant cough/popping/misfire

Post by **bmcecosse** » Sun Sep 20, 2009 9:36 am

Get it warm and see if it's ok!

Post by **mike.perry** » Sun Sep 20, 2009 12:55 pm

Have you checked the carb. piston is dropping freely?

Post by **cadetchris** » Sun Sep 20, 2009 1:38 pm

right, bought a timing gun and discovered the timing needs retarding by aprox 2-3 degrees. this is out due to me changing the timing chain a couple of weeks ago.
how does one retard the timing?
the workshop manual is typically tosh when it comes to this.

Post by **eastona** » Sun Sep 20, 2009 2:15 pm

1. Advance it on the micro adjust until it just pinks going up a hill in a high gear. Then retard it a couple of clicks until it doesn't. Bingo it'll be fine. Don't bother with a timing light.

Note: in an earlier post you said the timing was fine, then bought a timing light and said it was out 2-3 degrees. Was the clamp tightened, has it moved or was it not really OK? How were you checking it before?

2. Check the choke is returning to the "fully off" position when it's pushed in.

3. The mixture adjustment should be done in small stages once the initial adjustment (i.e. right in then back off two turns) is done. One "flat" at a time as Mike says.

With choke when it's cold it should run fine. You don't need choke for too long though. A few gentle miles and it'll be nice and warm.

It's always best to check the basics, points condition, gap, plugs, rotor arm etc before tuning the timing and carb.

Has it run well since the timing chain was out?

Andrew

Post by **cadetchris** » Sun Sep 20, 2009 2:20 pm

when my dad drove it after i did the timing chain, he said it was "hunting". not knowing what it was, i ignored him and carried on as normal. however its constant misfiring is really doing my nut in, so considering i have to drive it everyday to work it needs fixing

Post by **bmcecosse** » Sun Sep 20, 2009 3:11 pm

Ahh - so now we hear the timing chain has been changed! Are you SURE you put it back on correctly ?? If it's one tooth out - it will never run properly! If interested - or not ABSOLUTELY SURE you put it back on correctly - I can list up how to check.
And btw -the method above for setting the ignition timing is spot-on, timing gun is big waste of money! You have no idea where to set the timing - any figures quoted are years old and were in the days of 'leaded' petrol! They are completely irrelevant today. 'Not quite pinking' is absolutely the way to go!

Post by **cadetchris** » Sun Sep 20, 2009 5:04 pm

i am 100% i put the chain back on right, but its probably worth checking that its 1000% on right

Post by **bmcecosse** » Sun Sep 20, 2009 6:41 pm

There is a way to check - only requires taking the rocker cover off. Do you have a dial gauge - or just feelers ?

Post by **cadetchris** » Sun Sep 20, 2009 7:29 pm

i have a set of traditional feeler gauges

Post by **bmcecosse** » Sun Sep 20, 2009 11:14 pm

So - rocker cover off - spark plugs out - turn the engine so #4 cylinder is firing - both valves will be closed -and set it exactly at Top Dead Centre. Looking now at #1 cylinder - the two valves will be slightly open (this is the overlap at TDC) , if the timing is right they will each be open by exactly the same amount. If you had a dial gauge - you would use it to measure how far each is open. Since no dial gauge - you need to slacken off the valve gap adjusters on both valves until there is the slightest of gap at each valve - check with say 5 thou feeler. Now crank the engine over one turn - and measure the valve gaps now on that #1 cylinder - they should both be the same at ~ 40 thou or so. The value doesn't matter - but they should be the same! If not the same (within 5 thou) - then the camshaft is not timed in correctly. Simples !
Be sure to reset these valve gaps before running the engine !

Post by **cadetchris** » Mon Sep 21, 2009 1:10 pm

thanks, ill do that this afternoon

Post by **bmcecosse** » Mon Sep 21, 2009 5:28 pm

Let us hear how you get on!