head up arse... engine is driving me out of my mind.

[antoine]

the background...
1600 TP, 1.25:1 rockers, 34ict carbs, lecky ignition and fuel pump, everything else stock.


The story...
i went to the rolling road, the timing got re-set... again and after a bit of fiddling we came to the conclusion there is something wrong, its idling on cylinders 3 and 4, but not 1 or 2, but when you get the revs up the other two kick in, it sometimes sounds like its missing at higher revs. so we tried a compression test on no.1 and it was very low.
And i went off to fair bank and craven in scarborough (couldn't help much since so busy but great blokes)
they gave me some workshop space to fiddle with stuff and plenty of time and assistance they probably couldn't afford with their days job list.
the timing was re-set... yet again, and the carbs accused of being the problem, not in the sense that they need setting up, but more that they have never seen a set that worked properly.

so after tweaking things enough to get me home i headed off.

through the gears it was a bit slow, and when the power is let off then put back on it gets a bit jumpy, but then smooths out.

50 mph is registering as about 3000revs,


and I'm slowly loosing the will to live...






after a short stop off for a cup of tea we thought the issue could be with the coil since its at least 30 years old, has a couple of live feeds taken off for ignition controlled gubbins (fuel cut off and pump) and its the two longer HT leads that are struggling, but numb nuts here fiddled with wires and made things stop working so i couldn't check the spark strength. i will sort out the wiring back to the right place and get it going on friday but i just want it to run properly now. any ideas or assistance would be greatly received.

 

[sparkywig]

You did strip, clean and set up the 34s before fitting didn't you?
Also change your plugs, modern spark plugs don't like getting wet with fuel if the engine's not running right.

 

[doz]

You've got low compression yet your looking at the carb? Take a look at ya ratio rockers make sure the clearance is ok. Sounds to me like you've got a couple of tight tappets.

 

[vwvanman0]

Engine needs to be cold to do tappets as well.

 

[BJ1]

With very low compression you are probably running on 3 cylinders. Most likely a burnt valve. Take it out and rebuild the heads before that valve drops into the piston.

 

[antoine]

see all this is what we were thinking to start with, but we did another compression test afterwards and cylinder 1 was showing fine.

yep, carbs were all sorted before i put them anywhere near the engine, i was hoping to not have these issues so made sure valves were propperly lapped, carbs clean and set right, heads fully torqued, rockers mounted measured then mounted again before measuring and mounting again to get clearances bang on.
the spark from 3 & 4 leads is a good fat blue spark, but from 1 & 2 doesnt look quite as strong, iv got some new plugs and a new coil on its way so if nothing else it will rule out that as an option.



christ knows where my timing is now, so im going to have to redo that and re-connect the vac can.


this shitty weather doesnt help the decklid doesnt stop it raining down the arse crack. :roll:

 

[mattd1984]

Running webber 24ict its very common for the engine to idle of 3&4 only. Do a search on google and you will find lots of information.

 

[sparkywig]

Running webber 24ict its very common for the engine to idle of 3&4 only. Do a search on google and you will find lots of information.

Really? Never had a problem with mine.

 

[antoine]

Running webber 24ict its very common for the engine to idle of 3&4 only. Do a search on google and you will find lots of information.

iv heard of them running on two cylinders but surely it would be on opposite sides of the engine and should be ironed out with the timing and mix set right.

 

[doz]

Do 34's run a balance pipe between the manifolds?

 

[antoine]

Do 34's run a balance pipe between the manifolds?

mine do.

 

[sparkywig]

Do 34's run a balance pipe between the manifolds?

mine do.

And mine.

 

[Zcat7]

I had similar symptoms when I first fitted a pair of solex 40s. See this thread -

http://forum.earlybay.com/viewtopic.php?f=4&t=27582

Basically the accelerator pump was flooding the offside bank on idle but all was fine once I pulled off and the revs rose. Don't know much about your carbs or their setup but I thought this might help.

Neil

 

[67panel]

check the contact gap on all 4 lobes cos might have a bent/worn cam in dizzy ,I would also check carb idle jet is ok ,when you adjust it does it make any differance ,and it should tick over on 4 cyl ,idle on 2 with 34s is an old wives tale told by peeps who dont know how to set up carbs.have you checked them with air flow gauge.dont have a balance pipe on mine and there fine 8)

 

[lard]

check the contact gap on all 4 lobes cos might have a bent/worn cam in dizzy ,I would also check carb idle jet is ok ,when you adjust it does it make any differance ,and it should tick over on 4 cyl ,idle on 2 with 34s is an old wives tale told by peeps who dont know how to set up carbs.have you checked them with air flow gauge.dont have a balance pipe on mine and there fine 8)

Don't have a balance pipe on mine and they are o.k. too (touch wood! - do have slight popping on idle but am getting it retuned before MOT and will hopefully solve)

The 2 cylinders thing - isn't it because of the vac signal being weak as it's only from one of the carbs causing pulsing? This is what I read on (iirc samba) and have fitted an anti-pulse valve in line with the dizzy vac line to prevent this...

 

[antoine]

right, a slight update, had a fiddle today, put on a new coil which is giving me a much better spark, the lecky ignition was buggered so went back to points. lovely little bits of engineering, i might keep them just because they interest me.
got everything back up and running then had a fiddle with all the plugs etc...
after accidentally putting plug leads on the wrong bits on the dizzy for 1&2 then swapping them back it ran on all 4. but after revving it it blew out a load of old carbon and dropped back to the same 2 as before.

We have decided its something to do with the valves.


now the question, could it be;
-mismatched rockers, would the tappets still be able to set to the same gap if the rockers were spaced too close or too far from the mounts in the head. as this could stop them opening or closing properly.
-buggered valves, i was told that these valves are made from two separate grades of steel and sometimes stretch. this would obviously cause issues, but this issue had persisted since the engine went in with brand new heads and valves, and had only been run at idle and short periods of revs to set things up.
-the push rods be buggered in some way, everything seems to move when I'm setting tappets but something could be wrong.
-any other suggestions.

everything is sparking, fuel feeding and running as it should other than this, and after checking everything else over this is the only thing i can think of it being.
just not sure what specific problem out of the many options it could be.
Im hoping the engine doesn't have to come back out, and the heads come off, but if it does i will have to take the shit happens approach and just do it.









was nice and smooth when 1&2 kicked in though :roll:

 

[67panel]

MORE LIKING A CARB FAULT IF ITS CYL 1&2 DOES IT GO ONTO 4 WHEN ITS REVED?

 

[antoine]

MORE LIKING A CARB FAULT IF ITS CYL 1&2 DOES IT GO ONTO 4 WHEN ITS REVED?

we looked at the carbs and checked there was fuel. that was the first thing i thought to check, but I'm getting fuel to all four, its an odd one. when we backfired it into running on 4 it ran absolutely brilliantly until we picked up the revs then when it dropped down again we were back to 3&4. i got very close to some fast moving parts to check that one :shock:

 

[doz]

You've got to take a close look at the valves and valve clearances. After that rotate the engine with the cam covers off and plugs out and see if your getting correct amount of lift from the cam. If after that your still stumped it's head off I'm afraid.

 

[ZedBed]

Mate - has this sat for ages? (well I know it has!) and you're running on shitty old fuel? Sounds like that to me - had the same problem with one today.

Easy effortless check - squirt some easy-start up the air filter and see if all the pots fire then for a few seconds. If yes, your fuel/fuel supply is prob, not elec. It's great to narrow these things down. I'd come look just for fun if you weren't so far away...