Pinto getting hot on 2 cylinders

[mk2maniac]

Evening,
Just fitted a new cylinder head to my 2.4 pinto which is running split weber 48's. When starting the car up the manifold on cylinders 2 and 3 are getting so hot the manifold is starting to glow just on 2 and 3. I've checked for air being drawn in on the inlet manifold but nothing, the carbs and exhaust manifold have been on the previous head with no issues.
I've been told that retarded timing would cause this but its only two of the cylinders so I've drawn a blank.
Any help much appreciated

[Graham]

Evening,
Just fitted a new cylinder head to my 2.4 pinto which is running split weber 48's. When starting the car up the manifold on cylinders 2 and 3 are getting so hot the manifold is starting to glow just on 2 and 3. I've checked for air being drawn in on the inlet manifold but nothing, the carbs and exhaust manifold have been on the previous head with no issues.
I've been told that retarded timing would cause this but its only two of the cylinders so I've drawn a blank.
Any help much appreciated

everyone seems to think a glowing manifold is retarded timing, it can be but its often just a high idle speed, its quite possible cylinders 1 + 4 are running a bit richer, thus cooler.

below we took a picture of this engine doing a dyno run with the lights off. theres absolutely nothing wrong with that engine it makes a healthy 175bhp, but even in that picture the manifold branches are not all exactly the same colour

[mk2maniac]

When I got the engine started I got my infrared heat gun out to measure the temps 1 and 4 were around 130deg and 2 and 3 were 450 plus within 30 to 40 seconds of running.
I pulled the spark plug out of no 3 and the electrode and the top of the piston had a white deposit on them.

[katana]

Correct me if i'm wrong but when running splits - one carb barrel serves 1 & 2, and the other carb serves 3 & 4? If so that would seem to rule out carbs. Also if this set up was running ok on a different head recently that would reinforce that diagnosis. An ignition problem also seems unlikely unless 1&4 are actually running badly so making 2&3 look hot? Pretty unlikely though. That leaves the only other thing that's changed - the cylinder head! So check timing, valve clearances and piston to valve clearances as you may have clouted a couple and they aren't seating?

[Graham]

on splits i wonder if it could be charge robbing related, so i still wouldnt rule out intake air leaks, especially around the misabs. if you look at the firing order cylinder one fires after two and four after three, so the cooler running cylinders fire after the hotter ones

[Miniliteman]

Is the engine running rough/uneven or smooth and normal on all 4?

[onecamohv]

what manifold is it?
Id say Graham is on the money with charge robbing
a poorly designed manifold can easily cause this problem, and the fact that its on the two inner cylinders of a split manifold is where i would definitely be looking first.
Ive seen yanks before (im actually nearly sure it was at esslinger on a pinto even) make deflector plates inside the manifold to get the exhaust temperatures equal as they were way out

[mk2maniac]

Correct on the carbs, 1 choke on one carb serves 1&2 cylinder the other carb does 3&4. I've checked valve clearances and all seems in spec, carried out a compression check, cylinder 1 254psi cylinder 2 245psi cylinder 3 245 psi cylinder 4 249 psi.

[mk2maniac]

The manifold is a dave brooks splits manifold

[mk2maniac]

Seems to be running fine, I'm not letting it run that long as the issue I'm having with the primaries getting hot

[katana]

If it was charge robbing - why didn't it do it before? That's the limit of my diagnostic skills and as the dragons say 'I'm Out!'

[Graham]

Seems to be running fine, I'm not letting it run that long as the issue I'm having with the primaries getting hot

but are they? what was going on when you saw them get hot, were you bedding the cam in? was it running fast?

glowing manifold branches isnt actually any real concern, unless its at a normal idle speed

[Miniliteman]

but are they? what was going on when you saw them get hot, were you bedding the cam in? was it running fast?

glowing manifold branches isnt actually any real concern, unless its at a normal idle speed

It is when 1 and 4 exhaust are 130 degrees and 2 and 3 450.

[mk2maniac]

but are they? what was going on when you saw them get hot, were you bedding the cam in? was it running fast?

glowing manifold branches isnt actually any real concern, unless its at a normal idle speed

Yes, I'm running in the cam so the idle is up around 2000rpm. I'm starting to think its drawing air in from somewhere, as I was trying to balance the carbs with the syncrometer the idle screws on the sides of the carb were nearly off and the revs were not dropping, although it doesn't make sense as to why 2 cylinders are hot.

[mk2maniac]

Something that was also carried out to inlet manifold (which I forgot to mention but have spoken to brooks about it who said it wouldn't cause the issue) is on the splits manifold there is a balance tube??? I think its called where there was a hole each end on the inside where the carbs bolt to I have had welded up. Spoke to mikeanics who said its something they have discovered recently that causes running on issues but smooths out idling when they are blocked off. Is this the issue of unequal charge to each cylinder? I'll try to post a pic of the manifold so you can see the balance tube

[Sidways93]

As you’ll be aware, there are many many people running splits using the same manifold so I can’t see it being that. The balance tube is similar to what you’ll see on SU manifolds, I was under the impression it’s better with it than without certainty for road cars but again can’t see it causing your issue. I run a single IDF on a one off Holbay manifold that works the same way I.e feeding 1&2 off one choke, 3&4 off another and has no balance tube, don’t suffer any issues from it.

Is the new head a Brooks one?

Cheers

[Miniliteman]

Is it running on a distributor or a DIS system?

[mk2maniac]

As you’ll be aware, there are many many people running splits using the same manifold so I can’t see it being that. The balance tube is similar to what you’ll see on SU manifolds, I was under the impression it’s better with it than without certainty for road cars but again can’t see it causing your issue. I run a single IDF on a one off Holbay manifold that works the same way I.e feeding 1&2 off one choke, 3&4 off another and has no balance tube, don’t suffer any issues from it.

Is the new head a Brooks one?

Cheers

Yes new brooks historic spec head. The mod on the manifold is something they've discovered recently I believe so maybe not many have done it. I've spoken to brooks who said it shouldn't cause the issue

[mk2maniac]

Is it running on a distributor or a DIS system?

It's running a h&h distributor , the same as before with no issues.

[HonkyWhiteTrash]

Something that was also carried out to inlet manifold (which I forgot to mention but have spoken to brooks about it who said it wouldn't cause the issue) is on the splits manifold there is a balance tube??? I think its called where there was a hole each end on the inside where the carbs bolt to I have had welded up. Spoke to mikeanics who said its something they have discovered recently that causes running on issues but smooths out idling when they are blocked off. Is this the issue of unequal charge to each cylinder? I'll try to post a pic of the manifold so you can see the balance tube

Did Dave Brooks say that welding those holes up wouldn't cause an issue? If that's the case, I'm surprised, because he puts those tubes in for a reason? I wonder why he puts them in then? I think that sounds likely the issue, particularly if it ran fine before you had the holes welded up.
What sort of cam have you got? Long duration with loads of overlap?