Very high idle ...

[jjbunn]

I've replaced the manifold gasket (didn't use any type of sealant on it, just cleaned the surfaces well), and cleaned the carburetor - a Weber DCOE 45 on a Warneford manifold, setting it to the Red Line recommended initial positions. When the engine starts (on the choke out) it does so readily, but RPMs climb to around 4000. After putting the choke back in, the RPMs don't really change much. After half a minute or so, I turn the engine off as I'm worried about damaging something.

Clearly I have one or more problems, but I'm at a bit of a loss where to start!

The timing I have set very roughly by rotating the distributor so that the engine runs - if I move it much away from the working position, the engine stumbles and dies.

I'd welcome some advice: this is a new problem to me, but no doubt you guys will have seen it before and can suggest what I should do!

Thanks,
 Julian

[EuropaTC]

Hi Julian,

I don't normally use any sealant on the inlet gaskets either. Classic answer for high idle is an air leak somewhere but as you've also had the carburetor apart then there's a few other things I'd look for.

• is the idle adjustment screw fully back so that the throttle will close ? On the same theme, the throttle cable is slack & freely moves ?
• ditto the choke assembly
• are the spark plugs white, normal or dark ? With only a short run time this isn't a definite pointer but a white plug would make me think lean mixture, dark plug too rich for example
• did you remove any jets ? (thinking they might be a loose one)
• float height is important on the 40 DCOE so I assume the 45 is similar. Normally this is set for life but have you checked/altered it ?

From your description I'd be looking at fuel. The fact it starts up easily from cold and jumps to high revs make me think of rich mixtures.  Ignition timing will increase the revs a few hundred or so but I've never seen an increase of 3000rpm from turning the distributor.  I'd leave that as it is while you work through the fuel side of things.

I'll bet it's something simple and you kick yourself when you find it 

Brian

[jbcollier]

4000 rpm?  You have too much air getting in, period.  Rich/lean mixtures, timing, float height, etc mistakes will not result in 4K.  Questions:

What are the "Redline recommended settings" ?

Is this a Spanish or Italian DCOE?

Is this a Renault engine with a single DCOE manifold?

Assuming it is a R engine with a single DCOE:

Spanish DCOE:

Idle mixture screws set to 3.5 turns from LIGHTLY SEATED
Idle speed screw 3/4 of a turn from where it just touches the throttle arm

Italian DCOE:

Idle mixture screws set to 1.5 turns from LIGHTLY SEATED
Idle speed screw 3/4 of a turn from where it just touches the throttle arm

Idle still fast?  First back off the idle speed screw.  If the idle stays high then you have one of the following:

1) an air leak in the inlet:
- all ports either in use or plugged? (vacuum take-off for the brake servo?, some vacuum ports may be located on the head as well)
- warped manifold (a concrete floor is usually flat enough to use as a guide)
- manifold gasket (OK to use sealant and you should use sealant on metal gaskets, do not use silicone sealant, use hylomar or permatex aviation)
- carb mounts (not tight enough -- some flex required but not much, o-ring misplaced, split or otherwise damaged
- you can use a length of vacuum hose as a stethoscope: stick one end of the hose in your ear and search around with the other end to find the air leak

2) inside the carb
- throttle plates not closing properly due to obstruction, improper installation or twisted throttle shaft (easily done if not careful), remove the carb and check that both throttle plates fully close
- missing internal parts: starter carb air pistons (a DCOE doesn't have a "choke")

3) throttle linkage
- disconnect the throttle linkage/cable to eliminate that cause

[jjbunn]

The carb is pictured here - I don't know if it's Spanish or Italian:



This is on a Renault engine.

Red Line settings are online - but admittedly they don't picture quite the same carb as I have so maybe they are inappropriate.

The carb has new soft mount fittings I installed - perhaps these are too loose, but I did tighten them exactly to the spec. in the instructions.

There are ports that are plugged, on each leg of the Warneford manifold. I didn't notice any others when cleaning it.

The manifold gasket is a new one I got from Steve Veris.

The throttle cable is disconnected, so I think that is not an issue.

I should have also mentioned that the mechanical fuel pump is also new ...

Thanks very much guys!

4000 rpm?  You have too much air getting in, period.  Rich/lean mixtures, timing, float height, etc mistakes will not result in 4K.  Questions:

What are the "Redline recommended settings" ?

Is this a Spanish or Italian DCOE?

Is this a Renault engine with a single DCOE manifold?

Assuming it is a R engine with a single DCOE:

Spanish DCOE:

Idle mixture screws set to 3.5 turns from LIGHTLY SEATED
Idle speed screw 3/4 of a turn from where it just touches the throttle arm

Italian DCOE:

Idle mixture screws set to 1.5 turns from LIGHTLY SEATED
Idle speed screw 3/4 of a turn from where it just touches the throttle arm

Idle still fast?  First back off the idle speed screw.  If the idle stays high then you have one of the following:

1) an air leak in the inlet:
- all ports either in use or plugged? (vacuum take-off for the brake servo?, some vacuum ports may be located on the head as well)
- warped manifold (a concrete floor is usually flat enough to use as a guide)
- manifold gasket (OK to use sealant and you should use sealant on metal gaskets, do not use silicone sealant, use hylomar or permatex aviation)
- carb mounts (not tight enough -- some flex required but not much, o-ring misplaced, split or otherwise damaged
- you can use a length of vacuum hose as a stethoscope: stick one end of the hose in your ear and search around with the other end to find the air leak

2) inside the carb
- throttle plates not closing properly due to obstruction, improper installation or twisted throttle shaft (easily done if not careful), remove the carb and check that both throttle plates fully close
- missing internal parts: starter carb air pistons (a DCOE doesn't have a "choke")

3) throttle linkage
- disconnect the throttle linkage/cable to eliminate that cause

[jbcollier]

Are the spacer plates and o-rings between the carb and the manifold new as well?

John

[jjbunn]

Are the spacer plates and o-rings between the carb and the manifold new as well?

John

Yes, they are. Perhaps I should tighten the carb to manifold bolts up tight just as a test?

[jbcollier]

No, they look tight enough, at least the top ones that I can see.  Are the two hoses going to the centre of the manifold coolant hoses?

[jbcollier]

The photo's a bit small to tell for sure but nuts holding the manifold on look wrong.  Can you post a photo showing how the nuts are holding on the intake and exhaust manifolds?

[jjbunn]

The photo's a bit small to tell for sure but nuts holding the manifold on look wrong.  Can you post a photo showing how the nuts are holding on the intake and exhaust manifolds?

The hoses are indeed coolant hoses - there is a small chamber in the Warneford manifold that they connect to.

Here is a higher res photo of the way the manifold is held on. The nuts are new, the studs original:



The two centre nuts at the top are not really tight as they have nothing to seat to: when I got the car, there were no nuts in that position at all!

There are two other nuts at the top. On the bottom, there are two nuts at the extreme ends, and just under the carb are two barrel nuts tightened with a hex wrench.

I must say, it doesn't feel right, but that's how it came to me.

Here's a photo of what it looked like then:

[jbcollier]

Well that's a right mess.  It bolts to, and flows through, the exhaust manifold flange?!

Do you have a new cylinder head to exhaust manifold gasket (one piece)?

Do you have new exhaust manifold to intake manifold gaskets (2 pieces)?

If you have all those gaskets new, then you need longer studs so you can use special thick washers that allow the centre nuts to properly tighten the intake down.

[EuropaTC]

hmmm.  I think I'd describe that design as a bit of a challenge. 

I'm sure it can be made to work but to my eyes it doesn't look right. Routing the inlet tract through the exhaust manifold plate gives you more surfaces to seal and with the bolting arrangement and the weight of the manifold and weber hanging off the end, it sure has lots of potential for leaks. I'd be tempted to get some lugs welded on to get a proper loading on the bolts.

Air leak is the classical answer and having seen the set-up, you've got plenty of potential for leaks.  But for some reason 4k seems high even for an air leak without getting more fuel in as well.  I'm thinking if the mixture is 14/15:1 at 1000rpm then you're in (or past ?) lean burn technology if you push to 4k with the same amount of petrol. I didn't think our old engines would run that high !  (you live and learn as the saying goes)

I can see you've disconnected the throttle linkage and presumably the stop screw is backed up so I'd be tempted to unbolt the carb and see if both butterflies are fully closed. I assume you've tried pushing the throttle closed with your finger to try and drop the revs ?

Other random thoughts - the carb should be flexibly mounted and from your first photo you look to have the thackeray washers about right, so I wouldn't tighten it up solidly. Is there an external return spring on the throttle ? (although pushing the throttle closed would eliminate that as a potential cause)

I'll be interested to hear when you find the solution, so please keep posting the progress.

Brian

[Grumblebuns]

My S2 has a side draft Weber DCOE45 manifold similar to what you have pictured. The mounting of the manifold appears to be similar also. Each runner is secured by two nuts and studs. There doesn't seem to be anything for the top inside nuts to clamp on to.

My spare parts S2 came with a Hermes manifold and has a more secure mounting system. Each runner is secured by four nuts and studs (see pic).

The country of origin is stamped on the top of the float bowl. 

[jbcollier]

I was going to suggest you'll have to make up special "stepped" washers/tubes so those nuts tighten down on both the intake and exhaust manifolds.  Thankfully Mr GB posted a photo of roughly what's required above.   In your case you'll need a thick washer with a half a thick-walled tube extending to the exhaust manifold.

[jjbunn]

Yes, Grumblebuns' photos are instructive.

I have no gasket between the Warneford manifold and the exhaust flange - should there be one?

Here is a photo from a different angle, where the barrel nuts that secure the bottom of the manifold to the engine are visible. There are no washers - should there be?



I think the throttle butterflies are well closed by default. This is a photo taken when I was cleaning the carb:



Thanks for all the input on this problem!

[jbcollier]

Yes, you need a gasket between the intake and exhaust manifolds!!