Last week I posted about the replacement gearbox and how it jumped the queue for the next post. The post that knocked down the pecking order is this one. It’s about the technicalities of fitting a carburettor spacer or replacing one.

Do you need a spacer, what does it do and what types are there? I aim to answer the questions as well as showing you how to do it. Regardless of this spacer being fitted on a Mustang, the principles are the same for most carburettor based cars, all be it the connections may vary a bit.

Why did I do this in the first place? Well it’s because I can’t go to any car shows, i had cleaned the car and I wanted to do this little project for a while now.

Types Of Spacers:

To work out what spacer style you want you need to understand if you need one in the first place. I have a problem when I sit in traffic in hot weather where the car runs erratically on idle when the temperatures gets real hot. So my research tells me that I needed a thermal barrier to replace the aluminium one I have currently.

There are usually two main reasons to fit a spacer between the carb and the intake manifold.

1) To increase horse power.

2) The carb is experiencing fuel evaporation when the engine gets hot. This causes the engine to run very erratic at idle with possible poor starting when hot.

3) Not really a reason, but fitted just for looks or bragging rights.

Spacers can come in a variety of sizes and styles depending on application.

Wood, the best heat insulator, but it’s porous and will need to be replaced fairly often. Cheapest.

Phenolic Resin. The second best heat insulator. Expensive.

Polymer. Third best insulator and lower budget compared to the phenolic option.

Aluminium. No heat insulation at all. These are very durable and the only type allowed for racing.

Styles:

There are two basic styles of spacer.

1) An open plenum: This style of carb spacer is ideal for maximizing horsepower. Their design will increase the intake manifold’s total area to build more mid-range, high-RPM power. This allows as much air fuel mixtures into the cylinders at medium to wide open throttle as possible.

If you decide this is the type for you, these can easily be stacked to multiply their effect.

2) A 4 hole plenum spacer: This type of spacer will increase the velocity of your vehicle’s air-to-fuel charge by creating a vortex to mix the fuel and air. This means you build up low to mid-range torque and a better throttle response. This style of spacer is most effective when it’s made from phenolic resin or a polymer. Both the phenolic resin and the polymer spacers can also be stacked in the same way as wood or aluminum spacers. But you should check the bore sizes are the same.

If insulation and durability are both priorities, then Phenolic would be a good bet.

Variations of spacer:

There are many types of spacer that can fitted, mostly a variation on a theme. These have slight design tweeks to help the engine at certain power bands or torque curves. These are generally aimed at the specialist tuners and can ramp up in price and complexity.

Sizes & Colours:

The thickness of the spacers can vary from the standards of, 1/4″, 1/2″, 5/8″, 1″, 2″. Of course mixing of thicknesses or stacking can be fine tuned to individual requirements, or even get a custom one made for you. The bigger the spacer tends to increase the horsepower within reason of course.

If you do stack the spacers you will need to be careful with clearances under the hood.

Colours can vary, but are mostly black for the plastic styles, wood is the colour of the wood and metal can be brushed or polished etc. Sometimes the colours can denote the insulation or particular property of the material.

Choices:

I can’t tell you what to fit, that would be based on your needs and what you want it for. I will go on the assumption that it’s a standard style, either open or bored and what ever material or thickness you go for, they are all fitted the same way.

Considerations:

The gaskets can also vary in cost, but I seriously recommend that you get some top quality gaskets as you don’t want fuel or air leaks.

Is there enough clearance under the hood to add a spacer or stacking of spacers?

Are the studs long enough from the intake to go through the spacer AND the carb? If there has been no spacer(s) before you might have to replace the intake studs for longer ones.

Adding a spacer will give you more horse power, but if you have a restricted air flow into the carb itself it may not be worth it!

When you stack spacers, you are actually improving their insulation properties, and at the same time you’re getting more horsepower.

Costs:

The total costs can vary depending on material used for the spacer; metal, phenolic or even wood options all have their own unique properties. I have seen options anything from £10 to £100, choose wisely.

What’s in the pack:

If you buy a kit, make sure the spacer fitting will match with the carb, Holley, Edelbrock, Autolite etc. The chances are that you may have to get the gaskets separately as well. If you are lucky some kits come with longer bolts for the intake manifold.

Background:

I prefer the low down torque improvements and feel of the power delivery (throttle response) that the 1″ spacer provides.

The spacer I had that came with the carb was an aluminium one with it’s own PCV recycle input. This worked faultlessly when moving, but when the engine got hot queuing to get in a car show on a hot day, the heat traveled from the engine manifold up the spacer to the carb body. The carb in turn also got hot and started to vapourise the fuel before it had a chance to enter the intake channels and cylimders. Hence the engine ran erratic, having to slightly rev to keep fuel flowing, this just got the engine hotter. The colder the fuel and air mixture that gets into the carb the better.

My personal choice was to keep the low down torque power but swap the metal spacer for a phenolic equivalent. The phenolic spacer is a special material, a little bit like a brittle plastic or simlar to the old school bakelite material by feel. This material stops heat transfer from the block to the carb. In theory this will act as an thermal insulator or heat barrier between the engine and the carb. Having a good heat barrier will also aid in hot starts of the car as the fuel shouldn’t evaporate during standing.

Tips:

1) Take plenty of photos of what goes where for your own sanity before you pull it apart!

2) If in doubt don’t mess with it. Failure to refit the carb correctly could cause fuel to pump out where you don’t want it and be a potential fire hazard on hot exhaust manifolds. I won’t take any responsibility for any of that. Get a mechanic to help?

3) If this is the first spacer you are fitting you may well need to adjust the carb to run correctly. Get a mechanic to help? If this is a swap out all should be the same, but I had to have a litttle tweak on idle.

Process:

Removing the carb:

This is obviously how the Holley 600CFM carb is removed and refitted. But the principle is the same, wether it’s a Holley, Edelbrock, Autolite or any other manufacturer. The fuel connection, electrical connection (for electic choke if fitted), vacuum advance (if fitted), PCV recycle connection, air filter pan and the throttle fitting.

Removing the air filter:

Unscrew the air filter top and remove the filter and mounting pan. This is exactly the same process if you were just changing the air filter. Most of the time the filter is held to the carb via centre threaded bolt. Once this is removed it will expose the carb and fittings. There should be a gasket that fits between the pan and carb, which needs to be removed, shown on the right hand pic.

Removing the PCV pipe, if fitted.

This small pipe takes excess hot oil vapours from the top of the valve cover and pipes it to the carb to be reburnt as part of the air fuel mixture. Most of the time the PCV valve is just pushed into a grommet on top of the valve cover, the other end is usually connected to the back of the carb or spacer in my case. The end connected to the carb (spacer) may just be a push fit, or held in place via a clip of some sort. Either way remove from the carb (spacer) and pull out from the top of the valve cover.

With the PCV pipe removed check for any damage, splits, perishing or cracks. If all is well, clean out the pipe if it’s clogged ready for refitting later.

You may prefer to do all the cleaning in one go with everything disconnected and removed, but that’s a personal choice of course.

Disconnect the vacuum advance, if fitted.

Disconnect the choke if fitted.

This can be done via a number of variations most common are, manual, water (heater) pipe and electric connection.

Manual choke: This is (usually) a single cable coming from inside the cabin through the firewall to the carb. The picture borrowed from Holley is the white cable on the lower left side of the picture. The cable is either a pull and twist to lock in place, or simply a push pull idea to hold the choke plate in place. The fitting is usually a single screw holding a steel cable which needs to be released. Make a note of where the fitting is secured. A possible way to do this is with a permanent marker or wrap a piece of tape around the wire to mark the location of the original positioning.

Water heater pipe: The hot water pipe from the heater matrix runs alongside the carb to heat a bimetallic strip that in turn opens the choke plate. This can be identified by following the heater pipes coming from the firewall across the top of the engine block, and is held close to the carb’s round choke housing for the bimetallic strip by a clip.

Electrical connection: This is a wire going to the bimetallic strip. A small 12v current is feed to the strip and heats it to rotate the choke plate. This can be adjusted by rotating the housing if you need it more or less aggressive.

Disconnect the Throttle linkage:

The throttle is linked to the carb in a number of ways, most of the time it’s a rod or cable that attaches to the carb’s throttle linkage. If an automatic transmission there could also be another wire that goes down to the transmission box for the kickdown function. This again will need to be disconnected.

In my case there is a rod from the top of the pedal assembly which attaches to the top part of the throttle linkage. In order to make the throttle return to idle there is a spring. In my case there is two springs, one inside the other for safety reasons. If the throttle sticks open you could be in a ride with an accident about to happen. Unclip the springs. Picture below on the left.

The throttle linkage can be held in place by either a nut, split pin, R-clip or similar. Remove the retaining fastener and the throttle rod will be able to be pulled from the throttle mechanism. Two pictures on the right.

All other fittings should now be disconnected apart from the fuel. (If not disconnect them).

The fuel is usually connected via a rubber hose to allow for some movement, and which is connected to the carb by a flared fitting and some sort of clip. In my case I have a “bango” fitting on the corner, where I don’t need to remov the fuel pipe from the fitting. Place a rag or similar to catch any spilt fuel under the connection. Undo the fuel line to the carb slowly in order to catch any excess fuel if removing the fuel line.

Depending on your fitting or option how the fuel is fitted to the carb; the fuel line could be held in place by a number of fittings, single ear clip, double ear clip, jubilee clip or variations there of. If there is no way to disconnect the fitting from the carb itself, you may have to remove the fuel line itself as I mentioned above. Plug or clamp the fuel line to stop any more fuel leakage.

The other option is that the fitting can be removed with the fuel line still attached with my example of the “bango” fitting. A center bolt with a hole for the fuel to travel into the carb, can be removed and the fitting is removed with the fuel line as one section from the carb. The fitting for the fuel entry into the carb sometimes have some form of filter within it. Undo the nut slowly as there should be a small rubber/synthetic seal an “O” ring ans possibly a filter. Bottom right shows the small O-ring being removed.

Check if there is a filter, which may still be inside the fuel bolt opening. Left picture below shows the filter which pushes into the bottom of the special bolt with the hole in it. The right picture shows the O ring inplace. The hole in this bolt corresponds to channels within the banjo to allow to allow the fuel in through the centre.

At this point they can be cleaned or do it at a later date. Pay special attention to the wire gauze filter to remove any debris or blockages.

Removing the carb itself:

With everything now disconnected there will be four bolts one in each corner. They will have washers under the nuts. In one corner near the throttle rod there may be a fitting where the rod, cable mount, spring holders could be held for the throttle. In my case the spring fitting, main pic on the left below. Make a note of the location and remove all the nuts, washers and fittings if any.

Place more rags around the carb as close as you can get it. The carb will hold an amount of fuel in the bowls depending on the carb size, float chambers, double pumper etc. The fuel may spill out when the carb is tipped.

The carb will undoubtedly be stuck in place due to the gasket(s) being being stuck between metal to metal. The tolerance for the bolts through the carb is tight and the carb will need to be lifted up evenly. If it’s stuck a small flat implement to prize up or a gentle tap to dislodge. Don’t whack it with a hammer, common sense. A leather or light rubber or plastic hammer tap could help to start it moving.

If there is a spacer already fittd there remove the carb, then the spacer. If there is no spacer lift the carb up. Picture below shows the gap opening up.

If the gasket comes with the carb so be it. If not, you will need to remove it after the carb is safely out of the way. Place the carb on a surface, with more rags. (Optional).

Warning:

With the carb off the car there will be a large hole, a divided hole, holes (depending on design), where the air/fuel mixture gets sucked into. Keep this clean. DO NOT let anything go down this intake hole. Anything in here will go down the cylinders potentially damaging the engine. Place a clean lint free rag down the hole to block it it, or cover it with masking tape. If using the masking tape remember to remove it before refitting the carb!

Remove the spacer and all gaskets carefully.

The main gasket to the intake manifold could well have fuel or oil or both on it like mine here. Be careful when removing that nothing goes down that intake.

That’s carb off and now time for the clean up and prep. I seriously recommend that new gaskets are used when refitting. You can buy these or make your own like I did depending on your level of skill and confidence. If in doubt – buy them. You can see the distortion of the lower gasket above. The chances of this fitting back together again exactly without leaks just won’t happen to be honest, especially if adding a spacer for the first time. You will need two gaskets for the spacer. One between the top of the intake manifold plenum and the bottom of the spacer. The second on top of the spacer and the bottom of the carb.

Before refitting clean the intake plenum surface to remove any contamination or stuck gasket. Work away from the intake hole towards the outside. Below I used a sharb blade scraper to get it cleaned. Then cleaned the surfaces again with degreaser and a lint free cloth.

Once cleaned thoroughly and the surface should be dry and smooth. Don’t gouge chunks out of the metal!

Now get to cleaning the bottom of the carb to make sure that is also clean ready for the new gasket. Watch out for fuel spillage if tipping the carb up onto it’s side.

While the carb is off the car check all the rubber fittings that block off the additional connection points have not perished or split. Any leak into the carb will compromise performance and introduce poor running.

The spacer should also be clean and smooth on the upper and lower faces before fitting. Make sure the bore holes are clean and free from debris.

Refitting the Carb.

Double check that what ever you are going to clean has been cleaned. Now is a good time to clean all those moving parts on the carb before refitting back onto the engine as it’s much easier off the car and to allow you to see what you are doing. Lubricate the throttle linkage, lubricate the choke plate pivots. Check it all over.

Place one of the gaskets onto the intake manifold. Make sure that it’s fitted the correct way round. The spacimg of the studs is not exactly symmetrical. There should be no ripples or taught sections and should lay flat.

Below is a comparison of the metal spacer with the Phenolic black spacer on top. The black spacer has a very slightly larger diameter bore holes than the metal one below. Most of the spacers have a single way to fit them. The open side is the underside to lay on the gasket. Underside of the spacer is showing here in the pic below.

Place the spacer onto the gasket. The smooth side (top) of the spacer should be facing up as in the picture below.

Now add the second gasket on top of the spacer, making sure it too also fits correctly with no tears, ripples or stretched areas.

Now you can take your carb and gently lower it onto the spacer and gasket. Lower the carb evenly in order to not dislodge the gasket position.

Note of observation:

The old metal spacer had the PCV valve breather attacher to it under the carb itself. With some of the phenolic spacers they may do away with the breather port and use the carb’s own intake port. Below is the comparison of the spacer on the left and the carb fitting on the right. Both connections are still situated at the back. Those who are eagle eyed among you will see that the carb is a slightly smaller diameter and will require a little more tightening to get a good seal. This is fine as I used a jubilee clip as before. The carb uses a flanged end so a push fit should be possible depending on the internal hose diameter itself, but I want to make sure it stays on so I use the clip just to make sure.

Now you will need to secure the carb to the engine intake. Tighten the fasterners and washers finger tight into each of the corners. If you have a spring bracket then replace that as required. Tighten fully with the correct torque settings for the carb in an opposite corners sequence.

How you reconnect the all the linkages and fittings is up to you of course. But, with the throttle linkage out of the way the PCV pipe is much easier to fit.

Refit the mechanical throttle linkage to the carb throttle linkage and refit the springs. Check that everything moves without any snagging or any of the moving parts being hindered under the full motion of travel.

Lubricate any of the fittings that need it with the correct grease or oils. In my case the self locking nut will need a little white grease behind the washers to avoid any sticking, marked with the arrows.

Next up is fitting the electrics back to the choke, this is the single 12v wire.

The fuel fitting (banjo fit) needs to reconnect, ensure that the filters are cleaned and seated correctly when refitting them. Failure to do so could allow debris through or not allow fuel to flow through at all in the worst case scenario. Check that the O-ring is in good condition, not split or perished or you could be introducing a fuel leak. Below is the O-ring seal in place and the cleaned carb internal metal gauze fuel filter.

Vacuum pipe should be a straight push onto the carb if it’s fitted or required.

Finally check that all the connections are in place and secured properly. You can either start the car with the air filter off to see what is going on, or put it back together again.

With everything in place you can start the car. I would suggest cranking the car over for a few seconds to make sure that there is no fuel leaking after the fuel has been pumped up to the carb and fills the carb bowls.

Once you are happy there is no leak and everything is OK, then start the car normally.

1) If there was a spacer there before, you shouldn’t have to adjust anything – as long as it was the same size of course.

2) If this is a new spacer you will probably need to adjust air fuel mixtures and idle for the carb.

3) In rare cases you may have to make some minor timing adjustments.

Time Taken:

Two hours with all the cleaning.

Like I said at the beginning it was after replacing this spacer and going for a test run that I noticed the noise in the gearbox. The two are completely unrelated and didn’t cause the gearbox issue. But there is an improvement in the car’s performance.

This is definitely a worthwhile project if you are having issues in the heat with fuel evaporation, or warm starting problems. If you want a little more power then this is a quick win for relatively little money. However as you have to take the carb off the engine this isn’t for the faint hearted. It’s a straight forward enough procedure, but you need to put things back where they should be. The fact you are playing with fuel lines tells you that you will need to take care of course.

If you mess it up – don’t blame me! 🙂