Carburettor installation and troubleshooting guide from The Carby Shop

Dirt that has been freed-up by moving the fuel line will finds its way into the carburettor and cause flooding.

This will help the filter start clean and also remove dirt and grit that is in the system.

Lines and hoses must be in good condition and properly fastened. Any leaking can give the appearance of a carburettor problem.

When you install the carburettor compare it with the one on the vehicle. Make sure all switches, solenoids, linkages, vacuum lines are the same and transferred from the old carby.

To prevent vacuum leaks and carby contamination, clean thoroughly the mounting surfaces of old gaskets. DO NOT use sealants or silastic silicone when installing base gaskets under carby. Tighten nuts evenly in a criss cross pattern. DO NOT over tighten as damage will result. Vacuum lines are the source of many vacuum leaks. If they are hard and brittle they must be replaced. Replace them one at a time, matching old with new.

All carburettors have been fully tested. They had to pass rigid testing before leaving the factory. If engine performance problems occur after installation be sure you carefully check the following list of possible causes:

a) Engine must be at normal temperature and choke fully opened.

Using a tachometer adjust idle 50RPM above manufactures curb idle speed.

b) Setting the idle mixture is best done with a vacuum gauge. Plugged into a direct vacuum port on manifold or carby base. Turn mixture screws inwards equally until vacuum reading drops, then screw out to obtain highest smooth reading. If vacuum gauge is unavailable, using a tachometer idle will drop & when screwed out will increase to specified idle speed. 

a) Is there fuel to carby, low fuel pump pressure, clogged fuel filter or lines? - Assuming that the fuel tank is full!!      

 If there is fuel in the carby, check for flooding, if it has ,press the accelerator flat to the floor & do not pump, keep holding down until engine starts & clears.   

b) Check electrical system for spark, remove plug lead & test for spark at spark plug, check or replace coil, condenser, rotor, distributor cap, high and low tension wires, modules. 

Flooded 

c) Engine compression – check each cylinder.

  

a) Engine is started and fuel flows over the top of the carby and pours in intake manifold, this is generally caused by either dirt or contamination between needle and seat or stuck float, a light tap on the fuel inlet or blowing air into the fuel inlet will sometimes cure this condition. If this does not, call us.

b) The engine is shut off and fuel drips down the barrel(s) of the carby & is hard to start. Fuel has been forced past the needle & seat.

Check fuel tank is not pressurising fuel lines, noticeable if fuel continues to flow under pressure when the fuel line is disconnected from carby. Back off fuel tank cap to relieve pressure & check venting for blockage or canister.

c) This condition can also be caused by the fuel line being located too close to the heat source. This causes the fuel in the line to expand and be forced past the needle and seat causing flooding. Also fuel can boil inside the carburettor as a result of missing insulator gaskets beneath the carby. A heat riser stuck in the closed position will also cause the fuel to boil when the engine is hot.  

d) Excessive fuel pressure can also be caused by a defective or worn fuel pump causing flooding. Check pressure by referring to manufactures specifications.

e) Flooding into secondary throats is generally caused by throttle butterfly not completely closing. (Engine will also be running very rough).

f) Flooding while engine is running, not over the top but through the booster venturies can be caused by vacuum leaks, incorrect timing, faulty idle solenoids, blocked idle circuit, incorrect idle mixture screw in too far, or idle setting too high. Check with vacuum gauge, secondary shaft slightly open.

a) All the items listed under hard starting.

b) Mounting gasket improperly installed.

c) Heat riser valve operation. & EGR sticking

d) Vacuum leaks. Check all diaphragms including vacuum advance on distributor should hold vacuum when suck on. Manifold leaks, brake booster, PCV valve not working properly.

e) Idle mixture and speed adjustment should be set to vehicle manufactures specifications. Check for flooding through venturie’s secondary shaft when slightly open.

f) NO IDLE – blocked idle jet, idle solenoid not working or incorrect voltage.

Double wire solenoids can have bad earth through wiring system

It is nearly impossible for a carburettor to cause a vehicle backfire. 90% of carburettor problems are caused by electrical faults. Make sure that the plug wires are properly and correctly attached. Check ignition voltage to and from t he coil and complete ignition system including the ignition switch, distributor cap and rotor. A bad vacuum leak can cause a mixture to lean out enough to cause an engine to backfire. Check the manifold vacuum with a vacuum gauge, this can show many engine faults, leaking, burned or stuck valves, a worn camshaft or timing gears, incorrect valve settings.                                                                                                                                                                      

a) Check for proper EGR operation.

b) The EGR should be closed at idle and when engine is cold.

c) Check the distributor and timing, make sure the distributor advanced mechanism and vacuum advance is functioning properly.

d) Check manufactures specifications and check again for vacuum leaks. Check accelerator pump linkage is not bent or out of adjustment from shipping or installation.

e) Check accelerator pump discharge inside the carburettor is strong and consistent. Some leather accelerator pump caps must be soaked for about 12 hours to function properly, especially if used with LPGAS.

f) Check for clogged air filter and weak fuel pump.

g) Check for clogged exhaust system, check carbon canister and carby venting. Check fuel tank venting systems.

h) Carburettor may require re-jetting to suit your particular engine.

a) All items under POOR IDLE.

b) Clogged or inoperative gas tank venting carbon canister blocked.

c) Dragging brakes.

d) Clogged air filter.

e) Low tyre pressure.

f) Automatic transmission malfunction.

g) Wrong or malfunctioning thermostat.

h) Choke not opening completely when engine is warm.

i) Restricted exhaust system.

j) Incorrect fuel mixtures, carby may require rejetting to suit individual engine.

k) Faulty distributor and ignition systems.

l) Poor driving habits.