I can get the engine to run at one speed and load okay, but it won't run right if I try to speed it up or slow it down.
This is probably caused by the idle screw being open too far, and the load screw turned in too far. This wrong combination will run the engine at one speed and load. You should close off the idle screw completely, open the main load and get the engine running okay at governed speed. Slowly reduce the speed and as the engine tends to run a little rough, open the idle needle screw just enough to make it run smoothly. Keep working the speed down and keep the idle needle screw adjusted until you reach the desired idle speed.
My engine was idling too fast so I closed down on the idle mixture screw to reduce the speed but it runs rough.
Never attempt to control idle speed with the idle mixture. Idle speed should be controlled with the idle stop screw near the governor. This adjustment controls the throttle butterfly valve opening at idle and in turn the idle air flow. At that air flow, always set the gas idle mixture screw for fastest speed.
Engine runs but won't come up to full speed or power.
In most cases poor power is caused by a mixture that is too lean. This lean mixture is often caused by too many pressure regulators in the system or some small or restrictive fitting causing poor flow. Almost all conversion kits are designed so that the engine will loosed power if the load adjusting screw is opened too far. Our propane conversion kits are made to connect to full propane tank pressure. If you want to install the conversion kit by connecting into a pressure line at a reduced pressure or low pressure, call us.
I have a vapor withdrawal kit and the engine runs fine for a while and then frost starts to form on the regulator. Is it possible the vapor pressure reduction and flow is causing this?
No. Frost is always caused by drawing liquid from the tank. Your tank may be over filled or oriented wrong.
Engine won't start or is hard to start.
More starting problems are caused by over priming or dirt on one of the regulating seats causing gas to leak through. If propane or natural gas make up more than 10% of the fuel air charge, the spark plug will not ignite the mixture, it is too rich. Propane and natural gas require from 50% to 100% higher temperature to ignite a charge as compared to gasoline. The ignition must be in good shape. You might try changing the spark plug gap to around .025
Starting has never been a serious problem when dealing with single fuel alternate fuel engines. However, with dual fuel applications, especially those under 250 cid, there are many factors that can contribute to hard starting. These are:
1. Vacuum and air leaks
2. Incorrect carburetor sizing
3. Improper idle mixture adjustment
4. Over richening by start assist valve
5. Incorrect location of carburetor, regulator and or fuel lock
6. Improper location of electric fuel lock head
7. Incorrect spark plug gap
8. Cold ambient air temperatures
9. Incorrect starting technique
10. Poor engine condition
Vacuum and Air Leaks
In dual fuel applications on small displacement engines, an air leak, which would not bother a larger engine, becomes critical, especially at cranking speed. Any leak downstream of the air gas valve will reduce the amount the valve will rise off its seat during cranking.
In extreme conditions, air enters through the leak during the entire stroke, while the gas valve is lifted only during part of the stroke. This creates a mixture too lean to burn. A primer may furnish the added fuel around the metering valve to allow the engine to start, and with more numerous intake cycles the leak may be overcome.
Vacuum leaks may be detected by spraying gasket sealed surfaces with a soapy solution. If a leak is located, the engine will speed up due to the richer mixture. This technique is quite effective around the gasoline carburetor area. Air leaks may also be found in the engine, through intake valve seals or past rings, which are not seated. The orifice in the PCV valve, which is open during cranking and closed under vacuum, can add a sizeable amount of air. Be sure the PCV valve does close properly after the engine starts.
It is important to correctly size the air flow capacity of the mixer to the engine requirement. Use of a mixer that is too large for the engine displacement makes idle adjustment extremely sensitive. When the larger mixers are applied to smaller engines, enrichment for acceleration or power occurs too high in the RPM range to be practical. The small engine cannot lift the large air valve quickly or as high as a larger engine will.
Idle Mixture Adjustment
Correct idle mixture adjustment is critical to ease of starting. This is compounded if the mixer is over sized for the engine. When the idle mixture (air bypass) adjustment is closed, the air valve will open farther at cranking. Thus, the air flow volume remains the same but gas flow is increased.
If the engine starts hard, check the idle mixture adjustment, following this procedure: Tighten the idle mixture screw in. If the engine starts more easily, slow the engine down while adjusting the idle mixture to prevent stalling from an over rich mixture. Setting the idle mixture to the best idle (high vacuum) cold will give a reasonable lean but satisfactory mixture after the engine warms, however it should be adjusted to specifications in the fuel mixture adjustment section.
Start Valve Enrichment
Use of the SV start assist valve for priming during cranking is helpful. However, on engines two liters and under, a restriction such as the Impco J1-20 (1/16" I.D.) should be used. If these are not available, a spark plug nut, approximately 1/16" I.D. pushed into the hose will prevent over priming.
The sizing of the orifice to the engine can be checked for accuracy by energizing the SV valve separate from the starting circuit. When activated with the engine idling, it may slow the speed or actually kill the engine. However, if by opening the throttle it will start in a turn or two, the orifice is satisfactory.
The SV should always connect to the air valve vacuum, not the intake manifold
Location of Components
Mounting the converter and fuel lock off the engine is desirable when carbureting 4 cylinder engines. The vibration of the engine moves the converter rapidly back and forth while the secondary diaphragm assembly tends to stay still. This causes the gas pressure to pulse, and can cause excess fuel consumption. The added weight of an LPG mixer and adapter on a gasoline carburetor, if not properly braced, can combine with the vibration of a 4 cylinder engine to cause the gasoline carburetor fasteners to loosen, creating air leaks.
Electric Fuel Lock Connection
Attaching the electric fuel lock vacuum switch power lead to an ignition coil terminal often leads to starting difficulties. The coil terminal is a weak source of current, and having the fuel lock's power lead attached to it robs the ignition system of needed amperage.
Incorrect Spark Plug Gap
Spark plugs should be in good condition and gapped to factory specs. A protruded nose plug is helpful if it will clear the piston at the top of its stroke. On smaller engines a .025 gap is usually helpful
At very cold ambient temperatures -30 F -34 C or below, there may be insufficient vapor pressure in the fuel tank to supply fuel to the converter / regulator, resulting in no start or hard starting. Another condition, which may prevent starting in cold weather, involves over priming. If this condition is suspected, attempt to start the engine with the primer disconnected. The primer can be disconnected by removing the electrical connector or by pinching the fuel hose.
Incorrect Starting Technique
Over cranking the engine, especially in cold weather, causes over priming and flooding, a common starting problem.
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