ZAMA C1Q Carb trouble-No Fuel


Old 08-06-08, 10:09 AM
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ZAMA C1Q Carb trouble-No Fuel

I have a Troy Bilt TB70SS trimmer with a Zama 1Q P18,A carburetor. While trimming it suddenly stopped, as if out of gas, but there was gas in the tank. I suspected the carb was dirty. I tore it down and cleaned all parts. After assembling the trimmer it started using the start assist plunger . When I pull the throttle trigger which releases the start assist plunger, the engine stops and was not getting gas. The start assist has a plunger that appears to close of extra gas supply. I bought a new start assist plunger and a rebuild kit (ZAMA Rebuild Kit RB-52). I replaced the inlet needle, metering lever spring, metering lever, gaskets and the diaphragms. It still won't run except with the plunger start assist engaged. It appears no fuel is being fed into the carburetor with the throttle.
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Old 08-07-08, 12:01 AM
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Check the fuel lines for cracks, pinholes, or other leaks.
Old 08-08-08, 09:08 AM
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I've replaced all fuel lines, as well as cleaning the fuel filter. It appears no fuel in being pumped into the carb.---Thom
Old 08-08-08, 09:28 AM
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2 cycle engines are a bit more complicated tan 4 cycles. Here is a link that may help.

I do not have time to write my own piece but here is something that may help written by Nevada Walrus on another forum:

For a crankcase tester you need a hand pump such as the Mityvac, and get one that does both vacuum and pressure. They come standard as vacuum only. You need a spark plug hole adaptor to connect the hose from the Mityvac. Last you need an old inner tube.

You cut a piece from the inner tube to place between muffler and block and between carb and insulator block. Run piston to bottom dead center and hook up the pump. Pressurize to no more then 10 psi and see if it holds. With piston at bottom the pump covers the entire block by feeding through transfer ports open with piston down.

Then you vacuum the block around 8 "in. HG" scale on vacuum side of gauge. This as well as pressure check should hold steady for basically ever. However a very slow leak will probably not effect much. A rapid discharge will.

The gaskets being checked will almost never leak under vacuum if they do not on pressure. However, the cranks seals can leak in only one direction so if you get a leak in only at only vacuum or pressure the problem is a crank seal.

While muffler and carb are off make sure to inspect the piston for any kind of damage or distress. Any and all tests can test good but if there is damage on the lower half of the piston the pressurizing of the crankcase may not be up to par when piston is going down. The piston must handle this pressurizing without aid of the ring(s).

A 2 cycle does not suck fuel/air into the combustion chamber but into the crankcase. Failed proper compression in the crankcase will not transfer air/fuel through the transfer ports into the combustion chamber. In reality a 2 cycle has a built in blower via the crankcase and anything that lowers that pressure building ability of the crankcase will render the engine either weak or non functioning.

Carburetor and or fuel problems are always the first concern on 2 cycles just as with 4 cycles. That includes the entire system from fuel cap to carburetor insulator block.

You asked about compression. First, use as small a gauge body and hose as you can find. It hard for these little engine to fill and pump up full size automotive gauges. Always crank the engine until the gauge no longer climbs.

Basically any compression check that shows under 90 psi indicates a serious problem. Engine should run but never will be up to snuff. Anytime I find one below 110 psi I'm looking for the reason. A good engine should be 115 to 140 psi depending on 9/1
Old 08-08-08, 12:44 PM
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Airman- Thanks for the info. I paid only 120 bucks for the trimmer, but It has a number of other attachments. It's only 2.5 years old and never been used a lot, like a commercial trimmer. Without buying more test tools I like to use some of the tools I own. I ride a Harley now, before I had a Moto Guzzi which had 4 carbs. I bought a Motion Pro Mercury Carb Synchronizer to tune the carbs. It has 4 tubes that draw mercury up a scale based on the vacuum. Without digging out the manual, I not sure how the scale reads. The scale reads from 2 to 54. I have inserted a image of the latest Motion Pro, but mine is much older and uses real mercury. Anyway I hooked up one of the tubes to the carb intake line. It read just above 10. I not sure what that means, I thought you may give me more guidence.

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