Re: force 125 bogging down
OK! In the previous post I explained why the engine is running like it is. Now that you know what the problem is, the only way to find the solution is through methodical checking and logic. Your '89 should have the old style 2 stage pump built as part of the bypass cover. I will, however, include some advice on Merc style pumps.
Note that the fuel pump operates on about 2-5 PSI pressure. Most of the times with a full clog, it will collapse the primer bulb. But with a partial clog or a restriction past the bulb, it will not collapse it.
So: Start right at the pick-up in the tank. Does it have a screen? Is the screen clear and free flowing? Now check the Quick-connect if the fuel line has it. Unscrew the male end and check inside the threaded part. Crap tends to collect around the spring that holds the ball shut. Also check to be sure the gasket around the ball is ok and check that the sealing O ring inside the female end is not leaking air. An air leak will give the same symptoms as a bad fuel pump. Check the screen on the pump. BTW: If you need to replace it, that O ring is an oddball size and I don't think the dealer sells them separately. However, PEP Boys and probably other auto stores sell an O ring kit for GM air conditioning systems. These are the correct size and you get about 6-8 of them.
Next, since you have already replaced the pump diaphragm and fuel hose, we will automatically eliminate them.
Check the short vacuum/pressure hose from the block to the pump. If it has air leaks, the pump --even if new-- will not perform at full capacity. The base of most pumps were cast as part of the bypass cover, however, some were separate and used an O ring seal between them and the bypass cover. If you have this kind, be certain that the O ring is not missing and is sealing.
Check the pump button valves to be certain they are sealing. If you blow into them and they pop shut, they are good even if they pass a very little air.
If it is a Merc pump, check the gasket behind the pump or the small O Ring seal. If missing or improperly installed, either will cause an air leak that will reduce pump efficiency.
Finally, and most difficult so we save it for last, Check the needles and seats in the carbs. Sometimes the seats will swell, causing a restriction to fuel flow. Just be aware that the seats have a very small orifice to start--less than 1/16 inch. So don't look at them and automatically say they are bad.
Sometimes crap gets past the pump and clogs the carb inlets and needle seats. If this has happened and both carb needle seats were clogged CONSIDER YOURSELF LUCKY! If only one carb clogs , the other carries the engine, two cylinders run lean and two pistons will melt. Always -- ALWAYS--put a small, 3 dollar disposable plastic auto fuel filter between the fuel pump and the carbs.
