A few fuel related questions.

[401-J10]

So i recently got an M38A1 and got it running pretty quickly. It idles great but won't really rev up or move because it dies under load. This problem may be partially because of the timing not being dialed in but i was wondering if there may also be a fuel problem. My first question is how important is a fuel pressure regulator? Right now the pump goes straight to the carb. Is it most likely getting too much gas? Would a filter with a return line be a good idea? It sure seemed like it used a lot of gas in the short time it was running. It also starts right up and idles perfect without any choke when its cold. I thought this was also a little strange. I was also wondering about the distributor. Does it have a mechanical advance?

Sorry for the long post. Any thoughts are greatly appreciated.

Evan

[wesk]

Evan, Step One Is Buy the Manuals, Step 2 is Read The Manuals and Step 3 is Apply what you learned by reading them and come here for help filling in the gaps.

Ryan has made these manuals available free and immediate by loading on our download page.

Download TM 9-8014 and open to page 81 Paragraph f.

Proper Troubleshooting
The right way is to use an organized process of elimination. The manual offers just that. A step by step approach that starts with the easier and most likely causes first.

The fact that it starts and idles smoothly with no black smoke or backfiring means basic timing is very close and fuel delivery is adeqaute.

A stumble on initial acceleration is normally either the accelerator pump in the carb or the mechnical advance (centrifugal advance or governor).
If you have the stock carb you cannot see the venturi to observe fuel delivery. Therefor it's best to eliminate sources by starting with the mechanical advance. Connect a timing light, point it at the timing marks and run the engine. If the timing light shows a 5 or 6 degree advance when you increase RPm then the mechanical advance is working and it may be your accelerator pump. On the other hand if it does not then remove the distributor cap and grasp the rotor and try to rotate it in both directions. One way will not move but the other should move and spring back when rotor is released.

As I mentioned above if you have the stock waterproof carb (YS950S) then the accelerator pump will not give you that extra squirt when you are running unless the vacuum diaphram that it uses is functional and in tact. You'll have to remove the accelerator pump cover and check the condition of the diaphram and it's return spring.

The carb and fuel pumps have their own TM's (TM 9-1826A for the carb and TM 9-1828A for the pump) and yes these are available above by clicking on downloads!

So far we assume the engine will eventually speed up but not quickly. If the engine will not accelerate above idle period then we must suspect fuel deliver and air management first. Since you need fuel and air mixed at the right ratio it makes sense that either in the wrong amount will screw up the works. IE, not enough fuel can just as easily be a case of too much air. For example an open vacuum line will cause your problem. Too much air and not enough fuel to compensate for the increase in air.

As you can see this could become a very lengthy post but it is getting late and instead of me writing another 20 paragraphs of troubleshooting steps you can go to our downloads above, get a copy of the manual and read the steps in the troubleshooting chart and press on.