fuel question on volvo pent aq131d

[rdengil1]

Replaced the fuel tank, hoses, rebuilt carb, replaced fuel filter. I turned the boat over and it just cranked and cranked and cranked, no fuel coming to the pump. Pump is mechanical and works fine. do I need to syphon gas into the filter first? Do I fill the carb bowl with fuel or just keep cranking until the pump draws the fuel. Could this be air in the line? Not sure what to do after carb rebuild. also, original fuel filter was 1/4 inch hose to the fuel pump, any issue if I use a 3/8 fuel filter vice the 1/4 inch? Dennis

[2stroke1971]

Highly dangerous, but have you tried disconnecting the line to the carb, and basically try to pump gas thru the pump and into a jug or something?


That would rule out a stuck or mis installed needle valve in the carb. I can imagine that if the needle valve is not opening, the pump will just vent off and not pump.

Or, you could further isolate the pump and have it draw from a jug and into a jug.

As far as priming it, I basically just went thru this with an AQ125, it had not run in a long time, I put a new tank on, new lines and I just cranked it and it pulled gas. Didnt take too awful long to fill the carb either.

Another hack idea, dump a quarter cup of gas down the carb throat, and see if it fires up...the higher rpms of running a few seconds might draw it thru!

[rdengil1]

got the fuel to flow to the carb. How do you set the dwell? Would I be better off changing to an electronic ingnition? I cannot get rid of the backfire.

[Greebo]

Hi there,
I also run an old Volvo Penta. The difference in performance and starting etc when I fitted electronic ignition was incredible. Go for it.
The are other 'bush mechanic' ways to start if you are having troubles bringing fuel up to the carbi.
1. Fit a outboard motor hose hand pump to the fuel line - you can then easily prime the carbi before starting. As I often don't use my motor for long periods I have done this.
2. Spray ether into the intake and use no throttle. The motor will start if you have spark and should run long enough to pump fuel. Here in Oz ether is sold in pressure packs (called "Start U Bastard") and it is great for emergency starting of all motors, including diesels.
Anyway, enjoy. There are a lot of people who knock these motors but with a little preventive maitenance they are good performers and can be very reliable.

[captmello]

I have to disagree with using ether to start the engine. There should be no need to use it if the engine is tuned properly. Many people switch to electronic ignition to try to solve starting problems. The only reason it would help is if you are not able to adjust your timing and dwell properly.

Setting the dwell is not difficult if you have a dwell meter and a little patience. Start by setting the points to .40mm. start the engine and check the dwell with a dwell meter. Dwell should be @62 +/-3 deg. From what I've heard you're better off with a dwell reading at the higher end, 64-65. Once the dwell is set correctly, you will need to readjust your timing as changing the dwell also changes the timing.

Keep in mind, those Carbs have no choke so it is normal for them to be tough starters, but with a couple pumps of the throttle, assuming the carb is working properly, it should start. Let the engine warm up at 1200 rpm for a minute or two. This isn't a fuel injected car engine, it takes some practice and getting used to.


Good luck and let us know how it turn out.

[rdengil1]

I replaced the fuel pump and rebuilt the carb, also changed the plugs, cap, rotor, filter, and installed a new below deck tank. during the rebuild of the carb, I followed the guide I downloaded on this site and adjusted the air valve to the proper turns, it stopped backfiring, started fairly easy, still took some pumps of the throttle. Now it idles up and down between 900-1200 for 6 seconds then drops, then goes back up? It keeps doing this. I did not adjust the dwell or timing, did check it with a light, and it appears to be set correctly. I have a dwell meter, just no idea what I am doing. Thanks.

[captmello]

Hook the dwell meter up and see what it says. Typically the red probe would go to the neg post on the coil and black to ground. You may not need the black lead at all. What does it say the dwell is set at?

[PiratePast40]

That idle going up and down sounds suspiciously like a vacuum leak. Certainly get the dwell and timing worked out and adjust the idle mixture. Spray carb cleaner (with the little straw) around the base of the carb to look for leaks. The engine will bog down if the carb cleaner is being sucked in. The inner stud at the rear of the carb is a bear to get tight so pay attention to that area.

[rdengil1]

Not sure how to use the dwell meter. Actron type older model It has a green alligator clip, black and red battery type clips, a clip for the spark plug wire, and the two wires that are black and have the slip on type ends to clamp to a shunt (which I don't have). It also had a switch to select different tests and a button that slides up to amps or down to other tests. Anyway, I did notice that my fuel filter, which is clear only has fuel when I am cranking it and when it runs. Once it is off, it will drain back to the tank. Is this normal or is it a leak or do I need to place something between the filter and the tank to prevent the fuel from returning to the tank? Thanks. Dennis

[captmello]

I'd go with the battery wires connected and the green clip on the neg side of the coil. Set the switch to 4 cyl dwell.

The fuel should not drain back. It's usually a carb issue.

[rdengil1]

I'll try the dwell meter again when the rain stops. As for the fuel draining back, what might be the cause? I just had the carb rebuilt and it hasn't been on the water at all this year. Only run to test for leaks. I also have not tried the carb spray around the base of the carb yet either. Thanks.