Idle problem - Volvo AQ120B

[Hitech]

I have a Volvo AQ120B. When I first start it and it's cold it idles fine. Once it is fully warmed up it won't idle for very long. When running at speed and slowing down when I get near idle it dies. If I wait (30 seconds or so), it will start up and idle, for a few seconds. If I accelerate while it is idling fine it runs fine. It will stay running perfectly, until I slow back to around idle speed. If I don't accelerate, it will start to run VERY rough and if I try to accelerate then it does not have any affect. Pumping the pedal has no effect. I have to shut it off and wait. I tried starting it up and waiting for it to run rough. I then pumped the bulb in the fuel line and it did nothing, and felt fairly full. Also, before rebuilding the carburetor I tried hooking up an external gas tank to the fuel pump. No difference.

I have the hot spark ignition module, and a coil with a internal resistor.
I have new spark plugs.
The cap and rotor looked new when I put the hot spark in.
I have rebuild the carburetor..

So, I'm assuming it is the fuel pump? Who knows how old it is. I was thinking of bypassing it with an electric pump and see it that fixes it. Do you have to use a special electric fuel pump or can you use an automotive one?

I'm thinking of adding a ballast resistor just in case the problem is to much current through the hot spark module.

Any other ideas?

Thanks.

 

[Hitech]

Re: Idle problem - Volvo AQ120B

bump

 

[Hitech]

Re: Idle problem - Volvo AQ120B

Bump

 

[bruceb58]

Re: Idle problem - Volvo AQ120B

First question I have is why do you have a bulb in the fuel line?

Second question is who rebuilt this carb? Have you looked at your plugs to see if you are running lean or rich?

 

[Hitech]

Re: Idle problem - Volvo AQ120B

First question I have is why do you have a bulb in the fuel line?

That's the way it was when I got it. I did replace it with a new one, just in case it was a problem.

I've also replaced the fuel filter.

I'm thinking of putting an electric fuel pump right at the fuel tank and see if that helps.

 

[bruceb58]

Re: Idle problem - Volvo AQ120B

Have you done the basics like check timing and dwell, spark plugs, cap and rotor?

Who rebuilt the carb?

 

[Hitech]

Re: Idle problem - Volvo AQ120B

I haven't checked them since I put in new spark plugs. However, it had the problem then. The cap and rotor looked good then, and the plugs were new. I put in a Hot Spark electronic ignition module (the points were very worn). Set the timing then.

It really sounds like a fuel delivery problem. When it starts running extremely rough and you give it more throttle it ?bogs?. It sounds like it's slowly running out of fuel.

If I can find the electric fuel pump I'm going to install it. However, I think I'll pull a plug and check the timing, just in case.

And I rebuilt the carb. It's doing basically the same as before, except that it doesn't run quite as rough as it did before and it takes a little longer before it dies. Before it would die in a second or two, now it takes about twice as long. Not really much difference, but it's a little better.

And I did soak it in Chem-dip.


Thanks.

 

[bruceb58]

Re: Idle problem - Volvo AQ120B

In your first post, you state that when it is cold it starts up and idles fine and then you say that once it is warm it won't idle at all. Sure sounds like your carb is set up too rich to me. I know those carbs are tricky beasts and that it takes a good rebuilder to really get them running right.

 

[Hitech]

Re: Idle problem - Volvo AQ120B

There is not much to them. However, you could be right as it does idle just fine until it COMPLETELY warms up. However, if it was running rich I would expect it to try to rev up when throttling up as the influx of extra air would lean the mixture out. But, the runs fine when it's cold is a typical too rich scenario.

When I took it apart I did not like the way the idle jet was installed. It does not have any gasket and it looks like it's not seating all the way down. There wasn't a replacement gasket of any sort in the kit, and it looked the same when I put it back together. I wish I had another one to look at...

Thanks for the replies.

Anyone got a picture of one of these carbs apart?!?

 

[Don S]

Re: Idle problem - Volvo AQ120B

Get yourself an outboard 6 gallon tank, then hook it up directly to the fuel pump, WITHOUT the bulb, and go for a run and see how it works.

 

[Hitech]

Re: Idle problem - Volvo AQ120B

Get yourself an outboard 6 gallon tank, then hook it up directly to the fuel pump, WITHOUT the bulb, and go for a run and see how it works.

UPDATE: I'm NOT sure I by passed the bulb when I ran with the seperate tank. I probably did not as it was easier to prime with it in there and it's new. I'll have to try it again without it.


I guess it's not susposed to be there?

 

[Hitech]

Re: Idle problem - Volvo AQ120B

Okay, these are the on the water tests I plan to make, hopefully on Friday as we are leaving for a camping/boating vacation on Saturday. I will have the electric fuel pump ready for quick installation ahead of time.

Run the boat until the failure. Verify consistent failure. All retesting will be three attempts.

1. Bypass bulb.
2. Run from external gas tank without bulb.
3. Attach electric fuel pump with bulb in-line.
4. With electric fuel pump, bypass bulb.
5. With electric fuel pump bypass mechanical fuel pump.
6. Connect electric fuel pump to external gas tank bypassing mechanical fuel pump (not sure if I can do this).


I'll post the results.

Thanks for the time guys.

 

[Hitech]

Re: Idle problem - Volvo AQ120B

Well, NONE of that made any real difference. I even managed to hook the electric fuel pump up to the external gas tank and directly to the carb. Even that didn't help.

So, it is either the carb, or something else.

I'll check the timing and pull a plug at some point. But, we are on vacation starting tomorrow, and at least it runs.