Logo
FULL SITE MENU

Volvo AQ171 won't stay running

T

tompowers85

New member
I have a Volvo AQ171a that will not stay running. I had the engine rebuild with the new pistons, rings, carbs rebuilt, plugs and new fuel pump. I can get the engine running, but only by pumping the throttle and shoot fuel into the intake manifold but it stall right away after a few seconds. I can pump a bunch of fuel in and get the engine running long enough so I can manually pump the throttle and get it to stay running, but if I just hold throttle at a steady idle it stalls. It seems to only stay running if I am pumping the throttle and getting fuel from the accelerator pump. I checked the plugs and they are black and dry. If I let it stall it sometimes spits a puff of gray smoke out of the carbs. I am not sure where to look. I have kept it running long enough to warm up but still has the same behavior. The only difference is it starts up easier.
 
If I cover the top of the carb rear carb with my hand the engine revs up and stays running without me pumping the throttle. Does this mean I have a vacuum leak at the rear carb. When I just cover the front carb I really do not notice a difference.
 
Sounds like its not getting gas.

I have two fuel pumps in my boat, high pressure and low pressure. I've had two low pressure pumps go out on me already. When it does, I experience similar symptoms as you describe. The boat will start, but not stay on. I take the flame arrestor off to see if my TB are pumping gas. I can see that they are not and know what the problem is. When both fuel pumps are fine I can see gas being pumped in.
 
I have a new mechanical and an electric pump. I tested both pumps and they are working great. If I look in the intake manifold it is full of fuel, and when I have the engine running by continually pumping the throttle I can see the fuel coming out of the carbs. It seems like not enough fuel is getting into the engine. I ordered a vacuum guage to test the vacuum. From everything that I have read and researched I have a vacuum leak somewhere.
 
Get a portable gas can and insert the hose going to your fuel pump in it and see if it runs fine then.


I've had an anti-siphon valve get rusted almost shut and prevent the engine from getting gas. Have you checked it?
 
You either have a vacuum leak or the main metering jet is clogged. You can check for a vacuum leak easily enough with a can of carb cleaner. Just spray around the base of the carp and near the intake manifold and see if the rpm's increase. If you don't find anything there, remove the carb and check the float adjustment or an obstruction in the metering passages.
Good luck and happy boating!
 
tompowers85 said:
I have a new mechanical and an electric pump. I tested both pumps and they are working great. If I look in the intake manifold it is full of fuel, and when I have the engine running by continually pumping the throttle I can see the fuel coming out of the carbs. It seems like not enough fuel is getting into the engine. I ordered a vacuum guage to test the vacuum. From everything that I have read and researched I have a vacuum leak somewhere.
Click to expand...

Not sure if you solved this or not, but I have the same engine (AQ171C, DOHC), a pretty rare (and pricey) one of the red original Volvo's.

First, you should not have (or need) and electrical fuel pump. This engine has a mechanical one built in. I think/fear that an electrical one might be a potential fire danger (in case of a leak).

Second, on the rear most of the two carbs, there's a solenoid valve (connected via a cable harness) that allows the engine to get additional fuel (most likely at cold start - I have never figured out what really controls this valve), and I had similar issue a few years ago. Tore down both carbs to no avail. But as soon as I got this "valve" to function properly again, everything's fine.

It is at least worth trying since you have a great engine when it's running. Small, powerful, lightweight, lean on fuel, but the parts if it does fail are horribly expensive due to the fact that there are not many out there of this engine (compared to the AQ151 and earlier).

Volvo did build a very modern engine (DOHC, electronic ignition, etc) but were likely 5-10 years too early.

If you ever want/need to get rid of this engine, call me, or sell it to someone who auto-cross Volvo's in your area. These engines (never found in any automobile) are very popular due to their high-flow head and can be brought up to 300-400 hp for racing.
 
Back
Top