Volvo V8 Petrol Pt III

[Fire99]

Evening everyone,
I trust everyone had a good weekend? Weather has been great for boats.

Things have moved forward on the engine issues but still having issues.
The story so far Volvo V8 Petrol (AQ200d) running single carb.

Well i've replaced the Coil and now a brand new Fuel pump and new fexible fuel line from filter to pump with all new fittings.
Good news is the engine now runs.. It idles fine and runs under load on the pontoon.

However, prior to a sea trial she still seems to gasp if i snap the throttle open under load.. You can hear the carb sucking air hard and the engine 'catches up' after a couple of seconds or so.

Its getting close to asking an 'engineer' to take a look over her but i'd much rather diagnose the problem myself for future reference and if i have issues whilst out at sea.

So any further suggestions always appreciated and dare i say, worst case scenario if anyone knows a good marine engineer not a million miles away from Tollesbury that wont charge the shirt off my back id be interested to know...

Many thanks,

Nik

 

[Its_Only_Money]

All carbs have some form of acceleration enrichment, commonly a small pump that injects extra fuel into the carb throat as the throttle is opened. From your description it sounds as if this arrangement is either mechanically duff (linkage from the throttle spindle fallen apart??), the valve that feeds the pump is stuck or the jet(s) into the carb throat are blocked. Very slow throttle opening should behave better, fast throttle opening will lead to the engine bogging down for couple of seconds due to the momentary fuel starvation.

Hope this helps!

 

[Fire99]

ooh flippin heck.
Dont tell me that is playing up now.
The engine was freshly serviced in November and running like a dream up until a few weeks ago. At this rate the boat will be running fine just in time for the end of Summer /forums/images/graemlins/frown.gif

Thanks for the reply though.

 

[Fire99]

Just a quick update. The Rochester 2GC carb on mine doesn't list an accelerator pump (unlike the 4 barrel version) so this is more than a touch confusing..

 

[misterg]

[ QUOTE ]
Just a quick update. The Rochester 2GC carb on mine doesn't list an accelerator pump (unlike the 4 barrel version)..

[/ QUOTE ]

...which explains why it 'gasps' if you snap the throttle open...

Andy

 

[Its_Only_Money]

[ QUOTE ]
Just a quick update. The Rochester 2GC carb on mine doesn't list an accelerator pump (unlike the 4 barrel version) so this is more than a touch confusing..

[/ QUOTE ]

I have a Clymer manual covering the Volvo V8's and V6's, the Holley 2-barrel and 4-barrel all have accelerator pumps, so does the Rochestor 4-barrel in the Volvo manual I have - AFAIK carbs won't function correctly on throttle opening without an accelerator pump. The accelerator pump is also why pumping the throttle on a cold engine helps starting - it physically injects extra fuel even without the engine running.

Look for a linkage off the throttle spindle or disconnect the throttle cable, looking down the throat you should see and hear the pump work when the throttle is opened quickly (literally you'll hear the fuel squirt in). Be careful as you are working with petrol and too much testing and you'll flood the engine...

 

[PeteCooper]

[ QUOTE ]
All carbs have some form of acceleration enrichment, commonly a small pump that injects extra fuel into the carb throat as the throttle is opened.

[/ QUOTE ]


No they don't.

 

[Fire99]

Thanks chaps.. its all clear as mud now /forums/images/graemlins/smile.gif
I'm guessing that the issue could be something to do with the accelleration system. However when you prime the carb (pumping the throttle) for a cold start, that seems to work ok..

I was wondering if an air leak in the Water separator could cause this problem as under sudden load it may suck air instead of fuel..

Just a thought.. (i'm going off old carb engines!)

 

[ontheplane]

PM Spannerman - he solved an incredibly difficult Volvo problem for me last year just from the symptoms - and was spot on with some to-ing and fro-ing - and an alround really nice guy as well.

 

[Fire99]

Thanks for that.
I'll drop him a polite mail and see if he can throw a little light

 

[Its_Only_Money]

[ QUOTE ]
[ QUOTE ]
All carbs have some form of acceleration enrichment, commonly a small pump that injects extra fuel into the carb throat as the throttle is opened.

[/ QUOTE ]


No they don't.

[/ QUOTE ]

OK enlighten me, SU's did it via the damper, Webers and US tin commonly does it via a pump, Fi does it via the electronics. So which carbs don't provide any acceleration enrichment???