ticks over nicely but loses power under load

mcmental · Post by **mcmental** » Tue Apr 23, 2013 5:12 pm

hmmm more questions now folks, rover 3.5 v8 twin draw thru turbos running through twin SU carbs, car sits and ticks over lovely but as soon as i slip it into gear the revs drop down and nearly stall, i can drive it but theres no power what so ever, if i blip the pedal it revs up and wants to set off but then it bogs down straight away, fuel regulator is set at 5psi at the minute.

driving me potty is this as i need the car running for my wedding

please help

cheers
chris

mcmental · Post by **mcmental** » Tue Apr 23, 2013 5:55 pm

neutral is fine but if its in R D 2 or 1 its a no go.

ChrisJC · Post by **ChrisJC** » Tue Apr 23, 2013 7:54 pm

Does it have an AFR measuring gauge / lambda readout?

Chris.

mcmental · Post by **mcmental** » Tue Apr 23, 2013 8:13 pm

Yes but its not reading true because the exhaust is so short that the lambda is 3" from the open end.

ramon alban · Post by **ramon alban** » Tue Apr 23, 2013 8:29 pm

Hello Chris, If what follows is a load of crap someone will be along to confirm that, but just going back to basics and not knowing about your car and its fuel metering system, just thinking about the reported symptoms suggests three possibilities.

# The first and most likely is fuel/air mixture too weak causing loss of torque when ever you try to launch.

When an engine accelerates from idle there is a need for acceleration enrichment which, if I am right, is not happening.

If that is the case, then inspecting a spark plugs after the engine stalls would show NIL signs of a rich mixture, slightly damp and/or a touch of carbon/black.

That means that you have to make the appropriate mixture adjustments or investigate why any acceleration enrichment is not occurring.

# That leads to the second possibility, which can be seen when you inspect the spark plugs, and that is that the mixture is way too rich plugs wet and smelling of unburned fuel, thus the resultant flooding is quenching the sparks causing the reported stalling.

No! I'm not hedging my bets here, but simply pointing out that you could provide more evidence of mixture control by the simple expediency of spark plug condition.

# The third possibility that occurs to me is that there is an ignition timing problem at launch.

Going only by basics, because you have not mentioned what ignition system you have!

If you have an ignition vacuum advance function, then prior to launch, normal practise being inlet manifold vacuum is high and the automatic vacuum advance only senses manifold depression when the throttle plate moves away from the idle position and advances the timing to capture maximum efficiency from the combustion process at low engine speed before handing over ignition advance duties to the mechanical system.

If your vacuum advance system is not working then the RV8 launch efficiency maybe so poor that the engine simply dies.

Going along with that train of thought, what is your normal ignition timing setting at idle - somewhere between 2 and 6 degrees BTDC if you are using regular unleaded?

mcmental · Post by **mcmental** » Wed Apr 24, 2013 5:14 am

Plugs are black but not damp,I have the dizzy vac plugged plumbed into stub between carb and turbo, I will check the advance out as I've not altered since fitting turbos! Ignition is just a coil and balast resistor.

DEVONMAN · Post by **DEVONMAN** » Wed Apr 24, 2013 7:45 am

On a draw through system the dizzy vacuum advance pipe should be connected to the stub on the carb that it was originally connected to before you fitted the turbos.

If you connect it to the stub between the carb and turbo you will get full vacuum advance at tick over which is not the way the RV8 is normally set up.

Regards Denis

ramon alban · Post by **ramon alban** » Wed Apr 24, 2013 10:27 am

From devonman's observation, I would surmise two resulting problems.

1 to set timing at idle if the vacuum pipe were not removed then the timing would be off by the (typical ) 15 degrees of a standard vaccy unit.

2 when the throttle plate is open - after launch - the mechanical advance might never achieve the typical 28 - 32 degrees of advance needed.

Thus the engine may be running seriously retarded, making for an incomplete fuel burn and black plugs, not wet, exactly as you describe.

mcmental · Post by **mcmental** » Wed Apr 24, 2013 5:54 pm

heres where i have connections at minute

mcmental · Post by **mcmental** » Wed Apr 24, 2013 7:21 pm

sidecar · Post by **sidecar** » Wed Apr 24, 2013 8:26 pm

If that's your vac advance pipe running from the manifold then I think that the vac advance will be working in reverse, you will have manifold pressure not a vacuum. I suspect that the vac canister could then remove timing rather than adding it.

Turbo's and vac advance systems are not really my thing so I could be wrong!

mcmental · Post by **mcmental** » Wed Apr 24, 2013 9:12 pm

That's for boost gauge,the dizzy pipe goes to 1 of the carbs.

ramon alban · Post by **ramon alban** » Wed Apr 24, 2013 9:16 pm

Chris, I got your PM, but before you call (tel 01234 838770 available any time) you might want to study my two essays on typical electronic ignition which answer all the likely ignition related questions in particular setting timing and vacuum advance subjects raised in this thread.

http://www.vintagemodelairplane.com/pag ... ion04.html

http://www.vintagemodelairplane.com/pag ... ion05.html

mcmental · Post by **mcmental** » Wed Apr 24, 2013 10:28 pm

Advance dizzy pipe

Whole thing

sidecar · Post by **sidecar** » Thu Apr 25, 2013 4:36 am

ramon alban wrote:Chris, I got your PM, but before you call (tel 01234 838770 available any time) you might want to study my two essays on typical electronic ignition which answer all the likely ignition related questions in particular setting timing and vacuum advance subjects raised in this thread.

http://www.vintagemodelairplane.com/pag ... ion04.html

http://www.vintagemodelairplane.com/pag ... ion05.html

Your method of setting up the ignition timing is WRONG.