"Kick Back" of lull coming out of bends on RV8

MendipWursel · Post by **MendipWursel** » Sun Oct 09, 2011 8:30 pm

Dear Friends

I get 'kick back' or a lull in the engine and it jurks forward as I come out of bends. It happens when the throttle is applied, after the engine has been shut back for a while going into the bend and it is more pronounced at speed.

The timing is approx 14deg at tickover with max of 35deg and vacuum disconnected so I don't think this is the problem? Does anybody have any suggests as to why this is happening?

(Current Specification - 3.5 V8, Edelbrock Performer carb, Lucas dizzy, Stage 2 Real Steel heads, Luminition electronic ignition, Viper Hurricane Cam all in Lotus 7 type kit car).

Many Thanks

Kevin

sidecar · Post by **sidecar** » Mon Oct 10, 2011 4:52 am

What is the setup of your carb?

Also how did you set the pilot screws?

Eliot · Post by **Eliot** » Mon Oct 10, 2011 7:51 am

Fuel sloshing down the carb?
On my dakar (big 4x4) when i turned a corner fuel would slosh down the inlet causing it to go rich (could see this as i have a wideband).

sidecar · Post by **sidecar** » Mon Oct 10, 2011 8:27 am

Eliot wrote:Fuel sloshing down the carb?
On my dakar (big 4x4) when i turned a corner fuel would slosh down the inlet causing it to go rich (could see this as i have a wideband).

Good point Eliot, these carbs are certainly not a 'racer's carb'

I have also seen the mixture go down the pan when corning REALLY hard, the engine will mis-fire too.

I guess in this case a good test would be just to just come of the gas whilst going in straight line then re-apply the gas maybe 5 seconds later, if it bogs then it can not really be down to g-force.

stevieturbo · Post by **stevieturbo** » Tue Oct 11, 2011 10:28 am

Try disconnecting the vac, or retarding the dizzy a bit.

But more likely it is a fuelling issue.

sidecar · Post by **sidecar** » Tue Oct 11, 2011 2:30 pm

stevieturbo wrote:Try disconnecting the vac, or retarding the dizzy a bit.

But more likely it is a fuelling issue.

I think that the OP stated that the vac was disconnected.

kiwicar · Post by **kiwicar** » Tue Oct 11, 2011 4:03 pm

Hi
Re-attach the vac advance (to the correct port on the carb) then reduce the mechanical timing a bit try about 28 degrees total and a bit less at idle say 8 to 12 degrees, that way it will give you lots of advance to burn the mixture when on light throttle and stop the plugs fouling, and when you open the throttle a big chunk of that advance will drop out as the cylinders fill properly and avoid over advance timing under load. They fit Vac advance to distributors to enable you to accomodate both these very different requirments.
Best regards
Mike

sidecar · Post by **sidecar** » Tue Oct 11, 2011 4:44 pm

kiwicar wrote:Hi
Re-attach the vac advance (to the correct port on the carb) then reduce the mechanical timing a bit try about 28 degrees total and a bit less at idle say 8 to 12 degrees, that way it will give you lots of advance to burn the mixture when on light throttle and stop the plugs fouling, and when you open the throttle a big chunk of that advance will drop out as the cylinders fill properly and avoid over advance timing under load. They fit Vac advance to distributors to enable you to accomodate both these very different requirments.
Best regards
Mike

If you do that the engine won't run more than 28 degrees on WOT which is not enough for a 3.5 lump.

The basic problem is that the Edlebrock vac take off point just does not suit the Lucas vac canister. Either the Speed Pro book on these carbs or on Distributors devotes some pages to this problem and does suggest that it maybe possible to set up some sort of vac bleed system. (I can't remember which book!)

If the carb is calibrated correctly then there is no way that it will foul the plugs on a light throttle opening. Note that I stated calibrated correctly, many are not.

kiwicar · Post by **kiwicar** » Wed Oct 12, 2011 9:44 am

OK I said about 28 degrees, try 30 then, but either way reduce the advance without Vac attached and sort out a proper operation for the vac advance. If the tapping off the carb doesn't work then stick a 1/2" spacer under it and take a tap off that in between the primarys under the carb or put a tapping point into the manifold, experiment until you find out what works.
I strongly suspect that unless this an exceptionally prepared mechanical secondary 4 barrel, that by you get beyond about 4500 revs then there will be a fair chunk of manifold depression comming in (especially with Vac secondarys) and the vac can will start adding 3 or 4 degrees of advance as you aproach 5500 even under full throttle and infact 28 degrees will work well.
This aproach used to work well on Minis and they had much better breathing than the rover. You certainly stand a better chance of getting transition to fulll throttle to work with the Vac advance than without and it will be more tolerent of the poor metering offered by the 4 barrel.
Best regards[/b]

MendipWursel · Post by **MendipWursel** » Wed Oct 12, 2011 9:26 pm

sidecar wrote:What is the setup of your carb?

Also how did you set the pilot screws?

Thanks for all the good advice. In terms of the carb setup I set the mixture screws to the fastest tickover and then weakened it a little.

Going into a bend and breaking steady is fine. It is when I come into a bend quick and brake hardish; I get the kickback at I re-apply the throttle out of the bend. The car sort of slows and then jurks forward, most anoying.

If it is sloshing of the fuel then how do I stop this problem. Maybe reduce the float level height? I will try a slight retard of the ignition as suggested.

Many Thanks Friends

(The dizzy is set to full advance at about 3500rpm).

SuperV8 · Post by **SuperV8** » Wed Oct 12, 2011 10:40 pm

Does it do it in either a left or right had turn?
If yes what fuel tank are you using? Does it have a swirl pot? Does it happen when the tank's full?
Where is the fuel pump mounted? Should be below the tank.

Obvious but I had to ask.

Tom.

sidecar · Post by **sidecar** » Thu Oct 13, 2011 4:50 am

Do you know what the other settings on your carb are? The primary jet and the rod sizes? (Please don't say it an RPI setup! )

Also it would be worth taking the carb off the manifold and checking the manifold with a spirit level to see if your carb is tipped forward of backwards. This may sound mad but after messing about with a wedge plate I found that the carb angle does change the mixture strength quite a bit. (You would think that g force would also mess it up....maybe it does!)

Eliot · Post by **Eliot** » Fri Oct 14, 2011 12:15 pm

MendipWursel wrote:If it is sloshing of the fuel then how do I stop this problem.

I solved that problem about 8 years ago by binning the damm thing and going over to injection.

kiwicar · Post by **kiwicar** » Fri Oct 14, 2011 1:10 pm

Hi
The solution Eliot offers is the best as it works.
You can get kits to modify the carb float bowl that basically fills up the thing with bits of packing and thereby reduces the amount of fuel that can "slosh". You can even fit second float bowles and extra plumbing that helps a bit. The problem is that 4 barrel carbs are designed down to a price then manufatured to an even lower one and as a result aren't actually very good.
To stand a chance of getting it to work with the sort of responce you are clearly expecting you need all the ignition system working properly (including the Vac advance) to get the optimum spark at the right time, you need the carb in new condition, pretty well dead level, and the float levels set dead on, most likley you will need a some sort of anti slosh kit, the jetting will need to be spot on and it will need to operate the idle and transition systems as they were intended (ie you need it ideling on the idle circute and not the start of the transition circute.
People tend to forget these carbs were intended to operated on engines of about 4 to 5 litres producing 170 to 220 bhp in about 2 tons of car with loose torque converters (well by our standards anyway) and 3 speed auto boxes. They never had to do a particulally good job of acuratly metering fuel in transition because you would never notice the odd flat spot or hesitation all they had to do was rev up to a few more revs and wait for the torque converter catch up. You want the engine to respond acuratly to the throttle and transition smoothly on an engine about 2/3 the intended size, not much then

Best regards
Mike
Best regards
Mike

jefferybond · Post by **jefferybond** » Fri Oct 14, 2011 1:31 pm

sidecar wrote: Good point Eliot, these carbs are certainly not a 'racer's carb'

I'd second that! I used to get fuel leaking out of the accelerator pump pushrod hole in the top cover in right-hand corners, due to the fuel sloshing about!

With the carb poking out of the bonnet, the fuel used to go all over me!

Swapped to a holley 390 and it's much better in this respect.

Jeff