16 replies to this topic

[Aussie Paul]

G'day forum members,

 

I know I have discussed this before however I had some developments and need some final advice.

 

The Car

Reconditioned A+ 998 converted to unleaded (most likely a Metro engine from around 1985)

RA40 exhaust system with extractors ( bought as a stage one kit)

Twin 1 ¼” Carby’s with ABC needles

Pancake filters

65DM4 distributor with the GLC143 coil

Fuel is delivered through an electric pump through a filter king regulator at 3.5psi

Fuel bowl levels are fine.

 

I have 2 options with this car.

 

I can set the car at 5 degrees BTDC and the car will idle perfectly but it will not drive well.

Or

I can advance the distributor off scale, I would guess 30 degrees, and the car will run excellently but will idle like rubbish.

 

At 5 degrees, when the car is driven, will struggle like the engine is labouring under its own load. The car sounds like it wants to die and car stumbles like its running out of fuel. So in saying that the fuel side of things are fine. I can rule this out because I can advance the timing and the car runs fine.

 

I can’t find a happy balance between the two.

 

Until now I have focused on the electrical side thinking it may have been the ignition system. Everything on the electrical side stacks up and other than the timing side of the electrics it all seems to test correctly.

 

On advice from a retired carby guy I was told that the issue is that the Carby is not getting rich enough, fast enough. He based this on 2 main reasons.

1. When idling perfectly at 5 degrees when I lift the piston in the carby 1/32" the engine wants to die where it should slightly increase in revs

2. When the car is struggling I can pull out the choke and the engine improves to a near perfect level

 

He recommended that I get needles that have a slightly higher start point to get the carbys the correct mixture from the start.

 

So has anyone had a similar situation that they have managed to sort out? and more importantly can anyone recommend a needle that will give me a higher start point? I sure that selecting a needle that gets really rich towards the end of the range will also cause a whole new set of issues which also hope to avoid. I have looked over dozens of needles however I really need some guidance from people who know how they perform not just what looks richer on paper.

 

Thanks to everyone that has help out so far. It has been helpful and got me to this point which I hope is near the end.

 

 

[Dusky]

Is it a 998 metro engine or a 1275 metro?
Are you Sure the distributor is for a 998?
I would try a AAN needle wich seems to be the equivalent to a lean cooper 998 needle

[nicklouse]

first things. 3.5 psi is a little high for the SU floats but if it is not flooding the carbs it will do, i would drop it ti 3 psi.

 

and yes it does sound like in is running lean.

 

personally i would bin the twins and fit a sorted  1 1/4.

 

but that is just me.

[Aussie Paul]

Thanks for the feedback.

The engine is a 998c and I am sure as I can be without seeing it on a 998 that the distributor came from the same.

I will take a look at the AAN and see how it's looks on paper.

As for binning then twins, well I guess sometimes we have to work with what we got.

If the car didn't power on when the choke is pulled out or I could lift the carby Pistons up 1/32" without the motor wanting to die I would think for sure its the distributor but before I go back down that way I just want to be able to rule out carby/fuel/mixture

[dklawson]

I defer to others on mixture adjustments and suggesting needles.

 

When you were setting the timing, did you have the vacuum line from the carb disconnected and plugged?  As an altenative to setting the idle advance you can set the max advance and let the idle advance fall where it may.  See the thread linked below for more information:

http://www.theminifo.../310600-timing/

[carbon]

Paul, do you know what springs are fitted in the twin SU dashpots? Should be blue springs.

 

It does sound like the dizzy timing is not suitable for your tuned 998, even if the unit came off a 998 in the first place the new carbs and exhaust could make a difference to the advance curve.

 

Have you checked that both the mechanical advance and vac advance on the dizzy are working correctly?

[Aussie Paul]

Thanks for the ideas.
I have been tuning the car with the vac off.
The springs are blue.
Both the vac advance and mechanical advance are all working.
Maybe it is just a wrong distributor.
Any ideas what would be the right distributor based on the details above? I guess I need to buy a new one

[Dusky]

The problem with distributors is that each housing (45d,59d,65dm) has different curves. There will be a serial number printed /engraved on the dizzy with that number you can check the curve.
Also, if you buy a new dizzy, buy one for a 998 specificly, i think minispares dizzies have the Right curve, but accuspark etc don't.
Cheers

[Aussie Paul]

Thanks, I tried to find the serial number online but it's not showing up or it is with no data. It's 42659 if anyone has a old lucas catalogue around it might be in there.

[nicklouse]

to be honest any dizzy that fits can be used. the bob weights have the amount of advance they give stamped on them. and the springs can be changed.

 

and the bob weights can have material added or removed to adjust the max advance that the dizzy can give. the springs can be changed to give a "suitable" advance "curve".

 

might be worth having a good look at what is in there before going mad buying stuff.

[Aussie Paul]

Good call. I might pull it down and have a look at what I have got. I must check the mechanical advance again too, I assume the 65 works the same as other distributors.

Edited by Aussie Paul, 25 November 2015 - 11:32 AM.

[Dusky]

Thanks, I tried to find the serial number online but it's not showing up or it is with no data. It's 42659 if anyone has a old lucas catalogue around it might be in there.

Sounds like the same I had

 

65DM4

RPM  -  advance

3250     10

2750      9

1000       2 

500         0.5

[carbon]

Paul,

 

As long as mechanical and vacuum advance are working on the dizzy this should work. If it was a 1275 unit it might benefit from a weaker primary spring to bring the advance in a little sooner, not sure if same applies to 998s.

 

Would go back and have another look at the carbs. I'm not sure ABC needles will do you any favours here, the sizing of first station is 0.0855, whereas most of the fixed needles for twin carb set-ups used 0.085. It's a very small difference in size but may affect mixture throughout the whole range.

 

Also sounds like by adjusting to get blue Colortune you are way too weak. Try dropping the main jets by a whole turn and see if it runs better on the road.

[Aussie Paul]

Thanks, I may need to invest in new needles.

I can narrow it down to a few maybe a EB, M, AAN or even a GG.

Thanks again for you input

[Dusky]

You ll only be able to use AAN due to the difference between fixed and swinging needles