FE-FC Holden Discussion Forum

I having some minor issues with the carby coughing while rounding right-hand turns (canberra roundabouts).

New carb has been installed but issue persists. Have dropped float level to handbook specs and serviced fuel pump.

Engine is a stock grey in my FC holden ute which I have restored.

Can you guys also advise the ideal fuel to be used in the old grey. I've been told both 98 Octane with the advance wound forward, or 95 with stock setting.

does it do it just while cornering or if you mimic the roundabout throttle position in a straight line does it do the same?

Sounds like you got the carby fixed to get rid of this already existing problem and it hasn't solved it, right  ???

If so have you checked the timing ensuring it is not retarded. Also it could be a fault condensor if you are running one. It could also be a vaccuum leak. My first bet would be an ignition issue either not advancing or the condenser. Put timing light on it and give it a rev and see whether it is advancing properly.

If you are dead set thinking its the fuel type and not the other things a simple test is to set the timing back to factory at idle (noting prior what your base setting is now at idle), if its lower than the prescribed base setting, then that could be the problem because the timing needs to be a bit more advanced to burn the unleaded fuel. So assuming your point dwell is right, try this, get it set to the base factory setting then very slowly advance the timing at idle until it runs rough and not satisfactory, then mark that spot, then slowly turn back the other way until the idle is satisfactory or comparible with a factory setting idle. Mark that spot then take for a test drive under same conditions as before. I would have thought an octane issue would have happened moreso not going around a roundabout, but at higher revs, sound like your problem is engine under load at low rev.

ThankS FE 350, ill check vacuum line again etc.

She runs well now as the original carb had a worn throttle shaft. The reco'd one sorted the issues with idle and surging at about 45-50 mph and now she runs well through the range and sits at cruising speeds without an issue.
Problem is just when i turn right on thees wide Canberra roundabouts and only when turning to the right.
It's not a major issue, just more annoying than anything else because it coughs, then gets a head of steam up again shortly after.

Should have clarified, on the fuel. I have no issues with the fuel and not linking it to this issue.
Just wondering what forum users recommend. I've been using 98 BP ultimate, but a few old blokes have told me to use the standard non-ethanol blend due to consistency to older fuel and also the fact that ethanol blends are hydroscopic and eventually will rust the tank out.

And thanks for tips on timing / dwell, ill check again tonight.

Its better now you have provided some extra info.  ;). Sometimes after carby overhauls and things, because the denser fuel mixture, or volumetric increase in mixture entering the cylinder is what is should be, the old blocked up carby can make it run lean or rich and underlying ignition problems can then be made more predominant. When doing the timing I would do it in 2 degree increments and then test drive. Not sure why it would only happens on right turns so you were right in assuming it could be float related.  Remember that higher octane fuels like LPG and 98 burn slower so need more advance (with stock compression ratios), so I was assuming that you were running higher hence the advance is not enough.

One other thing it could be is you base idle mixture could be too lean, so under partial throttle, when you are turn the roundabout, or feathering the throttle lightly, the transition is now requiring the base setting to be a bit richer than previously so try

Before doing this remove vacuum advance line (if you have one).

1. (Using the lean drop method) get your idle screw and wind it in slowly until you get the engine to slow in revs, then back off until you get smooth running. If idle is a bit too high, set it correctly now as a base setting. This will richen the mixture (by reducing idle).
2.  (Its always a two step process if you change the idle) if you did change the idle do step 1 again without changing the idle speed by winding the mixture screw in until a slight drop in revs is noticed, then wind it out until it runs smooth.

Is this the method you used when setting the carby. Its best to reset after a carby build a few thousand kays after cos of all the new parts etc.

An interesting thing to note is that many carby builders will go with original specs when rebuilding the carby, when in fact when using unleaded of any octane rating, it requires a bit richer mixture, especially in the transition from idle position. So the best old method is to check the plug for colour or put a meter in the exhaust. The only other thing I have thought of is that the advance calibration in the dizzy might need to be calibrated differently to standard too, to cope with the BP ultimate. I always used BP ultimate in my kart that does 15000 revs due to its better stability over 13000 revs, so I think it must have a lot of chemical in it suited for turbo force fed engines, so only use a fuel that doesnt cause pinging when you need to. I would think that a fc has fairly low compression ratio, so that fuel is a bit over the top for your application (in my opinion), other 98's used to burn more like normal fuel so perhaps of to one of those. You will actually get less horsepower with a low compression motor that hasnt been modified for it rather than more, a common mistake made by people.

Ta mate, ill give it a crack. Appreciate your help.

 Hi, is the coil new or used, i have seen an oil filled coil cause a similar symptom, and it also was only while cornering.

  cheers
  Scott

Are your engine mounts in good order?
Regards
Alex

Coil is non-oil filled but would have a few years on the board - have a spare to switch out.

Engine mounts were new in 2009.

I really appreciate the tips, thank you.