9 replies to this topic

[callMeMayfair]

Hi all. I'm almost done with my resto and am really looking forward to using her after 3 years.

My problem is as the title suggests, but for context;

My engine seems to idle fine just under 1000 rpm, but when I pop it in first and try to pull away, the car will stall unless you give it some beans.

It seems to be a little less harsh when the engine has warmed a bit but I still have to hit the accelerator I bit more than i normally would to pull away.

I'm not sure if this is the same when going up gears as its not ready to drive fully yet.

 

I recently have finished rebuilding the engine (998 A+) and the dizzy. its had new bearings, new rings new chain, tappets and may other things. its also got a brand new clutch, and exhaust in there. I've also rebuilt the carb (hs4) and took the opportunity to change the needle to a stage one needle (cant remember the number but I can look this up if needed). It also has a fletcher air filter rather than the standard one.

 

The timing seems ok and it idles well. the car starts perfectly and revs well (thinking fuelling).

 

The vacuum pipe is new and at full length (haven't trimmed it yet). there are no breaks in this. 

I have noticed that oddly, I haven't replace the vacuum unit on the dizzy. Its still rocking the original.

 

Does anyone have an idea of what to investigate? Maybe the car needs tuning for the different needle?

Id appreciate any thoughts/advice in checking this off the list.

Edited by callMeMayfair, 23 April 2022 - 04:48 PM.

[panky]

Try re-fitting the old needle and see what happens.

[semag]

the problem appears to be a weak mixture when the engine is put under load; which suggests to me that you have  an air leak somewhere between the carb and the cylinder head. the easiest what to find it is to gently spray brake cleaner on the joints when the engine is idling if the engine speed picks up when the cleaner is sprayed on the carb to manifold joint for example then that`s at least part of the problem. if that all checks out ok, it may be that the new needle is causing an off idle weak mixture. you can check this out by looking up comparing the sizes of the needles at the off idle point in the SU needle guide. 

 

Hope this helps

[sonscar]

Is the dashpot correctly filled?Does the timing advance when just opening the throttle?I also think it may be too weak,Steve..

[callMeMayfair]

Thanks so much for advice. Ill try to dig out the old needle for comparison tomorrow. ill also look at air leeks as semag suggested. @sonscar; when you say dashpot correctly filled, do you mean oil? I filled with a small distance from the top as suggested on a forum. What is the correct way to check timing advance please? I set my dizzy up with the engine at tdc and slightly offset i believe (still new to mini tuning). thanks.

[Ethel]

It could be a few things, but it's best to start with the ignition as you can check and adjust more of that & the fuelling is affected the ignition while the ignition isn't affected by the fuelling so much. Eliminate the possibilities like air leaks & damper oil already mentioned. There's enough oil if you can feel the resistance when you remove/replace the plunger.

 

Double check the points gap (if applicable) and their wiring - if you have a spare condenser it could be worth trying  that too.

 

Is the vacuum advance connected & working? It only comes in to play when you open the throttle beyond idle? Sucking on the pipe should just about be visible on the linkage inside the distributor: to prove the diaphragm isn't holed.  You should be able turn the rotor arm & baseplate manually and both should spring back unless they're seized. At least if it's running you can tinker with the timing "by ear". Slacken the clamp and turn the whole distributor clockwise to advance, anticlockwise to retard. Make a mark across the dizzy & engine so you know where you started. If it's running it's likely to only need a few degrees of adjustment, try and find the spot that gives the highest idle & arrive at it by advancing before securing the clamp.

 

... and try not to get shocked! Turn it by the metal body.

[Mr Piggy]

Does pulling the choke out make it better or worse?

[callMeMayfair]

Thanks all for the replies. Sorry I've had a few long work days and couldn't get to the garage. Keeping the choke out does seem to make it easier. I checked the vacuum hose is not blocked/ broken, however if i suck on the vacuum hose there is no vacuum. If I blow on the pipe, I can head air escape from the distributor. Can I assume that the vacuum unit needs replacing?

[Ethel]

Maybe, but check a bit more thoroughly first. It takes quite a bit of effort to move the vac advance, but you should feel some resistance and you should see it "take up the slack" a little bit. It'll be easier to make it leak by blowing and expanding the rubber connections than sucking, but they may well be split on the inside, certainly more likely than a split diaphragm in the can. A syringe would make a much better "vacuum simulator" than your lungs.

 

You could create  more advance by turning the dizzy body instead (for diagnosis), but avoid opening much throttle or it'll be way overadvanced. Though it would also need more to begin with, for a faster idle, to avoid stalling

[coopertaz]

try sucking slightly on vac pipe with strobe on crank pulley you should see timing advance if not then retard unit split. also is there a spring in dashpot? fitting red or yellow spring a good idea.