Restarting when hot...

[Matt7c]

My TwinC is running pretty well at present. However, twice I have encountered a problem restarting the engine when it is hot (not too hot, just after a long run). The engine can be re-started after several minutes with some persistance and will start very easily if left to cool for more than an hour.

Suggestions? Could it be a problem with the mixture running rich and fouling the plugs? (I confess that the plugs are black, but I'm never sure whether that is down to rich mix or oil in the pots).

Could this be related to another problem which others might have encountered. When I tune the carbs I set the idle speed at about 750-800 rpm, which it will maintain for a long time when starting from cold and the engine just idling in the garage. Then after a long run, the engine idles at 1000-1100rpm. What would cause that?

Matt

PS: The re-starting problem is not fuel starvation. The carbs never get hot and the electric fuel pump works very well.

[alaric]

Hi.

Assuming that the spark plug gaps are set correctly, the plugs are in good condition, and that the ignition system is running properly, with the correct ignition advance, then I would suggest air leaks in the carbs, a possible incorrect float level in the float chambers, and maybe the thackary washers have been overtightened or are old leading to frothing of the fuel from vibration. I'm not sure how you verify this without stripping down the carbs, but I'd start by making sure that the ignition system is spot on. You didn't mention what carbs you have. I have dellortos, and have found a very useful book on them from eurocarbs on ebay.

Hope this helps.

Sean.

[Matt7c]

Hi Sean,

I have the Webers on my TwinC and they were refurbed less than a year ago. If the problem is an air leak in the carbs, would it make a difference whether the engine was hot or cold? The re-starting problem only arises after a good drive (+45mins approx).

The ignition system uses an Aldon Ignitor dizzy, with a Lucas Gold coil and silicone leads. The static timing is set at 12 degrees (can't currently remember whether thats before or after TDC, but I read it from the book when I did it it!) and all the gaps are correct.

Diverging slightly, I find it impossible to get the timing set perfectly. Does anyone have experience with vernier cam cogs? Is it possible to use just one of them (ie just put the vernier on the exhaust side and use the standard cog on the inlet)? If so, that should ease the setup, right??? I hesitate to go the vernier route because it adds a whole new level of complexity, but it may be the only way to get the timing spot on.

Matt

[steveww]

I purchased a pair of adjustable cam sprokets from QED. You are right it is the only way to ensure the cam timing is correct.

Setting the cam timing is not that difficult. You will need a dial gauge and some means of supporting it plus a degree wheel. I find it easier to set the timings by valve opening. E.g The sprint inlet opens at 26BTDC. With the valve fully closed I set the dial gauge to read 2mm. Turning the engine over by hand keeping an eye on the dial I stop as soon as the dial moves. Reading of the degree wheel I see where the valve has opened. Using the adjustable sproket turn the cam to adjust. Repeat as required.

[M100]

Matt, If I read your post correctly (and I've done it a few times) are you contemplating using vernier cam sprockets to correct an inability to set the ignition timing accurately?

[alaric]

Hi.

I was thinking back to a problem I had with a Fiesta XR2 (I know, I sholdn't admit to it, but there you go). It would warm up really nicely, then once warm, it didn't want to idle and would stall at junctions. I messed around with ignition and valve stem seals etc etc, but in the end a simple rebuild of the carb sorted it out. I concluded that it was air leaks, and that in warm up it ran ok with the rich mixture from the automatic choke. I was wondering if you had an air leak somewhere (maybe it's not from the carbs) it's leaning the mixture slightly, which will give rough idling, and could increase the tickover depending on how your idle mixture is set up. Only a suggestion though...

When you say you find it impossible to set the timing perfectly, is that because it never idles very well, or because the timing seems to be different each time you measure it with a strobe with the engine running? As it's a mechanical system is should be repeatable - I've got an Aldon ignitor too and it just replaces the points doesn't it? Are the centrifugal weights in the distributor working properly - maybe they're a bit sticky and sometimes hold it advanced. Is the screw holding the Aldon thing in place too long and fouling on the base plate? Again, only suggestions.

Sean.

[steveww]

If the timing is not consistent when using a strobe, you are getting what is known as timing scatter. This is down to a worn out dizzy, pack it off to H&H Ignition for a total rebuild. I had the one off my S4 done last year and it cost ?75 and they turn it around in a week.

http://www.h-h-ignitionsolutions.co.uk/

[M100]

If the timing is not consistent when using a strobe, you are getting what is known as timing scatter. This is down to a worn out dizzy

While that is a prime reason for timing scatter It can also be due to a worn timing chain, low timing chain tension, worn crank/cam/jackshaft sprockets, worn jackshaft thrust plate, worn jackshaft skew gear or a worn distributor gear - and probably a few other reasons I can't think of right now.

[masermartin]

I don't know how much you can compare the two, but I had the same problem with my 1970 MGB.

It turned out that because it was running a little rich, it wouldn't start hot. I adjusted it to a little leaner of a mixture and now the problem is gone.

[Matt7c]

Matt, If I read your post correctly (and I've done it a few times) are you contemplating using vernier cam sprockets to correct an inability to set the ignition timing accurately?

I may not be explaining myself very well! When I was talking about the timing, I didn't really mean the ignition, but the cam alignment. Hence the vernier cam sprocket angle. My dizzy was new last year and is electonic so it shouldn't have worn out yet (its less than a thousand miles!).