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Excessive Cranking - Likely Causes?

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#1 Minitransition

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Posted 02 December 2017 - 03:20 PM

Only using my 998 auto rarely and so cranking the fuel up is expected to take a while, but as most of my other cars have electric pumps - what is reasonable?

 

After 3 or 4 weeks rest it takes about 20 seconds - starts and then runs fine.

 

Now I notice after just an overnight it also takes a similar time to fire.

 

Pump valve leak back? Air leak ?

 

Any tips on locating please?

 

Thanks



#2 absx2

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Posted 02 December 2017 - 07:29 PM

At 3-4 weeks the supermarket fuel is past its best which doesn`t help but my bet is a bad earth/ lazy battery and or a lazy starter motor.

Depending on the age you may have a 12 volt coil or a ballast coil that runs at a lower voltage so it gets a bigger spark when cranking the motor.

Either way any of the three above can starve the sparks when cranking the motor...... or it may just be the ignition timing is slightly out.

As for fuel, the float bowl is always full and ready for action with an SU carb.



#3 BaronVonchesto

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Posted 03 December 2017 - 05:38 AM

I used to have a similar problem. Have a 998 with mechanical fuel pump. Check how strong your sparks are. Disconnect the lead from one spark plug and connect it to a spare good spark plug. Wearing glove, touch the outside of the spark plug to the engine body properly, and have someone else crank the engine. You should get strong blue sparks with a clear sound (like breaking match sticks). Do this for all 4 spark plugs.

 

In my case changing the ignition coil made all the difference.



#4 Rorf

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Posted 03 December 2017 - 07:36 AM

Not sure what carb you have but the fuel bowl might be leaking, so excessive cranking due to having to fill the bowl first.



#5 Ethel

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Posted 03 December 2017 - 01:38 PM

I think I'd start by investigating that there is fuel in the carb before the engine turns over. You can do that by blowing down vent/overflow pipe (if there is one) and looking for fuel emerging from the jet (dashpot and piston removed). Alternatively, or additionally, you could rig up a gravity fuel feed to the carb with a length of hose and a funnel or syphon, 4-5 foot of head will be roughly equal to the pump, but a lot less would work to refill the float chamber.

 

A few weeks is also long enough for a weak battery's voltage to drop enough to affect the ignition, so swapping, charging or jump lead starting might be worth a go too. A volt meter across the battery terminals should show at least 9 volts while it's cranking.



#6 Minitransition

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Posted 07 December 2017 - 10:47 AM

Thanks for help. Fuel seems fine. Identified that the coil fitted (by prev owner) was a non-ballast type. This means that when cranking the battery load is not compensated for and when running it is via a resistor. Have ordered the correct coil and hope this perks things up a bit !

 

Will report back.



#7 Ethel

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Posted 07 December 2017 - 02:56 PM

If that's the case it could try to start while it's cranking - the bypass behaves like it's unballasted ignition, but it would have 1.5 times the resistance when the starter is released som may cut out as soon as it starts.

 

You could just run 12v to the unballasted coil that's fitted. Take a feed from a white wire on the fuse box (not via the fuse), you might even find a white's already in the loom near the coil for alternative models.







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