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cold start problems

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XK120SE

Freshman Member
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Hi there JagLovers

Since a few months, I can hardly start my XK120 (2 SU HD8 with UVO needles) when cold. I checked plugs, timing, needles, solenoid of AUD, damper oil... for hours and hours, and nothing helped, all seems to be ok. I'm near to set the thing on fire (no, just kidding).
When it finally is running (it sucks sometimes the whole battery), everything is ok, also starting when warm is never a problem.
What can I do? Please help me!

Thanks to all
Christian
 
Just a few possibilities:
1. Is the choke functioning properly?
2. Is the fuel pumping well (no clogged filter?)
3. Is the diaphram in the carb in good shape (not cracked?)

Just s few things you might check.

Basil
 
When trying to start does it turn over very slowly or at what you would consider a normal speed?

Bruce
 
Hello Christian,

if it cranks over OK, then I suspect that the AUD (I'm assuming you meant the AED, auto enriching device) is either not funtioning or is adjusted too weak. This basically is a starter carburettor. The solenoid should energise at start (cold) so I would check that first, use a piece of wire to earth the cable that goes to the thermo switch. This should activate the AED. The central needle has a mixture adjustment nut and is adjusted, unfortunately, with the engine running. Turn the needle nut anti clockwise to richen the mixture.

Alec
 
Cranking is ok, sparking is ok, solenoid of AED is working. There is no difference in (not) starting behaviour whether the solenoid is working (connected) or not. I'll try to strenghten the mixture of the AED.
By the way: does the position of the needle seat influence the cold start behaviour? I tuned the carbs to have a good mixture over the whole rev range, which worked well. Then I tried for better cold start to lower the seat about 1 mm, but without any success.

Any more ideas? Thank you all!
 
Hello Christian,

firstly, the main carburettors should be adjusted correctly for normal temperature running. Basic setting should be close to 2.5 turns of the mixture screw from the jet being flush with the bridge.
You say the solenoid is working, but when it starts can you hear the characteristic hissing noise of the AED? IF you can then the solenoid assembly certainly is working. I would remove the assembly and see if the fuel feed has been choked with debris that does accumulate over years, particularly if the banjo bolt fuel filter has been lost.
The simplest check is to dribble fuel into the top of the AED while you crank it. If it fires quickly it is certainly a fuel problem and a blocked or restricted feed is prime suspect.

Alec.
 
If you hear the AED sucking air when cold, then you have a blocked fuel feed to the AED. If it does not suck air when cold, check the solenoid and associated wiring including the temperature sensor. Clean up the device and try again. The position of the main needles in your carbs have little to do with cold starting.
 
Christian,

I had similar problems with my elderly S-Type, and after cleaning and then rebuilding the carbs, overhauling the AED and just about everything else, I finally looked into the fuel lines to the AED and found them full of crud. After cleaning these out everything started to work again as it should.

I think it might have had something to do with using premium fuels and the occassional valve protection stuff.

Hope this Helps
Cheerio

Neil
65 S-Type
76 SIII Landrover
93 MAzda MX-5
49 ES2 Norton
36 Model 9 Sunbeam
 
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