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Advice for an Amateur refitting SU carbs


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#101 stevo_gj

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Posted 26 June 2009 - 09:04 AM

Bad news, apparently cylinders 1-4 have verry low compressions.

These are the results sushi and I got a couple weeks ago:
140,150,115,110,120,110

And now the guy reckons cylinders 3-6 are between 60-80, and 1,2 are 140.

He is getting a nearby store to see if the tappets are causing this compression loss, but if not then he reckons its most likely gonna need the head off, and that means I can't drive the Z to Sydney next week.

#102 Lynton

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Posted 26 June 2009 - 01:40 PM

does the car spit when properly warmed up or only when cold or always? Lynton 8)

#103 stevo_gj

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Posted 26 June 2009 - 01:49 PM

When warm with the choke off yep, it feels like it encounters a flat spot then it spits if I have pushed the accelerator in far.

When warm with the choke on it doesn't, it still has the same flat spot but it doesn't spit.

When cold with the choke on it doesn't, it drives ok but unable to determine if it has the same flat spot.

#104 stevo_gj

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Posted 26 June 2009 - 01:50 PM

Steve, did your mechanic set the timing with the vacuum advance plugged?


Yeah Mike he had it disconnected, just spoke to him.

Can't figure out why in a single week the compression had dropped so much...

#105 stevo_gj

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Posted 26 June 2009 - 02:27 PM

Good news, Carb and Gas just called and said that the tappets were tight as hell, and that the car is now running 100% better. All cylinders have equal compression, and therefore the car can now be tuned properly.

Edit:

Cost me $240 to get diagnosed and have tappets adjusted.

On the drive home it was still choppy as hell, but the difference by adjusting the tappets was noticeable in the feel of the engine.

I got home and took the airbox off, and all of a sudden its running great... !?

So I tuned it and took it for a spin with the airbox off, it drove beautifully.

Got back, put airbox back on, and it stayed good.

Apart from the choppy drive home (might have been caused by sticky choke) having the tappets adjusted seems to have fixed the problem - touch wood.

#106 2+2er

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Posted 26 June 2009 - 02:32 PM

Good stuff! I think its safe to say you are no longer an amateur with the carbs.

#107 xa1973

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Posted 26 June 2009 - 03:43 PM



Good result..

Whats the story. things just dont repair themselves or come good over night

#108 Zedback

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Posted 27 June 2009 - 10:51 AM

...and said that the tappets were tight as hell...


Great news you got it running Steve.  We would have got there eventually, in a couple of months, just before pulling the whole engine apart!  ;D

So the tappets being over tight meant that some of the valves were not closing fully and combustion pressure was being blown back into the manifold causing the spitting?  ???

#109 stevo_gj

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Posted 27 June 2009 - 04:47 PM

Thanks guys!  I am glad its finally over :)

Great news you got it running Steve.  We would have got there eventually, in a couple of months, just before pulling the whole engine apart!  ;D

So the tappets being over tight meant that some of the valves were not closing fully and combustion pressure was being blown back into the manifold causing the spitting?   ???


I'm not sure Mike. I think it was more related to the fact that you can't tune carbys when the cylinders have such different compressions, since the problem did disappear when the choke was on (although the flat spot was still there). I don't know enough about the process of intake after the carbys to make infer why the tappets caused this.

I would just like to thank everyone who posted their input in this thread, your suggestions kept me working hard! And an extra big thanks to Sushi and Mike who got their hands dirty helping out.




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