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grunta's 67 vc valiant


grunta

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I think it is very unlikely that you are over-carbed with a stock style 2 barrel on a slant 6 and the fact that things are OK at wide open throttle suggests that the carb size is just fine for your engine. 

Maybe try running it with your vac advance disconnected and the port on the carburetor blanked off or even try knocking the timing back a few degrees. Slant 6's make a fair bit of manifold vacuum and at part throttle you will almost certainly be pulling vac advance . This could be contributing to the part throttle problem while at wide open throttle the vac advance shouldn't be active.

Not sure if it will make any difference but it's very easy to try.

 

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Funny you mention that as It did run much smoother when I knocked off the tube and didnt realise ... had a vac leak too and was smoother... initial timing has been played with and im set around 8'btdc and it looks to advance to around the 30-35btdc mark under full throttle ... (thats just in the garage not under load... ) ive been to both exrtrams of initial timing 2-12' and it made little difference .. is it a known problem with the vac advance causing thibgs ljke this because it would make sence with the symptons... ? I will definitely try it... any idea on what the mechanical advance will advance it to by its self? .. .. also went for a massive drive this morning which was choice .. I really dont drive it at all above 1/2 throttle anyway so it really isnt a problem... drove nice tbh

 

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I know fouling of #6 can be a symptom of timing issues. 6 runs hottest and can be prone to pre-ignition/poor combustion if the timing curve is not correct. Vac advance modifies the mechanical advance curve and if it's pulling too much in the mid range maybe it's contributing to the problem. 

Like cletus I have had to disconnect the vac advance on a modified engine because it just wouldn't run properly with it connected, that engine also carbon fouled #6 and that's actually what prompted me to suggest disconnecting it. 

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  • 4 years later...
On 29/10/2017 at 09:44, RUNAMUCK said:

Something to check is that it hasn't spun the damper. That will give you an erroneous baseline. 

Turns out no bolt in damper … you know that front main one … then I just drove it with out one for last 4 years haha

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im gona get new timing chain and prob replace the harmonic balancer anyway but will degree it before putting her back in ... engine is going to get a bit of a sweetee up and full tranz rebuild...

 

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