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Thoughts...rough running at cruise.


Freshman Member
Hey Friendly People, I'm after suggestions,
My 100 4 has had heaps done over the last year, Ive done about 5000mls since engine and carbie rebuild (carbies done by sumidel, so done properly), now it has plenty of power , idle is smooth, mixture is great nice light brown plug tips and grey exhaust.....BUT it will run rough at cruise and after a decelleration downhill seems to starve for fuel and dies. If i pull over and try to start it again away it goes after one turn no problem. Like i said power is great, accelerates beautifully so fuel supply and timing (electronic ignition) is ok , if the road is rising it will cruise under load very well.
I have tried blocking off the vac advance , made no difference to anything.
Increased idle speed to 1000 rpm , no difference.
Removed air cleaners, slight improvement but still roughish and stalled after decel.
The timing at the moment is set at tdc i advanced it a tad coz it should be 5-8 deg adv , awfull very rough but again power was good and idle was fine.
No one I have spoken to has any idea what the problem could be and I am at a loss, what else can I try?


Jedi Hopeful
Country flag
Brett, are you saying the internal colour of the tailpipe is grey? This is not normal for unleaded fuel IMO and may mean you are running pretty lean.



Freshman Member
Hi Guys,
To answer the question ,Rough on flat, and tail pipe is a black grey but not black black so I call it grey.
Anyway as it happens after I posted the above description of the symptoms I thought I'd go over it once more. My thinking was there must be an air leak between the carburettor butterfly and the head...all looks good , inlet manifold is firm on the head as are the carbies on the manifold...however i took a spanner to the manifold/ head nuts anyway and was able to tweak them 1/4 turn.....Problem GONE. Dohhhh. Wish i had done that a few weeks ago.
I know i should have checked them before but honestly they must have been just loose enough to allow air in under major vacuum but not any other time.
Thanks for the responses anyway . Brett.
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