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Lumpy Idle And Revving

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#1 MurphyShaw

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Posted 14 October 2019 - 10:22 AM

Hi everyone,

seen a few similar threads to this so forgive me if this is repetitive!

 

Recently I upgraded my 998 from a single hs2 carb to a single hs4 - along with the stage one kit (manifold, exhaust, needle etc.).

 

Did a quick little home tune with the gunson colourtune tool and went for a drive and was running sweet as  :D got home to adjust the choke and fine tune a little and the car started to run like dog sh*t. It has a really lumpy idle and rev and im almost certain its only firing on cylinders. #3 being the one that seems to not make a difference if i disconnect while car is running.

 

leads are providing spark and plugs are pretty new. 

 

Any help would be greatly appreciated. Really hoping this isn't a head gasket. :(

 

 



#2 MiniMadRacer

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Posted 14 October 2019 - 10:24 AM

When you say recently, how recently... I am guessing if done very very recently the heat cool cycle has allowed an air leak in the manifold or carb gasket areas... spray some WD40 around with the engine running and see if that improves anything



#3 JXC Mini GT

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Posted 14 October 2019 - 10:35 AM

Carry out a compression test to see if cylinder 3 has a problem.



#4 cal844

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Posted 14 October 2019 - 07:43 PM

Check the manifold is tight. Did you replace all the gaskets?

Do you have a fuel filter fitted?

How old is the fuel you are using?

#5 Algordo1100

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Posted 15 October 2019 - 08:03 AM

Check the manifold is tight. Did you replace all the gaskets?


+1
I'd definitely rule out air leaks first. When you drove it, it got hot and maybe moved about.

You can do the old wd40 test?

#6 MurphyShaw

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Posted 15 October 2019 - 11:30 AM

thanks for your responses! ill do the wd40 test asap. 







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