The V8 Owners Forum -

Hi,
1st post - please be gentle!

Living Downunder, running a TR7 v8 - Holley 390 carb, Edelbrock dual plane manifold and Mallory twin points distributor, tubular manifold, yella terra roller rockers.

Thought it was running OK before attempting to upgrade to electronic ignition - epic failure.
Back to points again, dwell angle spot on 33 degrees, points gap 18 thou against target of 22.

Always though engine bay surprisingly cool after a run - checked exhaust manifold temps with laser pyrometer - cylinders 2,4,6,8 = approx 200 celcius, 1, 3,5,7 approx 60 celcius!!!!

Spark tester shows reasonable spark getting to all plugs.
When I pull leads off 1,3,5,7 there is no change to the engine note.

Clearly left hand bank of cylinders are doing very little work...... but why?

Any ideas please.

Can you see if fuel is being drawn in both sides of the carb relative to how the inlet manifold is divided ?

Presumably with an old dizzy, sparks will be ok.

But the inlet manifold and carb will be divided in a particular way. So there could be an issue there, whether it's the carb, gaskets, install etc

Are the plugs on that side wet or dry ?

Thanks for the ideas - I'll check them tomorrow.

Fuelling would seem to be the issue - the cold side plugs are cleaner.

The dual plane manifold is not split left hand and right hand - so a blocked jet would logically affect cylinders on both of engine.

I'll check every possibility.

Thanks

Just discovered my inlet manifold is the often criticized Offenhauser JWR 7001.

Does anyone have a schematic of the internal design - trying to trace back my engine lack of fuelling (?) on LHS to a particular barrel of the Holley 390.

Google appears devoid of such information.

Thanks

Get a can of EZ start and spray around the inlet and see if revs rise as some point.

My guess is that there is a leak,on the inlet side, drawing in external air as,opposed to through the carb

Ian

I actually had one of those years ago....cant remember totally how they're split though.

https://www.woolfe.uk/product/jwr-7001- ... fold-4bbl/

I've a funny feeling the two single ports do each feed one bank, with the rear large port feeding all 8 ?

Or something like that

https://www.woolfe.uk/product/jwr-7001- ... fold-4bbl/

Solved, Thankyou.

Air leak - for some strange reason there was no cap covering the unused PCV inlet to the carb.

Finger over the inlet - harmony returned to the world.

Exhaust manifold temps now pretty consistent on both sides.

Now I can start sourcing my Holley sniper EFI kit. happy times ahead.

good stuff

Although I wonder if that manifold design might affect a Carb style injection system ? I'd be asking that question for sure.

Time for me to learn something. Why would an air leak cause those symptoms?

scudderfish wrote: ↑

Fri Dec 31, 2021 9:16 am

Time for me to learn something. Why would an air leak cause those symptoms?

Drawing in far more air than fuel....no chance of combustion. The air leak itself must be for runners only linked to that bank.

And a carb will only lift fuel from the venturi....if air has passed through the venturi. An air leak in the manifold...means that cannot happen

stevieturbo wrote: ↑

Fri Dec 31, 2021 3:06 pm

scudderfish wrote: ↑

Fri Dec 31, 2021 9:16 am

Time for me to learn something. Why would an air leak cause those symptoms?

Drawing in far more air than fuel....no chance of combustion. The air leak itself must be for runners only linked to that bank.

And a carb will only lift fuel from the venturi....if air has passed through the venturi. An air leak in the manifold...means that cannot happen

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