Suction from rocker top?

auction1st · Post by **auction1st** » Sun Jan 15, 2012 8:18 pm

Hi all, I have an 86 efi engine fitted with twin su's. I've renewed all the ignition system but she is not firing on 5 and 8 all of a sudden! Theres a spark on all 8 plugs timing is correct but no joy until you rev hard. Today whilst trying to find the problem I took the oil filler cap out whilst she was running and the revs dropped write off and there is a dedefinate suction preasure. This is obviously some sort of induction leak but I am open to suggestions from where? I fitted new head gaskets etc before I put the engine in the landrover but haven't managed to get it running spot on yet so all help will be welcome

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RoverP6B · Post by **RoverP6B** » Sun Jan 15, 2012 8:31 pm

Which rocker covers have you fitted and how have you set up the engine breathers?

How have you linked the SU cabs into the breather system?

Without proper crankcase ventilation which to me sounds the problem, your engine will never run properly.

Ron.

auction1st · Post by **auction1st** » Sun Jan 15, 2012 9:14 pm

Hi Ron I think they are old P6 covers linked to the SU's through what apears to be a filter. The problem is I bought it as a non runner project which was in bits! Have you any idea why 5 and 8 are the only two that don't fire?

ian.stewart · Post by **ian.stewart** » Sun Jan 15, 2012 11:16 pm

change the plugs, For some strange reason, if you manage to wet Rover plugs they never seem to work well again, I always had a spare set in the glovebox in my cortina.

RoverP6B · Post by **RoverP6B** » Mon Jan 16, 2012 7:11 am

There needs to be two flame traps, once for each carburettor with the hoses running from each rocker cover.

Is there a breather pipe with filter running into the rear of the lifter gallery?

Ron.

auction1st · Post by **auction1st** » Mon Jan 16, 2012 12:54 pm

There is the two as described one to each carb but no other breathers fitted that I can see!

ChrisJC · Post by **ChrisJC** » Mon Jan 16, 2012 1:11 pm

You could try disconnecting the breathers and plugging the carb ports to see if it runs any better.

Chris.

DEVONMAN · Post by **DEVONMAN** » Mon Jan 16, 2012 7:15 pm

Plug leads 5 & 8 are directly opposite on the dizzy cap.
Are you sure the leads are in the correct position in the dizzy cap.
If 5 & 8 are reversed, the plug will fire on the exhaust stroke on both.

Grasping at straws
Denis

RoverP6B · Post by **RoverP6B** » Mon Jan 16, 2012 8:00 pm

The breather off the lifter gallery is important as air will be drawn in at this point. The exit is via the flame traps into the carburettors.

Ron.

auction1st · Post by **auction1st** » Mon Jan 16, 2012 9:10 pm

Thanks for that Denis but all leads are right and it has run on all 8 since the build? After reading through a few other threads 5 and 8 are fed from the same carb! Tied with this induction problem I m going to have another try this weekend at disconecting the breathers and setting the carbs up again, unless sombody has a better idea?

RoverP6B · Post by **RoverP6B** » Tue Jan 17, 2012 6:30 am

auction1st wrote,...

Tied with this induction problem I m going to have another try this weekend at disconecting the breathers and setting the carbs up again, unless sombody has a better idea?

Unless your engine has a proper crankcase ventilation system in place, attempting to tune your carbs will be a waste of time. The engine will never run properly, crankcase pressure will increase and oil will start to leak from all the seals.

Ron.

DEVONMAN · Post by **DEVONMAN** » Tue Jan 17, 2012 8:44 am

Going back to your first post ,you said it's an EFI engine running on carbs.
The early carb engines normally have an air inlet to the crankcase at the rear of the valley area and this hole would be plugged on an EFI block. So, besides the breather pipes fitted to the su's, you also need a small inlet with a small filter on it. Otherwise you will be sucking air from the block and the crankcase pressure may become excessively negative and there will not be propper ventilation.

Another point to check is the dashpot piston in the carb feeding 5 & 8.
If this is stuck down then again the suction in the breather pipe will increase and half the engine will not run properly including 5 & 8.

Denis

auction1st · Post by **auction1st** » Sat Jan 21, 2012 8:38 pm

Thanks everybody I ve fitted a secondry breather to relieve the negative preasure in the crankcase as sugested

When I came to set the carbs up I realised the r/h carb was drawing a lot more air than the other side, I've blanked the breather off and she ran on all 8!!! Sunday job is to strip the carb and find the problem happy day, thanks for the help.