Offroad-Express

Hi Guys,

Im having some trouble with the engine in my project vehicle. Its been frustrating me for 4 months and at point where prepared to pay someone to help fix it .

Engine is a Leyland P76 V8 fitted with an early P6 V8 timing cover and dizzy, and manifold adapted to take SU HIF6 carbs.

Symptom: misfires under revs and load but idles beautifully.
timing is ok, new plugs, leads, coil and just fitted pertronix ignitor electronic ignition kit. Nothing. Carbs known to work when on old rover v8 engine, but suspect may have been running a bit rich.
Vehicle launches well but then putts out around 2000rpm.


Does anyone know someone/ a good mechanic in Auckland area who has the right gear to diagnose this problem?

The vehicle is a Suzuki Jeep so trying to tune and test it on my street is getting a bit hairy....

pertronix ignitor electronic ignition kit

Just a hunch but when i was sorting replacements for my ignition with electronic ones the guy said that some dont do the advance correct. I'm no tuning expert though

Mike

If in Sth Auckland you could try Otahuhu Tuning. Corner Salesyard rd Otahuhu

Two places:
- Morris @ Stag 4x4 in New Lynn
http://www.stag4x4.co.nz/

or if you want a P76 specialist
- Ross Calgher (in Waitara)
http://www.roverv8.biz/

xorph wrote:Hi Guys,


Engine is a Leyland P76 V8 fitted with an early P6 V8 timing cover and dizzy, and manifold adapted to take SU HIF6 carbs.

Symptom: misfires under revs and load but idles beautifully.
timing is ok, new plugs, leads, coil and just fitted pertronix ignitor electronic ignition kit. Nothing. Carbs known to work when on old rover v8 engine, but suspect may have been running a bit rich.
Vehicle launches well but then putts out around 2000rpm.

The good old brit V8 can be a handfull to tune at times. Generally the worse part being the carbs. they are HIF6 and not HIF44 s?
I've got the Pertronics kit in my 3.5 and it works a treat -magic in fact.

Although the simptons do point to a ign problem . You would think fuel would cause a bog out or flood thru the rev range rather than a distinct miss?

A tuning specialist with a dyno should be able to suss it pretty quick.

Thanks guys,
I'll try some of them. I have actually tried Stag 4x4 before and they said its not really something they would do any more. i suppose nowdays you plug a computer into it and it fixes itself....
Yes they are HIF6 carbs.
All the bits on the engine are off a P6 v8 about 1972ish.
Whats wierd is that when i first got it going it seemed to work ok, then i took it to friends farm for a thrash and it slowly seemed to loose power and start missing in the first minute we were using it. played with it back at home again, thought id fixed it so took it to neavesville and it had about 10 hp.
Im wondering if one of the carbs has pooed itself-does anyone have an old set of Su's lying around? might try them on and if something changes know its a carb prob. I took one apart the other day but cant tell, everything seems fine.

Sounds like there might be shit in the fuel filters. Remember that the SU's have a little brass mesh filter adjacent to the bowl fitting.

Im no mechanic but have you checked the condenser in the dizzy...it might be faulty & not giving the correct voltage to the coil causing poor spark under power...or maybe the float level in the carb is too low or the main jet in carb is partially blocked.

Good luck..i think youll need it.

electronic ign - no condenser
Twin carbs on 3.5V8s are on a dual plane manifold, each carb feeds 4 cyls of its own - thats why it's important that they're balanced. So yeah I spose if one carb is dodgy you are gonna get 4 sick cylinders.

Is your modded P76 manifold still dual plane. maybe bite the bullet and get a offroad 4 barrel carb and manifold - probably get more hp too.

I've got a standard lr manifold and carbs down here, swap ya for an engine stand .

Manifold is a hi-tec super secret rovertec drill port.
i.e I dremeled it out with a Hitachi and a broken drill bit....
Its effectively single plane now because there is a gap between the planes.
Its not a terrible job and should flow fine.
What plug gap do you run with the ignitor?
Dont have an engine stand sorry.
Also, cant remember seeing the little guase filter things, maybe they are only on HS6 not HIF6 (integral float chamber). Ill have another check, might take second carb apart. really hoping to see some dramatic mechanical carnage, like a dead possum stuffed inside the float chamber.
But alas, something is not set right and thats all it takes.
Makes me wonder how they ever got the first piston engines to work at all.

I have a .85 - .9 mm plug gap with a Bosch GT40 coil I think. Out to 1mm
gap would work I reackon.

Unless theres some crap getting in the carbs It's hard to say why it was running ok for a start? Float levels etc don't go adjusting themselves (unless the valve is wornout or float sinks) :scratch:

Although they are fussy engines. Tried to run mine on Avgas and it hated it, tried to retune it for the higher octane and couldn't do it without new jets and a bit more compression etc etc so gave up and went back to pump gas

hey, i hav just had the same problem as you, idles fine, put put under load.

I found one of the diaphragms in one of my carbs was split, might be worth a check if you havent.

cheers,
gary

Very interesting.
Can you describe what you mean by the diafragm? cant remeber seeing a diafragm in the carb I took apart

hey, these are out of my 175 CD's ("Stromburg's") on my Rover 3.5L

hope u can see in one of the pictures the split around the top where it folds over.

Hey , HIF's dont have diaphrams so that would be why u cant find them

Its a long shot but one that had me stumped on an old series 2 that had a holden in it .... the feul pump wire was shorting out, it was getting enough fuel at idel, just .... but any revs and it would soon start missing and die back

Cheers Reece