Thread: 3.5L V8 not engine braking smoothly

G`day Edward

I`d suggest you have a look at the vacuum unit and see if your leak is not a diaphram hole/split from running full vacuum , you know suck on the pipe and see if it holds your tongue .

If the vacuum was hooked up this way prior and the problem was there , I`d suggest if the unit works , plug the full vacuum hole and hook the pipe up where it gets partial vacuum , near the butterfly .

The vacuum advance normal works at times of partial throttle and overrun etc when your problem is occuring .

I`d suggest if it has a miss you fix it

We have 2 V8 RRs on petrol/lpg and have found that Bosch super sports leads do the job without trouble .
Infact with you County other than the coil lead you can use leads that suit both Windsor and Cleveland V8 Fords of approx 1970 - 84 , they will often be found cheaper than Rover .

If none of that helps the carbs would be where i`d look next , does yours still use the popet valves on the butterflys ?
Does yours still run twin carbs and what type of setup gets the lpg in , ring , gas carbs ? .

Does it backfire/pop on over run and have you check the exhaust for leaks/holes ?

Cheers

Thanks PLR!

I’m not actually running a vacuum advance unit atm. I’ve removed the hose and plugged the hole.

That’s good to hear that you have not had any trouble with your Bosch super sports leads. I was looking at these at Supercheap Auto the other day and the price seemed right. I’ll just have to look for a set for a Windsor or Cleveland!

I am running twin SU carbs with the ring for delivering the LPG. I’m not sure what you mean by ‘poppet valve’ though. Do you mean those temperature compensator things behind those cream coloured plastic covers?

Yes the car does pop a fair bit when engine braking down steep hills, but I presume this is just due to a lean LPG mixture? (I sometimes run a tad leaner to save fuel). The surging does not occur at high revs, it only really occurs when you are slowing down for a very tight corner (generally when you are engine braking in third and about to negotiate a tight corner that would see the revs drop to around 1200 rpm). I have played around with the mixtures and it still surges when it's been richened up.

The exhaust does have some leaks in the spots where the extractors join to the bottom sections of the exhaust (couldn’t find the exhaust cement on the day of fitting!). How would this cause problems?

Thank you!

Edward

I suggest trying a little less advance, I usually set the V8's at 10 degrees. Your advance curve might still be a little quick, use your timing light to see how much advance you get by 1200-1500 rpm. Most dissies I modify to LPG get the primary (weak) advance spring tightened up by 30% or so, and the slack on the secondary spring reduced by 70%. The Bosch leads are good, they are not usually the issue with your running problem. The popping in the exhaust will disappear when ALL your exhaust leaks are fixed. The extra air is what leans off the LPG in the exhaust. Lean => fast flame speed.

I spent the dollars and initially bought the Magnacore leads, only to find them perish at the plug ends from heat after about 2 years, the casing over the core disintegrated.
I replaced them with Bosh ones and have no problems or probs on LPG

Thanks bee utey and It'sNotWorthComplaining!

I'll retard the timing to 10 degrees and give it a go.

I'll also look into getting a set of those Bosch leads. I priced a set at Supercheap Auto and they weren't that dear at all!

Thank again everyone!

Edward

I can vouch for these Bosch leads as well. Have had them on for 60k km with no probs. Seem to maintain quite low resistance. Think I paid about $6 per lead on special at SC.

cheers, DL

Incidentally the Bosch leads come with a 100,000km warranty, fine so long as you remember where you put the receipt!

I've looked into the Bosch leads and they do look good, but they have 3500-7000 Ohms resistance per metre. I was looking at Eagle LPG leads which are just a little dearer, and they only have 1300 Ohms resistance per metre and still have good RFI suppression. Might look into these a bit more.

Thanks again!

Edward