mleadbeater Posted July 15, 2023 Report Share Posted July 15, 2023 Hi, being new to the Lucas PI system, I am wondering if the tendency of my ‘6 to bog , or miss fire, momentarily when opening the throttle from tickover, is a characteristic of this system, or is there a fix? all the carb systems I am used to have had an enrichment device, to overcome this by briefly enriching the air/ fuel mixture. Is there something I am missing? Or do I have to live with this? cheers, Mike. Quote Link to post Share on other sites
TR NIALL Posted July 15, 2023 Report Share Posted July 15, 2023 2 minutes ago, mleadbeater said: Hi, being new to the Lucas PI system, I am wondering if the tendency of my ‘6 to bog , or miss fire, momentarily when opening the throttle from tickover, is a characteristic of this system, or is there a fix? all the carb systems I am used to have had an enrichment device, to overcome this by briefly enriching the air/ fuel mixture. Is there something I am missing? Or do I have to live with this? cheers, Mike. Shouldn’t Bog or Miss maybe check that the Throttle Linkage is operating all the Butterflies at the same time. Quote Link to post Share on other sites
mleadbeater Posted July 15, 2023 Author Report Share Posted July 15, 2023 Niall, thanks, will check, the linkages have been modified, using rose joints and an overhead shaft, they all look to work together. The timing is set to 9.5 degrees advance at around 900 rpm tickover, could this be wrong and cause the miss? Mike Quote Link to post Share on other sites
TR NIALL Posted July 15, 2023 Report Share Posted July 15, 2023 9 minutes ago, mleadbeater said: Niall, thanks, will check, the linkages have been modified, using rose joints and an overhead shaft, they all look to work together. The timing is set to 9.5 degrees advance at around 900 rpm tickover, could this be wrong and cause the miss? Mike I’d be advancing the Timing to about 12degs and try it. Quote Link to post Share on other sites
PodOne Posted July 15, 2023 Report Share Posted July 15, 2023 No expert but isn't the MU responsible for enrichment via the diaphragm/vacuum. If its split might this cause the momentary bog down before the injectors catch up? Andy Quote Link to post Share on other sites
mleadbeater Posted July 15, 2023 Author Report Share Posted July 15, 2023 Sounds plausible, thanks Andy. Is it easy to check, and replace? mike Quote Link to post Share on other sites
PodOne Posted July 15, 2023 Report Share Posted July 15, 2023 Hi Mike Fortunately mines refurbed so never had to do it yet. But fro what I understand not too difficult and there will be a post on here somewhere dealing with it.. Easy win would be first to try advancing the timing first to 12 degrees as suggested by Niall before diving in too deeply. Andy Quote Link to post Share on other sites
Mike C Posted July 15, 2023 Report Share Posted July 15, 2023 Check for manifold leaks with a vacuum gauge on the brake booster connection. My MU is calibrated to run correctly with 10" Hg vacuum at idle. Quote Link to post Share on other sites
Mk2 Chopper Posted July 16, 2023 Report Share Posted July 16, 2023 As the PI system uses vacuum to set the amount of fuel, its critical to have all the throttle plates (butterfly's) in sync, using an air flow meter can be useful here. Also the valves (tappets) need to be checked and set. This way you should ensure that the vacuum is at the most consistent and not changing with each cylinder. Next I would check the ignition, plugs, points and timing. For timing it's best to turn the distributor to the position that the engine idle's fastest, and then on the road check if it pinks when in fourth gear at a lower speed as you accelerate. If it does use the vernier adjustment on the distributor to retard it until it no longer happens. You could then see where your timing degree marks are so you know in future where to set it. Gareth Quote Link to post Share on other sites
mleadbeater Posted July 16, 2023 Author Report Share Posted July 16, 2023 Thanks guys for the suggestions, I’ll try advancing the timing and check for leaks and throttle flows. If the diaphragm is leaking, would this affect all running, not just bogging on acceleration.? I found a Lucas manual online, so will try to get genned up . cheers Quote Link to post Share on other sites
Andy Moltu Posted July 16, 2023 Report Share Posted July 16, 2023 Check the timing try 3o to 32 deg at 4k. Tinker to stop pinking. There is no facility to for the PI system to enrich on sudden WOT. This is why they need to run relatively rich. Throttles out of balance tend to be more of an issue at light throttle. Do you have a dribbling injector? Noticeable accelerating at low revs but less apparat high revs. Quote Link to post Share on other sites
JohnC Posted July 17, 2023 Report Share Posted July 17, 2023 +1 for balancing the butterflies. That's really critical for the initial pickup. Quote Link to post Share on other sites
mleadbeater Posted July 18, 2023 Author Report Share Posted July 18, 2023 Can you recommend an airflow meter please, is the Gunson any good, or the dearer but similar one that Rimmers sell. I guess it is not possible to check individual port’s vacuum , correct, or is there a connection tapping for each? cheers Mike. Quote Link to post Share on other sites
Mk2 Chopper Posted July 18, 2023 Report Share Posted July 18, 2023 (edited) I use a Crypton Synchro Check B89, you can find them on ebay. Gareth Edited July 18, 2023 by Mk2 Chopper Quote Link to post Share on other sites
John L Posted July 18, 2023 Report Share Posted July 18, 2023 I have one of these, fits the inlets well, is available from lots of different places and prices, but a good meter. https://classiccarbs.co.uk/product/weberdellortosksolex-twin-carbscarburettors-airflow-metersynchronizer John Quote Link to post Share on other sites
TR NIALL Posted July 18, 2023 Report Share Posted July 18, 2023 2 minutes ago, John L said: I have one of these, fits the inlets well, is available from lots of different places and prices, but a good meter. https://classiccarbs.co.uk/product/weberdellortosksolex-twin-carbscarburettors-airflow-metersynchronizer John I use the same one. Quote Link to post Share on other sites
mleadbeater Posted July 19, 2023 Author Report Share Posted July 19, 2023 Thanks, gents, will get one on order. Mike Quote Link to post Share on other sites
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