Peter Dracup Posted April 3, 2020 Report Share Posted April 3, 2020 (edited) I have a 1973 TR6 that was rebuilt in Czechoslovakia so I'm not sure about the exact engine spec but it feels to have a fast road cam. It has a bad miss fire at a constant speed but is OK when accelerating. I have checked the timing, 11 degrees BTDC and had the injectors out which all look to be giving an even spay on tick over. I would welcome suggestions at to the next steps to identify and cure the problem. I have changed the points, condenser and rotor arm but unfortunately this has not helped. However, in doing this work I noticed that there is fuel leaking from the control unit end of the metering unit. Suggestions? I'm reasonably competent but wary of taking the metering unit to bits. Edited April 11, 2020 by Peter Dracup Update Quote Link to post Share on other sites
Mike C Posted April 3, 2020 Report Share Posted April 3, 2020 Do a plug cut to see if the plugs are wet- it could be running rich at constant speed. Quote Link to post Share on other sites
tr graham Posted April 3, 2020 Report Share Posted April 3, 2020 Might need a bit more advance , depending on the cam graham Quote Link to post Share on other sites
harrytr5 Posted April 3, 2020 Report Share Posted April 3, 2020 Always check the rotor arm first. If it has a rivet in it change for the red rotor arm of Dizzy Doc. Condenser and points from Dizzy Doc Even new spark plugs can have issues Regards Harry TR5 Nutter Quote Link to post Share on other sites
Keith Warren Posted April 3, 2020 Report Share Posted April 3, 2020 Before you go deep into things how old is the fuel, this time of year if it’s been left in the tank all winter it will have lost a lot of its bang, mine is on EFI and for the first time this week had a miss fire until a fresh couple of gallons went in. Worth checking. Keith Quote Link to post Share on other sites
astontr6 Posted April 3, 2020 Report Share Posted April 3, 2020 40 minutes ago, Peter Dracup said: I have a 1973 TR6 that was rebuilt in Czechoslovakia so I'm not sure about the exact engine spec but it feels to have a fast road cam. It has a bad miss fire at a constant speed but is OK when accelerating. I have checked the timing, 11 degrees BTDC and had the injectors out which all look to be giving an even spay on tick over. I would welcome suggestions at to the next steps to identify and cure the problem. Fast Road Cam? At what RPM does your car come on cam? if it is 1500 RPM I would suspect that it has a non standard cam? As already advised a mixture/plug check should be done using an exhaust gas analyzer. I have a fast road cam in my car and had to use a KMI Sprint M/U for the engine to run cleanly without any missing, which also gave a smoother tick over!. Bruce. Quote Link to post Share on other sites
c.hydes Posted April 3, 2020 Report Share Posted April 3, 2020 Bruce, I believe I have a fast road cam fitted, how do you check ......."what rpm it comes onto cam"? Colin. Quote Link to post Share on other sites
Mike C Posted April 3, 2020 Report Share Posted April 3, 2020 6 hours ago, c.hydes said: Bruce, I believe I have a fast road cam fitted, how do you check ......."what rpm it comes onto cam"? Colin. Does the engine start pulling hard at a particular RPM? Quote Link to post Share on other sites
Peter Dracup Posted April 4, 2020 Author Report Share Posted April 4, 2020 23 hours ago, Mike C said: Do a plug cut to see if the plugs are wet- it could be running rich at constant Mike, Will do. 19 hours ago, c.hydes said: Bruce, I believe I have a fast road cam fitted, how do you check ......."what rpm it comes onto cam"? Colin. On 4/3/2020 at 9:55 AM, Mike C said: Do a plug cut to see if the plugs are wet- it could be running rich at constant speed. 23 hours ago, harrytr5 said: Always check the rotor arm first. If it has a rivet in it change for the red rotor arm of Dizzy Doc. Condenser and points from Dizzy Doc Even new spark plugs can have issues Regards Harry TR5 Nutter 23 hours ago, astontr6 said: Fast Road Cam? At what RPM does your car come on cam? if it is 1500 RPM I would suspect that it has a non standard cam? As already advised a mixture/plug check should be done using an exhaust gas analyzer. I have a fast road cam in my car and had to use a KMI Sprint M/U for the engine to run cleanly without any missing, which also gave a smoother tick over!. Bruce. 23 hours ago, tr graham said: Might need a bit more advance , depending on the cam graham Harry, Will check and change rotor, condenser and points. On 4/3/2020 at 9:47 AM, Peter Dracup said: I have a 1973 TR6 that was rebuilt in Czechoslovakia so I'm not sure about the exact engine spec but it feels to have a fast road cam. It has a bad miss fire at a constant speed but is OK when accelerating. I have checked the timing, 11 degrees BTDC and had the injectors out which all look to be giving an even spay on tick over. I would welcome suggestions at to the next steps to identify and cure the problem. Quote Link to post Share on other sites
astontr6 Posted April 4, 2020 Report Share Posted April 4, 2020 19 hours ago, c.hydes said: Bruce, I believe I have a fast road cam fitted, how do you check ......."what rpm it comes onto cam"? Colin. Hi Colin! If the pull rate is flat until about1500 RPM and then the car starts to really pull I would suspect that you have a fast road cam but some people go beyond that and have put in a sprint cam where there is no power below 2000 RPM and it is difficult to drive in town because of the lack of bottom end power. Its a bit of a fiddle to check the valve timing on a fully assembled engine, in situ, as some bits have to come off or be adjusted and you need to fix a timing disc to the front pully, reset the tappet clearance and use a DTI on the rocker's to detect the opening and closing of the valves. In my view any cam with a longer duration of 280 degrees is going to be tricky to dive on the road as the power is not in the right place at low revs. Bruce. Quote Link to post Share on other sites
Andy Moltu Posted April 4, 2020 Report Share Posted April 4, 2020 Pull each injector out one by one and check if injecting. Pull the plug caps off one by one and see if tick over slows down - if it doesn’t it might be the car isn’t firing on that cylinder. Check plug and lead if ok pull that injector is working. Quote Link to post Share on other sites
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