I pulled the plugs today on my XK140 MC OTS. (see picture pf plugs attached).I’m using NGK BPR6ES spark plugs.
I’m hoping for some guidance from those far more experienced than I as to reading their condition and what it says about adjustments needed to my engine/carburetors/etc. The car does not pull steadily in third or fourth gear but seems to struggle to get to the higher revs.
Kind of mystified by the condition of 1 and 6 being so much more “fouled” than the others… Wondering if I need to use a slightly hotter plug (like NGK BPR5ES)?
Any opinions, advice and guidance would be greatly appreciated!
Yep, you’re running too rich.
How is the oil in the dashpots?
Have you tried a mixture adjustment?
Floats set too high?
Starting carb staying on too long?
Getting black smoke or black soot out the pipes on startup?
Burning any oil, blue smoke?
Thanks Rob! Oil in the dashpots seem to be fine. No blue smoke or black soot out the pipes on startup and the starting carb goes off about 2 minutes after starting (also it starts up quickly).
So I’m guessing a mixture adjustment is what is needed. If I understand my H6 carbs correctly, I would need to remove the cap on the bottom of the float bowl to reveal the mixture screw - is that correct? Any advice you could offer for the mixture adjustment? Also I’m curious why #1 and #6 are so much worse than the other 4 plugs?
Yes, the brass cap that sits at the very base of the carb body, be careful not to lose the small fibre washer. In order to weaken the mixture rotate the jet adjusting screw clockwise or upwards. If you have the workshop manual it fully describes the process (page C.12). In order to get the ‘correct’ setting in the past, following adjustments, I would often take the car for a run and then on return pull a couple of plugs and check the colour. You want to lean it out more than it is at the moment, but not too much. If you get a lot of crackle from the exhaust on the over run you’ve gone too far!
I don’t know the WHY of 1 and 6 being rich…the others look good. so…who can explain that? Once carbs are in pretty good adjustment…I think your pulling power will be in a timing adjustment. Depending on your car set up, starting out static may be 10 BTDC, with the dizzty dial adjuster set in the middle, points at 016. Road test. As with exhaust crackle that shows too far, same for timing…Advance a little…until slight ping under load on a warm day, .then back off to no ping. Or…if happy just leave at 10. For pulling power it all works together. Your BP-6 seems ok…especially if most your driving is at cruise. You may also check a few of your spark plut wires for “resistance” dizzy end to plug end should not be more than 1,000 ohms or so. Most new spark plug wires are way hi…in the 10K to 20K range…then you add the “R” resistor spark plug which is 1 to 5 K. It is still possible to find the BP6ES…not the “R”. Use the Lucas Sports Coil. By the way…installing a used plug…(crush gasket already used…finger tight and one to two flats more…Far less than a half turn.
Snug and barely firm tight. Do not overtighten.
Nick
Nick, do I understand you to say that the fouling of my plugs might be because my wires and/or coil might not be getting enough spark to the plugs? In other words, are you suggesting that I should check the ohms of those wires first, before trying to adjust the mixture? (with the idea of replacing them if the reading is higher than 1,000 ohms?). Same question with regard to trying the non-resister plugs (BP6ES)?
Makes no sense to me doing anything to the carbs,seems impossible to me that one carb feeding three cylinders has two that look good one that is all sooted up. Regards Gerry 62 Ots Ontario Canada.
I certainly understand your point. If the number 1 and the number 6 plugs are the ones most fouled (apologies to Shakespeare!) it would seem that those wires would be the first suspects to check?
So if you were me what would be the first thing you would check? wires? coil? timing?
Testing the wires to start is certainly the easiest way to begin!
Am I understanding correctly that the “entire” wire should not exceed 1,000 ohms or that the 1,000 ohm reading is “per foot”? (so a three foot wire should measure no more that 3,000 ohms?). Or is there a maximum ohm reading per wire?
Thanks again everyone…you are definitely adding to my knowledge base!
Chet
I’m thinking it has something to do with valves. A compression check wouldn’t hurt. I don’t believe it is a mixture issue. It has to be something that’s cylinder specific. Pull the plug wires from the dizzy cap and make sure the brass tips are good. I soldered mine.
Pat
I was out for a while…as others have suggested…and the reason for my “guess”, is the #1 and #6. If carb richness was the culprit…you expect 123, or 456 or all. It may contribute some…but it seems 1 and 6 are not burning as well. Anyway…dizzy cap brass is one check, plug wires another…not just resistance, but condition…maybe 1 and 6 have some arcing… (can sometimes be seen at night…while running engine)…or cross arc to another wire or metal. As to resistance, in the standard distributor–stock, points etc, you want little to no resistance spark plug wire…an auto speed shop or on line…in 7mm, Yes resistances is measured per foot…but can be zero or 100 or so per foot. Modern wires as said are 10to 20K. The NGK resistor plug is 5,000 ohms. I was sad to see NGK stop producing the non resistor…I bought up a good supply…some still on web. So a few checks ., and yes a compression check is quick and easy…I like to use the rubber push in…not the threaded…just push hard and straight…all plugs out…(threaded comp testers seem to be easy to cross thread…don’t want to do that in your alum head !!) While overall compression numbers are of interest, it is a difference of more than 10-15psi that you are looking for…and really a difference a bit more than that would be of note. I would not fiddle much with carbs–yet…if they are close. My overall reasoning on the things suggested is that you say it does not pull well…in 3rd, 4th…if it was richness alone…it would do ok, maybe a little off, but with some black exhaust…
Nick
oh dang…forgot one…not to speak as to the two plugs…but for the lack of power …accelerating you described: …do check the mechanical centrifugal advance springs (the rotor should turn a little against the springs with light twist…and spring back into position) in the distributor…that add more advance as revs pick up. Weak springs or gummed up mechanical advance could provide little or none…that would cause weak power. For those that like to use points distributors…(ME ! )…a rebuild by either British Vacuum Unit (he will recurve to your car…along with a new revised vacuum unit) , Distributor Doctor or one of the few other trusted builders…makes for a great running car…all else being well tuned.
Nick
