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Plug gap

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Pat.L Avatar
Pat.L Patrick Ledford
New Wilmington, PA, USA   USA
I am running both a Pertronix coil and Dizzy. I had read with that coil I could increase plug gap and lean the mixture. What can I take the gap out to? .040; .045, or more?

I had electronic ignition with the Lucas sport coil on my TR6 and when I opened the plug gap on that car I really saw no difference.



Patrick
1980 TR8 DHC TPVDV8AT209637
1957 TR-3 Under restoration TS20462LO
Western Pennsylvania Triumph Association
North Coast Triumph Association
TWOA

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sliproc Avatar
sliproc Kevin Quistberg E
Long Beach, CA, USA   USA
Patrick,

If you've already widened the gap on your electronically equipped TR6 and saw no difference what's the point of doing it on your TR7? Unless your TR7 came originally with points you probably won't realize much improvement in performance with the Pertronix setup, since the TR7 electronic system is basically the same thing. Also, I'd be careful about how much you lean your mixture, too lean is a good way to burn an exhaust valve.

This is my experience with gap widening. My '74 Jensen-Healey came to me with a stock points system. I replaced the points with a Pertronix unit, upgraded the coil with a Lucas Sport model, and added an MSD ignition module. I widened the gap to .045 (wider than that it starts to miss) after this there was a small but noticeable power increase and the motor seemed to rev in a smoother, silkier manner.

POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
How would you intend to lean the mixture anyway? I am assuming you have Stromberg carbs and their set mixture is not easily changed. As I'm sure you know Strombergs have no separate idle system. Idle to WOT draws fuel from the bowl, up the main jet past the metering needle and into the venturi. It's the metering needle and it's location in the main jet that determines mix and that changes with throttle/air-valve position. You may be able to lean it a bit by lowering the needle in the carb's air-valve but I doubt it will make any appreciable difference in economy or running, but you will more than likely be rewarded with a rougher idle. Leaving the very upper portion of the needle alone and modifying the needle would be the way to go IF you have the experience to know what you are doing and have a micrometer and or access to other needles and a needle chart that shows the different tapers for comparison. There is potentially a good chance in quickly ruining needles if you are not careful. All that being said, there is a member on this forum who has modified his TR8's Strombergs needles by chucking them up in a drill press and carefully 'turning' them down using just fine emery cloth with apparently good results. However, he is pretty experienced with both his modified engine and it's carburation. - Pete

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Pat.L Avatar
Pat.L Patrick Ledford
New Wilmington, PA, USA   USA
I asked the question becasue I wondered if having a system with matching coil and Dizzy would make a difference over the sport coil and generic electronic ignition. I am running rich now and while I did make an adjustment I haven't had it our of the garage to make a drive to check the plugs. I will probably play around with the gap and timing.

I am aware of too lean a mixture will cause burnt valves.



In reply to # 1526935 by sliproc Patrick,

If you've already widened the gap on your electronically equipped TR6 and saw no difference what's the point of doing it on your TR7? Unless your TR7 came originally with points you probably won't realize much improvement in performance with the Pertronix setup, since the TR7 electronic system is basically the same thing. Also, I'd be careful about how much you lean your mixture, too lean is a good way to burn an exhaust valve.

This is my experience with gap widening. My '74 Jensen-Healey came to me with a stock points system. I replaced the points with a Pertronix unit, upgraded the coil with a Lucas Sport model, and added an MSD ignition module. I widened the gap to .045 (wider than that it starts to miss) after this there was a small but noticeable power increase and the motor seemed to rev in a smoother, silkier manner.



Patrick
1980 TR8 DHC TPVDV8AT209637
1957 TR-3 Under restoration TS20462LO
Western Pennsylvania Triumph Association
North Coast Triumph Association
TWOA

Pat.L Avatar
Pat.L Patrick Ledford
New Wilmington, PA, USA   USA
I am using SU's.

In reply to # 1526946 by POW How would you intend to lean the mixture anyway? I am assuming you have Stromberg carbs and their set mixture is not easily changed. As I'm sure you know Strombergs have no separate idle system. Idle to WOT draws fuel from the bowl, up the main jet past the metering needle and into the venturi. It's the metering needle and it's location in the main jet that determines mix and that changes with throttle/air-valve position. You may be able to lean it a bit by lowering the needle in the carb's air-valve but I doubt it will make any appreciable difference in economy or running, but you will more than likely be rewarded with a rougher idle. Leaving the very upper portion of the needle alone and modifying the needle would be the way to go IF you have the experience to know what you are doing and have a micrometer and or access to other needles and a needle chart that shows the different tapers for comparison. There is potentially a good chance in quickly ruining needles if you are not careful. All that being said, there is a member on this forum who has modified his TR8's Strombergs needles by chucking them up in a drill press and carefully 'turning' them down using just fine emery cloth with apparently good results. However, he is pretty experienced with both his modified engine and it's carburation. - Pete



Patrick
1980 TR8 DHC TPVDV8AT209637
1957 TR-3 Under restoration TS20462LO
Western Pennsylvania Triumph Association
North Coast Triumph Association
TWOA

POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
In reply to # 1526953 by Pat.L I am using SU's.



Well sorry to waste your time about all that Stromberg stuff, but essentially you are up against the same thing. Tuning of both brands of carbs is essentially done for the smoothest idle. If using the standard needles, anything you do that will lean, or make richer for that matter, will mean pulling the needles out a bit (leaner), or pushing them in a bit (richer). Either action will degrade your idle from optimum. If you happen to be using older SU's with up and down adjustable jets and stationary needles you will still be moving away from best idle with virtually no change in cruise mixture. The only practical way to lean or richen this type of carb's mix is to change needles, or work out a profile you think may work. - Pete

Pat.L Avatar
Pat.L Patrick Ledford
New Wilmington, PA, USA   USA
It was not a waste of my time. When ever I learn something it is beneficial. It is also possible that I may go back to the Strombergs. I am probably a pure novice on carburetors but I am willing to stick my nose in and try and fix, improve, or break it. I am running HIF6's and there is a jet adjustment screw on the side of the carburetor. Also, according to Rimmers since I am using K&N filters I can run the next richer Jet and if I go to headers I can go another richer jet. I have the stock jet and I can go back to it if I can not lean the gas to a probe working level.

Our local club carburetor guru hates the HIF6 carburetor because they seem to be problems. Last fall I scored a set of 1975 TR7 Strombergs that have the factory choke set up and I might convert the TR8's Strombergs to manual choke if I can get the water chokes to operate correctly.

In reply to # 1526973 by POW
In reply to # 1526953 by Pat.L I am using SU's.



Well sorry to waste your time about all that Stromberg stuff, but essentially you are up against the same thing. Tuning of both brands of carbs is essentially done for the smoothest idle. If using the standard needles, anything you do that will lean, or make richer for that matter, will mean pulling the needles out a bit (leaner), or pushing them in a bit (richer). Either action will degrade your idle from optimum. If you happen to be using older SU's with up and down adjustable jets and stationary needles you will still be moving away from best idle with virtually no change in cruise mixture. The only practical way to lean or richen this type of carb's mix is to change needles, or work out a profile you think may work. - Pete



Patrick
1980 TR8 DHC TPVDV8AT209637
1957 TR-3 Under restoration TS20462LO
Western Pennsylvania Triumph Association
North Coast Triumph Association
TWOA

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Attachments:
Engine from Firewall.JPG    66.1 KB
Engine from Firewall.JPG

RossL Silver Member Ross LoMonaco
NJ, USA   USA
Joe Curto may have the parts you need to adjust your mixture. Joe's web page

I rebuilt a pair of SU's for my TR6 and he had everything including needles and jets in stock.

I have never noticed a difference when opening the gap on plugs. Even tried this on a Chevy v8 that was equiped with an MSD multi spark capcitive discharge box. Same with my TR6 with a sports coil.

It may help burn the fuel better assuming you have a larger spark....



Edited 2 time(s). Last edit at 2018-04-18 08:29 AM by RossL.

POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
Knowledge is power my friend. This is a pretty small blow-up of an HI S6 but note #'s 16 - 21. Number 21 is an idle mixture adjust only. It will have little to do with overall mixture change at cruising - WOT RPM. I'm pretty sure the main is fixed, and changing needles is the only way to effectively influence Mixture. This carb really does not look too difficult to set up. - Pete

https://www.scparts.co.uk/sc_en/british-cars/mg/mgb-1962-1980/carburettor-and-air-filter/su-hif6-internal-carburettor.html


https://www.facebook.com/PracticalClassics/posts/772455786106044


I really don't know what RimmerBros means by going up a jet size with K&N filters and another jump with headers as it looks to me jets are all .090" and varying the mix can ,once again, only be done varying the taper of the needle that goes into it. - Pete



Edited 1 time(s). Last edit at 2018-04-18 12:29 AM by POW.

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Pat.L Avatar
Pat.L Patrick Ledford
New Wilmington, PA, USA   USA
In reply to # 1527116 by POW
I really don't know what RimmerBros means by going up a jet size with K&N filters and another jump with headers as it looks to me jets are all .090" and varying the mix can ,once again, only be done varying the taper of the needle that goes into it. - Pete

Sorry for naming the part wrong, it is the needle that is changed from a BAF to a BAC. I just wrote the reply before looking up what I was talking about.

Thanks for the articles, the Facebook page does address the issue of one carb running richer than the other. I am making an exhaust change and I have new BAF needles if needed. If that does not correct the issue I will probably go back to the Strombergs.

I have resisted the the 4BBL change becasue I do not believe the expense is justified with my driving style, no autocross or racing. Of course that option is out there.



Patrick
1980 TR8 DHC TPVDV8AT209637
1957 TR-3 Under restoration TS20462LO
Western Pennsylvania Triumph Association
North Coast Triumph Association
TWOA

POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
In reply to # 1527141 by Pat.L


I have resisted the the 4BBL change becasue I do not believe the expense is justified with my driving style, no autocross or racing. Of course that option is out there.

This is a smart move. My '81 originally had EFI and I was experiencing issues with the system. Because I thought the expense and admittedly the unknown repair procedure would be too much, and because HUGE gains were promised with just the simple installation of a "pre-jetted" kit. A cam, a rebuild to higher CR, a better ignition system and THREE (3) ! carburetors later, each one of them with hours and hours of work in an attempt get good power and drivability, I'm finally at a happy place with my engine. In retrospect, If I wanted to change from FI I should have gone with Strombergs or SU carbs. They are simple, well engineered carbs and flow pretty well.

Your set-up looks very clean. do you know the history of the SU carbs. I ask because US 8's only came with Stomberg carbs so it's possible the needles are not correct from the start. Are you experiencing black plugs? I realize your initial thread is about plug gap but leaning the mix seems to be your goal. I would think the base needle in your set-up would be whatever was run in the 8.13:1 CR British Rovers. They are essentially the same engine as the US version but with SU carbs. I honestly don't know if those Rover engines used the HI S6 version though. - Pete

Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR8 "Wedgie"
In reply to # 1526759 by Pat.L I am running both a Pertronix coil and Dizzy. I had read with that coil I could increase plug gap and lean the mixture. What can I take the gap out to? .040; .045, or more?

I had electronic ignition with the Lucas sport coil on my TR6 and when I opened the plug gap on that car I really saw no difference.

Widening the plug gap allows you to run very lean mixtures because lean mixtures are more difficult to ignite, and a hot coil and wide gap increase the reliability of igniting the lean mixture. Lean mixtures give you better fuel economy and lower emissions and are desirable for this reason.

For POWER, you want slightly rich mixtures, because the extra fuel cools incoming air and allows a denser charge in the cylinder. So a mixture down to 12:1 is optimum for power, but crummy for economy and emissions. 16:1 is great for economy, but difficult to ignite and reduces power. 14.7:1 is stoichiometric and is the best balance between the two extremes.

Can you have the best of both worlds? Yes. You select a needle profile that runs lean at lower RPMs, and runs rich at high RPMS.

For a car running a near stoichiometric mixture, I would not expect a hot coil and wide gap to do much if anything.

As to "how wide", well obviously that depends on your compression ratio, fuel mix, and the output voltage of your coil. 0.035 should be easily obtainable (that is what the injected TR8s ran), but as always your mileage may vary. The is no harm in experimenting to see how wide you can go, but you would need to test over a wide variety of conditions; hot, cold, WOT, high altitude, etc. to be certain.

Vance

Vance



1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore

Darth V8R Avatar
Darth V8R Vance Navarrette
Beaverton, OR, USA   USA
1980 Triumph TR8 "Wedgie"
In reply to # 1527033 by Pat.L It was not a waste of my time. When ever I learn something it is beneficial. It is also possible that I may go back to the Strombergs. I am probably a pure novice on carburetors but I am willing to stick my nose in and try and fix, improve, or break it. I am running HIF6's and there is a jet adjustment screw on the side of the carburetor. Also, according to Rimmers since I am using K&N filters I can run the next richer Jet and if I go to headers I can go another richer jet. I have the stock jet and I can go back to it if I can not lean the gas to a probe working level.

Our local club carburetor guru hates the HIF6 carburetor because they seem to be problems. Last fall I scored a set of 1975 TR7 Strombergs that have the factory choke set up and I might convert the TR8's Strombergs to manual choke if I can get the water chokes to operate correctly.

Pat:

At the risk of causing controversy, I can say that I am very happy with the water chokes on my TR8. My car is cammed with higher compression than stock, a mild port job, and K&N filters. I had to go to the richest needles that Rimmer sells to get the fuel mixture close, and ended up tweaking my needles in a drill for a final adjustment.

The water chokes do require care during assembly, as there is a thermostatic spring inside that requires a small tang to engage the enrichment needle. Also, the enrichment needle has an itsy-bitsy o-ring on it that must be in very good condition to insure the cold start circuit shuts off completely when the engine is warm. Put them together carelessly, and the choke function is disabled. Also, a very small adjustment (1 mm) of the choke housing makes a very significant difference in the cold start and warm up characteristics. I suspect some people over adjust them, then tear them apart in frustration, and get them back together such that they are inoperative. But that is a guess. The Haynes manual on Zenith carbs was very helpful when I rebuilt mine.

I ran an HIF6 carb on my mini, and was very happy with it. I did replace the original butterfly as it had a HUGE bypass valve in the middle of it that adversely affected flow, but it worked great, and was easily adjusted to get an optimum mixture.

The best advice I can offer is to get a detailed manual on whatever carb you decide to use, and read up on the carb. You will avoid a bunch of mistakes that will cause to believe the carb is crap, when all it needs is a little TLC to perform admirably. The factory shop manual typically does NOT have sufficient detail, at least in my experience.

Vance



1980 Platinum Metallic TR8, navy blue interior
Bare metal respray, Crower cam, raised compression
ported heads, modified Zenith carbs, 0.060" overbore

sliproc Avatar
sliproc Kevin Quistberg E
Long Beach, CA, USA   USA
Patrick,

It seems like you've got two things going on at the same time. Personally I've found it better, when possible, to tackle one problem at a time. Plug Gap being the title of this thread I'd say this, the stock(generic)unit and the Pertronix are basically the same thing, pointless electronic ignition. With this setup I don't think you'll be able to widen the gap that much, I've found the stock unit to be quite adequate which is why I never replaced it with a Pertronix unit. Still, you can always try increasing the gap by increments of .005 until it starts missing to see how far out you can take it. If you add an MSD unit you'll definitely be able to increase the gap.

As far as your mixture goes, I wouldn't worry to much about it until you're happy with the ignition setup. However, when in doubt I've found it's better to run too rich vs. too lean. Too rich you'll foul plugs, too lean you can burn a exhaust valve and the head has to come off.

Pat.L Avatar
Pat.L Patrick Ledford
New Wilmington, PA, USA   USA
Sorry for the late reply guys, but the site would not load last night

After I install the new exhaust and a couple of little minor adjustments and the car is back on the ground I will get into the ignition and carbs. Re-check the settings on the plugs and timing. Drive, pull plugs for color and determine whether to go back to the stock needles, which I have. Joe Curto sent the stock needles with the rebuild kits I ordered from him based on the carburetor tag numbers. The needles installed now are the ones that came with the carbs, which was from a UK SD1 1980ish year. After reading Peter's links to articles it may be those original needles may be too worn to work correctly.

Vance, if it wasn't for the horror stories from local club members about the water chokes, mostly from Spitfire owners I probably would have kept the Strombergs and as I said before I may end up going back.

Peter, I installed the Petronix because of bad Lumenition ignition and it was suggested I change coil and dizzy.

Thanks for all the help.



Patrick
1980 TR8 DHC TPVDV8AT209637
1957 TR-3 Under restoration TS20462LO
Western Pennsylvania Triumph Association
North Coast Triumph Association
TWOA

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