What carb needle do you use in your *standard* TR7?

[edgyWedgy]

Hi guys,

I have found that my engine is stuttering while above around 4000rpm,
using the choke really improves the performance and eliminates the stuttering. Acceleration between 1000-3000rpm is excellent though, really love the torque in this low-end rev range. This would mean the mixture is too lean at high rpm, which probably means that the needle is too lean in high rpm.

atm i'm using 20W50 as dashpot oil (which is too thick, so i'm looking for an alternative), so this can't be the cause of the stuttering.
Everything on the engine is stock, filter, manifold, exhaust etc. The only thing is that it has been revised recently, and thus it is still in it's running-in period, it's covered 800 fairly sporty km's now. The cylinders have been honed and oversized pistons have been placed so the stroke volume might be somewhat higer, and due too the running-in period, compression might still be slightly low. I'm using RON95 fuel by the way.

I'm curious about what needles you guys use. The most important for me is that it runs well, additional goal is that it runs fairly economic, but still has reasonably performance. I'd like to hear about your opinions.

Cheers

[Beans]

Standard TR7 engine (so with stock BDM needles) should easily get passed 5500 rpm in the lower gears.

20W50 for the carburettors is OK (actually that's what the instruction handbook prescribes for temperatures above 0°C).
Get rid of the RON95 fuel and get some decent RON98, or if you're close to the German border RON100 or RON102.
After that check the carburettors get enough fuel, and if there are any blockages in the fuel line.
Also carburettors state of tune (aim for CO 3,0 - 3,5% and Lambda ±1,0) and check the the spark plugs colour.

If that doesn't solve the problem start with the wiring ...

p.s the engine is pretty new but check the valve clearances just for good measure

[edgyWedgy]

My tank is nearly empty now, so i'll take 98RON for a try if you advice that.
It's recently been tweaked with a professional CO meter, and because of the running-in period the guy who did it said it would be beneficial to enrichen the mixture a bit. It's set at 5% CO at idle. That is indeed high if you ask me, but the guys there have epxerience with classic cars so i think they know what they're doing. It can be set to 3-4% or so when the running-in period is over.

Something that bothered me ealier; the coil should be a 6volt because that's what you get from the ignition wiring after starting, but i couldn't say whether the coil is a 6 or 12V one. Just to rule out the potential cause, i connected 12V to the coil, and now it runs fine up to 5500rpm. I immediately thought that this was the cause, but after driving 10km the coil felt really warm, i wouldn't touch it for more that 2 seconds. Coils aren't meant to become this warm i believe so i'm a bit confused, because the result was very nice. But i think i'm killing the coil by using 12V. If it actually is a 6v one, then i'm just overloading it to get a fat spark.
Would a performance coil that is rated to ouput this power be beneficial?

These were the results of the gastest, its done by Toncar in Berkel, so meybe you know them.
HC value is pretty good if you ask me, which would mean no air leaks according to the mechanic.

Valve clearances are fine btw.

[Hasbeen]

Hi Wedgy.

You did not mention air filter. The standard filter, is a very restricting thing. Many have sports filters & one manufacturer of performance filters makes an easy breathing filter to fit the box.

I have sports foam filters on a pretty standard 7. It was happy on stock needles with a standard filter, but ran into very lean mixture when I fitted the foams. It would not rev past 3500 RPM to save it's life in 4Th or 5th, & struggled at 4000 in 3Rd.

I went up 3 stages in needles & ended up with BAL, which perform pretty well. They only get richer above about 2200 so have no effect around town, except at traffic light grand prix. When this was discussed some years back many others had ended up on the BAL needles on mildly tuned 7s.

Hasbeen

[saabfast]

Not sure where you are (not in the UK I guess) but 5% is too high and would fail a UK MOT (max 4.5%). As beans says, 3-3.5% is ideal as its not too rich and does not lean out too much at higher revs.

As Hasbeen notes, BAL needles are what is normally supplied for high flow filters and tubular exhausts, this is what Rimmers have in their air filter conversion kit.

[Beans]

Setting the engine slightly rich won't harm on a fresh engine. And although 5% is outside the APK/MOT range it shouldn't influence overall running very much.
The fact that with 12V @ the coil improves running might point to an ignition problem.
With the ignition switched on measure the voltage you get @ the coil.
Might be that the resistance wire is getting old (= getting more restrictive).
If the reading is between 6V and 8V try another coil. But make sure the distributor is in the correct position

As for a new coil, Bosch high performance 6V comes highly recommended ...

[edgyWedgy]

@Hasbeen I indeed still have the standard air filter. in comparison to other standard filter, they look quite good, ie. they have a fairly great surface, more than the k&n filters. They could still give more resistance though, which i think is the case. I would place sport filters, but the thing is, the standard airbox takes its air from before the radiator, which means it takes fresh cold air, whereas sportfilters take hot air from the enginebay. Hot air = less oxygen which means less power and less efficiency. There are sportsfilters that do give an option though, i believe theyre called 'green storm'. You can mount a hose to them to make them take fresh air from elsewhere.

You say BAL needles perform the best for you, do you have a sprint or a normal tr7? then i know what needle i'd need if i switch to sportfilters.
The weird thing still is that it performs excellent with 12V on the coil(which probably is a 6V one..)

@Beans i think you're right about the ignition problem. I have measured the voltage that i get from the ignition before, which is around 6V. I haven't tested it under the load of the coil, the voltage could drop when under load, so ill check that tomorrow.
The 6V is in fact right i found out a while ago, you just have to place a 6V coil and the 7 itself has a balastresistor(they call it eureka wire i believe..) which is bypassed during starting to temporarily overload the coil and get a fatter spark and an easier start.

The high temperatures of the coil when under 12V load tell me it actually is a 6V one i believe. I think it gets only 4V or so when under load, thus giving poor performance. Probably due to wear of the balast resistor in the 7. Its an easy job to fix that though. If it's still not fixed, ill look for those Bosch coils.

@saabfast It might be too high, but i believe they don't check that at our MOT tests here in the Netherlands, but @Beans correct me if i'm wrong. When running-in period has been completed, i'll set the mixture at 3.5%.

[Beans]

All TR7's need their emissions controlled during MOT.
Cars registered before 1-1-1974 are exempt from this.

[sonscar]

I was always led to believe a newly built engine was best set up slightly lean until run in to avoid rich mixtures washing oil from the bores.Steve

[Hasbeen]

Modern engines don't need running in, if they have been built properly. That requirement went out with inaccurate hand machining, & poured hand scraped white metal bearings.

To back up this claim, I built a new F2 engine in 1966. Then & when ever it was rebuilt, we ran it at about 2500 RPM long enough to bring the oil up to operating temperature, [a serious requirement before working the thing], & went racing. That engine not only finished every race it started, but won outright or it's class when racing in F1 races, in every race for the next 20 months.

We used to be highly amused at people putting a hundred miles on their racing cars to "run them in". After a hundred miles, with the lousy fuels of the 60s, you needed a decoke to get full performance back.

Wedgy if your engine does not have marginal cooling, you can leave off the blanking piece beside the radiator. Your carbs will get all the cool air they require, even in my tropical area. Mine out performs most tuned 7s.

I do believe the warm air feed is probably important in cold areas to avoid icing, but performance would still improved by about 10% with an easy breathing filter in the box, & rich needles. Believe me they are dreadful things, dramatically reducing the charge available to your engine.

In an extreme example, my new in 62 Morgan +4 came with a similar type of box supplying the SUs. It was fitted with a single air filter, fed by outside air. It went onto 2 cylinders at 4500 RPM, as the front carb took all the air available.

The dreadful thing on our 7s as standard, [from the Jaguar parts bin], could not possibly flow 90 BHP with the standard filter. Take it off, fit the necessary needles, & see what an increase you get.

Hasbeen

[edgyWedgy]

@Hasbeen i knew from engines built nowadays that they don't need running-in, because that already happened at the factory, and because of the better and more accurate machinery. It is news to me though that engines built to 70s specs also don't need running-in when rebuilt.
My engine is really properly been rebuilt by a guy who has a lot of experience in rebuilding engines, especially racing engines. Hes a real precisian. He filled the engine up with running-in oil though and recommended me to run it in. i.e. not ro rev it too high above 4000rpm, and push the accelerator to the floot every now and then, in order to create a varying load on the engine, not to make it lazy.

Could it be depending on what kind of engine it is? the 7's engine has notably higher compression than most american engines back then.
The running-in period is almost over already anyway, so it doesn't matter. i'm at 900km now and 1000km is recommended, i'll change the oil to 20W50 then.

I get enough cooling, temps are really high this week in the netherlands, at around 34degrees and the engine keeps perfectly cool with the needle exactly in the middle of the temp gauge. I think i could remove the flaps beside the radiator without any problems.
It's still always better for your engine to take cold air though, so i think i'm going with those green storm filters, or something alike.
Funny that the standard air filter is so restricting, i wouldn't guess it when i look at the size and surface.
The performance is excellent i think, but i may still be missing out on more performance.
And besides, those sportfilters also just look cool :p so ill take them

@sonscar : that's what i have heard too, but i believe bore surface flattening only happens when the mixture is excessively rich.
I have a friend with a 1 series jag E-type who has that problem. He had it setted too rich for a while, and now it's consuming 1liter oil in 1000km. not really that of a problem, but still annoying.

[Beans]

... And besides, those sportfilters also just look cool :p so ill take them ...

They indeed do look good and they will raise performance when you put matching needles in the carburettors ...



But the downside is that they also raise the sound/noise level. Plus to work properly they really need a fresh air duct.
That's why I replaced them with a slightly adapted version of an original early TR7 filter box ...
http://tr7beans.blogspot.nl/2015/04/cool-air-and-noise-reduction-part-2.html

This actually did improve performance slightly, despite the smaller filters.

[edgyWedgy]

Now that's a smart solution! you get the best of both worlds that way. you don't get the looks on top of it, but i guess there's also less noise this way? I think i'm going to do it the same way.

[johnnyj]

I know that the SUs on my '77 fixed head had BDMs fitted and it ran well on them with the standard air filter arrangement.

Unfortunately and as the car is now a shell being restored, I nicked the carbs and now run them on my Bond Equipe as they are pretty much a straight swap in place of the original strombergs. I run them with trumpets and "socks", which I think does give the Bond some breathing problems. Ironically my TR7 originally-originally had strombergs fitted as it had a Dolomite 1850 engine in it. Whatever, either the Bond or the TR7 will need a new set of carbs when the TR7 is finished, as two cars into one set of carbs don't go!!

Sorry, probably none of that is at all helpful!

John

[edgyWedgy]

I runs well on stock needle, or better said; it runs. The point is that it could probably run better.
The high-end(ie.3500>rpm) torque could be a lot better. I haven't read about other people's fidings on how to improve performance, but maybe that is achievable by a needle that is richer in the high-rev range. I know the valve overlap is really big, so that may be limiting the performance, but it's worth trying.

all the best of luck with your project btw