Refining My T120V

[Rudie]

establish what jets are now not right following downpipes (slightly larger diameter) and silencers (bigger, longer, a restriction, larger outlet) swap.

Fwiw, when I started down that slippery slope many years ago, the rule of thumb for real Dunstalls (it was that long ago) and K&N filters was a 10% increase in main jet size for each ...

dunstall-type silencers have a perforated disc half way down.

Real Dunstalls have something similar. Is necessary.

No tacho or Speedo cables; true there's no working tacho or speedo, but trivialities, trivialities...

This company builds electronic versions of the Smiths tacho and speedo on your bike.

 

[solomon]

Fwiw, when I started down that slippery slope many years ago, the rule of thumb for real Dunstalls (it was that long ago) and K&N filters was a 10% increase in main jet size for each ...

I'm not sure, because it's only me here, no one with experience to verify. But matches a description I've read. Goes, ha, ha, ha, ha, ha. and there's no more increase in power as throttle is twisted. Stops ha, ha-ing on easing off the throttle. There's no pops or backfire. So, I think it's eight stroking. Which means too rich, which means smaller jet?



Been on a few miles run, tested at different speeds and revs, both fairly hot and heat-soaked engine. Opened throttle smoothly. Always eight strokes/whatever-it-is at exactly half throttle. So that's needle jet/needle?

Can't test main jet because playing up before main jet comes into play at 3/4 to full throttle.

 

[solomon]

This company builds electronic versions of the Smiths tacho and speedo on your bike

Think they cost about £300 each. Any future owner who concerned about authenticity won't like them any way.

I've order separate smaller (2") speedo and tacho clocks. Speedoiis £45, tacho £15. Didn't really like the 3" electronic Speedo/tacho anyway, didn't look too good.

 

[solomon]

Been on a few miles run, tested at different speeds and revs, both fairly hot and heat-soaked engine. Opened throttle smoothly. Always eight strokes/whatever-it-is at exactly half throttle. So that's needle jet/needle?

Can't test main jet because playing up before main jet comes into play at 3/4 to full throttle.

Reading this helpful info...

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commons.princeton.edu

I raised the carb jet-needle clips to their highest point (needle now lower). And went for another test run. Difficult to find a long steep hill with no traffic (run out of road) or old ladies walking their old dog. Found one, and could open throttle wide under load.

The good news is ... it now ha-ha-ha-ha-s at 3/4 open throttle.
I'm guessing that means the needle jet and needle are now okay.
Main jet comes into play at 3/4 throttle, so that needs to be smaller. No idea how much smaller, just have to buy a size down a see.

 

[solomon]

Just read this from the above Princetown link...

Twin mixture Plug reading should only be treated as a rough guide as it can be misleading. For instance, by examining the plugs of a parallel twin it might appear that the right hand cylinder is running slightly richer than the left. On a twin carb engines this may be so – but there is another factor to be considered. On most twins the main oil feed to the crankshaft is from the timing side and, consequently, that cylinder is likely to get a shade more oil than the other. Therefore, the plug deposit is possibly the dark carbon of burnt oil rather than the soot of richness.

Now I can stop worrying one plug is always a bit blacker.

 

[solomon]

Main jet comes into play at 3/4 throttle, so that needs to be smaller. No idea how much smaller, just have to buy a size down a see

Took a main jet out to look. It's 180. Would mean trying a 170 or 160. Never seen a posting with someone having such a small main jet in a Triumph 750. So...





Removed the air socks. Probably done less than 1,000 miles since I fitted them, so clean, not clogged.

No more eight stroking at WOT. Fairly easy mod! Most of the day has still gone somehow...

Will now have to try putting needle back to middle clip.

Or, I now know, jet is not far off, can buy one size smaller.

 

[solomon]

What’s the plan for the seat?

Bought a leather jacket off eBay especially. Got one with a horizontal, not vertical seam, in middle of back.

 

[Rudie]

main jet comes into play at 3/4 to full throttle.

Not true. Main jet size affects the mixture throughout the rpm range. Is why every Amal tuning guide says to tune w.o.t. first ... because then nothing else in the carb is affecting the mixture.

I discovered main jet size affects the mixture throughout the rpm range when I took the bike on a long journey. No way I was riding a triple at w.o.t. all the time, or even most of the time, but main jet size changed the fuel consumption noticeably = one size = 5 mpg.

main jet
180.

Given the standard main jets in a T120, I highly doubt these are correct if your bike does not have standard air filters and possibly has less restricted silencers. Ime, more likely the previous 'tuner' set the main jet size for fuel consumption and never rode the bike at w.o.t.

Finding something like a main jet so far from standard, when neither air filtration nor exhaust are standard, I would never follow what any previous 'tuner' (and I use the inverted commas advisedly) did. A pair of standard genuine Amal main jets might not be cheap but they are a lot cheaper even just for a starting point than a complete engine strip because it objected to your tuning efforts by lightening one or both pistons for you ...

If you think tuning for a one off air filtration and exhaust combination is going to be cheap, refit all the standard parts and fiddle with something else.

Would mean trying a 170 or 160. Never seen a posting with someone having such a small main jet in a Triumph 750.

Precisely.

View attachment 54632

Consider replacing that tap (and its twin on the other side), they break easily just under the tank. I saved a near full tank of fuel because the-then girlfriend was close by and could fetch empty cans, tip full into car, etc. while I held a finger over the hole in the tank. Others with same have been less lucky ...

 

[solomon]

Not true. Main jet size affects the mixture throughout the rpm range. Is why every Amal tuning guide says to tune w.o.t. first ... because then nothing else in the carb is affecting the mixture.

I discovered main jet size affects the mixture throughout the rpm range when I took the bike on a long journey. No way I was riding a triple at w.o.t. all the time, or even most of the time, but main jet size changed the fuel consumption noticeably = one size = 5 mpg.


Given the standard main jets in a T120, I highly doubt these are correct if your bike does not have standard air filters and possibly has less restricted silencers. Ime, more likely the previous 'tuner' set the main jet size for fuel consumption and never rode the bike at w.o.t.

Finding something like a main jet so far from standard, when neither air filtration nor exhaust are standard, I would never follow what any previous 'tuner' (and I use the inverted commas advisedly) did. A pair of standard genuine Amal main jets might not be cheap but they are a lot cheaper even just for a starting point than a complete engine strip because it objected to your tuning efforts by lightening one or both pistons for you ...

If you think tuning for a one off air filtration and exhaust combination is going to be cheap, refit all the standard parts and fiddle with something else.


Precisely.


Consider replacing that tap (and its twin on the other side), they break easily just under the tank. I saved a near full tank of fuel because the-then girlfriend was close by and could fetch empty cans, tip full into car, etc. while I held a finger over the hole in the tank. Others with same have been less lucky ...

I get 60 to 65mpg. About right.
Plugs always fine. No flat spots.
Not possible to start with main jet if there's something out lower down, and that's one but not the only school of thought. I'm aware of John Healey's observations. Now everything is working, I can and will work down. Going out later to check repositioned needles.

The fact it started eight-stroking showed it was running richer after fitting more restrictive silencers. That's normal.
Taking air socks off then made it run slightly leaner. That's to be expected, which is why I did it.

I've done a bit at 80mph, and a fair bit of lively acceleration. Generally, though, I ride 20-60 mph. Nothing wrong in tuning a bike to be more economical with fuel. I'm perhaps unusual, a biker that's concerned with the amount of carbon spewing into the atmosphere.

Main jet, I understand, should just be off eight stroking. That way it's not too lean, no holes in pistons. My main jet is now just off eight stroking, which is correct.

Ridden thousands of miles with the present main jets. Taken head off few hundred miles ago, no issues with piston tops, no pitting.

Carbs are on there way out, could effect things perhaps. But, I'll get a few thousand more miles from them yet.

It's not expensive to fit new jets, they are five pounds each, and I have some factory size, 210, anyway.

What do you mean about the petcock? Seem standard to me. Which type is better?

 

[solomon]

Well, been out. With new GPS speedometer fitted, testing running through throttle range.



The second GPS module with all that wiring is temporarily there because thought first module was faulty.

The second empty clip is for the tachometer, when it arrives.

Module not faulty. Got similar/same issue as with previous GPS clock. Switch ignition on. Clock/module finds GPS signal. The coordinates can be seen in the display. Start bike, and it loses GPS coordinates, so no speed registration.

I'll get some resistor spark plugs. Have read this can help with onboard electronics.

My Wassel electronic ignition and dual coil should be okay with resistor plugs.

*

Other than that, bike is running well through all the throttle now. I can't do WOT plug chops in the city, get to an insane speed within seconds, even uphill and pulling from low revs; the bike doesn't lack power. I'll wait until I do a trip to the countryside, see if I find a suitable road. For now, it's okay though.

 

[Rudie]

What do you mean about the petcock? Seem standard to me.

"Should've gone to Specsavers" ...

View attachment 54632

Assuming that is the reserve tap in your photo above, it is 60-7267; it and main tap 60-7266 were not o.e. until mid 79 onwards, were fitted until Meriden swapped to Italian-made tanks with male-thread spigots for the Paioli taps during 82.

When your bike was new, it would have been fitted with 83-2800 main and 83-2801 reserve. What is sold now under those part numbers are:-

... which look remarkably exactly like the 82-4971 and 82-4972 taps Triumph fitted for years before ...

Btw, your photo also shows the wrong tap-to-tank sealing washer - it should be a 70-7351 Stat-O-Seal with a 83-0002 plain washer:-

... otoh, the copper outer of the sealing washers in your photo can scratch (have already scratched?) the tank paint when the tap locknut is turned; the correct 70-7351 will not scratch the tank paint.

Which type is better?

Depends what you want:-

. main only on one side, reserve only on the other side, the 83-2800/1 combination above;

. otoh, since the Co-op fitted the Paioli taps, I have preferred both main and reserve on both sides - whenever the bike needs reserve, I can switch with whichever hand is free, changing the other tap when more convenient:-

.. generally, easiest are In Motion Trial Competition and In Motion Trial Competition I have a pair; however, their sometimes problem is not all are threaded fully as in the photos, but that is easy to fix with access to a 1/4"BSP die;

.. the other alternative, that I have also used, is an 83-7970 adaptor into each tank thread and a pair of handed Italian taps - either original Paioli or current BAP sold by Moto Guzzi dealers for the large capacity air cooled engines (the Co-op originally made the 83-7970 male-male adaptor so pre 82 Triumphs with 1/4"BSP female threads in the tanks could use the original Paioli taps, as they had and the Guzzi/BAP taps have metric female threads).

 

[solomon]

Ok. I'll get a 83-2800/1 pair. Look easier to turn lever. Present ones difficult with thick gloves in a panic.

I've got those trials petcocks. Recommended by a mod on a forum ...



Bought for a Brit OIF tank that has enormous separate halves. Plasticky lever, but nothing's perfect. They look alloy though, so no stronger than the present ones?

Other problem with them is, once a nut is found and fitted, there's not a lot of thread. My Brit tank is alloy, so might not use them in that, don't want to stress the tank threads...

 

[solomon]

Once the resistor spark plugs arrive, if tacho and speedo still don't work, I'll disconnect the stator to battery. Assume this won't damage stator windings when engine runs at highish revs?

If clocks then work, means the regulator isn't producing a clean enough DC current. The clocks are not designed for motorcycles.

I'll then buy a MOSFET regulator, if that is the case.

The tacho arrived today. Looks good! Will need sealing at back with silicone. ..

 

[Rocky]

Good luck! I hope everything works for you.

 

[Rudie]

I've got those trials petcocks.
They look alloy though, so no stronger than the present ones?

Most taps at least have alloy bodies, except the 83-2800/1 and similar, that have brass bodies. However, only a 60-7266 or 60-7267 has broken on me, and I am not the only one that has posted such an occurrence.

Once the resistor spark plugs arrive, if tacho and speedo still don't work, I'll disconnect the stator to battery.

I assume you mean you will disconnect the reg./rec. from the battery? If so, as long as the (alternator) stator remains connected to the reg./rec., the latter should regulate the stator's output as normal.

If clocks then work, means the regulator isn't producing a clean enough DC current

... or the reg./rec. is just faulty? What reg./rec. are you using?

 

[solomon]

an occurrence.

I assume you mean you will disconnect the reg./rec. from the battery? If so, as long as the (alternator) stator remains connected to the reg./rec., the latter should regulate the stator's output as normal.

... or the reg./rec. is just faulty? What reg./rec. are you using

Thanks. I'll be sure to leave the reg/reconnected to stator.



Reg/rec came on bike. The handlebars voltmeter is steady-reading on riding, if that means anything. It looks like the £10 ones that can be bought on eBay. I've got a spare similar one (actually bought for £10 on eBay), but a MOSFET reg/rec can be bought for £40 anyway. Although as a MOSFET looks no different, who knows what one's being sold?

 

[Rudie]

MOSFET reg/rec can be bought for £40 anyway. Although as a MOSFET looks no different, who knows what one's being sold?

MOSFET reg./rec. from a well-known company

 

[solomon]

Just been out for a ride. The new resistor spark plugs have solved the problem. Both tachometer and speedometer now work perfectly!

Here's the dash now...


Tacho, speedo, oil guage, voltmeter. GPS module is zip tied on top of voltmeter. The six feet of cabling from GPS module is coiled in headlamp. The little black switch is day riding lights, 10w LEDs in the indicator shells.

Tacho and Speedo have a shared dedicated earth direct to battery -ve.
*

The new downpipes without crossover pipe do sound better. There's the distinct thump of a each cylinder, even at medium revs.

They are rather loud though. A woman grimaced at me when I started the bike. Considering she was shouting in her phone in a public space, thought I was doing the neighbours a favour, drowning her out. Just to annoy her more, I spiritedly accelerated away. The road was resurfaced a few months back, and there's still gravel strewn all over it. My back wheel did a bit of a wobble, which might have looked impressively hooligan even though I was out of control.

 

[solomon]

Just in case anyone wonders, here's why the resistor plugs solved my problem

https://www.ngk.com/what-is-a-resistor-spark-plug

The bike started, idled and ran just as well as with the non-resistor plugs previously fitted.

I'm now using NGK BR7ES. Previously used NGK B7ES.

 

[Rudie]

The new resistor spark plugs have solved the problem.

Just in case anyone wonders, here's why the resistor plugs solved my problem
https://www.ngk.com/what-is-a-resistor-spark-plug

Digital electronics needing HT suppression was posted for you some time ago ...

I'm now using NGK BR7ES. Previously used NGK B7ES.

When Triumph built your bike, they fitted Champion N3 plugs. Their NGK equivalent is B8ES (BR8ES with a built-in resistor). B(R)7ES is a 'hotter' plug; if you intend to do high rpm to then look at spark plug colour, while it is now an even less reliable method of determining mixture and jetting, the wrong plug heat range can affect the spark plug colour, possibly misleading you further.