revtothelimit - motorbike forum

Can't help on specifics, as I know SFA about Triumphs. But the process can't be too dissimilar to running in a newly rebuilt LC, and I have plenty of experience of that... I'd suggest that you check in minute detail that the jetting is the same on both sides (I'm presuming it is a twin carb model?) , and if so track down why the RH plug is so much richer than the LH.

Once that's established (probably easier said than done) you need to arrive at a jetting setup that errs on the side of richness (but not stupidly rich) and then complete the running in process. Then find yourself a Triumph specialist who has a rolling road/dyno and take it to him to get it set up bang on.

You can waste days/weeks/months (delete as appropriate) chasing jetting issues, when an expert with a dyno can pinpoint the correct setup in an hour or so.

Its actually a piece of piss to check both sides are the same cause

A) the carbs are right there You could change the main jets without even getting off.
B) I bet you can buy more complicated lawn mowers.

All joking aside, I will sanity check everything first.

I have considered the dyno option. People always say the correct way to do it is to mark up the twist grip etc. The correct way to do it is with a dyno and an exhaust gas analyser. Massively more expensive though.

In that case it's a lot easier than on an LC. Checking main jet sizes means taking the whole carb off the bike and dismantling it. Old Trumpet - 1 : LC - 0

Compared to the time, effort and money of replacing all the bits you've just lovingly fitted, dyno time is cheap. As soon as I get back from France my LC is going to a Man who Can with dyno to get the jetting set up spot on.

Life's too short to piss about...

The other problem with Dynos is finding someone who knows Amal carbs/these engines. Obviously you can just pay for the time, but it'd be better to find someone who knows these engines.

I've read loads of threads etc. about setting up Amals and no one ever mentions Dynos. I think maybe it's a cultural thing, for want of a better term. Old brit owners don't need no steeenking technology to fix their bikes!

Totally agree it's the full solution though.

Mr. Dazzle wrote: Sun Apr 17, 2022 8:07 am The other problem with Dynos is finding someone who knows Amal carbs/these engines. Obviously you can just pay for the time, but it'd be better to find someone who knows these engines.

I've read loads of threads etc. about setting up Amals and no one ever mentions Dynos. I think maybe it's a cultural thing, for want of a better term. Old brit owners don't need no steeenking technology to fix their bikes!

Totally agree it's the full solution though.

Back in the day of Amals, dynos were rarer than rocking horse shit. Dynos that you could just book for a session for your bike were just plain unknown. Is it any wonder it was all fiddle, run, pull the plugs and repeat?

Yeah in the 60s and 70s for sure....but this is 2022.

I suppose it's a pretty rare beast ; Someone who done lots of dyno running but who's also mostly into old bikes.

I know someone who knows dynos and knows Mikuni carbs, dunno if that's any use, or whether he'd be interested in doing a Triumph, he's booked up for months with old Japanese bikes, but I can put you in touch.

Sounds like it's running rich, float height effects mixture, it sounds like one of your fuel levels is high.

The floats on these carbs are easy to adjust, literally just bend a tab.

There's a tap on each side of the tank, each tap goes to one bowl and the bowls are also cross connected. The right tap had a little pipe which sticks up into the tank, the left is the reserve which can drain the bottom dregs from the tank.

When I tickle them I do the RHS first and it takes ages, the left then tickles almost straight away. Presumably that's cause on the right you're waiting for both bowls and the cross tube to fill up.

Anyway...my point is, I don't think there's any issue with more/less fuel actually getting to the carbs. I wouldn't bet against the float height being wrong on one side though.

The 'proper' method for ascertaining float height is to get a little bit of clear tube and make a manometer type thing. You can plug the tube straight into the bottom of the bowl and directly observe the level in the carb using said clear tube.

That's the proper way to do it on all carbs, Mikuni do an expensive plug with a pipe for their race carbs, most people make one by drilling a hole in the much cheaper ordinary plug.

If you have doubts about fuel flow you can see how much runs out of the float bowl drain plugs in a minute.

You have changed too much in one go...revert to standard and change onething at a time.....

If I revert yo stock there's a good chance it'll be way too lean and melt something.

It's non standard pistons, cams, inlets and exhausts after all.

Le_Fromage_Grande wrote: Sun Apr 17, 2022 10:47 am I know someone who knows dynos and knows Mikuni carbs, dunno if that's any use, or whether he'd be interested in doing a Triumph, he's booked up for months with old Japanese bikes, but I can put you in touch.

Sounds like it's running rich, float height effects mixture, it sounds like one of your fuel levels is high.

Round slide Mikunis are very like Amals (but better made). They are more difficult to tune, for the perverse reason that there is (or at least was) a much bigger choice of metering parts.

This is a Mikuni chart of what is influencing mixture at different throttle openings. The depth of the bands indicates how much influence. Hope it makes sense.




This is the same chart for an Amal.



Maybe you can be bothered reading this lot, maybe not.

https://vintagebikemagazine.com/techni ... cles/amal/

I'm pretty comfortable with what all the adjustments do to the mixture and how/why.

The bit I struggle with is knowing what is actually going on inside the engine. I know how to make it richer/leaner at any one throttle position, but should I?

Plug chops are also only ever half an indication right?

This is why they invented exhaust gas measurement after all.

There's a guy on the LC forums who has an excellent reputation for setting up LC jetting on his dyno. Given that a carb is a carb and as long as you have the various jets/needles/slides to cover all eventualities, would you like me to ask if he'd be willing to sully his stinkwheel dyno with a diesel?

Assuming there is no problem with fuel flow and float level is about right (I’m assuming. You should not assume):

If it pulls well at full throttle, the main jet is not miles off. If it goes into a rhythmic blubbering at full throttle, that’s 8-stroking caused by much too big a main jet or a restricted air filter. You may only see the effect of air filter restriction at high rpm.

If you reduce throttle opening from full throttle, to 7/8 throttle and the engine speeds up a little, the main jet is too small. Go up two sizes and try again.

If you reduce throttle opening from full throttle to 7/8 throttle and the engine hesitates, then recovers, the main jet is too big. Go down one size and try again.

If your needles are in too rich a notch, response to throttle in the throttle ranges you use a lot will be horrible and surging.

And it will soot up the plugs.

If it runs well in the middle notch, don’t try the weakest notch. That can cause dangerous overheating.

mangocrazy wrote: Sun Apr 17, 2022 1:59 pm There's a guy on the LC forums who has an excellent reputation for setting up LC jetting on his dyno. Given that a carb is a carb and as long as you have the various jets/needles/slides to cover all eventualities, would you like me to ask if he'd be willing to sully his stinkwheel dyno with a diesel?

I reckon I'll give it a go and getting it broadly working first, plus get some more miles on the engine, before I decide exactly what I'm doing but this certainly worth bearing in mind ta.

At the moment I'm assuming there must be something obviously wrong for the two cylinders to be so 'mismatched'. It's also something that wouldn't have shown up when the mechanic was working on it, but he didn't actually ride the bike and hence only really ran the engine at idle.

When I used to fiddle with LCs I used to make an adjustment, try it, if it made it worse, I knew I had to go the other way, if I made it better, keep going that way until it got worse, but with LCs you could always ask Leon Moss for a rough idea of where to start from.

yeah that was my vague plan.

I need to get the feel of the bike again a little bit too first. On this bike for example, even if the carbs are perfectly set up, you can't just crack the throttle open. So some of the rough running could just be my usage rather than the bike.