66 Bonneville T120

[Oggers]

Fettling the Triumph and in checking the exhaust valve clearances, I noted the LH side was too tight. re-checked and set to 4 thou. as per manual

A few things

Corresponding exhaust is coated far more with soot than the other. Could the tight valve be a factor, or is this purely a function of the associated carb?

Setting exhaust valve clearances on my old MG, received wisdom is too slack is better than too tight - valve burn out etc. Does similar apply. If anything, I have set both slightly more than 4 thou.

Needle jet is 220 on my 930 Amal concentric. Reading around it seems a tad high - try 200 perhaps?  This may also explain the rich mix perhaps.....

How on earth do you measure needle jets to check the orifice size?

Cheers

Mark 

 

[R]

Needle jets often wear oval, so eyeballing this will often show a less than round shape shall we say.
Just comparing/trying new ones will often show an improvement in fuel economy, if you are patient enough to record such stuff.

If one pipe is sootier than the other, and you have a single carb bike (it sounds like it ?, not knowing your bike personally),
oil burning can also produce a sooty exhaust. Unless it is chronic, the difference between dry soot and oily soot can be tough to spot..
Doing a compression test on both cylinders (hot, throttle wide open) may show something, although this may not detect one poor oil ring for example.

[chaterlea25]

Hi Oggers,

Needle jet is 220 on my 930 Amal concentric.

Something wrong there??
That sounds like the main jet number ?
You need to remove the part the 220 brass jet screws into and the needle jet is threaded into the top of that
Likely it will have a number like 106 on it
These jets wear and so do the needles, these govern the mixture approximately from 1/4 to 3/4 throttle
so have more influence than the main jet except for WOT running

John

[john.k]

Amal jets were sized in an Amal jet sizing machine,which measured flow of a calibration fluid.........consequently its very difficult to guesstimate jet size ,if wear or alteration exist...........i would assume that a properly calibrated jet would only be available from the current manufacturers.....all the aftermarket ones will have approximations of dimension.

[Oggers]

Chaps

Apologies... Yes needle jet is a .106, Main jet is 220. Thinking then to replace the needle jet as original may have worn.

Bike is Bonneville, so twin 930 concentric carbs.

What say you to my valve clearance settings/technique?

[Grunt]

Have a look here for as much carb information as you are likely to need.

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

He states that a .106 needle jet is .106” diameter which is the size of a number 36 drill, I can verify this having checked a new set bought last year from Amal. However not everyone has a set of number drills, so you if you’re in any doubt jets aren’t that expensive so why not replace them as a matter of course.

As far as valve clearances are concerned why bother setting them tight or slack when it’s just as easy  to set them correctly. I dunno if you’ve come across the tip for setting them by winding them down onto the valve tip by hand and then backing them off. You will have to determine what thread pitch the adjusters are, I would guess yours are CEI, then working out how much of a turn gives you 0.004. This is a particularly good way of setting valve clearances if the valve tips are worn.

[Oggers]

He states that a .106 needle jet is .106” diameter which is the size of a number 36 drill, I can verify this having checked a new set bought last year from Amal. However not everyone has a set of number drills, so you if you’re in any doubt jets aren’t that expensive so why not replace them as a matter of course.

As far as valve clearances are concerned why bother setting them tight or slack when it’s just as easy  to set them correctly. I dunno if you’ve come across the tip for setting them by winding them down onto the valve tip by hand and then backing them off. You will have to determine what thread pitch the adjusters are, I would guess yours are CEI, then working out how much of a turn gives you 0.004. This is a particularly good way of setting valve clearances if the valve tips are worn

Yes - think I will replace the needle jets and the mains - to 200 as per various recommendations
VV clearance  - 40 deg from stop is the setting if doing it on the thread. The point about setting them slightly slack is that it avoids any risk of ex valve burning. I am not convinced it is at all easy to set them spot on, so I prefer slightly slack.   

[iansoady]

I agree set on the slack side - often there is a range of clearances specified and I always go for the high end. Using the thread as a micrometer by counting flats etc is a good plan and it also prevents getting a misleading feeler blade reading due to indented valve tips etc.

CEI / Cycle threads are 26 tpi hence one complete revolution is.038"; one flat is therefore just over .006". If they are UNF (not sure on your bike) then corresponding figures would be .035" and just under .006".

.004" sounds quite tight for exhaust valves but as I say I'm not familiar with the bike. Triumphs of this era were commonly known as rattlesnakes by we Norton owners. Rattle because they did; snake - well if you're used to a featherbed.......

[Oggers]

I agree set on the slack side - often there is a range of clearances specified and I always go for the high end. Using the thread as a micrometer by counting flats etc is a good plan and it also prevents getting a misleading feeler blade reading due to indented valve tips etc.

CEI / Cycle threads are 26 tpi hence one complete revolution is.038"; one flat is therefore just over .006". If they are UNF (not sure on your bike) then corresponding figures would be .035" and just under .006".

.004" sounds quite tight for exhaust valves but as I say I'm not familiar with the bike. Triumphs of this era were commonly known as rattlesnakes by we Norton owners. Rattle because they did; snake - well if you're used to a featherbed.......

I will have you know Mr Soady that my Bonnie handles utterly sublimely!  Ex is deffo 4 thou, 2 thou on inlet -  which given the differing mating angles of the valve and the tappet is a swine to achieve correct clearance. 40 degrees CCW or a tad less than a flat from bottoming out on the valve is correct for 4 thou....

[chaterlea25]

Hi Oggers,
Make sure to follow the manuals instructions for positioning the crank/cam before you adjust the tappets

Correct main jet size is dependent on several different factors, it can vary from one bike to another
and on fuel available, exhaust type fitted, air cleaner type, atmospheric pressure, altitude and more
It can be sized by road testing or better again on a rolling road diagnostic
Remember too lean and you risk piston damage or seizure

John

[R]

And if one exhaust is still sootier than the other, and there is no mechanical reason for this (oil burning, rings, valve guide etc),
then it might well be worth checking the float level in each carb.
And also the throttle synchronisation, if one cylinder is doing more than its share of the work...

[iansoady]

Despite Amal's tuning instructions I always leave the main jet till last. I start by fitting one which is oversize - say 250 if a 220 is specified - then get all the other bits right as the vast majority of running is done in the cutaway / needle jet area. Good idling is also very important to me. It's a point of pride to get a steady idle and clean progression although sometimes it takes a lot of effort to achieve those.

The main jet only comes into effect at wide open throttle (unless it's too small of course). And apart from racers (and feeble 2 strokes), who uses that for any length of time these days?

[Oggers]

Gents

Yes indeed - all good stuff. I appreciate the main jet reasoning. Amal recommendations for the 930 concentric 4 stroke mk1 premier - which I think I have - specify 200 for main jet - I have 220, so perhaps leave it alone. I will change out the needle jet for another .106 - in case it has worn.

I also noted that my needle has 3 rings - cannot see a number anywhere. I believe this is incorrect for the needle jet part 622/122B - it should have 2 rings - part no 622/124. This may contribute to the apparent rich running.

Agreed that balancing is a factor. Will be done after all the above tinkering.

Floats are the stay up (plastic?) things with a tipped needle.