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Hi Folks, my name is Brett and I have a carb problem! There - I've said it - it feels much better now that it is out in the open....

A month ago I put in new carbs - old ones were worn and running erratically. (71 Bonnie Motor with Morgo conversion everything else stock filters, pipes etc.) Started off stock with 190 mains, #3 slide, the needle on middle and 106 needle jet. All supplied from a reputable AMAL dealer in a premier carb. Timing recently checked, valves also and compression is very good.

They seemed to be running a bit lean when I first put them in (some spitting on throttle opening) so I checked float height and lifted the needle to the bottom notch. It seemed to run well but I knew I was probably lean at WOT (folks here had indicated I should have 200 main minimum for the 750 kit and modern fuel).

I did not get much chance to ride for a few weeks and it's now much colder and more humid than when I last rode (10C vs 20C). Did a short ride and the spitting was back and even worse than before, now the bike would die if I snapped the throttle open from idle. Strangely this did not seem to be affected much by choke positions.

From the various tuning bibles on this forum and elsewhere the spitting carbs seem to indicate a smaller cutaway slide is required. This should not be affected by the main jet I understand but from the AMAL tuning guides the do say to start there and then work your way back up from the pilots.

My question is should I buy a handful of main valves as well as new 3.5 throttle slides? (shipping to Switzerland is dear on top of the price of the slides!) or should I try anything else before I start spending money?

I decided to try a plug chop but did not have too much success on the higher openings - was hard to keep it WOT for long maybe 30 seconds in all with a short break in the middle due to a bend. Seems lean from the pictures below, especially the right cylinder.

I'm thinking of trying a half throttle plug chop with the mains removed to see if that makes any difference - would there be any sense in this? At least I would get to know Mr Petes "8 stroking feeling" so in future I can follow his advice RE going " two main jet sizes below the 8 stroking threshold"

Here are the plug chop pics if anyone notices anything there.







I then realized that 3/4 might also tell me more about the needle jet so went back and did that:

I'd stick with the #3 slide. I run 220 mains in my T140. Now I installed new Amals on my 70 T120 and had similar issues. Turned out to be a vacuum (air) leak between the bowl and body. The bowl was warped slightly and on a new AMAL to boot. Once fixed, all was well. How many miles on your plug chop? What plug is that? There seems to be carbon way up the threads on the right plug.

Are the plug chops the same plug or different plugs each time?
The speckling on insulator on the right hand plug is very concerning. That could be tiny bits of the piston. This can be caused by too lean of a mixture or too advanced timing. Strange you don't see it on both plugs. I would not ride the bike until you sort this out.
What ignition system are you using? Most of the popular electronic ignition hold the same timing on both cylinders but points can have different timing. The ground strap on the right hand plug is clean all the way to the threads. Timing possibly too far advanced.
You definitely need to try a larger main jet. Jets are relatively cheap.
As I understand it you have the needle clip in the bottom groove of the needle. This would be the richest setting.
3.5 slides are leaner than 3. The higher the number, the leaner the slide is. I doubt that you need to go to a 2.5 to get richer but maybe.
Your hesitation on opening up from idle may be helped by going to a richer idle jet. Are your's #17 that generally come with the new Premiers? Nice thing about the new carbs is the ease of changing pilot jets. You may need try 19's.

good reference
https://www.princeton.edu/ssp/65-cub-data/library/amalbritbike.pdf

They look to be NGK B8ES ??? ... Did you run with these on your old original carburettors , I'm thinking maybe part of your previous running problems could have been plug choice ? .. I run B6ES in my 750 , runs good .. I worked my way up from the 8's to 7's to 6's - the NGK 8's used to cough splutter & eventually foul up with normal riding and the 7's weren't that much better either ,
My money's on your not that far off on the correct mixture 'But' looking at your first 2 pictures try richen right side up slightly to match the colour of the left & then switch to a hotter plug and take things from there ? , That engine dying thing when you snap the throttle open could just as easy be the 8's starting to fouling up slightly when first hit with that extra splash of fuel ,

Quick twiddle with the pilot mixtures & couple of hotter plugs might be the easier cure ,
Just my

Hi Brett -

Most people who run the NGK equivalent of the Champ N3C seem to use the B7's.....why are you using a cooler plug? A cooler plug that looks that clean would almost have to be too lean, IMO.

+1 on the 'peppering' on the right plug. Detonation. Too lean or too advanced. You running points? Double check timing on that side if so. If EI, perhaps an air leak around manifold/float bowl?

Have you verified fuel flow through the carbs? You want a minimum of 300ml/min out of the bottoms of the float bowl(s) with the petcocks on.

Did you pull apart new carbs and make sure all air/fuel passages/ports are open and proper size? Operating properly? I bought a new set of AMAL Premiers a little over a year ago and had to do a fair bit of fettling to get them right....

Steve

i've used nothing but B8ES plugs in my T120s for lots of years.

i could never keep the N3 or N3G-- the old gold palladium plugs--from fouling, with Concentrics.

plugs are weird. even with apparently identical motors, some like one type and some like another. got B7s in a Commando, i think.

It takes several miles for spark plugs to get "color" Wide open runs on my race bike for 30-40 seconds have plugs that look like the ones in the photo above...Plug reading experts have said mine look good.......They are looking deep down inside and at the carbon on the steel shell....They are not looking at the tip of the center electrode insulator...For part throttle a five mile ride should color the center insulator...

Full throttle color

I agree with the comment, "Don't ride this bike until you sort it out!!"

Hard to comment when not knowing which plugs you are using. Are they really B8ES???? Hard to tell if they are B6ES (IMHO not good!) or B8ES

N3C Champion is the plug Triumph did all of their testing with for the engine. It is the standard to work with when you are having problems.

Do you have points or an electronic ignition.

What is the size of the new carburetors: 30mm, 32mm?

Those speckles on the porcelain part of the plug are from detonation. Not good!

You should be seeing only 2 or 3 threads that show discoloration from heat, not 9 (right plug).

As an aside we are seeing more people changing the standard 17 pilot jet in the Premiers to 19 (especially 850 Nortons)

It takes years of experience with a specific engine to be able to "read" spark plugs.

You have to be anal when checking each stage of the carburetor for jetting. You have to note the position of the slide for reference to which fuel circuit you are using when you turn off the ignitions switch. The ignition must be cut to stop combustion. Just running with the ignition on and the throttle closed, for the time it takes to slow down will/can mask what the plug looked like before you shut the throttle. When they say "chop" it is the ignition they are chopping, not the throttle.

Even so, the change in fuels has tripped me up. Now, my plug reading skills are basically, "that's good, and that's bad"

And that plug on the right side is "bad". It could be "blowtorching" which is a gas leak around the threads. Makes a plug very hot.

How bad? Hard to tell. That plug thread may be ready to let go. And that can be bad. A friend of mine nearly got killed by a flying spark plug that shot out of a lowly cub motor. He said it flew a long ways at a high speed....

I wouldn't put myself in front of that plug until you know if the threads are any good.

I read with great interest anything written here on reading plugs. What I'm seeing varies dramatically from bike to bike, brand to brand. Those Harley plugs look pristine without any color whatsoever after huge mileages.

Triumphs often look rich no matter how I tune them, but run just fine and get good fuel economy. If there are no problems associated with the rich looking plug, I don't mess with things.

Cheers,
Bill

Agree with that, Bill. With the soup they sell as gas today, I think the days of trying to get that perfect tan ring on the base of the porcelain are long behind us (racing applications and fuel aside).

If the plugs are black, but still starts and runs well, then all is good in my book too. These are the plugs from mine. A few thousand miles and a number of years with no problems:

Cheers,

Steve

T140 plugs

Hi Folks. Thanks for all the input. I thought I had all the background covered, thanks for digging deeper on this to assist me.

Carbs are standard 901/300 premiers (except for the 190 jets - I chose this as the old carbs had that)

The bike is running a Boyer micropower ignition for the last 4 years. Timing was checked with a strobe two weeks ago, was still spot on (have never had to adjust it). Plugs are B8ES, as I have also used for the last 4 years. (but with the old carbs obviously). I changed the plugs when I changed the carbs maybe a hundred kilometers ago. The same plugs were used for the chop. I thought about using new plugs but read that they don't have enough carbon to show up in a test properly. Pilots are stock RJ17.

Running 100 octane as standard. (always seem to have a special on it at the station around the corner)

Bike is very easy to start hot or clod (rich at idle?)

Plugs were the same plugs each time. ( I understand that with new plugs you have to cut the thread away to "read" them. Not sure if this is true but I was not up to that).

Htown you are correct, I had the slides mixed up - I would need to go smaller number to be richer. And thanks for the reference, I actually had that before and have been studying it for a while now.

Steve, I did find a few problems with the carbs originally (chaff etc.) but cleared that out. All passageways are clear and jets etc as specified. Not sure of holes and ports are correct size - are there any details of this somewhere I can check?. Have not tested total fuel flow. will do that. It does piss out from the ticklers at the moment though when tickled.

Mr. Healy, I was using your AMAL tuning guide and had marked my throttle based on the physical position of the slide as seen with air filter removed. I ran at each throttle opening (as close as possible - but quite close) for about 1.5 miles. Clutching and cutting the engine within a few seconds of that.

My plan of action is:
- New plugs and richen right mixture though idle adjustment.
- Run the engine and look for leaks on the right side
- If I find nothing take a short ride at maybe half throttle max and check that the two plugs are now even (as left was)
- If that works then go larger and larger on main jets to get the 8 stroking feeling and then dial it back two jets (what size max jets should I order? say up to 230 or 240?)
- then see if the spiting and dying on snapping open the throttle is improved.
- If not improved then try larger idle jets
- If not improved try smaller slide cutaway

does that sound about right?

One thing that surprised me was that the choke made no difference to the spitting/dying on throttle open snap. I would expect that to richen the mixture and improve that. Any idea what is going on there?

Re the detonation I understand it has a similar sound to pre-ignition - I do know what that sounds like and have not heard that since the carb change, can it be more subtle that I could have missed it?

Any other ideas RE the more complete background info given above?

thanks again all.

Detonation can make very subtle noise to a very loud ping.

Pre-ignition is silent and it only takes one or two turns of the crankshaft to hole a piston!

Detonation can go on-and-on-and-on-and-on until it does something catastrophic as long as the cylinder pressure is high and the throttle is open.

So it looks like it is not timing as the Boyer fires both cylinders at the same time.

How did the bike run before the carb change? Did you make the change for no good reason other than you wanted new carbs? Or was the bike running poorly and you thought new carbs would help?

I would do a lot of my looking on the right side!

Following John's first order of diagnosis when something like this happens to me, what was the last thing, or things that YOU did? It has worked well for me over the years.

We use 200 main jets in stock T140's. Putting in a pair of 220 jets would NOT hurt. This will do nothing substantial below 3/4 throttle but IMHO it is a better place to start.

What happens when you turn the pilot air screw in and out from 1 1/2 turns out? Does the spitting get better when you turn in the pilot air screw? If so a 19 pilot might help the transfer from the idle carburetor to the main carburetor. It is cheaper than getting a pair of new alloy 2.5 slides.

Right carburetor:
Is the float bowl warped?
Is the mounting flange warped
Did you use the original large "O" ring (70-9711)
or use the thin one (622/101) that came with the carb.
If you used the original thick one did you tighten the lock nuts so you have .040" to .060" between the flange and the carb adaptor?
Has the balance tube fallen off, or you didn't put it on when you changed the carbs?
At this point the last thing I would do at this point is put a hotter plug in it. That right plug looks scary!!!

As I mentioned in my first post, the specks you are seeing on the right hand plug are tiny bits of the pistons. If you keep riding it like that you will soon have a hole in the top of the piston. Something is too hot in that cylinder, either lean mixture or advanced timing.

Thanks for all the input and clarifications folks. Hope I caught this before real damage was done.

Hope this post is not too long - I've italicised the questions to assist.

Mr. Healy, I changed the carbs as I was struggling to keep a low enough idle rpm and while tuning the carb I found the slides sticking somewhat (I had previously had to straighten the carbs flanges after I got the bike to stop them sticking then). So I decided to go with the new spare carbs I had in the cupboard. However bike was running fine before the change.

I used the o-ring that came with the carb.Is that acceptable?
I was very careful not to overtighten that flange based on my previous experience having to straighten it.
I'll take the carb apart and recheck the passageways and check whether the float bowl is warped at the same time. Would fuel not leak out from a warped bowl at rest though? I presume one checks it on a plate of glass for flatness or is their another test?
Before I disassemble though I plan to first try with starter spray/WD40 to try to confirm a leak. This will work on the carb flange but I imagine not on the float flange, is that correct?

Balance tubes are present (I checked them recently as I was planning to attach my vacuum gauges at some point and was looking at diameters).

You mention "Putting in a pair of 220 jets would hurt." Did you mean "would not hurt"? I was thinking of starting high - around that jet size or even higher. Mr Pete indicated how even he couldn't read plugs and went with the 2 steps back from 8 stroking to get main jets right. Is there general support for this method?

As more background, the idle screws are around 1.5 to 2 turns out so in the range they should be. Fuel levels were checked (well, float height, I could not get the float levels measurement to work with a tube connected to the float base so reverted to float height (which was correct from the factory))

Regarding what has changed since changing the carbs : I've checked my log and no changes were made to any engine components besides the carbs. Two things jumped out though that I had forgotten. 1. Just after putting the carbs on ( a few days after) I found a crack where the air filter backplate is spot welded to the threaded ring that mounts to the carb. Maybe an inch long. I found it the same day as I had the filters off in the morning, no crack, then later took them off again, crack. I would not have missed it as it flexed when screwing/ unscrewing. However, this was on the LEFT side. I have temporarily repaired that with that steel putty stuff which is holding well (trying to buy just the rear plate but having no luck. I have loads of spare front covers and chrome covers, no back ones - Murphy!) 2. I shortened the plug cables as they were way too long and interfering with the tank. there is still good slack but routing is better now. During this I found the NGK LB05 plug cap on the right side had a loose screw - the screw where one screws the HT lead to the cap was loose - turning when I tried to screw the ht lead in to. it was replaced. However, this was done a week before the carbs were changed.

Mr. Tiger, if air is leaking past the right plug thread would a spray of wd40 their show up a leak by increasing RPM as with the intake flanges?

Mr. Htown, thanks for the advice. It is taken. However I believe I will need a short gentle ride to check plug temps after going through the carbs, would you agree?

I was thinking of retarding the timing a bit but considering the left good plug that should not be required.

Based on all this I plan the following action plan - does that sound about right?:

- Check right plug thread with endoscope
- Check right and left piston chamber/piston crown with endoscope for damage (what would I be looking for?)
- Check fuel flow rate with each tap and then with both taps open will check flowrate on left and right carb.
- Richen right mixture through idle adjustment screw to maybe 1/2 to 1 turns out
- Run the engine briefly at idle and look for leaks on the right side with starter spray/wd40 (at carb flange and plug thread)
- If nothing found pull right carb and make sure all passages are clean and flanges not warped
- New plugs (try NC3 if possible) and install 220 Main jets
- See if the spiting and dying on snapping open the throttle is improved.
- Take a short ride at maybe half throttle max and check that the two plugs are now even (hopefully same as left was)

Later will consider larger idle jets or smaller slide cutaway depending on above results.

Hi Brett - Not if the fuel level is below the top of the float bowl.

Yes, or a smooth/flat countertop with feeler gauge.

Steve

I have probably looked at a 100, or more, pages describing how to to read a spark plug. I have yet found one that the average owner can understand. There are several things that you look at. The professional way to check the air-fuel mixture is looking at the base of the porcelain where it inters the steel body where you are looking for a fuel ring. Google it! This isn't easy to do and to do it right requires cutting away the threaded portion of the body exposing the porcelain center.

So here are somethings you can do on the side of the road with only a spark plug wrench. It is also something these plugs display:



Note: The mixture ring is incomplete on the right plug indicating a lean air/fuel mixture.



Note: The timing advance mark is totally missing from the right spark plug having been burnt off from excessive heat.



Note: The threads on the right plug look a lot worse than the one in the illustration indicating the plug got real hot.


Pictures are from www.autorepairinstructions.com

And Yes, I would recommend starting with 220 main jets.

While this in my opinion is not a typical mixture problem learning to read the state of tune of an engine using your senses is very helpful. Learning to identify 8 stroking (not a problem here) where the mixture is very rich or sensing the slight increase in rpm as you roll the throttle closed a bit where the mixture is too lean goes a long way to learning how to tune a carburetor. One of the simplest ways of diagnosing carburetor problems where one carburetor appears to be causing a problem and seeing if the problem switches sides. With an EI, where both plugs fire at teh same time plug wires can be swapped to see if the problem switches sides. Have to go home - Susan got some nice meat balls and red sauce at the church fair. Got to make the wife and God happy. Lets talk about this some more!

Nice.
Will commit to memory.
Cheers,
Bill

DOH! Steve, of course, the level is below the flange!!! (embarrassed)

Thanks for the concise info Mr Healy.

I will start troubleshooting tomorrow. New jets ordered will probably take a couple of weeks to get to the island os Switzerland.

A quick question- if the broken plug cap damaged my coil I might be getting misfires (not that I felt any), I think this would lead to richer (unburned mixture) not leaner, is that correct? Just want to rule that out as a potential cause?

Hi Folks,

Did some troubleshooting today, Took out the plugs and checked threads (looked good), Bill, I was thinking, if the plug thread was leaking air into the chamber, would it not also blast exhaust gas out on the pressure stroke? The plug bodies are pristine so I doubt this is happening.

Then I took some pictures of the top of the pistons. Can clearly see the carbon has been burned up / turned to ash on both pistons. I'm sure you folks can see more. Don't see any damage but am not sure what to look for. But looking how clean the left is I'm sure it was close to detonation also as the right was doing. I'm wondering if the main jet does not have a greater effect on smaller throttle openings than I thought.

BTW a 10 $ Ebay endoscope is a magical thing. But don't expect the 90-degree mirror thing to work in dark places (the scopes have their own light that overpowers the mirror and makes it useless, one only sees halos, angels, etc;-)).

Ran the bike and sprayed wd40 around the intake and bowl flanges. No changes to the running. However have since been told to try with a water spritzer or even propane as apparently, WD40 is now less flammable than before as the recipe has been reformulated. Might try this but will probably just pull the carb and check physically what I can see.

Valves looked okay from what I could see with the scope.






Will keep you posted on further steps as I proceed.

Apollo 11 calling Houston, which bit should I land on?
It does look like the coke crust built up previously has been blasted away by explosive events. I suspect the carbon has saved you, a new piston might have failed by now.
The discolouration on the sparkplug threads that JohnH was referring to is (I think) the bluing (not the carbon which is evidence of gas leakage maybe) similar to his analysis of gudgeon pin colours, which would be worth looking at if you take it down that far.
But I hope that you've found it before disaster, and timing/carb changes will cool things down.

Hold on. blasted coke does not mean much I think. What we are looking for is the little bucky balls seen on the plug, which were I assume the black bits. I don't see any of those on the pistons, does someone else?

You have definitely removed all of the accumulated carbon. However, it looks like very little aluminum is missing and the pistons still look usable to me but John H might have a different take. It was definitely on the road to disaster. If those are NGK 8 plugs they are already a half a step cooler than the standard N3 Champions.

Btour, the black specs on the rh plug are the carbon blown off the top of the piston. As soon as the carbon is gone then little bits of aluminum will start to come off. It looks like this was just to the point of that happening.

Dear oh buckmiinster fullerine bollox dear, the structure of a C60 molecule is surely irrelevant?
But as you've raised it, the molecule is spherical, with the carbon junctions organised in the form of a classic football, with the hexagons and pentagons.

"The discolouration on the sparkplug threads that JohnH was referring to is (I think) the bluing (not the carbon which is evidence of gas leakage maybe) similar to his analysis of gudgeon pin colours, which would be worth looking at if you take it down that far."

I agree. You are reading the discoloration of the plating. The plug should never get that hot for that many threads to discolor! Reading the threads is a common diagnostic tool among drag racers.

From 4,000 miles away neither piston top looks that good. You were getting some detonation of both. The right being the nastier of the two.

As an aside we see a proper grade (Champion N3C) plug discolor like this occasionally on triples. Because of some fluke in the design the center float bowl is prone to collecting water. Because water is heavier than gasoline it will sit in the bottom of the bowl. When it gets to a height where the fuel flow through the lifts the water and it will partially, or in some case fully block the flow of fuel. At that point things start to get expensive!