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Discussion Starter · #1 ·
Quick questions pls Team.

Inlet and exhaust tappet clearances: manual gives 8 and 6 thou respectively (opposite to my Daytona). Not noticed before but exhaust is usually greater than inlet. Is the manual correct?

Mixture. Plugs look pale to me but no evidence of any damage to the pistons and it does not pink. Pulls like a train and no evidence of any lack of power over the rev range. 7.4:1 pistons fitted and running on 95 RON. If I wanted to richen it a bit do I raise the needle a groove or go up a main jet?

TIA

Andy
 

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Manual is correct for valve clearances.

The plugs should be fairly pale. If the bike is running well now, raising the needle a notch will probably make it obviously too rich at mid throttle.

If, at around 5,000 rpm, reducing throttle from fully open to 7/8 open gives an apparent slight power increase, then the main jet is probably too small.
If doing that same thing makes the engine hesitate, then pick up, the main jet is too big.
If there’s insufficient fuel flow through the tap or filters (which is quite common), then these tests won’t work.
 

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Hi Andy, The factory valve clearance spec for 750 you have is correct. Use it.

The only way to evaluate what changes will effect mixture is to mark throttle grip. Most our riding is on straight part of needle so main jet & clip have no effect until you are on taper of needle. Of course lower clip will bring you on taper sooner.

Study this tuning guide. Mark your grip!! Print pages of the manual pertaining to road testing etc. Take them on road tests. Found & road test route & stick to it that evaluates all stages of carb. Motor must be heat soaked. This is the best info I've found. However the premier carb has different float level that the older carb stated here.
Amal+MK2+Carb+Manual.pdf (squarespace.com)'73


Here's what I HAD!!! on my '73 Tiger. Had 8.6 pistons with .070 thick head gasket. head was skimmed .009"
Premier carb. Float level set perfectly with liquid level to center of spec.
107 needle. Clip on bottom groove. #3 slide. 290 main.

Our best fuel is 91 E10. My tests show E10 likes 5% ish larger on jets. If you are even slightly lean on main jet will hole piston at our 110f summer heat.

After installing 7.4 pistons I went down to 106 needle jet.

Here’s plugs with 107, then 106 jet.

One step is very big change.

The lean looking plugs is 106 jet. Nothing else was changed. Throttle roll of test shows no signs of weakness with 106 jet.

Amal sells 1065 jet if needed.

I find it hard to read plugs with California fuel. Even down deep on insulator.

Looking at shop manual & parts book for Tiger Trail whic has 7.4 pistons they use 106 needle jet, 3 slide, but tiny main jet. Is that main jet correct??

Photos show the great difference. Same road test route.
Don
 

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Discussion Starter · #4 ·
Thx TT and Don.

Don, my plugs do not look as weak as your 106, but much weaker than the sooty ones. Would have been 95 RON and 10% ethanol over the last couple of months, 5% ethanol before that. Amal carb has done maybe 2000 miles only. It's midwinter here and I live in an agricultural area so the roads are filthy and the 2 classics are tucked up in bed. Fine tuning of the carburation is not something I've done before so that'll have to be a springtime pursuit. Thx both for the responses. Appreciated.
 

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Hi Andy,
To limit the torque produced by the 750cc engine Triumph mismatched the camshafts, the inlet is a race spec cam and the exhaust is a mild tune cam. They also introduced quietening ramps; the unexpected tappet clearances inlet 8 thou and exhaust 6 thou are correct.
regards
Peg.
 

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Hi Andy,
To limit the torque produced by the 750cc engine Triumph mismatched the camshafts, the inlet is a race spec cam and the exhaust is a mild tune cam. They also introduced quietening ramps; the unexpected tappet clearances inlet 8 thou and exhaust 6 thou are correct.
regards
Peg.
They also used weird cam timings, possibly in combination to limit emissions? Re-timing for lobe centres of 100 inlet and 105 exhaust (ish) will liberate quite a bit of poke, and can be done without a stripdown. I have to assume that the "ramp" on the exhaust is different from the inlet, but certainly the 6 thou is correct. I do use 10 thou with the Spitfire 71-7017R exhaust cam, which has the same form as the inlet. Also on engines that have the E3134 form with no ramp exhaust cam fitted, you use 4 thou, as per the 650's.
HTH,
Mick.
 

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Discussion Starter · #7 ·
I never cease to be amazed by the breadth and depth of the knowledge exhibited on this forum. Many thx for the replies. I have become more sceptical of the WM and Parts Book as a result of posts on this forum but it seems, in this case the manual is correct. That's what I've set the tappets to; a couple were a few thou out but that was all and the piston crowns have very little carbon build-up and certainly no signs of pinking damage. Good for another season around the Cheshire / Shropshire lanes.

Carburation is a whole new wormhole to go down! At least there's only the one carb to play with.

Now, if someone could tell me why my Hinckley Bonneville occasionally triggers a Throttle Position Sensor code my life would be complete.......
 

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Hi Andy, Carb tuning is not all that hard. Very time consuming though.
Trust me on this. Print tuning guide. Study it. You will not understand it until some road test time & practice. Making grip accurately is import. Zero is take up cable slack bars straight ahead. Mark zero. Hold full throttle. Mark full. Divide in half. Again in half, until you have 8ths.
You can’t be too far off if bike runs decently.
Take several road tests. Do snap throttle test. Again fully warmed motor. Not fully warm Will skew tests.
If you removed main jet & road tested bike. It would run fine at lower throttle openings, until main jet comes into play. I experienced this years ago when my bike was new & main jet fell out.

Forget anything you know about about other carbs!!! Most all those have tapered needle. Amal needle is straight, then tapered!! When you are on straight part of needle clip position has no effect!!
On straight portion needle jet & slide cutaway sets mixture!
So now you see how important it is to accurately mark grip.
I personally set main jet by defaulting too rich. Go 65-70 up hill & roll throttle to full main jet. You need high road speed like this as it’s easier to feel.
Too rich will 8 stroke. It will scare you! Motor will misfire in odd way. Ah ah ah will be sound. Unmistakable! Backing off throttle will run normal. Rolling on will bring 8 stroking again reliably. Look at your marks. Now you know when main jet is in full effect.
I reduce main jet until 8 stroking completely goes away. I leave it there. Some go another step down. In my heat that scares me for holeing pistons. Seen it happen too many times.
After you feel 8 stroking you can hear it on snap throttle test if slide is too rich. Snap throttle test is done at standstill.
90 % of time I’m between needle jet size, clip post, slide. Now we’re really close. 3.5 slide is a tad lean on snap throttle. Yet #3 is tad rich. Barely hear 8 stroke.
Which is best running overall? 1065 needle jet with 3 slide, or 106 jet & 3.5 slide?
Then clip position? That’s throttle roll off mostly.
Tiger with factory air boxes is hard to remove carb for slide, clip adjustment. I get that! Paper air filter elements can really skew results. I avoid them. Non stock exhaust can effect mixture. With any changes like these & modern fuels, factory specs often don’t work.

Now you see why this takes time & practice. Trust me, you will soon learn cause & effect.

If you keep at it until it’s best compromise, you’ll be rewarded with bike that stars first kick & runs so good you won’t believe it! Might take 2 days to 2 months. There is a learning curve.

Again the very first step is check/set liquid fuel level of bowl. This is very important.
Don
 

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If, at around 5,000 rpm, reducing throttle from fully open to 7/8 open gives an apparent slight power increase, then the main jet is probably too small.
If doing that same thing makes the engine hesitate, then pick up, the main jet is too big.
If there’s insufficient fuel flow through the tap or filters (which is quite common), then these tests won’t work.
^^^this is always the first thing your should do if youre thinking of messing with the main jet. i ll add that if rolling the throttle back a bit immediately slows the bike a bit, and rolling the throttle on a bit immediately speeds the bike up a bit, then the main jet is likely close enough to right that you can leave it be.
 

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Discussion Starter · #10 ·
Thx Don for your comprehensive help. Think this is a right of passage for me, to understand how to test an Amal setup and correct it if required. Never had to do it but I suspect it'll be much easier on a single carb Tiger than my twin carb Daytona!
 

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Forget anything you know about about other carbs!!! Most all those have tapered needle. Amal needle is straight, then tapered!! When you are on straight part of needle clip position has no effect!!
don, this can vary. on mikuni needles, there sometimes is a straight portion in the needle jet and sometimes not, depending on the needle. on 6DH2, 6DH3, and 6DH4 needles, the straight portion of the needle is only the top two centimeters. but on needles like 6FJ6, 6L1, 6DP17, and 6N1, the straight portion is 3 centimeters, about half the needle. the straight needles tend to be richer than the tapered ones, but there's overlap. on the 32mm mikuni carb on my desk, the needle jet orifice is about 2 mm below th ethrottle bore, and at closed throttle, the 20 to 30 mm section of the needle sticks into it, roughly. so on mikunis, at least, you can have 10 mm of slide lift on the straight section in play during tuning, or not.

on the 6DXX needles i use, the tapered portion is always in the needle jet. but people use other needles.
 

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Hi Speedrattle, I didn’t know that. My Mikuni experience is very limited.

I guess my point was most of our riding is in straight part of needle. That used to confuse me. I’d change clip & saw no change. After reading the tuning guide it explained things. Marking my grip brought it all together for me.

I left the grip marking on for about 1000 miles. Simply shocked at how little throttle these bikes use.
West bound on hwy88 out of silver lake CA up the pass to 8000’ 70 mph was less than 1/2 throttle. Most riding for me just cruising along is 1/16-1/8 throttle.
No wonder the needle wears a flat spot there.

Another thing that threw me was paper Emgo filter elements. The air flow seems to be restricted at higher rpm in a different way than stock wire/gauze filters. I spent 2 months chasing my tail. Installing genuine CAW filters. Tuning went as expected. Bike runs perfectly to this day. Just rode with owner last Saturday.
Don
 

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Hi Andy, I think you’ll find twin carbs similar easy to tune. Cost is double of course.

I’ve never worked on 500. Or, T140E.
But I find the splayed carbs are easier to remove tops for slide or clip changes.

Worst is OIF single carb. Have to remove carb. TR7RV is worst as the boot is so hard to fit at bottom of carb.

I found “good enough” used slides for trial fitting to determine best slide. Then get new one.

Trust me you’ll tuning not all that hard. Where 90% of owners go wrong is failing to mark grip. They make a guess. Eventually it works out, but that’s the hard way.

Experienced tuners develop a feel for this. They don’t need to mark grip. Go for a good road test. They just know.
I am very far from that skill level. Follow the tuning guide, it works.
Don
 

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Hi Speedrattle, I didn’t know that. My Mikuni experience is very limited.

I guess my point was most of our riding is in straight part of needle. That used to confuse me. I’d change clip & saw no change. After reading the tuning guide it explained things. Marking my grip brought it all together for me.
my experience with amals is equally limited. i know how to tune them but it takes a long time because my experience with tuning british bikes is mostly with mikunis and keihins. i have bikes with amals but they run well mostly because i leave them alone.

whichever, the needle is really thebig difference between amals and mikunis. on mikunis, th eneedlenever quite leaves the needle jet, whereas on amals it lifts completely out. and the needles i use on british stuff-- 6DH2, 6DH3, and 6DH4 -- are the ones with a 20 mm straight section that never enters the needle jet.

an AF gauge is really an eye opener on these things. you can watch the gauge and see where you need to go. makes it very quick.
 
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