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Re: Bonnie Carb Jetting help needed [Re: BrettF] #720104
12/27/17 4:30 am
12/27/17 4:30 am
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As long as the length from the grooves to the taper tip, and the taper itself, are the same, I doubt that any slight difference of point will matter.
The needle never fully pulls out of its jet, but once it is raised to a certain level, its orifice is opened such that the main jet becomes the governing factor.
Unless one of the needles is grossly out of spec, I think it is a red herring.
Have Burlen got back to you yet? Dave

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Re: Bonnie Carb Jetting help needed [Re: BrettF] #720705
01/01/18 8:59 am
01/01/18 8:59 am
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Geneva, Switzerland
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Hi Folks, and a happy new year to all of you!

We had a nice 9 degree C day so did the final test of swapping the carbs around. The hypothesis was that after the swap the left would be very rich and right even more lean if the problem was with the bike, not the carbs. Remember that the plugs were very similar and just barely acceptable with a four size larger main on the right.

Well after the swap where I swapped everything, carb, slide, needle, filter etc. etc. and a good mile of WOT the plugs looked the same as before. Both borderline lean but fortunately no sign of detonation.

I've taken Burlen up on their kind offer to have a look over the carbs. This test was probably a wild goose chase as the excessively large main jets on both sides are already indicating that something is amiss.

Before sending them back I took as many comparative measurements as I could between the new and old carbs. One thing I noticed was that the throat of the old carbs seems marginally smaller than the new ones. I measured them in several places and while some were very close to 30mm others were closer to 29.7 or 29.8. But this might just be casting high spots.

Dave, from what I could measure it seems the needle clears the narrow "jet" portion of the needle jet by about 2mm when the needle is in its highest position. However, it seems it remains just in this "jet" section with the needle is in its lowest position. So I believe you are right and that this will not have any significant effect, especially considering I was running at the highest needle position. Note these measurements must be out a bit as Mr Healy indicates that the needle does exit the narrow portion of the needle jet in all settings.

One other difference I noted is the clearance between the bottom edge of the main jet and the bottom of the float bowl. In the new premier carbs the bowl seems a couple of mm shallower than my old original bowls. This means that the bottom of the main jet is closer to the float bowl base than before. On the old carb, the main jet sits about 2mm above the top surface of the drain screw whereas in the new carbs the main jet is level with, or even slightly submerged within the top surface of the drain screw (depending on the final thickness of the gasket). Could this have an effect, probably not considering the jet orifice vs the clearance around the main jet/drain plug internal cavity.

Over the winter I'll fettle the old carbs to get them straight again to ensure slides don't stick and if successful put them back on with new needles and needle jets, (old needle jets were worn to about one size larger based on my primitive "shade tree" measuring method) and probably 210 mains.

Will be interesting to see the result.


3D TV: A format that lost a format war without even having an opponent.
Bikes:
'69 T120 on average (1967 rolling frame and 1971 Bonnie engine)
'56 1/2 T110 on average (58 rolling frame - with 55 iron head engine)
Re: Bonnie Carb Jetting help needed [Re: BrettF] #720706
01/01/18 9:06 am
01/01/18 9:06 am
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PS, does anyone know if one can obtain the carb mount tufnel spacers and the thicker carb mount o-rings anywhere in UK/ Europe. I've only found them in the US and shipping is prohibitive.

I've noticed that the Tufnel spacers seem to come in two flavours, a shiny one and a more matt looking one, is one preferable to the other?
thanks


3D TV: A format that lost a format war without even having an opponent.
Bikes:
'69 T120 on average (1967 rolling frame and 1971 Bonnie engine)
'56 1/2 T110 on average (58 rolling frame - with 55 iron head engine)
Re: Bonnie Carb Jetting help needed [Re: BrettF] #720708
01/01/18 9:48 am
01/01/18 9:48 am
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Re: Bonnie Carb Jetting help needed [Re: BrettF] #720723
01/01/18 12:40 pm
01/01/18 12:40 pm
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Halfway down.


http://www.hitchcocksmotorcycles.com/amal-carburettors-miscellaneous

Also try putting "tufnol" or “phenolic” in the search.


Amateur Loctite enthusiast.
Re: Bonnie Carb Jetting help needed [Re: BrettF] #720749
01/01/18 4:12 pm
01/01/18 4:12 pm
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Originally Posted by BrettF
Over the winter I'll fettle the old carbs to get them straight again to ensure slides don't stick and if successful put them back on with new needles and needle jets


Better to check now. Just how do you intend to fettle them?


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
Re: Bonnie Carb Jetting help needed [Re: BrettF] #721271
01/06/18 4:18 pm
01/06/18 4:18 pm
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Hi Folks,

I was digging around Burlens site and found that there are different types of bowls, this made me wonder about the clearances between the drain and main jet. Does anyone know what exactly is different between the different bowls (i.e. what the different given measurements mean?)?

Here is a capture from Burlens Site.

https://pin.it/dtdjhe5szbifq2



3D TV: A format that lost a format war without even having an opponent.
Bikes:
'69 T120 on average (1967 rolling frame and 1971 Bonnie engine)
'56 1/2 T110 on average (58 rolling frame - with 55 iron head engine)
Re: Bonnie Carb Jetting help needed [Re: BrettF] #721291
01/06/18 7:13 pm
01/06/18 7:13 pm
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Those differences are in the size of the hole in the needle valve which lets fuel into the bowl.


Amateur Loctite enthusiast.
Re: Bonnie Carb Jetting help needed [Re: BrettF] #721303
01/06/18 9:04 pm
01/06/18 9:04 pm
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Brett,
TT is absolutely right. Most ordinary concs have 0.1" hole where the needle viton seals. The only question in that area was that skewed drilling on one of your carbs, which is probably unimportant, though not pretty.
Should you return them, I would ask for better, 'cos it's not good QC.

Maybe I've been lucky, but the usual bolting of a conc to a manifold has never given me air-leak, frothing or heat issues.
I've never done other than use the thickish waxy gasket with the std O ring.

If you must use the fat O ring, don't use a gasket. I think this is barking up a wrong tree, though won't do any harm.

Regarding the clearance between the main jet and it's available access for flow, forget it. Unless it caused a severe restriction, not worth thinking about.

Having said that, I've not observed these differences in bowl shape, apart from with and without drainplug. Any chance of a pic?

Dave

Re: Bonnie Carb Jetting help needed [Re: BrettF] #721712
01/11/18 9:52 am
01/11/18 9:52 am
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Hi TT, Kommando and Dave, thanks for the info sanity check.

I've subsequently found that AMAL also sell the tufnol spacer as well as the other great sources (but not the larger o-ring), Dave, I've also have not had any problems previously with the "standard" fittings so they are not on top of my list of culprits

Out of interest, do the larger ID float seat holes use the same Float needle or are their specific needles for each hole size? I never thought about this and so never measured my valve seat hole (sounds obscene i know).

Dave, Sorry - sent the carbs back to AMAL for a once over - so cant take any pictures. Will keep you posted on the results though. I'll cry if they can not see anything as I have no more ideas. I can't even sell them on in good conscience.


3D TV: A format that lost a format war without even having an opponent.
Bikes:
'69 T120 on average (1967 rolling frame and 1971 Bonnie engine)
'56 1/2 T110 on average (58 rolling frame - with 55 iron head engine)
Re: Bonnie Carb Jetting help needed [Re: BrettF] #721717
01/11/18 10:39 am
01/11/18 10:39 am
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Brett,
As far as I can see, the float needles are one size fits all.
There are brass and alloy versions of the viton tipped type, and an entirely alloy needle for alcohol use. Dave

Re: Bonnie Carb Jetting help needed [Re: BrettF] #721954
01/13/18 11:44 pm
01/13/18 11:44 pm
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Hampshire, England
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There is a firm called Toolex here in the UK that sells Swiss made reamers that could be used as pin gauges as well as for taking the needle jets out to the next size. See here:- http://www.toolex.co.uk/

You could also buy a Mitutoyo bore measuring guage, type number 368-022.

Good luck


BSA: '71 B175; '68 B25; '71 A65; '71 A75
Triumph: '87 T140; '72 T150v
Re: Bonnie Carb Jetting help needed [Re: BrettF] #721956
01/14/18 12:00 am
01/14/18 12:00 am
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The thick 'O' rings have dimensions of 34mm x 2.5mm

For a carb insulating washer, there is one on eBay - eBay item number:273019942044

HTH


BSA: '71 B175; '68 B25; '71 A65; '71 A75
Triumph: '87 T140; '72 T150v
Re: Bonnie Carb Jetting help needed [Re: BrettF] #722114
01/15/18 1:16 pm
01/15/18 1:16 pm
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Thanks for all the input folks.

Got news back from AMAL and (unfortunately cry ) they see nothing wrong. cry


3D TV: A format that lost a format war without even having an opponent.
Bikes:
'69 T120 on average (1967 rolling frame and 1971 Bonnie engine)
'56 1/2 T110 on average (58 rolling frame - with 55 iron head engine)
Re: Bonnie Carb Jetting help needed [Re: BrettF] #722920
01/22/18 5:11 pm
01/22/18 5:11 pm
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Seeing as I had no other options left, I decided to dig a bit deeper and managed to have a more detailed discussion with Burlen.

They have indicated that they could also not get a fuel level within the target range. Whether this was due to an original problem, or me modifying the seat height in my attempts to achieve this as well as sanding the bowl flange flat to ensure no leaks there, they could not say. So they have replaced the float bowls and feel that it should work well now.

My fiddling with the seats was because I had an 11mm fuel level out the box so if the level is now in spec I am already in a much better place. This did remind me of this comment by Steve though:

Originally Posted by JubeePrince

As for the warped bowls, not sure how long you've had them on the bike, but based on the marks/blemishes, etc. in the pictures, perhaps AMAL is supplying "refurbished" float bowls with their carbs?
Steve


Burlen strongly suggested using size 19 pilot jets on the 750. Interestingly they stated that the fact that I got the highest idle at around 1.5 turns on the 17 did not necessarily mean the 17s were the right size. They said that it is very likely that I would get best idle at 1.5 turns for both 17's and 19's but with better low throttle response with the 19's. So I threw some more money at the problem and got some 19's

I look forward to testing all this out in the spring, although I am currently leaning towards putting the old carbs back (straightened and with new needle jets) to recheck running as a known baseline. However, I fear if the plugs look good that way it will stay that way. laugh


3D TV: A format that lost a format war without even having an opponent.
Bikes:
'69 T120 on average (1967 rolling frame and 1971 Bonnie engine)
'56 1/2 T110 on average (58 rolling frame - with 55 iron head engine)
Re: Bonnie Carb Jetting help needed [Re: BrettF] #722925
01/22/18 7:44 pm
01/22/18 7:44 pm
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It is frustrating that nothing conclusive has come from Burlen's checks, except perhaps that they also couldn't get within spec.
That begs the question, was it ever a reaisable spec, or just a number?
Were they happy to describe their technique for measuring fuel level?
I wish I still had the bits to re-check the level with the plastic float and alloy or plastic needle.
But my records suggest that level was ~8mm, and as a 1st trial, I set my stayups to that, which worked very well. (I explained my logic in the text I sent you).
So all I could suggest, when you get them back, is to set the fuel level as high as possible without the float jamming against the upper body (please measure and record), then set everything on the rich side of options, with plugs a level cooler, and ignition timing say 35 BTDC, then play from there.
Dave

Re: Bonnie Carb Jetting help needed [Re: BrettF] #722936
01/22/18 9:11 pm
01/22/18 9:11 pm
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Originally Posted by BrettF
Hi Folks,

I was digging around Burlens site and found that there are different types of bowls, this made me wonder about the clearances between the drain and main jet. Does anyone know what exactly is different between the different bowls (i.e. what the different given measurements mean?)?

Here is a capture from Burlens Site.

https://pin.it/dtdjhe5szbifq2



Only just reading this thread - thanks for posting this screenshot, it shows that Burlen have expanded their range a lot since I last enquired. I wanted an alcohol or high-flow bowl a couple of years ago and they couldn't help. Looks as if they do one f every kind ever thought of now! They also didn't do Tufnol spacers (they sent me something made of a soft, almost black substance that wasn't what I wanted and was certainly not Tufnol). So it looks as if they've got this sorted now too. A funny company to do business with.


If anything other than a blank space is visible here, something's wrong.
Re: Bonnie Carb Jetting help needed [Re: BrettF] #722947
01/23/18 1:34 am
01/23/18 1:34 am
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Nick H Offline
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Originally Posted by BrettF


Burlen strongly suggested using size 19 pilot jets on the 750. Interestingly they stated that the fact that I got the highest idle at around 1.5 turns on the 17 did not necessarily mean the 17s were the right size. They said that it is very likely that I would get best idle at 1.5 turns for both 17's and 19's but with better low throttle response with the 19's. So I threw some more money at the problem and got some 19's

laugh


Is that a flow rate (Premier Concentric pilot jets from 17 to 19) comparable to 20 cc/min in the old Concentric pressed in bush?


1966 BSA Lightning
1967 Triumph "Choppa"
Re: Bonnie Carb Jetting help needed [Re: BrettF] #722971
01/23/18 8:49 am
01/23/18 8:49 am
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kommando Online content
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Old pilot jets are marked in cc flow so 25 is 25cc, premier pilots are marked with the jet size in thou ie 17 is 17 thou. For comparison a 25 old pilot has a 17 thou jet and so a premier 17 should be equivalent, seems the new routing is leaning out the mixture based on the 19's being found to be working better.

Re: Bonnie Carb Jetting help needed [Re: BrettF] #723017
01/23/18 4:52 pm
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Gee, did that do that just to make it confusing? Is there a cross-reference from size to flow anywhere?
It's been said to use a .016" wire or #78 drill to clean the embedded Mark I pilot jet.
The Premier pilot jets look a bit fancier with a cross drilled hole and an o-ring. I wonder if one could use them in place of the old pressed in bush?


1966 BSA Lightning
1967 Triumph "Choppa"
Re: Bonnie Carb Jetting help needed [Re: BrettF] #723023
01/23/18 5:51 pm
01/23/18 5:51 pm
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Quote
Gee, did that do that just to make it confusing? Is there a cross-reference from size to flow anywhere?


Only one I know of is the 25 = 17 thou, AMAL may tell you the rest.

Quote
It's been said to use a .016" wire or #78 drill to clean the embedded Mark I pilot jet.


Correct, you use a 16 thou drill so as not to oversize the 17 thou hole, its been found the 16 thou cleans out the 17 thou hole out but without enlarging it, the deposits seem to crack up and leave a clean hole.

Quote
The Premier pilot jets look a bit fancier with a cross drilled hole and an o-ring. I wonder if one could use them in place of the old pressed in bush?


You can convert an old body to take the premier, best done on a vertical mill as you need to machine past the cross way and beyond for a few mm so the premier jet tip has a step to seal against, you also need a 2BA tap to thread the hole part way. I have done one conversion and will be doing more as I have old unworn bodies and by adding the premier jet and the anodised slide I end up with a Premier.

Re: Bonnie Carb Jetting help needed [Re: BrettF] #723079
01/24/18 8:09 am
01/24/18 8:09 am
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Re the new pilot jet nomenclature,

I remember seeing this online on the vintage bike site with the proviso "Use these ONLY as a guide, as the final jet orifice is adjusted by hand during manufacture and checked with a manometer."

Flow in cc’s Jet Diameter
per minute in inches

15 –
20 .015″
25 –
30 .018″
35 –
40 .021″
45 –
50 .024″
55 –

Reference: – Vintage Motorcyclists Workshop by Radco page 129

This would indicate that the 19s proposed by AMAL can flow a maximum of about 35 cc per min versus about 25 cc for the 17s. That 10cc extra should also help me - giving another 10% of fuel at half throttle and 5% extra at WOT. If the extra 5mm of fuel level height I'm hoping to get also helps increase main and pilot jet flows a little I might be out of the danger zone - but indications are the latter is unlikely so hopefully the former plays its part. I'm starting to look forward to testing again. I'm not 100% sure that this logic holds though as the pilot circuit might not deliver linearly through the throttle range. For example it might deliver less at WOT due to different airflow characteristics etc. Would be interesting if anyone has and idea on this.

I will report back on the tube measured fuel level as soon as I get the carbs back.I have an excellent correlation now between drain tube measured fuel level and real fuel level so don't need to open up the carb to test anymore.I'll probably still start with the old carbs though to ensure a working baseline is present.


3D TV: A format that lost a format war without even having an opponent.
Bikes:
'69 T120 on average (1967 rolling frame and 1971 Bonnie engine)
'56 1/2 T110 on average (58 rolling frame - with 55 iron head engine)
Re: Bonnie Carb Jetting help needed [Re: BrettF] #723105
01/24/18 1:28 pm
01/24/18 1:28 pm
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I changed to a 19 and found it much better


If anything other than a blank space is visible here, something's wrong.
Re: Bonnie Carb Jetting help needed [Re: BrettF] #723115
01/24/18 2:54 pm
01/24/18 2:54 pm
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Hi Brett,

Thanks for the comparison table, useful reference.

However, I'd say the only conclusion to be drawn is that the 19's will of course enrich the mixture at very low throttle openings over the 17's.
By exactly how much is impossible to know without being privy to how AMAL's flow rate categories relate to actual flow under carb conditions.

To get some perspective, the cc figures suggest an increase of 40%, which seems rather a lot to me.
The aperture figures suggest an increase of 25%, based on the relative areas. For any relevance to reality, you pays yer money and makes yer choice.

Most importantly, this impact on mixture enrichment will be at a maximum at closed throttle. As the slide lifts, the impact rapidly reduces till at say 1/8 throttle it can be ignored. This is not because the contribution is smaller in comparison with the fuel being delivered through the main/needle jet route, but because the pilot circuit stops working as soon as the slide has opened a small amount.
The pilot circuit can only draw fuel when there is a high vacuum in the region of the 2 small holes, such a vacuum only exists when the throttle is nearly closed.
Beyond that amount of opening the carburation relies on the small pressure reduction under the slide from the venturi effect, which to all intents and purposes is far too small to activate the pilot circuit.

In a nutshell, the 19's may help with idle and pickup issues (I don't recall that you had such issues), but mixture issues at higher throttle openings will still have to be addressed separately.

I still think that once you have set the highest fuel level that you can sensibly achieve, that attention to needle position and main jet will get you sorted (along with maybe a cooler plug/a little retard of ignition). As I said, I chose to set my fuel level at 8mm, just because I had run it for so many years with the brass needles which I had discovered resulted in a level ~5mm lower. The improvement in engine behaviour was enormous.
With my slightly unhappily running engine for many years, I was overjoyed to get ~75mpg, the change to a trustworthy level of 8mm resulted in ~63mpg and flawless running, equating to ~19% enrichment.

Would you describe your apparatus for drain tube level measurement, and the correlation with direct measurement? It would undoubtedly be a more convenient check method in situ. Though if you're setting levels, the carb bowl has to be off anyway.

Dave

Re: Bonnie Carb Jetting help needed [Re: BrettF] #723131
01/24/18 5:44 pm
01/24/18 5:44 pm
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The pilot circuit serves dual purposes. It does this through the two transfer ports- primary and secondary.

At idle, (max vacuum on the primary port) the larger of the two (secondary - one under slide) transfers air from the atmospheric pressure under the slide to the mixing chamber under the two transfer ports (holes). At this point the air mixes with the incoming air/fuel mixture (Pilot jet and pilot air screw) and is transferred into the intake port through the smaller (primary) of the two holes. The primary is located at the back of the slide.

As the throttle is opened, and the vacuum balances either side of the back edge of the slide, the secondary port changes from an air port to a fuel delivery port. AMAL carburetors are referred to as a variable venturi instrument. The slide provides a venturi where the air speed increases as it enters the intake manifold. As air speed increases through a venturi the vacuum it creates increases. This variable venturi vacuum is how the needle jet, main jet and the pilot jet are able to deliver fuel into the intake manifold. The challenge to tuning is the increase in vacuum as the speed of the air increases is not linear, but that is another story.

You can compare the action of the secondary port, as the slide is lifted from idle, to the action of an accelerator pump delivering extra fuel as you open the throttle. This is why you see throttle response improve with a carburetor that has a too lean slide cutaway when you turn in the pilot air screw making the mixture richer in that 0 to 1/4 throttle position.

The fuel doesn't stop flowing through the pilot transfer ports, primary and secondary, as the throttle is opened! It is still flowing through the secondary and primary ports at full throttle. It is fair to say that its contribution decreases as a percentage of the fuel being delivered by the needle jet and main jet as the throttle is opened.


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Moderated by  John Healy 


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