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#698463 06/14/17 4:11 pm
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After the bike starting on stand ( new rebuild) it just dies if I let it dip under 2000 revs, like I've just turned the key off. It then didn't restart until I tickled carbs, and it's 25 c today. It held at 2000 revs and rose when throttle blipped fine. When I pulled plugs after a few minutes of holding at 2000 revs, they were tan. Sounds like it's only running off main jet. I had put these in an ultrasonic but clearly there's a problem. Is there a way of cleaning the idle circuit properly ? I know new carbs would solve this, but there's a 3 month wait.


A65L 1966
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Pdh1 #698468 06/14/17 4:26 pm
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Just did it on mine.

You can do some cleaning with the carbs in place.

1) Get a #78 drill bit. (It's a tiny little thing.). Take the red spray tube from a can of WD40, brake cleaner, or a similar aerosol, and glue the drill into the end of it so you have a handle.

2) Turn your pilot adjustment screw in until it lightly bottoms, and count the turns and write it down. Then take it all the way out. Take a can of carb cleaner (one that still has the red spray tube), insert the tube into where the pilot screw came out, wiggle it until it goes as far as it will go, hold a bit of rag against the carb so the stuff won't splash out on you, and spray it a bit.

3) Then take the drill bit and SLOWLY AND CAREFULLY work it into the pilot jet until it works in there. You DON'T want to scratch or upset any of the soft brass with this hard drill bit, you just want to pull out any varnish or crap that might be plugging the jet. See if anything comes out on the bit. Then squirt with the carb cleaner again.

4) Once there's no junk coming out, put the screw back in, bottom it lightly, turn it out the number of turns you counted when you took it out, and try the bike again.

If it idles now, you fixed it.

If it's doing exactly the same thing .... you need to take the carb apart and clean the passageway from the pilot jet to the carb throat that you couldn't hit with the drill bit. Carb cleaner, spray, soak, and high pressure air, same as any other carb .....

Good luck!

Lannis


"Why do you wear that thing, Dobby?" "This, sir? 'Tis a mark of the house-elf’s enslavement, sir."
Pdh1 #698471 06/14/17 4:42 pm
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The #78 bit is the key, also make sure that the fuel route from the underside of the carb into the pilot circuit is clear all the way to the mixing chamber, ultrasonic will loosen all the crud but its got to be able to make its way out of the carb or it just moves into another resting position blocking something else.

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


[Linked Image]

You need to confirm all the routes for fuel and air are clear and the pilot jet is at 16 thou. Note the yellow mixing chamber, the 2 dots are holes into the venturi, they need to be clear too.




Pdh1 #698476 06/14/17 6:35 pm
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Thanks for the tips, I'll try over weekend. Great article by bushman, a real help.

Last edited by Pdh1; 06/14/17 6:40 pm.

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Pdh1 #698493 06/14/17 9:44 pm
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You were a bit premature seeking help before. This time have you actually tried adjusting the pilot jet(s)? Get the motor running at the lowest rpm possible by adjusting the throttle slide stop (its the other screw on the carb). Turn the pilot jet in or out until highest rpm is achieved. Reduce the rpm to the lowest possible again by screwing the throttle slide stop screw out. Repeat these steps until a low steady idle is achieved. I've not done this a twin. Presumably you go from one carb to the other until results are achieved.

Last edited by LarryLebel; 06/14/17 9:48 pm.
Pdh1 #698495 06/14/17 9:50 pm
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I had a similar issue with a carb which hadn't been used for some time, it actually ran "ok" but from experience with that particular bike I knew the circuit must be blocked by how far the pilot air screw had to bescrewed in.

I used the ultra sonic bath with decon90, shifts most things.... didn't shift that.

I used Toluene, the solvent in petrol which attacks paint, excellent for cleaning... in this case it didn't break down the blockage. Even compressed air from a compressor didn't shift it.

I finished off with a spray can of IPA, this got the blockage moving and the bike running good again.

Before this I cleaned out the pilot jet bush with the #78 pilot jet, but my only conclusion is that the blockage was between the jet and along the pink line in the above diagram. Flushing it backwards got the path cleared.


Hth


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Originally Posted by LarryLebel
You were a bit premature seeking help before. This time have you actually tried adjusting the pilot jet(s)? Get the motor running at the lowest rpm possible by adjusting the throttle slide stop (its the other screw on the carb). Turn the pilot jet in or out until highest rpm is achieved. Reduce the rpm to the lowest possible again by screwing the throttle slide stop screw out. Repeat these steps until a low steady idle is achieved. I've not done this a twin. Presumably you go from one carb to the other until results are achieved.


You can't do that if the engine is just cutting off like turning off a switch under 2000 RPM, which is what happens with blocked pilot jets and what he's describing. In that case, the pilot jet won't have any effect anyhow ....

Lannis


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Originally Posted by LarryLebel
You were a bit premature seeking help before. This time have you actually tried adjusting the pilot jet(s)? Get the motor running at the lowest rpm possible by adjusting the throttle slide stop (its the other screw on the carb). Turn the pilot jet in or out until highest rpm is achieved. Reduce the rpm to the lowest possible again by screwing the throttle slide stop screw out. Repeat these steps until a low steady idle is achieved. I've not done this a twin. Presumably you go from one carb to the other until results are achieved.


Premature seeking help ? ? Oh, I'll solve the problem and then ask the question shall I ? I had dry plugs after repeated kicks, and after all my checks I had no idea why, so asked the question. I didn't see your reply of slipping clutch when I asked for help. When I posted that it was a slipping clutch that was the problem, you then stated that it was the slipping clutch. Genius. Also, read Lannis reply on your advice. He's right. Adjusting throttle stops and air screws when it can't hold under 2000 revs on base settings is pointless.


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Allan G #698501 06/14/17 10:45 pm
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Originally Posted by Allan Gill
I had a similar issue with a carb which hadn't been used for some time, it actually ran "ok" but from experience with that particular bike I knew the circuit must be blocked by how far the pilot air screw had to bescrewed in.

I used the ultra sonic bath with decon90, shifts most things.... didn't shift that.

I used Toluene, the solvent in petrol which attacks paint, excellent for cleaning... in this case it didn't break down the blockage. Even compressed air from a compressor didn't shift it.

I finished off with a spray can of IPA, this got the blockage moving and the bike running good again.

Before this I cleaned out the pilot jet bush with the #78 pilot jet, but my only conclusion is that the blockage was between the jet and along the pink line in the above diagram. Flushing it backwards got the path cleared.


Hth


IPA ? Isn't that beer ? Joking aside, what is IPA ? Pretty sure your problem was similar to mine. Also, I wonder if cleaning the jet just pushed crap into the pink line? I'm sure the idle circuit is blocked, despite the ultrasonic cleaning, as it's smooth and revs fine above 2000 rpm.


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Pdh1 #698502 06/14/17 11:05 pm
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Pushing the crap into the pink section is only ok if ou can get it out again (that's where the hole in the carb matches up with the float bowl.

Actually I'll throw in a daft question here and I'm sure the answer is correct, but I've seen it done wrong a few times... the float bowl is fitted with the banjo furthest away from the engine? I'm sure it will be but I've had bikes
Come in when I worked as a mechanic with this same issue.

Anyway. IPA, not only Indian pale ale, tastes great but useles on carbs lol. You want the IsoPropanol Alcohol. (The caps to signify the IPA bit) you can buy it in bottle form, but in aerosol form it works best for this instance. As your injecting under Pressure. Remove the carb is best way. Remove the float bowl and everything related to it.

Remove the pilot air screw.

2 things to check....

1, the two little holes which sit fore and aft of the slide get
Blocked, if you inject the straw through where the air screw was (not all the way) you should get two good streams of solvent through those holes, if you don't. Keep at it Till you do

2. If you put the straw in where the pink part collects the fuel from the bowl and spray, you should have a strong jet of IPA squirting directly out of the air screw hole. Although I suggest pushing the straw in fully as per step one, and spraying for a little While to try and blow out any crud from the rear. The first Part of Step 2 is Like A verification.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Pdh1 #698513 06/15/17 2:13 am
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The assumption has been made that you have pressed-in pilot jets - not necessarily the case if these are the original carbs on a '66. (For that matter, a '66 A65L would have had Monoblocs originally.) In any case, if they are older Concentrics, it's worth checking, if you haven't already done so. Just look at the underside of the carb body with the float bowl off and see if there's a threaded-in pilot jet. If not, then the pilot jet is pressed in behind the idle mixture screw as described above.

Either way, the prescription is the same; it's just easier with the removable jet.






Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
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Originally Posted by Mark Z
The assumption has been made that you have pressed-in pilot jets - not necessarily the case if these are the original carbs on a '66. (For that matter, a '66 A65L would have had Monoblocs originally.) In any case, if they are older Concentrics, it's worth checking, if you haven't already done so. Just look at the underside of the carb body with the float bowl off and see if there's a threaded-in pilot jet. If not, then the pilot jet is pressed in behind the idle mixture screw as described above.

Either way, the prescription is the same; it's just easier with the removable jet.






Good point ! I will check. I didn't realise this originally came with Monoblocs, it has Concentrics fitted. Thanks for the info.


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Pdh1 #698532 06/15/17 7:30 am
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IsoPropanal alchohol. Think that's the clear stuff I use for cleaning parts ? I only have it in a jar, I'll get some spray, thanks.


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Pdh1 #698548 06/15/17 11:50 am
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Quite possibly is, its a good cleaner and dries in atmosphere.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Pdh1 #698561 06/15/17 1:02 pm
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Originally Posted by Pdh1
After the bike starting on stand ( new rebuild) it just dies if I let it dip under 2000 revs, like I've just turned the key off. It then didn't restart until I tickled carbs, and it's 25 c today. It held at 2000 revs and rose when throttle blipped fine. When I pulled plugs after a few minutes of holding at 2000 revs, they were tan. Sounds like it's only running off main jet. I had put these in an ultrasonic but clearly there's a problem. Is there a way of cleaning the idle circuit properly ? I know new carbs would solve this, but there's a 3 month wait.

I had this same problem on a 1967 T120 and it ended up being the brass float needles were too heavy to allow float bowl to fill as it should..Replaced them with aluminum float needles and it works fine...It took a long while for tickling the carbs to work(empty float bowl) but would start and run above 2000....when let off throttle would die almost instantly and would not start without tickling carbs again...Just another thought...


Bill
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Pdh1 #698562 06/15/17 1:21 pm
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", the two little holes which sit fore and aft of the slide get
Blocked, if you inject the straw through where the air screw was (not all the way) you should get two good streams of solvent through those holes, if you don't. Keep at it Till you do"

Alan makes a good point here, these holes can be partially blocked and still sort of function, not easy to clean, a single strand of copper wire, ( from a multi core) with a right angle bend for access is a good tool to poke these.. They are meant to be about 0.028" but close up with oxidation. Carbs I have been messing with lately were barely 0.014" due to white oxides.


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Pdh1. Don't blame me for thinking you might not have tried adjusting the pilot jets.

Last edited by Allan Gill; 06/16/17 7:30 am. Reason: Edited for catty comments
Pdh1 #698628 06/16/17 12:50 am
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The only foolish question is the one you don't ask

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Originally Posted by AML
The only foolish question is the one you don't ask



Nicely put.

Originally Posted by LarryLebel
Pdh1. Don't blame me for thinking you might not have tried adjusting the pilot jets.


I'm watching these posts and will edit or remove if I feel necessary.

Thankyou


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Pdh1 #698718 06/16/17 7:34 pm
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For info the drill size mentioned (#78) needed to clean the pilot jet is 0.406mm thick, this equates to 26 AWG wire. You can get a 10m spool of 26 AWG stainless steel wire on eBay for less than £2.00 and this is what I have used in the past to clean the carb passage ways.

In addition I use carb cleaner and/or brake cleaner purchased from my local tool station for less than £3.00, see This Link, alot cheaper than Halfords smile


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Thanks gunner. I've ordered the drill bits from eBay, 2 for £1.70. I'll grab some cleaner from toolstation though.


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Pdh1 #698760 06/17/17 1:28 am
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Get yourself a cheapie ultrasonic clearer, that's the job that it's designed for and will do the job. Be careful about what solution you decide to use in it.


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Originally Posted by John Goodwin
Get yourself a cheapie ultrasonic clearer, that's the job that it's designed for and will do the job. Be careful about what solution you decide to use in it.


If using ultra sound, you need to dilute the cleaning solution around 50% .
You aso need o remover the carb before the machine stops and rinse in a slightly acidic solution 10% white vinegar works well
The follow up with a rinse in boiling water.
This will leave the carb bright shinny clean.
I do a lot of mower carbs and have found if ou leave them in for any length of time without the machine runnng you geat a reaction between the cleaner & the Zinc which is very hard to remove.


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Pdh1 #698959 06/18/17 9:24 pm
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It's quite OK to use a 16 gauge guitar string to poke out the pressed in pilot jet.

As far as cleaning the carb, you can use dilute (10:1) battery acid at room temp provided you leave the carb fizzing for no more than about 10 minutes.

DD


BSA: '71 B175; '68 B25; '71 A65; '71 A75
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