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Discussion Starter · #1 ·
I thought my problems with starting, idling etc. would be remedied when I had removable pilot jets fitted, but it has made no difference on my 70 Bonneville.
The bike will fire first kick, but will not pick up. Runs about 2 seconds then dies. After 20 or 30 kicks if I'm lucky it will catch and run. Choke makes no difference.On those rare occasions I have synched the carbs and adjusted the mixture screws, but idle is still rough and bike tends to die.
I have spent money for new needles, needle jets, gaskets, pilot jets etc. I'm wondering if I should just buy new carbs rather than trying new slides, resleeving etc..
Also I remember talking to an English guy in VA who had much lower prices than anyone else, but I've lost the contact info. If anyone has the slightest idea who I'm talking about, would appreciate a response.
Thanks Stu
PS Boyer ignition, good spark, timing correct.
 

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You don't indicate if this is something new or has gotten worse over time or you made other modifications or you have just picked up this bike, so it is a little harder to isolate. I can only assume that the pilot jets were properly installed and are correctly sized. As for the main jet and needle, I assume these are properly sized and installed with the needle on the second notch for a stock configuration. There was a thread a while back about bad stock parts. Somebody will probably fill you in further. If you have any engine modifications or exhaust changes you have to compensate accordingly. Don't mean to insult you with basics but only trying to cover all the bases...
Before going back to the carbs are you sure you have a full charge on your battery as you mention a Boyer system? You mention that even using the choke doesn't solve the problem. Have you tried using the ticklers when the bike is running? If this causes a performance change then your problem is related to the fuel valve needle and/or float. The float is too low, the needle is sticking or the float shaft is pinched. The only other problem is that those tiny passage ways that you tried to fix with the pilot jet repair are still clogged with dirt. Alternately a piece of metal from drilling out the slug is in there. If you have a can of carb cleaner with a spray nozzle and one of those tiny plastic nozzle extenders, remove the pilot screw and stick the spray nozzle right into the opening and against the jet. Protect your eyes!!! There should be a corresponding spray ejecting through the pilot way. Spray back the other way. While you're at it spray through all of the other passage ways in the carb body and float bowl. Blow everything out with compressed air.
Check that the balance tube is secure and the spigots are tight in the carb body. (Mine wasn't.)
When re-installing ensure that both the carb to manifold and manifold to head are sealed with no air leaks. If you have done all this and still have problems, your trouble shooting is going to have to go wider. Let us know how you make out

On the issue of the carbs new or replacing, try taking the slides off the cable and drop them in the body. If they are really tight at the top but loose further down then the body is warped. If you have play in the slides anywhere where the slides normally sit, then the carbs are worn. Either of these problems will cause problems but are repairable.
You can buy new carbs but you will be back to square one before too long as these carbs are made from a really soft material called pot metal. Tightening the mounting bolts to the flange distorts the body. Making matters worse the slide is made from the same metal resulting in a galling action between the two surfaces.
The best solution, from my experience is to have the carbs sleeved. This fix leads to a brass sleeve sliding against the pot metal preventing the former galling. You will end up with a closer fit than factory new carbs which equates to better carburation and they they will outlast most users.
The other problem is the way the carbs are mounted on the Triumphs. Either installation with the gasket and the small o-ring or with just the larger o-ring there is a tendency for the carbs to vibrate relative to the intake manifold flange that over time only gets worse as the mounting surface on the carb becomes more distorted. This leads to leaks. A quality re-sleeve includes truing up the these faces. The fix for this is to replace the Triumph gasket with a Norton gasket. They are made from a very hard dense material that is also thicker - the name of which escapes me now. Do include the small diameter o-ring to ensure sealing. If you've seen a Norton engine run you know how much it vibrates and yet the Amals pass the test with this gasket.
This will solve your carb problems permanently other than normal jet and needle wear.
Do keep us posted.
 

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Discussion Starter · #3 ·
Thanks for the comprehensive answer, that was quite a bit of typing!
The bike never ran well when I got it. It had the Boyer Micro MK3 on it, but I switched to 6v coils for a better spark. The pilot jets were clogged but the bike would start and run. I rebuilt the carbs with new jets and needles, and did unclog the pilot jets to where they would respond to adjustment. Then the bike sat for 6 months and they clogged up so I sent the carbs out to have the removable jets installed. Today I rechecked the carbs as you suggested and all seemed well. After frantic kicking the bike finally started and I warmed it up at 2-3000RPM.
There was some misfiring on one cylinder (new plugs), but I was able to get it idling at 1100RPM, where I synchronised the carbs and adjusted the mixture screws. It idled for about 3 minutes then stopped dead. More frantic kicking with the same result, i.e.it fires but doesn't catch. Finally gave up for the day. When your'e the wrong side of 70 in FL weather its no picnic.I have completely redone this bike cosmetically and mechanically, but I'm ready to send it to the scrap dealer. Beginning to wonder if its electrical. The battery and coils are new, alternator is giving good charge rate,maybe the box is going bad?
 

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Oops, I just noticed your footnote at the bottom of the post and now seethat you had a fair bit of mods. The air filters will lean things out. As for the exhaust I have no experience with the unit other than they are quite a bit noisier and assume less restriction and thus compounding the leanness. The procom igniter, I have never seen one on a Meriden. I have no idea how this works in tandem with a Boyer. My initial sense is that it may not be a good thing. What is a 17T? This in tandem with the rejetting, the needles, the combination of all of these brings it into a whole new territory that is beyond me. Someone else may have more experience. Please do keep us informed and good luck!
 

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Discussion Starter · #5 ·
OOPS! The stuff at the bottom refers to my 02 Bonneville. My problems are with a recently acquired 1970 machine
 

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That makes more sense. For I time I thought you had some kind of a radically modified machine that I was hoping you would enclose a photo of. I am assuming now that you have a fairly stock 650 cc Bonneville. You have to tell us because these computers although pretty slick, don't help with the diagnostics. One more try...
You didn't indicate if you had a chance to try the tickler trick. You are sure that the choke lever is withdrawing both choke slides fully. You are sure the gas is fresh and that there is an uninterrupted and continuous flow coming through the fuel petcocks. I think you are saying that when the bike quits it is still idling.
Try something different this time. If you can get the bike to start, jump on it right away and take it around the block a couple of times with a plug wrench in your pocket. Keep the revs up as you don't want it to idle. If you keep going, you now know that you have a compromised pilot circuit. This would seem to go in hand with the described very difficult starting problem. It should fire on the first kick. If, on the other hand, it conks out, pull the plugs right away and check if they are wet or smell of fuel. My guess is that the bike will keep running. You said the bike never ran well and earlier pinpointed the problem to a plugged pilot circuit. Also, it would be nice to know what needles and jets were installed including the pilot jet. The modification to the carbs was that the pilot jet blanking slug was removed and the hole is now thread tapped? The jet can now be fully removed? The jet was not damaged during the drilling? This opening is now secured with a small machine screw with an o-ring seal. How many turns on the pilot screw to set up your idle? While you're at it, verify the slide cutaway.
On the other hand if it does quit, I lose my bet and you get to push it home the half block. The search now broadens and has to be electric if the plugs are wet. Plugs and coils quit with heat. There should not be any misfires while the bike warms up on any cylinder. Try swapping out your plugs for an old set that worked and then do the same with the coils. What plugs are you running? You should have non-resistor plug wires and caps. Resistor plugs are OK. The MKIII is an analogue unit and would have difficulty with a combination of resistor plugs,caps and wires. Generally a Boyer either works fully or not at all. Seeing how a Boyer is a DIY project check the wiring connections to it including the pickup connections. Check for abraded wire. You seem to indicate that your battery is staying fully charged before and after the bike runs? thus negating a voltage drop that the Boyer doesn't like.
Next, check the wiring harness including the ignition switch itself. Alligator clips and a cheap tester combined with lots of wiggling and jiggling of all wires should speed thing up.
Hoping this helps
 

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Discussion Starter · #7 ·
I'm unsure how he drilled out the old jet because the blanking plug is still there, unless he put in a new one. The new jet is located in the pickup from the float bowl. The carbs do respond to mixture screw adjustment and are pretty standard at around 1 1/4 turns out. He also did my Norton Commando 932 carbs and it starts right up and runs fine.
I checked the Boyer last night after dark and get a nice fat blue spark. I'm using solid copper plug wires, non resistor caps,B8ES plugs, and new 6v coils. I have ridden the bike around in the past and other than idling it wasn't too bad to start as long as I choked and tickled it.
It got bad after sitting for several months which is why I went the pilot jet mod. Incidentally I had the exact same issue on my 02 Bonneville with the one second firing then stopping and the pilot jets were completely clogged with a rock hard white substance that took lacquer thinner 24 hours to dissolve. Interesting that the symptoms are exactly the same on the 70, but I have checked these jets are not blocked. I will try riding it today. Not to whinge, but I have a bit of a heart condition and the thought of pushing the bike in 90F, 100% RH would probably land me in the hospital.
 

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We can wait for a cooler day so long as you can. At 1-1/4 turns the pilot setting isn't too far from being right on the money.

You're not having a fight with your neighbors or anything are you? re the "rock hard white substance that took lacquer thinner 24 hours to dissolve." That or you have to start thinking about buying your gas elsewhere. In the meantime, I still think that there is something wrong with the pilot circuit. I would call your carb guy and ask him exactly what he did. There may still be loose stuff inside the passageways including possibly that "white rock" stuff especially if he did not open up the pilot circuit. There are two very small pin holes in the bottom of the throat and near the front. When you blow compressed air through the pilot airway (below the throat left side), you should feel a stream of air passing through both holes keeping in mind that the holes are quite small.
 

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My father lives in Ocala ... thanks, you reminded me that I need to call him ... If I ever get down there to visit him, I want to come by and see that Black Shadow ...

Anyway ... remove your idle mixture screw and take a strand of wire (or two THIN STRANDS twisted together) or a guitar string or something and physically clean out the pilot jet. It's clogged. It is the idle circuit and what allows the bike to start (or not) ... replace the idle mixture screw, too ... I've seen them messed up several times recently ... and they're cheap ... 10 minutes, it will be fixed right up.
 

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Discussion Starter · #13 ·
Anyway ... remove your idle mixture screw and take a strand of wire (or two THIN STRANDS twisted together) or a guitar string or something and physically clean out the pilot jet. It's clogged. It is the idle circuit and what allows the bike to start (or not) ... replace the idle mixture screw, too ... I've seen them messed up several times recently ... and they're cheap ... 10 minutes, it will be fixed right up.
See the first sentence in my original note! THats why I had the mod done, well worth $20.
 

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Okay ... I have no idea what this pilot jet mod is ... BUT ... the piilot jet is what lets the bike start ... it's what the bike runs on when idling ... your bike is hard to start and won't idle ... the problem is in your pilot circuit ...

good luck
 

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Discussion Starter · #15 ·
Today I finally got the bike to start and run fine by screwing the mixture screw all the way in. Sounds simple, but since all the passageways are clear, there was no reason initially to do this. (Yes they were all clear, including the two small orifices in the bottom of the throat.)
It appears that by moving the pilot jet to the pick up point in the carb bowl flange the atomization, velocity or whatever of the fuel is drastically changed.
The bike idles smoothly at 1000RPM and plugs look good.
Only took me a week, two coil changes, 6 plugs, new plug wires, taking the carbs off twice, adjusting float height to come up with this highly technical solution!
 

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Stu, earlier you had stated that the bike ran properly with the pilot air screw set at 1-1/4 turns. At this setting you reported the best idle but then the bike stalled etc. You now report with the pilot screw fully closed that you are getting a proper idle.
If you have to close the pilot airway all the way you are attempting to close off the air supply in order to enrichen the the mixture. This tells me that your pilot jet problem has not been remedied. The fuel supply side therefor still has some kind of restriction.
Either the pilot jet wasn't replaced, is the wrong size or installed improperly but most likely is still dirty
 

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Typically, a pilot jet needing to be turned all the way in to get the bike to run well is an indication of a worn carburetor that's sucking air past the slide. However, without actually understanding the modification to these carbs, I have no way of saying if that is the problem or something related to the pilot circuit ... I have my suspicions regarding this mod, though ... the good news is that you can ride it now ...
 

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Discussion Starter · #18 ·
I think sucking air past the slide must be the answer because I have checked and rechecked the passages are clear by squirting choke cleaner thru the orifices and I get fuel out of those tiny holes in the throat. I also checked the diameter of the pilot jet and it is 16 thou which is correct.Once the bike is started I can turn the mixture screw out a turn and the bike continues to idle Ok, but it won't start like that. I believe having the pilot jet at the fuel pick up point somehow affects the atomization or mixing of the air/fuel in the mixing chamber.
 

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my 2 cents

just on the off chance...

any kind of manifold leak like at the carb to head gasket or the balance tube and it's fittings as well as the slide itself can let enough air in that you can close the carb air screw and still have it run.

the diagnostic trick is to squirt WD40 along the gasket edges, hose ends etc. and see if the idle changes when the bikes running.

when triumphs change running/starting patterns quickly i look for loose carb nuts or leaky gaskets first.
 
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