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Got the bike back on the road today after doing some long awaited gas tank repairs. So I went for a ride. Overall, a pretty fun ride, BUT! One of my problems is back. I was riding around for about 20 minutes or a half hour and I was running down a straight going somewhere in the neighborhood of 60 mph and that all familiar stalling episode came back!! I paid more attention this time. I was running in 4th gear, not really accelerating and had been running about 60 for about a minute or so. Started to run rough and power was quickly dropped off... I knew I better get my *** to the right side of the road (was like playing frogger to get over there as fast as I could!). As soon as I got to the side it died right out. Gave it about 30 seconds and tried to kick it. Nothing. Waited another 30 seconds and got one pop, then I kept kicking it for about 20 more seconds (getting a pop on each kick) and the last one it started and stayed running. Ran great on the way home and I put it back in it's parking place and let the oil leak run it's normal course (next on the list to fix).

For those of you who aren't familiar with my bike, I'm running a '60 Pre-unit 650, pretty fresh rebuild, new Joe Hunt magneto, stock everything else, new clutch, fresh trans rebuild.

I am completely stumped at this point, but I have a suspicion. I have had some trouble getting my clutch set-up. Now, before we go into this, let me ask... if I'm having slipping problems (which I have very SLIGHT slipage once it's good and warm, nothing major and I know how to get rid of it) is it even possible for this to be my problem... too hot or something.

As for the mag, I talked to Joe Hunt awhile back and even sent them a very high quality photo, and they saw nothing to worry about.

ANY ideas, anyone???? confused I'm to the end folks. Can't even go ride for more than a half hour without having this stupid (and probably simple) problem.

Help me out guys! Sorry for the long post! shocked


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Well not sure what a high quality photo would do to help diagnose a electrical problem but have you checked the vent cap in the gas tank ?....make sure this is not plugged ....this will make the same symptoms as above mentioned .....check it ...or try running with the vent open alittle see how far ya get ....Hows the batt ......are yo u running a electronic ignition ?.


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Quote
are yo u running a electronic ignition ?.
He is running a Joe Hunt magneto. Don't believe there's an electronic version. It will be points and condenser.

-re-route fuel line (if too close to head or cylinders)--in case of vapor lock

- Check cap and contacts

-re-adjust points (check for correct setting first)

-check for cracks in plug wires

aside from fuel cap vent hole as sated by black13.

Check into mental institution for a break when done checking other components.

beerchug


Jon W.


1957 6T Thunderbird 650
1968 T100R Daytona 500
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1970 BSA A65F 650
1955 Tiger 100 - Project
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1972 Norton Commando 750 "Combat"


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Gonna hav to go with above post, sounds like vent cap . Might look at the carb insulator block , if you dont have one installed it could give similar symptoms , but usually more pronounced coughing and carb clouds ... how new are the plug wires ? Is the mag a new version , or the NOS hunt mag? it may be a capacitor gone bad from shelf life?? Too any possibilities to try and diagnose without more info ..

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It really does sound like the breather hole in the fuel filler cap. On some types, the rubber washer can rotate so the hole through it is out of line with the holes above and below it.

Try running the fuel line that attaches to the carb into a bottle, opening the tap and see if the fuel runs steadily for at least a pint.

Bear in mind, hot failure is also the classic sign of a failing magneto, at least on Lucas ones.


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Another vote for a probable fuel tank vent problem.
If it were vapour locking it would quite possibly get worse whilst stopped, until the engine cooled a little.
Vent problems are a little bizarre in that an almost empty tank will allow you to run further before the symptoms appear, "hysterisis" [elasticity] of the air volume in the tank will dampen the effect.
Get a full to the cap tank [little or no air] and symptoms will appear quickly.
I have good luck cleaning things of gummed up unleaded fuel residue with alcohol [applied to the part] laugh


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I vote for a bad mag. Although the mag may be new to you, it may also have been sitting on the shelf for 10 years. You need to put that thing on a mag tester and then blow a hair dryer on it to get it hot.

Right after you check the vent hole in the gas cap! :bigt:


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I checked my cap hole and it doesn't appear to be plugged, but maybe it's not big enough??

Here's some pics of my cap arrangement. Note the hole on the left side and the sealing arrangement when it's open.
[Linked Image]
[Linked Image]

QUOTE from black13: "Well not sure what a high quality photo would do to help diagnose a electrical problem"
Discoloration close or at the point are things that Joe Hunt techs asked me to look for. Also cracks or other things. I sent a picture to JH just in case they saw something I didn't, just by looking at.

I agree the mag should be tested somehow (if the gas cap isn't the problem). Any tips how I can do this without owning the "Acme 3000 magneto tester"?? :rolleyes:

An additional note I should add... I tried to start the bike up again about an hour ago to go for a quick ride and no luck. One pop in the whole leg workout session. Also, the compression doesn't seem as it was yesterday. It seems too easy to kick now. I lose half a kicing stroke just positioning my body to kick it. What the heck??? confused I hope damage wasn't done!! eek


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One more thing in response to how full the tank was... close to empty. I was running just above the reserve in a 2.4 gallon tank. Probably less than a pint in the tank. Sadly, I didn't expect a long ride... frown


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Try and work out a deal with Hunt to quick ship for a test and then back.They're close by. Maybe somebody has one close by to try on there for test. There isn't a piece of schmootz floating around in your tank is there?. If you have the mag tested you'll know for sure thats out.


You didn't take the DO NOT USE FOR AIRCRAFT sticker of that Mikuni did you? I heard the Serta sheep can wreak havoc. When are we gunna see the rest of your bike? It looks like a lot of work went into it.


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Condensers can fail when they get hot, but work fine when cold.

Step one would be to just replace the condenser (very cheap). Step two would be send the mag to SRM or someone with a proper test rig. My Vincent owner buddy would put his mags in the oven before installation to heat check them. He would then pull them out and hand spin them. The good ones kicked out a nice fat spark.
Of course, make sure the insulation block is installed between carb and head.
Also check for good fuel flow TO THE FLOAT BOWL.


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BTW, SRM has some simple and cheap uprades for the mags which improve performance/reliability, etc.


When people who should have known better cautioned me about the dangers of motorcycle racing, I always told them that a fear of death is nothing more than a fear of life in disguise.
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NOT THAT THIS HELPS....BUT KICK *** GAS CAP.

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Thanks for the compliments and I'll put up a couple pics in a minute for you! Too long in the making so the positive feedback is appreciated! REALLY!! laugh :bigt:

I know I'm going to figure out what this means as soon as I post it, but who's SRM and what is this upgrade kit we're talking about?? Fill me in, provide me a linke, something. I'm going to build some new plug wires, check a couple things including the spark. Hopefully there's no junk in my tank. I just spend 6-days resealing the damn thing with POR-15. Should be good.

Don't have anyone to provide me magneto assistance. I don't even know anyone else in town with a mag on their trump... so you guys are it. I would really prefer to leave taking the mag off as a VERY VERY LAST resort. That thing is a serious pain in the bizoo to get off and put back on and retime!!! Those of you with pre-units and mags no what I'm talking about when it comes to the re-time alone, I'm sure! Will check everything else out I can think of in the mean time.


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Pics for those of you who asked and hadn't seen these. This is before I polished out the covers and the transmission case. Sorry so big.
http://i23.photobucket.com/albums/b394/scootermcrad/scooter7.jpg


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That breather hole is big enough.


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Scooter..Might be the Mag,but it could be the Mikuni's..I had such Voodoo I cant tell you a few years ago..Went thru everything..electrical..Gas caps..vent problem's..Gas quality..condensation..water in tank..compression..plugs..Plug out of luck random Stalls continued..and it got pretty Hair raising on occassions,too...Turned out to be the float needle and butterfly were binding at random for one or two reasons..both of which you might look for...First..the float needle end which engages the Butterfly Tang..had a near imperceptable Burr..which had worn a near imperceptable Ridge line into the Tang which is a much softer metal..Round the needle end w\ fine file..smooth the tang[s][dual carb?]..w\emory...second possibility..with old mik's..such as mine were..the butterfly spindle wears out the softer metal of the armature slightly increasing the Hole size..and creating uneven play..which also can lead to binding or more likely in this case Flooding..either way..one of my Miks had both of these subtle problem spots..and when addressed[I 'bushed' the spindle..De-burred the needle and tang]..the Great Voodoo Stall mystery went Away..Give it a Look...and Good luck..You'll find it sooner or lator..no matter what it is..and BTW..very Nice look'n Chop!!...AZ

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_____________________________________
Also, the compression doesn't seem as it was yesterday. It seems too easy to kick now.
______________________________________
Have you retorqued the head lately?
Have you checked the valve clearance?
HTH


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Okay, now you're just scarin' me AZ! That was exhausting to even read! Great info though! :bigt: The carbs have less then 20 miles on them so I really hope they're not screwed up already. Still worth a look. I'm going to pull the bowls off anyway to make sure they don't have some garbage in them.

Could actually be gas quality. I've been milking a 5-gallon container of gas for awhile. Probably due to be replaced. shocked

The plug wires are newly built, but I made them out of cloth spark wires (early Ford) and they don't seem to be holding up too well. Will be making some new ones.

Steve in Tulsa... gone through my head quite a few times and I always seem to be retorquing the bolts. That was my thought also with relation to the low compression.

Nick or somebody... what's SRM and what's that kit. I want to look into it.

I still have all these silly problems to check out yet. Had to take a step back from it so I don't throw a temper tantrum! Aggrivated to no end now.


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Scoot -
Hate to be a pessimist. However, are you SURE that you're putting fuel in the right cap? I mean just because it says "GAS" doesn't necessarily mean that gasoline goes in that hole, does it? :rolleyes:

For instance, back in my younger days I worked on Alfa-Romeo sports cars. Believe me, there was anything but "Romeos" driving these cars. Most of the owners took after the first name and looked like Alfalfa from “Our Gang”. Anyway back to the story. Under the hood, on top of the valve cover, was an aluminum cap proudly labeled "Oleo".

Despite the explicit instructions, we never put any margarine in that hole. No, sir. So see how labeling can mislead? laughing

You be careful!


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I'm sure the fuel is going in the right cap. I had to label it to remind myself though... wink :bigt:

Funny story by the way...


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Some more Scary Mikuni Minutia which can make all the difference in the world regards flooding\starving..?..Make sure the float needle retaining clip is fit so that the OPEN end of the Loop is faceing forward..not sideway or backward..really..the needle can\will hang up sometimes due just to this easilly unseen\unsuspected little detail...Hmmm..Thats for Sure..!!....I like the Mikuni's..but they do have their little [email protected]##$ peckish peculiarities!!...

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Maybe the mag is losing it's edge when hot and cannot fire through the old plug leads ?

Electronics stores carry aerosol cans of refrigerant, you could empty a can of that over the hot mag.


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I'll take one more shot at this.
Plug wires? 7 or 8 mm, solid core or, maybe, coil, dying when hot?
It sounds like the gas cap vent but that's been covered and you know it's working (?).
And I don't hear you saying the carbs are leaking or flooding so float/needles/seats OK?
Could you be chasing two problems at once? Combo mag/HT wires/coil?
And , yes, nice cap.
HTH
Steve


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Yes indeed, nice chopper! (and I'm not that into the choppers)

Anyway... I had a similar problem a while back and it turned out to be the fuel filter. I don't know if you even use one, but if you do then you might remove it to see if it helps. When they get a lot of gunk floating around the filter element they can clog up and not flow enough to keep you running on the highway, so you stall out a bit and get to the road side. With the bike shutdown and not vibrating, the crud falls off the filter element and fuel fills the carb bowl and after a while you are on your way... only to have it happen randomly again.

Just thought I'd mention it...
Good luck,
Kyle


Kyle#44x

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