missing and popping out carb at high engine speed

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awander
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missing and popping out carb at high engine speed

#1

Post by awander »

Occasionally over the past year or so, i have had a situation where the pan would miss at high engine speeds, or when i gave it a lot of throttle.

I thought it was electrical, as turning off the lights would make it much better, though it wouldn't go away completely.

I put new plugs and a new ignition switch on it a few months back, and it improved quite a bit(the plugs were 6 years old, looked ok, but I figured it was time for new ones....)

2 weeks ago I parked the bike and have not ridden it until a few days ago. It usually starts up with 2 prime kicks, and then the first kick with ignition on. I kicked for 10 minutes with nothing, no sign of any ignition at all. Checked and I was getting a very weak spark. I tried cleaning the points with some cardboard, with no results. I then squirted a little "CRC 2-26", touted to "improve electrical contact" on the points, and the bike started right up. I took it for a 10 mile ride, and every time I would get on the throttle, it would start to miss; sounded almost like it was running on one cylinder.

This morning, I decided to replace the points, using the Echlin CS788s I saw recommended in the KB, but they would not fit my timer, as these CS788 points have a built-in post, which my timer also has.

I replaced the condensor, and cleaned up the old points. When I reinstalled them, and set the the gap to "bigger than 0.020 and smaller than 0.025", I found that even on the highest point of the cam, the points did not open! I figured that in the last 6 years(no new points since then) maybe the wearing block wore down.

So I had a set of points in an old aftermarket centrifugal-advance timer that was laying around, which looked ok. I took them off the old timer, and installed them on the bike. I set the gap, and found that I could not advance the timer enough to have the points open with the flywheels set for 35 degrees BTDC(I have S&S Flywheels, so the "F" mark was centered in the timing hole).

I disassembled the timer, and pulled the stem out enough to move the cam clockwise 1 tooth. Then I was able to adjust the timer so that the points just opened with the engine at 35 deg BTDC).

I took it for a short ride, and all seemed to be well. then I decided to take a longer ride this afternoon. I found that it was greatly improved over a few days ago(when i just barely made it home because it was missing so badly), but still, at about 55 or 60mph, if I really got on the throttle, it would miss and pop out the carb. This "seemed" to be engine-speed related, as I could gradually accelerate up to the point where it would happen, but it seemed more severe if I twisted the grip quickly.

Anyway, i was wondering if anyone has any ideas what could cause this? I have a couple of other NOS point sets coming in a few days, and will likely replace the used points that are on there when I get the other ones(assuming they fit). The plug wires also are looking kind of ratty, so I am thinking I will replace those as well.
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Re: missing and popping out carb at high engine speed

#2

Post by john HD »

Andy,

Every time my bike has developed a high speed miss it was the condenser. Try yet another....

john
awander
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Re: missing and popping out carb at high engine speed

#3

Post by awander »

Thanks, John, when I put the new points on I'll replace the condensor as well.
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Re: missing and popping out carb at high engine speed

#4

Post by 59Panman »

awander,

Try the easy items first. If you have a Linkert open up the low speed screw a turn or 2.
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Re: missing and popping out carb at high engine speed

#5

Post by 58flh »

Andy --Im with the other guys to!/But I would also check the Plugwires for a leak.Sometimes thats when they will shortout from the boots or wire itself.I found that the reason for it is when your at 55 or more MPH just the wind blowing over & moving the wire just enuff to let it open a leak past the insulater.Another good way is start the bike in a dark garage at night & move the wires around & the leak if there is one will be quite obvious as it will spark nicely in the dark.Did you check your timers shaft for play & is the cam-lobe within running condition?.---If everything checks out fine---Time to BUBBLETEST for a small Vacuum leak!.-A pinhole in the right spot, can do it at higher speeds!/Take your time & just eliminate each thing mentioned!.You will find your culprit!---(its usually the EASY things that make it seem more then what it is!).The timers bail should hold the cover on TIGHT,for a solid ground thru the timer.-----Respectfully----Richie
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Re: missing and popping out carb at high engine speed

#6

Post by 1962FLH »

I had a loose coil cover that caused my bike to do that once.
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Re: missing and popping out carb at high engine speed

#7

Post by Huck »

I've seen bad grounds on an assortment of bikes cause all sorts of issues. Might be worth a looksee.
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Re: missing and popping out carb at high engine speed

#8

Post by awander »

Thanks, 1962FLH-I actually took my (also loose) coil cover off earlier this year.

Huck, i will check all the wiring again, thanks.

Richie, thanks as always, I hope I have the stick-to-itiveness to fix this, even though the bike is running "pretty good" now.

ozwick, thanks, but really, a whole turn or 2 on the LS needle?
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Re: missing and popping out carb at high engine speed

#9

Post by steve_wood »

Is this a Linkert? What is the high-speed trim jet set at?
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Re: missing and popping out carb at high engine speed

#10

Post by Mark44 »

awander wrote:ozwick, thanks, but really, a whole turn or 2 on the LS needle?
I'm guessing he meant a click or two, not a whole turn or two.
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Re: missing and popping out carb at high engine speed

#11

Post by Mark44 »

steve_wood wrote:Is this a Linkert? What is the high-speed trim jet set at?
That was my thought as well, assuming that the problem is with the carb, and not an ignition system problem. At 55 mph the high speed circuit in the carb would be fully involved. A HS needle set too lean could cause the popping you've experienced, I believe.
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Re: missing and popping out carb at high engine speed

#12

Post by 59Panman »

Yes, I changed out my foam air cleaner to the stock copper mesh and had to open mine quite a bit. Open the throttle and twist it open to check for the issue you are having.
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Re: missing and popping out carb at high engine speed

#13

Post by 59Panman »

As for HS needle, I did not notice much difference.
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Re: missing and popping out carb at high engine speed

#14

Post by dean62 »

awander

I went thru this same process earlier this summer. Checked everything, carb,points,timing,condenser,gas flow,bubble test, all of it. It all seem to work for a few miles, but eventually it would start popping or what sounded like miss when I gave it gas or if it was under load. I started to notice it seemed to warm up before it would start. Finally I was setting in front of my 62 pondering what to do next when I noticed that the spring holding the timer in the advanced position, didn't have enough tension on it. Tightened spring tension and it's running good! Must have vibrated a couple degrees or enough to run in retarded! Can't say this is your problem, but it's exactly what mine was doing. Worth looking at.

Good luck Dean62
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Re: missing and popping out carb at high engine speed

#15

Post by 58flh »

Andy---Just for a heads-up---I bubbletest every month!/You never know when you will get a leak.Sometimes I dont have to do anything (no bubbles)/Sometimes It takes a 1/4 or 1/2-turn & the bubbles stop!.If you ride all the time ,I cant see not bubbletesting as soon as something changes -like more kicks instead of one.If you dont use your bike daily I would check-it as soon as its warmed-up/its a catch22-situation.They sit they shrink a little,You use daily its bound to get a leak here & there (especialy I noticed for RIGIDS!.---Anyway glad you worked it out----Richie
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