carb sputter / sneeze linkert

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Northman
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carb sputter / sneeze linkert

#1

Post by Northman »

Here's one that's had me baffled for some time now. When ever I fill up at the pump and get down the road a few blocks I get a sneeze out of the carb. Linkert m74 b.and it continues every so often as ride. I've been riding the bike for years now and done all I can do and have found nothing. The ol bubble test, fuel strainer, fuel flow. You name it if I thought it was related I more than likely investigated it. I'm down to thinking It's gas quality or temp change from the gas into the bike tank. I don't have the oem gas line covered with rubber tube between the cylinders but might do it just to see what happens. Too much mmo in the gas? None of it adds up for me. I fill the bike with a gas can and it don't happen. Good grief. Any ideas or coments?

Thanks, Northman
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Re: carb sputter / sneeze linkert

#2

Post by blewcrab »

I would try to open up the high speed needle while you are riding one click at a time until the cough / sneeze stops . its better to run rich than lean !
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Re: carb sputter / sneeze linkert

#3

Post by Northman »

Blewcrab, thanks. Yeah I'm not convinced by any means it has anything to do with gas temp from a pump or can but it just shows the oddity of tracking something.

I have the high set at 2 turns plus 4 clicks give or take. And the low set at 3.5 turns. If I go 2-4 clicks leaner on the low it is noticeable immediately. I just figured the high speed is set out of orbit where it is. I have another m74 b I've been thinking about swaping that I ran at 1 or 2 clicks out on the high and 3 or 4 out on the low. I remember I could close the high on that one and no change indicating probably wore.... but I'm stubborn since I had this one rebuilt. I hate to say it and again may have nothing to do with anything, but the other carb that was on the Bike at one time, not rebuilt, I don't remember this going on. Hope to get more ideas as this topic is viewed.

Northman
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Re: carb sputter / sneeze linkert

#4

Post by Bigincher »

So let me see if I got this right--- This happens when you fill up at a gas station, but if you fill up from a gas can, just pouring it in, then this coughing and sneezing doesn't happen?
Is this repeatable? I mean, can you try filling up from a gas can (that has sat undisturbed for awhile) for the next few fillups? (Even if it's only a gallon at a time.) And see if the symptoms disappear when you only pour gas in from a can. Call it an experiment. It's just very curious, don't you think? Rather than fool with settings and adjustments on a just-rebuilt carb, I find it significant that the symptoms disappear when you pour gas in from a can.
Have you tried getting gas at different gas stations? Something funny going on here....
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Re: carb sputter / sneeze linkert

#5

Post by Andygears »

Is your cap opening sequence the same from can or pump? I'm thinking one cap might not be venting right, maybe the left and when, at the pump, you fill the left, cap it, then the right. Maybe the left tank don't vent and hydraulic locks the gas in there till pressure equalizes from the right tank venting. If the left tank is half empty, it won't act up because the air in the left allows "bounce" so a vacumn is not formed in the left tank.
Just a shot, but try only filling the right tank at the pump, see if it coughs.

My two cents
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Re: carb sputter / sneeze linkert

#6

Post by nmaineron »

I would throw the book away on this and adjust the jet till you can't take it out any further.Its not going to hurt a thing.Actually if you are running so lean up top to have to deal with a high speed sniff you really have no choice. I had M 74's on my pan and had a few different carbs.One of them had a high speed jet and the others fixed.Its been way to long to remember what I had on it but I still have some jets.My point is that if you can't get the sniff out and you are convinced its fuel then maybe a jet is your answer
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Re: carb sputter / sneeze linkert

#7

Post by Northman »

Thanks to all for the input.

Bigincher exactly. I've done that and more than once. Yes it was consisitant enough to make a pattern to notice however not to the point of a result. There were hit and miss sessions adding confusion to the mess.

Andygears...done that too. But Switched caps at the pump. And tried filling visa versa. I usually fill right first then left a little less but have done both than topped both off.

Nmaineron...I did this awhile ago but with the gas at pump and gas in can routine I wanted to leave settings as is to not add more variables to my confusion. I agree I need to do something with the high speed but don't know what untill maybe I eliminate this crazy gas thing.....maybe.

Road all day today. 2 up. Filled at the pump. Started normal, normal kicks (that never changed) and ran with No sweet spot sputter. DIFFERENT GAS AND STATION! I have done this before but when you need gas you need gas and I have done half tank fill ups etc.so you can see the variables in that part alone. I'm starting to talk myself into believing that just because the pump says it's that grade of gas it don't mean it's so and just maybe there is something hokie going on with certain dealers. I've always been under the impression that it comes out of the same bulk supplier but different areas have different grades? Anyway I rode all day with no issues. Tomorrow who knows..... But I won't buy gas at this area dealer for awhile to eliminate that and see what happens. Has Anyone had gas issues as such? I really appreciate the advice.
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Re: carb sputter / sneeze linkert

#8

Post by Bigincher »

Pretty much tells me it's not the carburetor at all.
Most auto drivers use regular. I think most of us bike riders use premium. The odds are high that the last person to use the pump used regular. So the gas still in the hose is regular, but how far back in the system is it still regular? I've built a lot of different buildings and facilities in my construction career, but (luckily) never did a gas station, so I don't know the exact details. Logic would dictate that all grades are plumbed to the pump, the pump is the dispenser, so.... probably only the amount in the hose is of the previous users grade. Having said all that, the amount is probably minimal; a pint? A quart?
So rule out excessive dilution of grades. Wouldn't matter anyway.

Now consider the different brands. It's not true that all stations are supplied by one regional mega-distributor. The smaller mom-n-pop stations have to buy their gasoline from a distributor, but the big name brands all have their own distribution systems. As I know it, anyway.

There are some people- alarmists, conspiracy-theorists, mad scientist types- who suspect that hazardous chemical wastes are being illegally added to gasoline as a tidy little way to dispose of it. Totally illegal (isn't it?) and morally wrong. But when certain other covert activities of our government over the years are considered, is it out of the question?

Frankly, my first instincts upon reading the first post, made two things come to mind-
First- and this is something I learned years ago- when you see a tanker at a gas station filling the underground tanks- keep on riding and find another station. Why? Because when the tanks are filled, that rapid infusion of new gas stirs up all the sediment and crud from the bottom of the tank, and suspends it in the fuel for several hours until it can settle out again. The result of using that gas is obvious- plugged filters, screens, jets, air bleeds, etc.
But perhaps not the case here.
Second- likewise in the same manner that a tanker stirs up sediment in the u/g tanks, the filling nozzle we use at the pump stirs up sediment in the bottom of our gas tanks.
This was my initial thought on this issue.

Another thought I had- and this is pure speculation- is that the same pumping action somehow introduces air into the fuel. Like an old-fashioned fountain soda. Seems to make sense when you consider that the symptoms are not presented when gas is poured in from a can.

I do apologize for the lengthy dissertation. Northman, I think if you learn which station(s) to avoid, and which ones are favorable, I think your problem will go away. I think we all have "gas station stories" to tell, and none of them are happy.
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Re: carb sputter / sneeze linkert

#9

Post by Excalibur »

I had similar sneezing symptoms a couple of years ago. Some of my problem may have been the cracked heads but nevertheless... some thoughts,

Have you tried loosening the gas cap as you ride?

Have you put a strobe on the timing? The thought is it will show how erratic the timing really is. My old timer was badly worn and the strobe showed that clearly. In my case I'd marked the rear cylinder BTDC mark as well.

Are you running a manual advance timer? Now Murray's '52 will sneeze if the timing is too late. Usually I've seen this when he first starts it, then he warms it up without sufficient advance. My '61 doesn't do this at all.
If yours is an auto-advance timer, are the weights sticking? Here again the strobe light will tell all.

The old adage: 90% of carb problems turn out to be ignition. This catches out even experienced mechanics. Start with a full and proper plugs&points tune up. The carb always comes after. Dump any suppressor leads or plugs.

I recommend temporarily adding a digital voltmeter, perhaps taped to the handlebars. The object is to accurately monitor battery volts as you ride. These are crazy cheap out of China. (I use Ebay or Aliexpress.com)

Lastly, properly measure the voltage supply to the ignition coil under load. Don't forget to measure the ground return path as well. My '61 had several voltage losses including, ignition switch, timer base-to-ground and battery earth strap. I got a nice improvement in engine behavior particularly in starting which is what I was looking for.

Pick out whats applicable. Hope something works for you. Good luck.
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Re: carb sputter / sneeze linkert

#10

Post by 59Panman »

I chased a similar problem which pointed to a lean condition. Check your ignition switch. Mine was wore out. Found out when I turned it to the lighting position my issue went away.
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Re: carb sputter / sneeze linkert

#11

Post by panheadrider1961 »

northman i agree with blewcarb when i put the corn squeezings in and what ever else may be in it i have to ride and adjust till its gone when i put pure gas in no problem open your low speed 2 clicks and high side another 1/4 turn should get you their, and 95 degree 80 per cent humidity in middle ga don,t help stock 74 inch 1961 pan with accsy.
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Re: carb sputter / sneeze linkert

#12

Post by foundationapps »

My explanation takes a bit of history. Bought a 48 Pan from a guy almost 3 years ago now. It had an aftermarket auto advance timer S&S I think. Started perfectly after 5 years of sitting in a garage. Over the next 4-6 weeks, I had to re-tweak the timing (which wasn't messed up, but I thought it was), learned the hard way how to rebuild a bendix carb and set the float right). Fast forward to October last year, a knee high dog intercepted the front end which ended up in me doing a face plant on the pavement. Now this was my first ever rebuild of a HD bike. I put the 48 Pan engine in a KraftTech softail frame (request from the wife). All winter project in the living room.

Amongst the parts I got with the bike was the old original manual circuit breaker. I had the heads and jugs off, put new James gaskets and a set of James fire ring head gaskets on (which are working perfect so far) and put the engine back together. Having had trouble with the weights sticking and dragging on the breaker plate on the auto advance unit, I did a bold stop and put the original circuit breaker back in the motor.

Reassembled the whole bike, through the guidance of the masters on this site, I hashed out the timing as I was 180 degrees out. I added a Right Side Electric Start unit in place of the kicker on the 4 speed tranny. XL Evolution starter.

Longer story shorter.... once I got the timing hashed out using the light bulb method, the bike has been running perfectly. Starts with NO cranking. NEVER backfires (careful manifold sealing process).

Regarding fuel... I have been running Sinclair Premium because it's corn free in most places here. More and more gas stations have corn free gas, even in Jackson Hole, that was a surprise. About 40% of the riding, 2000 miles so far, I've had to run corn gas in the bike, I add 3 ounces of MMO when I can. I've run 3 tanks of corn gas back to back on one trip and it burned it perfectly. I use Autolite 65 plugs, V-twin dual fire coil, Accel plug wires, nothing special. The carb is perfect, but it's not my fault, I barely know what I'm doing.

More importantly, the biggest thing I have learned is that TIMING is the one thing that gets me through any bad gas situation. The old circuit breaker, using NAPA points and condenser is managing the ignition just fine. So for my two cents, timing, timing and more refined timing.
If you put all the things that have an engine run right on a pie chart to figure out the most important thing, TIMING would be the biggest piece of that pie, but I have only one machines of deep experience at these engines, they really are incredible.
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Re: carb sputter / sneeze linkert

#13

Post by Andygears »

I'll second the motion to put a strobe on the timing. My buddy's bike ran for months after I said the mark was bouncing all over, front, back, not steady at all. Turned out months later, the circuit breaker gear -stud- had broke free from the case inside the gear case. The problem surfaced when the gear chipped a tooth, went in the scavange pump and sheared a key.
It ran good too! Variable ignition timing🤔???

My two cents
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Re: carb sputter / sneeze linkert

#14

Post by Northman »

Interesting. I still have not used the gas from that station and have had no issues yet.

However I'm taking good advice and checked my timing again. (along with other tests one at a time) With a timing light I'm not getting a lot of bouncing just the quivering which I expected BUT after getting to opperating temp and at 2000 rpm give a little more, My mark moved to the front of the hole. In the hole but in that 1/4 section which caught me by supprise. No bouncing around just stayed at that location. Retarded? Is this worth trying to position to the center? On idle the line is smack center in the hole. I'd does bobble a little but not all over the place.

Thanks in advance, Northman
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Re: carb sputter / sneeze linkert

#15

Post by Northman »

Wow! that was a lot of dinking around re setting the timer to the light. Its real close, as close as possible, but I don't think I'd waste my time trying to get it dead nuts perfect, perfect again. Maybe an extra set of hands would have been helpful. The wifie poo? Not.

Northman
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