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Low speed surge. (Read 35 times)
Evanswv
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Low speed surge.
01/13/22 at 10:30:01
 
We have been having a couple days with high temperature in the mid 40s, but the lows at night are still well below freezing.  I have rode my newly acquired 2004 Savage around some. It is extremely cold natured, and after starting I have to let it idle a spell with the choke pulled, at a fast idle before it will take any throttle.  I have tried adjusting the mix screw after several miles of driving, and I can get a good smooth idle, and it runs, and pulls strong under moderate , and full acceleration, but it lopes, and lurches under light acceleration , as in the case of riding slowly on a side street.  I have tried turning the mix screw out further, and in as well, and I can't get it to run smoothly under light low rpm throttle. I thought my muffler was un modified, but it has had a few holes drilled in it I think .It has some holes about 3/8" in that plate inside the muffler, which I don't think are supposed to be there.  The bike often pops like a gun shot when I let of the throttle ,like coming to an intersection. It also will often pop when I shut it off.  Is this problem likely to go away in warmer weather, or do I need a jet kit? , Or is something else likely my issue.?  
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Gary_in_NJ
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Re: Low speed surge.
Reply #1 - 01/13/22 at 11:49:19
 
A few things here.

First, don't let your engine idle for more than 30-60 seconds before you start to ride.

Second, never let a cold engine idle while on the side stand and limit a warm engine to less than 30 seconds on the side stand. The oil pressure isn't strong enough at idle to properly lube the cams.

Third, other than the idle screw, you shouldn't have to touch anything else on the carb due to cold weather. Once then engine is up to temperature it will work mostly OK in near freezing temperatures. I say mostly because cold air is denser than the air that you have jetted the bike for, and as a result it will naturally run lean (on all circuits). But you don't jet or adjust jetting for a minimal use case.

Lastly, your pilot jet is probably clogged - that's why it wont idle and learches at very small throttle settings. So make good use of the warn weather and pull your carb for a cleaning. I typically don't clean jets, I replace them. However, if you have some old guitar strings, brake cleaner and a good source of compressed air, you can get the pilot jet cleaned.

And a BTW (since I already typed "lastly") a few holes drilled in the exhaust wont require significant jet changes (maybe a number or two on the main) and certainly wont effect the idle circuit.
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justin_o_guy2
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Re: Low speed surge.
Reply #2 - 01/13/22 at 12:56:11
 
Torch tip cleaning tool.
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ckahleer
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Re: Low speed surge.
Reply #3 - 01/13/22 at 15:08:19
 
Without removing the carburetor from the bike, you are able to remove the carburetor top and shim the needle with a small washer. This sometimes fixes low speed surge.
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Evanswv
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Re: Low speed surge.
Reply #4 - 01/13/22 at 15:25:44
 
Gary_in_NJ wrote on 01/13/22 at 11:49:19:
A few things here.

First, don't let your engine idle for more than 30-60 seconds before you start to ride.

Second, never let a cold engine idle while on the side stand and limit a warm engine to less than 30 seconds on the side stand. The oil pressure isn't strong enough at idle to properly lube the cams.

Third, other than the idle screw, you shouldn't have to touch anything else on the carb due to cold weather. Once then engine is up to temperature it will work mostly OK in near freezing temperatures. I say mostly because cold air is denser than the air that you have jetted the bike for, and as a result it will naturally run lean (on all circuits). But you don't jet or adjust jetting for a minimal use case.

Lastly, your pilot jet is probably clogged - that's why it wont idle and learches at very small throttle settings. So make good use of the warn weather and pull your carb for a cleaning. I typically don't clean jets, I replace them. However, if you have some old guitar strings, brake cleaner and a good source of compressed air, you can get the pilot jet cleaned.

And a BTW (since I already typed "lastly") a few holes drilled in the exhaust wont require significant jet changes (maybe a number or two on the main) and certainly wont effect the idle circuit.

The bike idles fine after it's warmed up.  I start it on full choke, and it idles but dies if  I try to give it any throttle, but it idles fast with the choke pulled, and as it warms up I shove the choke in a little at a time, but make sure it has a fast idle the whole time it is warms up.  I have rode it a few miles, and adjusted the mix, and get as best idle as I can get( which is a really good even idle, but it still acts lean under light throttle conditions like when you drive in a small town, or side street. It does fine once it gets opened up some. When it acting up, I can reach down with my left hand, and drive with the choke pulled out a knotch, and the engine picks up and runs smoothly.  I think I am going to pull the batteries out of my motorcycles , and bring them in till winter is over, so I probably won't be riding for a little while.  I just thought I would order a jet kit if that's what I needed, but I guess I should wait till things warm up. Thanks
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ohiomoto
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Re: Low speed surge.
Reply #5 - 01/13/22 at 15:57:47
 
Listen to Gary.  This is expected behavior with any engine in cold weather.  

  • Full choke is for starting it.  
  • Half choke is for riding it while it warms up.  How long it takes to warm up depends on the weather and how long/hard you are riding it.  
  • Once it warms up you go to no choke.  


I often commute to work on cold mornings (as low as mid-30s once in a while) and it can take 5-7 miles to get it warmed up.  In the summer it might only take 1/2 mile or less.

Most people don't realize this because modern fuel injection systems take care of this for you.  Even carbureted cars in the 70s took care of this for you.  

Old British cars had knobs on the dash that you had to pull to activate and control the choke via a cable. You had to manually control how much and how long you had to "choke" the engine to get i warmed up.

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