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sputtering (Read 170 times)
omahasavage
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sputtering
10/09/10 at 21:14:03
 
I went for about a 500 mile ride this weekend. It was mostly on the interstate, which in Nebraska means the speed limit was 75 and everyone goes about 82.

I had no problem staying up when the wind was at my back, but when I was driving into the wind at that speed, the bike did something new.

For the lack of a better word I would say it sputtered.  All was fine until after 65-70, but into the wind, it would cut out and lose speed.  There was also a light tapping noise, sounded like metal on metal.  If I turned the throttle back to 7/8ths, the sound and problems went away, most of the time that is.  When the wind was bad, it all would happen at a lower speed, and I would have to turn back more on the throttle.

when the wind was at my back, the problems still happened, but they were very rare.  in fact, i was up to almost 90 with no noise or sputter and at full throttle a few times.

at first I thought it was the transmission slipping, but it was less bad as I turned the dial a jet lean.  I have a performance carb from Lancer, a daj, a cone k&n filter, and a Harley muffler.

I'm sure I don't have the carb tuned perfect,  but does it seem like I'm on the right track thinking it is a carb problem?

I just don't know what the metal sounding tapping noise could be.

I don't know what the deal is with my mpg thing in my signature, I was averaging about 34 mpg, which is less than I usually get, but the bike was loaded down with stuff, high wind, and higher speed than I usually go.
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jamesmackelroy
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Re: sputtering
Reply #1 - 10/09/10 at 21:29:03
 
You try running it in prime? Mine sputtered at top speeds and a week later it wouldn't even start unless in prime. Search the links and follow the advice for testing the petcock.

I also readily admit to have less mechanical knowledge than 90% of the population of most underdeveloped countries.
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Charon
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Re: sputtering
Reply #2 - 10/09/10 at 21:38:11
 
"PRIme" would be my thought, too. The stock Savage has a top speed of around 85, give or take a little. At near wide open throttle, there is very little engine vacuum available to hold the vacuum-operated petcock open. Closing the throttle a little produces more vacuum, so the petcock would work better. This isn't a limit specific to the Savage (S40), but applies to all vacuum operated petcocks. I can't explain the noise, unless it was a bit of detonation from lean running, possibly a side effect of the petcock limiting fuel supply.
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Eschew obfuscation.

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Routy
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Re: sputtering
Reply #3 - 10/10/10 at 05:51:13
 
I think the below hits the nail right on the head,....exactly !

Any gasoline engine running hi speed at near zero manifold vacuum for very long, is seeing white hot temps in the combustion chamber !

If I had to run the bike under those conditions, I would surely
run 92 octane fuel,.......before the top of the piston......along w/ the valves go out the exhaust pipe  Shocked

Charon wrote on 10/09/10 at 21:38:11:
"PRIme" would be my thought, too. The stock Savage has a top speed of around 85, give or take a little. At near wide open throttle, there is very little engine vacuum available to hold the vacuum-operated petcock open. Closing the throttle a little produces more vacuum, so the petcock would work better. This isn't a limit specific to the Savage (S40), but applies to all vacuum operated petcocks. I can't explain the noise, unless it was a bit of detonation from lean running, possibly a side effect of the petcock limiting fuel supply.

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Rich
'07 S40 Blvd stocker, except drilled OEM exhaust and white spacer mod...1/2 (.055)
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omahasavage
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Re: sputtering
Reply #4 - 10/10/10 at 06:57:36
 
I forgot to share that I have already replaced the petcock with a raptor.  so I don't suppose it is a vacuum problem.  

I was thinking that the noise might be knocking, so I tried a variety of octane fuels.  87 is mt usual, so I tried 89 with ethanol and 91 and 93 with ethanol.  I didn't much difference.
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drums1
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Re: sputtering
Reply #5 - 10/10/10 at 09:18:42
 
Only 39 mpg?? Isn't that a little low?? I get about 75 mpg, if not a little more. I left town with a full tank and 80-some miles from home I filled up--1.1 gal.  Something don't seem right here.
OOps, now that I did the Fuelly thing I guess it ain't as much as I thought, but still not bad...
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« Last Edit: 10/14/10 at 13:43:02 by drums1 »  
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bill67
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Re: sputtering
Reply #6 - 10/10/10 at 09:20:47
 
He don't have a stock carb.He has a performance carb.
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william h krumpen
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Re: sputtering
Reply #7 - 10/10/10 at 09:50:04
 
A little better mpg is probably from the long distance riding.
can't say I know anything about the performance carb or daj.
but if you back off to 7/8's throttle and it picks up on a stock carb means the main is a little lean.  which may be the sound you're hearing, pinging.
but I'd also look into where the sound was coming from, top end, most likely a type of pinging, bottom end i'd take a look at the cam chain.
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omahasavage
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Re: sputtering
Reply #8 - 10/10/10 at 10:54:18
 
that's what I have been thinking, that the main is lean.  I am new to playing with carbs, so I really don't know.

Lancer gave me a set of main jets with the highest being a 200, which is what is on there right now.  I am going to have to get some bigger jets and see if that helps.

I also have the clip at the leanest position, so I am going to move that down a bit.
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omahasavage
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Re: sputtering
Reply #9 - 10/10/10 at 14:03:32
 
I re-read the Roll-Off instructions on Mukuni's website, looks like my main jet is too small.


ROLL-OFF:

The Roll-Off technique is the quickest and is almost as accurate as the Roll-On method. First, one gets the engine warm on the way to a safe roadway. If there is room, use fourth gear as this allows more time to assess the result.

Now, get the engine rpm high enough that it is on the cam and in its power band. This may need to be as high as 4000 rpm with some cam choices. Apply full throttle. Let the engine accelerate for a couple of seconds until it has settled in and is pulling hard. Quickly roll the throttle off to about the 7/8ths position. When you do this, the mixture richens slightly for a second or so.
If the engine gains power as you roll the throttle off, then the main jet is too small and you need to fit a larger one.
If the engine staggers slightly or has a hard hesitation, then the main jet is too large and you need to fit a smaller one.
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Routy
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Re: sputtering
Reply #10 - 10/11/10 at 06:47:50
 
Right on about something don't seem right here Shocked

drums1 wrote on 10/10/10 at 09:18:42:
I get about 75 mpg, if not a little more. I left town with a full tank and 80-some miles from home I filled up--1.1 gal.  Something don't seem right here.

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Rich
'07 S40 Blvd stocker, except drilled OEM exhaust and white spacer mod...1/2 (.055)
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bill67
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Re: sputtering
Reply #11 - 10/11/10 at 07:07:27
 
That would be 72.72 mpg,but putting in only 1 gallon and the difference angle a bike could be on could make a lot of differences.
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william h krumpen
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Re: sputtering
Reply #12 - 10/12/10 at 19:57:44
 
The other player is the air filter..yours is a K&N cone. At top speed into the wind, perhaps a little less air is getting thru..which should lead to too rich -  the opposite of what you suspect..too lean with a wide open throttle. Embarrassed Embarrassed
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