| Choppy throttle response around 4000 RPM [message #485354] |
Sat, 22 October 2005 15:26 |
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Hey all -
1980 KZ750 LTD back again.
When I open up the throttle on the freeway going about 50 mph, the power
delivery is not smooth at all. It's smooth if im going around 65, and I
haven't noticed it at lower speeds either. What could this be a symptom of?
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| Re: Choppy throttle response around 4000 RPM [message #485358 ] |
Sat, 22 October 2005 17:59 |
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"Masospaghetti" <gtg803xREMOVE [at] mail.gatech.edu> wrote in
news:djdelm$j83$1 [at] news-int2.gatech.edu...
> Hey all -
>
> 1980 KZ750 LTD back again.
>
> When I open up the throttle on the freeway going about 50 mph, the power
> delivery is not smooth at all. It's smooth if im going around 65, and I
> haven't noticed it at lower speeds either. What could this be a symptom
> of?
Weeell, it COULD be a symptom of this bike not delivering
smooth power in whatever gear you're in, at 4000 rpm.
Honestly.
The cure might be to change down one gear to avoid the
symptom.
I assume your carburettors are synchronized and your
spark plugs reasonably fresh.
SWHAC will be along shortly.
--
Ole Holmblad - Göteborgs Prima MCK / MK Pionjär
TDM850 / TT600R FL#44 OTC#489 UKRMSBC#08
SGFPTH#00 Remove hat to answer by mail
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| Re: Choppy throttle response around 4000 RPM [message #485360 ] |
Sat, 22 October 2005 22:17 |
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OH- wrote:
> "Masospaghetti" <gtg803xREMOVE [at] mail.gatech.edu> wrote in
> news:djdelm$j83$1 [at] news-int2.gatech.edu...
>
>>Hey all -
>>
>>1980 KZ750 LTD back again.
>>
>>When I open up the throttle on the freeway going about 50 mph, the power
>>delivery is not smooth at all. It's smooth if im going around 65, and I
>>haven't noticed it at lower speeds either. What could this be a symptom
>>of?
>
>
> Weeell, it COULD be a symptom of this bike not delivering
> smooth power in whatever gear you're in, at 4000 rpm.
>
> Honestly.
>
> The cure might be to change down one gear to avoid the
> symptom.
>
> I assume your carburettors are synchronized and your
> spark plugs reasonably fresh.
>
> SWHAC will be along shortly.
>
Yes, it doesn't depend on the gear i'm in. However, I get a lot of
vibrations at higher RPM so I try to avoid them if at all possible.
Spark plugs are new, carbs are synch'ed.
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| Re: Choppy throttle response around 4000 RPM [message #485361 ] |
Sun, 23 October 2005 01:27 |
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"Masospaghetti" <gtg803xREMOVE [at] mail.gatech.edu> wrote in message
news:dje6pa$11$1 [at] news-int2.gatech.edu...
> OH- wrote:
>> "Masospaghetti" <gtg803xREMOVE [at] mail.gatech.edu> wrote in
>> news:djdelm$j83$1 [at] news-int2.gatech.edu...
>>
>>>Hey all -
>>>
>>>1980 KZ750 LTD back again.
>>>
>>>When I open up the throttle on the freeway going about 50 mph, the power
>>>delivery is not smooth at all. It's smooth if im going around 65, and I
>>>haven't noticed it at lower speeds either. What could this be a symptom
>>>of?
>>
>>
>> Weeell, it COULD be a symptom of this bike not delivering
>> smooth power in whatever gear you're in, at 4000 rpm.
>>
>> Honestly.
>>
>> The cure might be to change down one gear to avoid the
>> symptom.
>>
>> I assume your carburettors are synchronized and your
>> spark plugs reasonably fresh.
>>
>> SWHAC will be along shortly.
>>
>
> Yes, it doesn't depend on the gear i'm in. However, I get a lot of
> vibrations at higher RPM so I try to avoid them if at all possible.
>
> Spark plugs are new, carbs are synch'ed.
Try rejetting......if your plugs are burning on the brownish side, thats
a good sign..... if a little white, then its running a lil lean.... if
black, too rich.... hope this helps..
Fwed
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| Re: Choppy throttle response around 4000 RPM [message #485362 ] |
Sun, 23 October 2005 02:43 |
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Masospaghetti wrote:
> Yes, it doesn't depend on the gear i'm in. However, I get a lot of
> vibrations at higher RPM so I try to avoid them if at all possible.
>
> Spark plugs are new, carbs are synch'ed.
Weren't you having some problems with low compression on one cylinder
and a head gasket leak?
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| Re: Choppy throttle response around 4000 RPM [message #485363 ] |
Sun, 23 October 2005 06:11 |
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Masospaghetti <gtg803xREMOVE [at] mail.gatech.edu> wrote in
news:dje6pa$11$1 [at] news-int2.gatech.edu:
> Yes, it doesn't depend on the gear i'm in. However, I get a lot of
> vibrations at higher RPM so I try to avoid them if at all possible.
>
> Spark plugs are new, carbs are synch'ed.
You might try shimming the needles. Though, before you do that, having the
bike run on a dyno with exhaust gas analysis might be useful.
--
Mike Freeman
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| Re: Choppy throttle response around 4000 RPM [message #485364 ] |
Sun, 23 October 2005 18:03 |
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krusty kritter wrote:
> Masospaghetti wrote:
>
>
>>Yes, it doesn't depend on the gear i'm in. However, I get a lot of
>>vibrations at higher RPM so I try to avoid them if at all possible.
>>
>>Spark plugs are new, carbs are synch'ed.
>
>
> Weren't you having some problems with low compression on one cylinder
> and a head gasket leak?
>
I thought so, I must have done the test wrong though, because now the
compression is very good on both cylinders - 150 psi cold.
The bike runs well now overall. Idles around 900 rpm, no backfiring,
plugs aren't AS sooty as before (little bit of soot around the rim of
the plug, the electrode is still clean though). Filled the handlebars
with birdshot and it's much more comfortable.
The head gasket may have stopped leaking too - not sure how thats
possible - but its a very slow leak now. Most of the oil was coming from
the chain tensioner with a bad seal.
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| Re: Choppy throttle response around 4000 RPM [message #485369 ] |
Sun, 23 October 2005 20:34 |
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Masospaghetti wrote:
> krusty kritter wrote:
> > Masospaghetti wrote:
> >
> >
> >>Yes, it doesn't depend on the gear i'm in. However, I get a lot of
> >>vibrations at higher RPM so I try to avoid them if at all possible.
Vetical twin do send a lot of vibration up towards the handlebars, but
that model has a counterbalancer. Have you done anything to adjust the
counterbalancer drive chain? It could be that it's loose.
> The bike runs well now overall. Idles around 900 rpm, no backfiring,
> plugs aren't AS sooty as before (little bit of soot around the rim of
> the plug, the electrode is still clean though). Filled the handlebars
> with birdshot and it's much more comfortable.
If it's not the counterbalancer adjustment maybe the bike is lean
surging?
When an engine lean surges, it pulls hard for a second, then it stops
pulling, and starts pulling again for second, etc.
If that's what it's doing, you might try turning the fuel/air mixture
screws out half a turn, or shimming the needles a little higher as
another poster suggested.
You can get a few 1/2 mm X 3 mm washers at a hardware store for about
$0.49 if you buy them in the package.
If you make the mixture too rich, the engine will start "8-stroking".
This makes the engine sound a bit like a 2-stroke that's all loaded up
with oil and is fouling its plug. It's a "Br-r-r-r-r!" sound.
The engine will fire every other compression stroke and the exhaust
will sound blubbery and you'll notice a lot of vibration when you try
to speed up.
The engine is expending half of its effort trying to pump unburn
fuel/air mixture when it 8-strokes.
Of course the spark plugs will carbon up if the engine is 8-stroking.
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| Re: Choppy throttle response around 4000 RPM [message #485390 ] |
Mon, 24 October 2005 04:26 |
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krusty kritter wrote:
> Masospaghetti wrote:
>
>>krusty kritter wrote:
>>
>>>Masospaghetti wrote:
>>>
>>>
>>>
>>>>Yes, it doesn't depend on the gear i'm in. However, I get a lot of
>>>>vibrations at higher RPM so I try to avoid them if at all possible.
>
>
> Vetical twin do send a lot of vibration up towards the handlebars, but
> that model has a counterbalancer. Have you done anything to adjust the
> counterbalancer drive chain? It could be that it's loose.
No, unfortunately...but from what I understand, adjusting the balancer
chain requires tearing down the entire engine :(
>
>
>>The bike runs well now overall. Idles around 900 rpm, no backfiring,
>>plugs aren't AS sooty as before (little bit of soot around the rim of
>>the plug, the electrode is still clean though). Filled the handlebars
>>with birdshot and it's much more comfortable.
>
>
> If it's not the counterbalancer adjustment maybe the bike is lean
> surging?
> When an engine lean surges, it pulls hard for a second, then it stops
> pulling, and starts pulling again for second, etc.
>
> If that's what it's doing, you might try turning the fuel/air mixture
> screws out half a turn, or shimming the needles a little higher as
> another poster suggested.
>
> You can get a few 1/2 mm X 3 mm washers at a hardware store for about
> $0.49 if you buy them in the package.
>
> If you make the mixture too rich, the engine will start "8-stroking".
> This makes the engine sound a bit like a 2-stroke that's all loaded up
> with oil and is fouling its plug. It's a "Br-r-r-r-r!" sound.
>
> The engine will fire every other compression stroke and the exhaust
> will sound blubbery and you'll notice a lot of vibration when you try
> to speed up.
> The engine is expending half of its effort trying to pump unburn
> fuel/air mixture when it 8-strokes.
>
> Of course the spark plugs will carbon up if the engine is 8-stroking.
>
Hmmm...hope its not the latter...I've had a hell of a time trying to
lean this thing out.
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| Re: Choppy throttle response around 4000 RPM [message #498634 ] |
Tue, 01 November 2005 22:04 |
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krusty kritter wrote:
> Masospaghetti wrote:
>
> krusty kritter wrote:
>
>
>>>Of course the spark plugs will carbon up if the engine is 8-stroking.
>>>
>>
>>Hmmm...hope its not the latter...I've had a hell of a time trying to
>>lean this thing out.
>
>
> Have you tried adjusting the idle mixture screws at all since you
> installed the new ignition points? There is the possibility that the
> idle mixture screw is actually a pilot air screw that works backwards
> from the normal pilot gas screw that CV carbs usually have.
>
> You might try adjusting both screws to 1.5 turns out and see what
> happens with that setting, whether it's really rich or if it leans the
> mixture up.
>
> You'd know if the mixture was getting richer by the fact the the idle
> RPM would hang up when you blipped the throttle open and closed.
>
I'll try that.
I made sure the pilot jets were the right size, they were...and valve
clearance is fine as well. It's better than it was though, i'm averaging
about 30 mpg instead of around 20.
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