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Well, my odd little stumble is perplexing me in what causes it. It almost feels like the timing isn't advancing properly. Just out of curiosity, what handles spark advance in 1st gear? It feels like when my kawasaki's mechanical advance was sticking. I know that 4th and 5th gear is vac advance, but what controls 1-3? Is it just mapped?

One thing that is interesting, is that if I am idling in 4th gear, the engine is running up around 1.5 to 1.75k RPM, but once I drop to 3rd, the idle drops to 1k rom. Anyone else notice that?
 

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I think we'll need Vic orPaulto answer that one! :)
 

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philcsand wrote:
Well, my odd little stumble is perplexing me in what causes it. It almost feels like the timing isn't advancing properly. Just out of curiosity, what handles spark advance in 1st gear? It feels like when my kawasaki's mechanical advance was sticking. I know that 4th and 5th gear is vac advance, but what controls 1-3? Is it just mapped?

One thing that is interesting, is that if I am idling in 4th gear, the engine is running up around 1.5 to 1.75k RPM, but once I drop to 3rd, the idle drops to 1k rom. Anyone else notice that?
philcsand, the timing table is built into theignition module for the lower gears (rpm sensitive). The upper two are switched over to the vacuum source for control.

On your stumble problem? There is a service bulletin out on the 84 & early 85 for just such a problem & that involved larger pilot jets & different slide needles (& possibly slides, I can't remember). Try opening the (4) pilot (slow jet) screws another 1/2 to 1 turn & see if that helps (it probably will). Then, if still not happy, shim all 4 slide needles up about .024" using small washers. I think between the pilot jet adjustment & needle shims it will eliminate the stumble completely.

I had a friend that bought an 84 & it stumbled bad enough to barley be drivable in cool weather. The person he bought the bike form said it had always been like that & he just lived with it. I'm not sure how people can live with a vehicle that runs like that.

I did a carb balance on that bike & it ran slightly better, adjusting the pilot jet screws helped more, & finally shimming the slide needles made it run almost as good as a fuel injected bike.

Twisty
 

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twisty
you think shimming the needles will work on my 86 1200 when its cold out I have to run on 1/2 choke

I did the carb sync and pilot screws its just when its cold out the stumble

and if so where would one get the shims
 

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There's also the possibility the electronic module isn't getting the rpm signal. Someone with the diagrams on the 1200 might be able to look at the electronic advance on the 1-3 gear range. I think if the module either fails or doesn't get the information it needs it drops back to an idle or starting advance setting. Could be wrong, but that's the usual system with electronic advances.
 

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wingwarrior wrote:
twisty
you think shimming the needles will work on my 86 1200 when its cold out I have to run on 1/2 choke

I did the carb sync and pilot screws its just when its cold out the stumble

and if so where would one get the shims

wingwarrior, probably so, I shimmed my 86 1200 needlesto rid it of that off idle stumble & so far it is running like a top. Haven't been able to get a good reading on the fuel mileage yet as most all my riding has been in the cold <40° with short trips.

I run about 1/2 choke (enrichener) until 1 bar shows on the temp gauge, then go to 1/4 choke at 2 bars showing, then all the way off at 3 bars showing.

Most mornings it takes about 2-3 miles for 3 bars showing but colder mornings (in the low 20°'s) it can take up to 4-5 miles to be at full choke off.

I can't believe how good it pulls now & will pull OD cleanly down to about 800 rpm's with no hesitation or bucking as I throttle up. I also opened my pilot jet screws a little from where they were (I can't remember if I'm at 2-3/4 or 3 turns open now) _I really need to document that before I forget.

If you shimyour needles be sure the washers fit in the little recess in the slide where the top of the needle sits.

Twisty
 

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exavid wrote:
There's also the possibility the electronic module isn't getting the rpm signal. Someone with the diagrams on the 1200 might be able to look at the electronic advance on the 1-3 gear range. I think if the module either fails or doesn't get the information it needs it drops back to an idle or starting advance setting. Could be wrong, but that's the usual system with electronic advances.
exavid, if it didn't get the RPMsignal it wouldn't know when to spark the coil so it is at least getting an RPM signal.

Twisty
 

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twisty wrote:
If you shimyour needles be sure the washers fit in the little recess in the slide where the top of the needle sits.

Twisty
twistyso where can I get the shims at and how thick or did you just use little washers??
 

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wingwarrior wrote:
twistyso where can I get the shims at and how thick or did you just use little washers??
I just used what I had in my carb parts extras. They were just some small generic flat washers that I bought for a carb tune on a Harley a few years ago. The .024" wasn't a sacred size (actually I was looking for .019" ) but that is what I had handy.

Most hardware stores have some small flatwashers & even carry them in brass.

Just make sure they (all 4)are all about the same thickness.

Pull one rear slide (the rears are real easy), then take the slide with you for needle size fit, & fit in the slide needlerecess. I also used small stainless steel screws for the slide covers as those are easier to remove later.

If you put the slides & diaphragms in the freezer for a few minutes they will shrink & stiffen up a little so are mucheasier to reinstall in the carb groove.

Twisty
 

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philcsand, if you want to check your advance it'll have 10' BTDC initial, 33.5' (electrically induced)BTDC all in by 2800-3200 RPM and a total of 45' BTDC when in 3rd or 4th gearsif there is 2.0-2.8 inches of vacuum being fed to the ECU.

Unlike a mechanical advance arrangement you can't alter any of these settings except for removing the vacuum to the ECU which has the hose starting on number 4 intake elbow and goes to the ECU. Check to make sure that it's in good condition.

I don't quite understand why you are idling in fourth gear. Can you explain that a little clearer please.

It may be possible that your hesitation is being caused by too much resistance in your spark plug caps if the carbs are clean andset properly. Use an Ohm meter and see if the spark plug cap resistor is between 3.7-6.3K Ohms.

Many other things could cause that stumble also like water in the float bowl, dirty or restricted jets, bad fuel pump electrical connection, ignition switch resistance, etc, etc, You'll have to do some thorough checking in a step by step fashion if you want to locate its source.

Also, if the bike has been running good all along until now, shimming the needles may not help. It would seem more likely that there may be some dirt causing the problem. Change the fuel filter and cut the old one open over a white piece of paper and see how much crud the filter has picked up.

Let us know how it all works out.

Vic
 

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twisty wrote:
exavid wrote:
There's also the possibility the electronic module isn't getting the rpm signal. Someone with the diagrams on the 1200 might be able to look at the electronic advance on the 1-3 gear range. I think if the module either fails or doesn't get the information it needs it drops back to an idle or starting advance setting. Could be wrong, but that's the usual system with electronic advances.
exavid, if it didn't get the RPMsignal it wouldn't know when to spark the coil so it is at least getting an RPM signal.

Twisty
Good point!
 

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Goldwinger1984 wrote:
I don't quite understand why you are idling in fourth gear. Can you explain that a little clearer please.

When I am coming off of the freeway, and I pull in the clutch, I start to downshift. I don't like to engine break too much, so I am moving at 60 MPH, and the engine is idling because I'm not on the gas, and the clutch is in.
 

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philcsand wrote:
When I am coming off of the freeway, and I pull in the clutch, I start to downshift. I don't like to engine break too much, so I am moving at 60 MPH, and the engine is idling because I'm not on the gas, and the clutch is in.
philcsand, I checked my 1200 on my ride home tonight & the idle is the same RPM whether it's in 1st, N or 4th, or 5th. That was taken while sitting still in gear. I didn't try it during coast down while in gear with the clutch in though.

More that likely when you do the clutch in coast down you are still back-driving the engine slightly due to some slight clutch drag. You could also be adding some timing advance as the gear position would allow vacuum control added to the module. That 4th/5th gear added vacuum advance didn't effect my 1200 at static idle in 4th or 5th though.

Twisty
 
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