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I'm calling it a "flat spot" when the engine won't accelerate as strongly as it will at higher rpms.

WOT is fine - very impressive acceleration, but half-throttle is half-hearted.

It doesn't miss, burp, backfire, or do anything rude - it just won't "git 'er done"! Especially when not completely warmed up (but it still is flat even when hot).

I'm wondering if anyone has a dyno run chart for the stock 1200 engine?
 

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Mine hits that same spot and then when I reach 2500rpm it takes off again. Have you tried downshifting to see if you can get it to rev up and take off? If I stay in OV, it won't wake up until it reaches 2500 but I can downshift to fourth and it doesn't have a problem.

If I take off and rev the bike up through the gears, I never have the same problem, only when in OV and I try to accelerate when doing about 40mph.
 

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Yes, now that I know about the flat spot, I avoid it.
But, I was wondering if it was "built-in" - like a cam issue, or if it is a carburation issue?
 

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The gl1000 my buddy has doesnt like to ride below 3k on the tach, I didnt feel the potential of my 1100 until I kept it above 3k and noy my newly aqquired 1200 has the same issue but my problem exist till about 2900. and the same in OD at above 4100. If I slam through the gears no problem, only when I am takin it easy. It sucks cause id like to get outta 2 to cruise around town but 3rd gear at 40mph and 1/4 to half throttle hesitates often.
 

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Try 'shimming' the needles. Took care of the same problem my 87 Aspy had, you wont be sorry....Any more info needed, just ask.
cheers,
Kevo
 

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I have the same problem in second gear turning about 2200-2700 rpm's. I did a major carb rebuid last year just to cure that problem and it still spits and sputters, backfires. Someone must know the real reason that this happens, I talk to the Honda guys and they have no idea. This issuse has to have been there since that they made the bikes in 84-87. I can't believe that nobody knows exactly what causes this. I am in the works to getting my bike ready for the summer and would like to correct this, if anyone has any sugestions I or we all would like to hear your ideas.



Thanks

Snowman
 

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The primary reason is that the bike was not built to be operated at that low rpm. The charging system does not become really effective until about 3k. Even putting in town my rpm's are not allowed to dip below 3k. All that said Snowman she should not "spits and sputters, backfires." at any rpm. there is still something wrong there.

Obviously a Flat spot is completely subjective to the rider. So it is terribly difficult to quantify. Typically a 1000 has decent acceleration from about 3k on up but really starts to "breath" about 4500 rpm. Torque and pull seems to run to about 500 below redline before starting to fall off.A properly running wing should pull from idle in 5th gear with WOT all the way to redline without bucking burping any any other complaints.

The 1200 being the 3rd generation was built with the continuing trend toward a flatter torque curve and more passing response at highway speeds. I am pretty sure I have a chart for it somewhere and I will try to find one to post.
 

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Check the timing advance. Might well be sticking a little
 

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Oh don't get me wrong, when I start out in 1st gear and crank on throutle bring it to red line no problem right up to 5th gear. I just doesn't like the rpm rang 2100-2700rpms. othe than that area it is a screamer.
 

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snowman6454 wrote:
Oh don't get me wrong, when I start out in 1st gear and crank on throutle bring it to red line no problem right up to 5th gear. I just doesn't like the rpm rang 2100-2700rpms. othe than that area it is a screamer.
If you want to lug your engine down to 2,ooo rpms you need a Harley. Honda is high rpm engine keep it above 3000 it will not hurt it.
 

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I'm thinking that maybe you need to sync the carbs or possibly s small leak in one of the carb-diaphrams.

My 1200 is a sidecar-rig. It definately has to be above 3.000 rpm. It will pull, (no flat spots) but it just doesn't sound right.

Soren
 

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OK guys update on mine. hopefully this will help you out. I had the same flat spot you speak of. I had to install a new choke cable and as you know you nearly have to remove the carbsa to do this .
I pulled the carbs and opened them up. The needles had a white chalky film on them. I scratched it off with my fingernail wiped them clean with seafoam.
Sprayed carb cleaner down the venturi and checked my synch.
They were off. A few minutes balancing and Viola no more flat spot. Smooth throttle from start toill about 5k. I will learn to live with this because I dont usually take her up to 5k. I preformed teh synch with vacuum guages and am psotively sure that the 5K flat spot I speak of would dissapate with a more sensitive carb balance guage.
So do a lazy mans clean and re synch.
By the way. highway running is much smoother. I have to get used to her all over again.
 

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Well you got her to go, now get her to stop.,,,,,,
 

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Minehad the same problem. I took off the throttle slides. Cleaned off some corrosion on top. Buffed the slides with 1800 grit wet sand paper with lite mach oil. Flat spot is completely gone. this was at the recommendation of a Goldwing mech of over 30 years. He stated that a hesitant or rough throttle slide ALWAYS causes the flat spot from 2200 to 2900 rpm. He told me there was actually a Honda service bulletin back in the late 80's covering this issue. Hal
 
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