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Discussion Starter · #1 ·
Thought I'd check in with something regarding the jumpy throttle on a 790 that people seems to complain about quite often and my experiences with it. I haven't seen a thread or comment that reports this, so I thought I'd start one to get some feedback from the more experienced people here.

What I've noticed is that the bike throttle behaves better if I stop and restart in the middle of a ride. It's not just an oil temp issue I don't think because it behaves one way right before turning the bike off, then differently upon startup. It's as easy as hitting the kill switch at a stop, letting it depressurize (That's what the whining is when you turn the bike on/off?) then repressurize a bit and start it back up. 15 seconds in-between, tops. Immediately before the restart first and second gear are jumpy to the point that going around a curve at less than 20mph without the clutch feathered is worrisome. The jerk that comes from a slight twist of the throttle at that speed is enough for me to worry about over balancing. After the restart it's much smoother in those gears with less chugging and more even throttle. Almost like it was a software difference that reflects a "state of the bike" at the ignition of the bike that makes for ideal throttle control.

Then I read this post from a Tenere forum. Dukes have something similar to the Accelerator Position Sensor Grip, right? Could this be the issue I'm describing above? Or would that be something that naturally opens up more as I twist the throttle as I ride?

Just wondering what people think.
 

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There has been quite a lot of chat about the jerky throttle response on this forum. From it's base origin to potential means to resolve it.

I'll need to apply some thought to the "warm reset". It's something that even old pre-EFI engines can demonstrate - usually it's due to de-harmonized warming of internal components.
I doubt the fuelpump/injection circuit priming (the whine) is the issue - But I'll apply grey matter.
 

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Discussion Starter · #3 ·
There has been quite a lot of chat about the jerky throttle response on this forum. From it's base origin to potential means to resolve it.
Yeah, just thought I'd add my two cents about it. It's just really odd that I can give it the cable modem treatment (off then on again) and it gets markedly better. Doesn't matter if I'm in rain, street or sport mode.
 

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I know this is contentious but my 790D was improved a lot by fitting a booster plug which enriches the air/fuel ratio below 6000 rpm according to the supplier/manufacturer. I seriously doubted their claims but purchased one anyway. In my experience is doesn’t completely fix the issue but makes it much better at low revs/light throttle. More significantly it improves the bike a lot in the higher gears too. There is a stretch of very flat road near me with an 80 kay limit that l used to run in 4th gear. With the booster plug l can run easily in 5th on a light throttle and 6th if l’m feeling lazy. I’m not connected in any way to this company but l really like their product on the 790D. Others report that it makes no discernible difference. Cheers
 

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I know this is contentious but my 790D was improved a lot by fitting a booster plug which enriches the air/fuel ratio below 6000 rpm according to the supplier/manufacturer. I seriously doubted their claims but purchased one anyway. In my experience is doesn’t completely fix the issue but makes it much better at low revs/light throttle. More significantly it improves the bike a lot in the higher gears too. There is a stretch of very flat road near me with an 80 kay limit that l used to run in 4th gear. With the booster plug l can run easily in 5th on a light throttle and 6th if l’m feeling lazy. I’m not connected in any way to this company but l really like their product on the 790D. Others report that it makes no discernible difference. Cheers
Hardly contentious. It works for you. Why and How it works - and whether it is a fully long term solution - MIGHT be arguable.
Other things that seem to help - 15Tooth front sprocket - Power Commanders - Chip Tuning - COOBER (both variants) - And of course thrashing the beast so it never runs at slow rpm.

As for the OP comments ( @HangryPete ). Thinking back (and I mean a long way - late 1970's) I recall some advice from an M/C cop (He was my best mate's dad). He said they (the cops) had found that if the set out - rode a couple of miles, then stopped (i.e Fuel fill) then rode off; the engine ran better then setting off with a full tank and just riding away. And I can attest to the fact that OLD Guzzis did and still do benefit from this. And certain Guzzis absolutely benefit - the ones with iron liners HAVE TO BE WARMED before thrashing.

I don't know enough about the materials inside the R8c block to be specific. But my money is on heat expansions. The engine by design runs VERY hot in the pots (very high AFR values). And a water jacket to take that heat away fast. I also don't know enough about the cold vs warm start algorithms - but digital stuff tends to be fairly predictable.

I should point out that my habit is to set off from home and usually ride 5kms to the fuel pumps, fill up, and ride off. But I will try and do a proper test - say over two consecutive days. It will be a while before the weather is predictable enough. I also have a COOBER which of course may mask the results.
 

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I know this is contentious but my 790D was improved a lot by fitting a booster plug which enriches the air/fuel ratio below 6000 rpm according to the supplier/manufacturer. I seriously doubted their claims but purchased one anyway. In my experience is doesn’t completely fix the issue but makes it much better at low revs/light throttle. More significantly it improves the bike a lot in the higher gears too. There is a stretch of very flat road near me with an 80 kay limit that l used to run in 4th gear. With the booster plug l can run easily in 5th on a light throttle and 6th if l’m feeling lazy. I’m not connected in any way to this company but l really like their product on the 790D. Others report that it makes no discernible difference. Cheers
My experience with yhe Booster Plug was that it repotred 2 degrees F lower thsn actual smbient to a circuit that operates only from idle to about 3200 rpm. It seemed to help for s few cold months and thrn became eorse than otiginal and eith high fuel consumption. So zI removed it. In the interim, engine management system seems to have learned s smoother response in that range, with a lot less “hunting” at steady throttle podition.
 
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