Flat spot/hesitation - RGS

Laverdalothar said:
I went to SR-Racing in southern Germany and they build a special made 3-1 that not only removed the drop in Torque but even increased the torque in that range which brought a dramatic increase of torque in midrange and roughly 8 HP more at peak. So - if your Bike feels like the red lines show on the following graph, I would know where to look for torque and power...:

sfc10007.jpg
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That's a beautifully crafted exhaust system to generate such a dramatic improvement in your power and torque curve (not to mention peak power), Lothar. I would have thought there was a market for a sys so well researched?? I'd hazard a guess that the Jota system never had such work behind it, or any other aftermarket system.

Makes me thin I need to do some serious work if and when I try to make up a 2-1-2 system for my 270 SF(C) motor - fitted with Keihin FCR 39s. Dynos are king!
 
that was my thought, too, but for what reasons ever, nobody did order a system at SR-Racing as far as I know... sounds also great... (go to 9:00 and enjoy...):

https://youtu.be/tuezyJWolUs
 
it was a combination I would say. We had one exhaust pot that improved peak power to even 110HP but lowered midrange a bit. we went back to the oval shaped exhaust and left it at 105 roughly, 'cause I preferred midrange over peak power. The funny thing is that cylinder 1 has a way longer downpipe than 2 and 3, which get joined together with a Y-joint. then the output of the Y-joint gets connected with cylinder 1's downpipe by another Y-joint. the end of that is going into a tapered tube that winds itself back to the large volume silencer.

Sepp from SR-Racing asked me a lot of questions about the engine, calculated and started testing. he killed 2 clutch slave pistons and several pushrods as I could not make him stop pulling the clutch lever at peak...  >:( But the result paid off ;)...

but keep also in mind, please: this engine only has 2 modifications: one is the exhaust, one is the carb system (FCR39). I just love how they work. I assume midrange would be a bit lower with Dell'Orto's due to their design compared to the FCR's, but I did not test that. seeing how flat the A/F ratio is, there is absolutely no point in going back...

The only thing that I will change on the bike is that it will get a fuel-pump. Due to the fact that the Keihins only have one fuel supply between carb 1 and 2, carb 3 does not get enough fuel at WOT. Changed that already on my Jota and can now go WOT without burning a valve...  ::)
 
Sounds a bit messy, but it clearly works.  I have been wondering about changing the gearing on my bike because if I have to ride at around 60mph/100kmh it feels 'not right'  Guess it's in that flat spot or about to fall in.  Certainly at 80 it's back on the pipe and feels great.  Sadly no chance of ordering up a fancy exhaust, and in any case I would have to have two silencers- dodn't think the RGS looks right with a 3 into 1. 
 
I agree with Reggie. A 3:1 on an RGS just looks silly.

I'm not even happy with Jota pipes on an RGS.
My original Corsa came to me with Jota pipes fitted but I managed to find a new pair of original Corsa silencers (this was some time ago) and the character of the bike was transformed. From a noisy brute it became the effortless grand tourer it was designed to be again.
 
Sorry Lothar- I meant the pipework under the engine sounded a bit untidy, no, wrong word- convoluted?- but haven't seen pix.

I agree with Grant- the RGS needs original pipes for both looks and sound (especially if it is a black bike :D) , but the SFC1000 I think would be fine to look at with a 3 into 1 as it is a much more brash looking machine.
 
Grant said:
I agree with Reggie. A 3:1 on an RGS just looks silly.

I'm not even happy with Jota pipes on an RGS.
My original Corsa came to me with Jota pipes fitted but I managed to find a new pair of original Corsa silencers (this was some time ago) and the character of the bike was transformed. From a noisy brute it became the effortless grand tourer it was designed to be again.
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Agree fully.  After all, it was intended as a gentlemans bike, not a hooligans'. :D

piet
 
Brett said:
Say at how many turns from seating are you mixture screws sitting at currently also are the O rings at the mixture screws in gtood knick or have they gone hard.
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Hi Brett, I checked the O-rings of the two outside mixture screws, and they looked OK, not cracked.
With the number one carb, the mixture screw was out about one and a half turns, number three was out one turn, and number two was just short of being one turn out.

eQwUDlG.jpg


I went for a ride on Saturday, for about 50k?s, and I was pretty pleased with the way it ran, up to a point. It pulled strongly in the tight stuff. In third gear, in the twisty stuff, it would rev cleanly up to close to 160km on the short straights. When I shift into fourth and get to around 180kmh, is when it pretty much bogs down, everyone would be flying past me on the straight.

Maybe WOT settings are a problem. I pulled the choke on while it was fluffing, it did not improve the way it as running, it slowed it down a little. Later on, when it was fluffing again, I tried backing off a little, and I thought it picked up a bit, but when I tried again, I didn?t notice anything the second time, so I?m not real sure.
Well, it goes really good in the tight stuff, with short straights. Gets up to licence losing speed easily. It starts easily, and settles down into an idle easily enough. The exhaust doesn?t stink so much of fuel anymore, so overall, I'm pretty happy with the changes. Maybe it won?t get much better up top with the exhaust I?ve got, it might be like the few Lothar tried, a lost cause.

It ran like this before I bought the Ignitech, it?s been like it for years, but I don?t very often need to cruise or race at 180kmh plus.

The black smoke it blows, and the sooty plugs and exhaust makes me want to try a smaller idle jet, just to see.

I took some photos of the plugs, after my 50k ride. One set is with no flash, but with a torch shining on them. The other is with the camera flash (a cheap mobile phone camera). It was hard to get the plugs looking the same in a photo as they look in real life. They are more sooty looking in real life. The camera and torch make the electrodes look lighter than they are. Photos without the torch or flash were too dark to be of any use though. (The mark on the centre plug is from where I dropped it on the concrete floor).

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OK - let's do it the right way...:

first of all, you need to be sure there is no issue with the carbs itself. Ideal would be to have them stripped, ultrasonic cleaned and all seals, needles and jets replaced. Everything else bears a big chance that a an issue is hiding that only gets more and more covered by changing the settings...

Then, when you have this done, the following steps need to be done:

-adjust float-levels to the righ 18mm setting on all 3 carbs, adjust the idle screws all to the same level (optimum is 1,5 turns out).
-put the carbs on the bike, mount choke cables and throttle cable and first of all synchronize the choke sliders (!!) and make sure they do move all freely and - much more important - fully close when you put them down!
-warm the bike up and make sure it's really warm
-now synchronize the carbs with vacuum gauges
-now check idle settings by going 1/2 turns out on all three cylinders and see if the revs drop or increase. If they drop, go back with all 3 and try 1/2 turn IN. If idle drops again, go back to 1,5 turns on all. If revs increase, go further in until you find the point where the revs drop again. Rule of thump is: If you have to go to 1 turn out instead of 1,5 out, your idle jet is to big by roughly 5 (so if you have 60, go down to 55) and vice versa.
When you found your carbs working good in idle, you can start looking at WOT. I wouldn't do that before you are sure your carbs are in best order, fresh jets installed, fresh needles and needle jets and all basic settings are done correctly. Everything else is as said before guesswork and will potentially only cover a bigger issue.

cheers
 
Dellortoman said:
Plug chops and guesswork probably won't get you to the happy place you're looking for. I reckon you need a dyno session to sort out the mixtures.
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Hi Cam, it seems that way.

Laverdalothar said:
the following steps need to be done:
-choke cables and throttle cable and first of all synchronize the choke sliders (!!) and make sure they do move all freely and - much more important - fully close when you put them down!
-warm the bike up and make sure it's really warm
-now synchronize the carbs with vacuum gauges
-now check idle settings
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Hi Lothar, I've done this, but I haven't stripped the carbies down.

Laverdalothar said:
If you have to go to 1 turn out instead of 1,5 out, your idle jet is to big by roughly 5 (so if you have 60, go down to 55) and vice versa.
Click to expand...

This, and info Brett posted on jet sizes on other bikes he has been involved with, is good to know.

Laverdalothar said:
When you found your carbs working good in idle, you can start looking at WOT. I wouldn't do that before you are sure your carbs are in best order, fresh jets installed, fresh needles and needle jets and all basic settings are done correctly. Everything else is as said before guesswork and will potentially only cover a bigger issue.
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I agree, I think I have run my course here, for now. I'm going to look at my rattling clutch next.

Thanks everyone.

 
Laverdalothar said:
1/2 turns out on all three cylinders and see if the revs drop or increase. If they drop, go back with all 3 and try 1/2 turn IN
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I do it one carb at a time. Set the idle to about 1200 rpm, then tweak a mixture screw and set it at maximum idle speed. Do the same with the next carb, etc. If the idle speed goes too high, adjust it back again on the throttle stop screw. When they're all done, re-set the idle to 1000 or less (whatever speed your bike will happily idle at). Might end up with the mixture screws at slightly different settings on each carb, but that's OK if it makes the engine happy.
 
mmmhhh - for me this covers potentially synchronization issues... I would do that only after my steps (first look for the same adjustment with the highest idle, then sync, then go individual carb by carb). But each to his/her own.  ;)
 
regarding the adjustment of the pilot screw, with the Laverda 500, the factory recommended setting is three turns out. This would suggest that a bigger pilot jet (standard is 55) is needed??? Curious...
 
Not in all cases. If it runs sweet as is, leave it as is.

On the triples, it is a good indicator to find the right idle jet on a tuned engine.

For more information on how to set up the carbs, refer to f.e. http://www.ask-ancenis.fr/documents/Rotax/DellOrtoMAJ01.pdf, starting at page 47/73
 
Dellortos - Dellortor's after changing Exhaust Pipes - Try running open carb and replacing the mains jets to a larger size to get a base line.

Careful you don't lean her out and hole a piston - If you hear her lick and loose power above 4000rpm back off and change to a bigger main jet. Whether or not you will ever be able to run an air filter is something else.

Breganzie 750SF's with VHB 30's are plagued with this issue and most run like stink without Air Filters and 2 into 1 pipes with 132 Main Jets compared to the original 125 main jets's and the FIX goes for any Motorcycle Engine.

Just a an input from my view and after 40 years of riding a Breganzie 750SF, I've never found a solution running Dellorttos - I've a couple pacs of Mukini's 34's but I've never had the will to change out the Dellortos as they perform great - Although they are DIRTY ;o)
 
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