1230 with RS36 race engine now used in street bike - jetting help please...

[Guest]

1230EFE with RS36 carbs, Mikuni velocity stacks with foam covers, standard cams, was a race engine but now in my street Kat.

Engine starts and idles fine and goes like a rocket when you open the throttle, but it does not like sitting at 3000 rpm. There is a pause at this RPM and then it starts to pull again.
I was heading through a set of twisties in the wet and at low RPM and the motor started to foul a plug/s.

Plugs look very dark / rich.
The Mikuni carb box came with 120 and 125 main jets in the box.

I have not removed the carbs to see what settings they are at, thought I would ask first. Any idea best place to start, I am hoping for a simple fix..... chances are I need to pull the carbs off and see what size the jets are but I would not know what to adjust.

I have a long ride this weekend with a gravel section to he camp site so if I can get them better it will help. May have to buy spare plugs.

[Carter Turk]

I just did a trackday on my 1229 Kat (63 laps). I've been running 142.5 mains for years on 36mm Slingshot Gixxer carbs.
When I first purchased the used carbs I fouled numerous plugs. I had Dyno Jet kit in it with 160DJ mains, but looked to be drilled out-not sure.
Bought a Factory Jet Kit and noticed the taper on the needles was hugely different than DJ-pointy vs. blunt. I soon discovered that the emulsion tubes (surrounding jet needle) had ovaled out, causing a mid-range rich condition.
Not sure how similar if at all RS36's are to these carbs, but our engine size is similar.
Recently put new pistons in checked a plug and it was running very lean.
Before the rebuild, the plugs had a nice light tan color.
I threw in some 145's and the bike felt smoother, but I now have some other rattling issue that I did not hear at the track.
It doesn't sound good at the moment.
I've fouled plugs in a heavy downpour with K&N pods, maybe some water got into the velocity stacks thru the foam.
Not sure if your pipe is 4-1 or 4-2-1, but might have something to do with the flat spot or where the idle circuit is transitioning to the needles.

[TxGSrider]

I don't have any experience w/the RS carbs yet, but Ive got a set of RS36 I'm going to try on my 1100 (stock except for exhaust), so Ive been doing some reading about them, and apparently allot of them come from the factory with the float levels wrong which could upset the mixture. Id start by checking them.
It sounds like its only happening at low rpms, which should mean low throttle opening too, if that's the case its probably not a main jet problem...

[cdnoel]

Might try raising needles rather than puting larger mains. Accelerator pump should also be set to go into action at .25 throttle. Accelerator nozzles are very tiny and easily clogged. Of the four accelerator nozzles I'm trying to clean right now they are all responding differently when I apply vacuum with my brake pump and observe the gauge while the pressure leaks down. One acts almost completely clogged, two slowly leak down and only one goes to zero pressure in a timely manner. If the chem tool dip doesn't get them to even out I'll be buying new ones. Pull the choke to test if richening is needed in the first place just before you reach 3k RPM.

[Guest]

went for a spin today and low down splutter from the carbs, like a miss and a back fire from the carbs, not a bang as such but a puff.
Plulled plugs and the look ok to me.

Also the hotter the bike got the worse it got, let it cool down for half an hour and tried again and pulled the choke on the way home and it seemed to pull better through the 3k mark, still rough down low in the RMP range.
Could this be electrical? I would not think so as it goes like a rocket once you get going. Riding slow for to long and it splutter as the throttle opens up and does not clear as easy.

Do these look ok?

20170829_184621.jpg

[Guest]

To add the engine had K&N pods on the carbs, I removed these and added velocity stacks and foam filters, will this make much difference?

[cdnoel]

If the choke made it better you need to richen. Needles and accelerator pump might be where to start. Are the Rpms climbing when hot? If so try new intake manifold seals. Hi temp bearing grease on new O rings is best.

[Guest]

Ok so I will lift the needle one clip, having not worked on these carbs before can this be done without removing them?
Can the needles be adjusted from the top?

And no RMP hang up, just starts to splutter down low more as it gets hotter or longer the ride.

[Guest]

Sounds right. Do I need to lift needle a clip or go bigger mains?
Fitted new plugs in to engine after a 15min ride, cooled down for 20min while I did this and it went perfect foe 5min and the back to farting in all throttle positions.

20170830_191229.jpg

[limeex2]

It needs more fuel, so one would raise the needle. Going to stacks can change settings also. You should get some specs from Sudco. They would give you a good starting point and items like fuel level and accelerator pumps need to be checked and at least eliminated as a possible cause

[GregT]

Where are you in NZ ? If I know that I can probably point you at someone local with experience on RS carbs.

I'm just outside ChCh.

[cdnoel]

By raising the needle you will be lowering the clip. You may already be large enough on the mains so you might not find any improvement with larger mains and your problem sounds needle oriented. Had this problem with my CV's as I couldn't put big enough mains in them to get more fuel past the needles.

Might want to run air filters. PX has some very nice foam filters that go over velocity stacks. They are two filters and each filter covers two velocity stacks for $75.00 on e-bay.

FYI. I have dipped my accelerator pump nozzles and they are much improved. No matter how fast I pump the brake pump on them the needle on the pump stays bellow 10 inches of Hg.

I have also ordered a SUDCO manual as this is the only manual I can find for Mikuni RS's. Haynes has a Motorcycle Carburetor manual as well by Pete Shoemark that I check out of my local library from time to time. Any other book on carburetors I can find as well.

[Guest]

I can't add to the knowledge already passed on, but I will say when I moved from pods to stacks (with foam filters) I did find the throttle response much improved, so I reckon you've done a good thing there.

I also need to say that's an awesome Kat, can't see enough of them! I ride with a couple of fellas regularly who have big bore Kats... one a resto-mod type Kat with a 1260 and the other with a pretty stock Kat but running 1360, and both are extremely fun bikes to ride The 1360 in particular has a nice linear power delivery with a kick about 6K RPM... and it pulls like a train!

[Guest]

Follow up on my tuning issue, decided to swap the coils one at a time. First one I swapped fixed the problem.
The coils are Dyna coils miniature series, don't know much about them.

I need to work out if it a the coil or leads, but it is going OK with a standard coil cable tied on to the frame.

Now back to carb issues with the RS36's. The carbs snap shut when sitting in the shed, push / pull throttle installed. when I let the throttle go the slides remain up and the bike is cruise control, I need to manually close the throttle. Back at the bat cave and snap goes the throttle, closes perfectly.

Any ideas?
Adjusted both cables in every ways from tight to loose and have it set with just a little free play. The spring setting is quite hard as its a heavy throttle.

Could it be cable routing?

[londonboards]

I've got RS36s on 2 of my EFEs and I sympathize with you.

These carbs are awesome but very sensitive to minor adjustments. Sudco manual (which is really just a parts catalogue) and the information supplied with the carbs (a very poorly typed out leaflet) contradict each other - especially with regard to adjusting the brass fuel screws (located underneath and on the engine side of the float bowls). You are basically on your own when it comes to set up.

I have yet to dial mine in perfectly and I own a DynoJet 250i dyno with an air/fuel analyzer.

Almost all my experience with my own bikes and dyno testing others, is that they run rich with the recommended jets for your bike, even with stacks and straight through pipes, which you would have thought made them leaner. This doesn't mean that yours is doing the same thing.

You really have to pull them off the bike (although you can change the main jets and adjust the needle clip in situ - it is very fiddly) and do a thorough set up before installing them again.

Check float heights (various opinions as to how much this effects mixture but worth doing anyway) as they have been known to come from the factory incorrectly set.

Check synchronization using a fine piece of wire under the slides to make sure they are all rising at the same time. Mine were way out straight from the box. The adjustment is very sensitive and requires a lot of trial and error to get it right. When they are back on the bike you will also need to test synch with engine running.

Leave the needle clip in the middle position at first. Use this clip for fine mid range tuning.

Check your jet sizes and make a note of them. Make sure they are genuine Mikuni and not DynoJet.

I would deactivate the fuel accelerator pump mechanism completely. It tells you how to do this in the manual I think or you can remove the stainless steel pin that makes it work. I would do this to remove the possibility that this is functioning incorrectly and messing up your other readings. You can put it back in use when you have got the carbs set up correctly for your bike and jetted with the right size jets.

Set your pilot screws to half a turn out from lightly seated. The manual says to set this at 1/4 to 1/2 turns out. On other carbs, you can adjust these screws to obtain the best or fastest idle. But these don't seem to work like that. My experience is that they don't make much difference to the idle speed. The way to test it is to ride the bike. You are looking for a nice transition from closed to open throttle. Keep opening these screws up half a turn until the transition is smooth - not snatchy.

Then start on the plug chops (there are tons of threads on this). Start with main jet tuning. So do plug chops that involve using at least 3/4 throttle position for as long possible (going up a straight long hill). Cut the engine and look at your plug colour. Change the main jet accordingly. Try it again until you get the correct colour.

Then do plug chops at 1/3 to 2/3 rds throttle position and change your needle clip position if the colour is out.

Then do plug chops at your idle to 1/3 throttle position. If this is not looking good you may need a new size pilot air jet. This is the small jet on the air side of the carb and can be changed quite easily. Bigger air pilot jet will make the idle mixer leaner and a smaller air pilot jet can make the idle mixture richer. You could also play with the fuel pilot jet, which works in the reverse way to the air pilot jet (bigger jet is richer, smaller jet is leaner) but they are harder to access.

My experience would be that you will be running rich at idle to 1/4 to 1/3 rd throttle position. This is not something you can be completely corrected by adjusting the pilot screws. Try larger air pilot jets.

If you get all that sorted and you haven't lost your will to live, reconnect the fuel accelerator pump, setting it up so that is squirts from about 1/3 rd throttle position. Having it squirt from the closed throttle position, in my experience, bogs the engine somewhat. I guess that depends on your riding style and if you are road riding or racing.

There is a ton of stuff on the web and on this forum about these carbs (and the problems everyone has getting them set up) and some give quite contradictory advice. Each bike and set of carbs is different. The only way to do it is to plough through all the plug chops (or get a dyno LOL) checking one circuit of the carb at a time (main jet, needle jet and pilot jet). Change only one thing at once.

Good luck