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105196 Posts in 11993 Topics by 1177 Members - Latest Member: fen tractor September 23, 2019, 08:00:07 AM
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XS1100UK Forum  |  Technical  |  Advice Needed  |  Topic: Mikuni RS36-D3K tuning help needed. Rough idle and stalling out on acceleration
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Author Topic: Mikuni RS36-D3K tuning help needed. Rough idle and stalling out on acceleration  (Read 459 times)

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fortj3

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My bike is a 1981 XS1100H. It's the US "Venturer" touring model.
Long story short: Original BS34s had a broken float post on #4 carb. Replaced them with Keihin CVK36 from a 2005 ZRX1200. Had some issues with them from the start. Ended up with 3 of them flooding. Instead of throwing more money at them, I replaced them with brand new Mikuni RS36-D3K flat slide pumper carbs (yesterday). This allowed me to get rid of the air box which got full of water whenever it rained (still haven't figured that one out), and full of gasoline because of the carb flooding issues.
So, I've got K&N pod copies on them. The carbs were installed  with no changes made to factory jetting. Main jets are 130s.
Since I'm currently still running the factory 4 into 2 exhaust and mufflers, I figure I'll probably need to install the 125 or 120 jets that also come in the box with the new carbs.
So far, the bike sounds a lot better than it has since I've owned it.
My problem is, when I snap the throttle open from idle, the engine bogs and dies.
If I ease into the throttle, I can snap the throttle open once the RPMs get above about 2000, and it roars like a homicidal wild beast.
However, the RPMs hang and drop slowly to idle once I release the throttle.
The pilot screws are 1/2 turn out.
Idle is a bit rough at 1000 RPM and better at 1050-1100 RPM.
I haven't taken it for a test ride, because I deem it unsafe in its current state.
I installed new NGK BP6ES plugs with the carb install, since the old ones were heavily petrol fouled.
The ignition coils are the green, 3 ohm Dyna coils with Dyna plug wires.
Vacuum advance connected or disconnected makes no difference.
When I tested my pickup wires and coil wires last year, they tested good.
I removed the TCI and checked for cracked solder joints and found none. I cleaned the terminal pins in the TCI and harness connectors with Deoxit.
I eliminated the OEM fuse box and went with blade fuses.

What say ye? Adjust the pilot screws richer?
Drop the needle clip one notch?
Swap the 130 mains for the 125 mains that come with the carbs? (after curing the idle/acceleration issues).

It's weird, because It definitely smells rich at higher RPMS and sometimes at idle, but dies upon whacking the throttle open.
Any advice greatly appreciated.
1981 Yamaha XS1100H Venturer
2015 Yamaha SR400
1996 Ford Mustang GT (First and only owner)
1977 Ford F100
1974 Dodge Dart Swinger (Leaning tower of power)

Tom

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Plug chops, that's all I can say
It makes you look a tvvat but question everything!!


Tom, belligerent old tosser!!
Dazed and confused

FJ111200

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What Tom says, plus everything you've mentioned in the last but one paragraph.
You probably won't hit the sweet spot first time around as you know and it can be bloody infuriating. Took me about 10 attempts with a set of carbs that had been pigged around with until they were about as much use as sh!te, though admittedly they weren't flat sides.
And i must admit to Tom that i've never done plug chops, lol.
Tight end down

https://www.youtube.com/watch?time_continue=12&v=TeyHPAdxuy0

Interesting thought... But don't you need 'members' for a 'Club'..?

If you can't bleed your bike's brakes then you can't have a bike.

XS1100 - it's old fookin' hat.

Tom

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Took me about 10 attempts with a set of carbs that had been pigged around with until they were about as much use as sh!te

And i must admit to Tom that i've never done plug chops, lol.


ANDÖÖÖÖÖ
Plug chops, that's all I can say

 :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl:
It makes you look a tvvat but question everything!!


Tom, belligerent old tosser!!
Dazed and confused

FJ111200

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They were pigged around with until sh!te by some d!ckhead not me. Mind you, i could be a d!ckhead.
Tight end down

https://www.youtube.com/watch?time_continue=12&v=TeyHPAdxuy0

Interesting thought... But don't you need 'members' for a 'Club'..?

If you can't bleed your bike's brakes then you can't have a bike.

XS1100 - it's old fookin' hat.

fortj3

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I guess I need to buy some more spark plugs, and find my Colourtune.
First thing I'll try, is to remove the pod filters and see what effect it has.
Someone had mentioned to me that they could be blocking the pilot air orifice.
1981 Yamaha XS1100H Venturer
2015 Yamaha SR400
1996 Ford Mustang GT (First and only owner)
1977 Ford F100
1974 Dodge Dart Swinger (Leaning tower of power)

fortj3

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After work today, I removed the pod filters and found that there are two air jets in the bell of each carb.
However, the way the filters are designed, there is nothing that can obstruct them.
It smells very rich at idle. I set my pilot screws to 1/8 turn out. No change.
I also noticed that I have some gas spitting out carbs 1 and 4 at idle. In fact, it washed some of the filter oil off of those two filters.
I also noticed that the stream of gas from the accelerator pump nozzles is hitting the slides.
So, I need to readjust the pump to stop from squirting fuel onto the slides.

But, what about the gas spitting out the carbs at idle?
These are brand new carbs, and I wouldn't think that the floats would be sticking, but I've been wrong before.
I guess I could whack the sides of the carbs with the plastic handle of a screwdriver and see if that improves things.

Could the restrictive OEM exhaust be causing this?
What else do I need to look for?

Thanks guys.

Also, I used carb cleaner to check for vacuum leaks. None found, so far.
1981 Yamaha XS1100H Venturer
2015 Yamaha SR400
1996 Ford Mustang GT (First and only owner)
1977 Ford F100
1974 Dodge Dart Swinger (Leaning tower of power)

Tom

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Going up 2mm in carb size will reduce the air flow speed through the carb, this can cause spit back at tickover from pulsing, longer stacks can cure this as it creates a ram effect smoothing the flow. You're using an unknown set up so anything could be happening, yes free flow exhausts will help, but asking here for an opinion that really needs to come from someone with experience standing next to the bike whilst running is difficult.

PLUG CHOPS!!!!

I don't really worry about tickover until I have the mains somewhere near, we don't ride at tickover. If your mains are a mile out you will struggle to get anywhere near with pilots and tickover.
It makes you look a tvvat but question everything!!


Tom, belligerent old tosser!!
Dazed and confused

fortj3

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Tom thanks for the input. I didnít have time to do plug chops yesterday, but I do plan on it.
Iím not ignoring that advice, quite the opposite.
Funny that you should mention stacks. I was thinking about making and installing stacks.
I have some rubber hose with the right OD and some exhaust tubing with the right ID, that I can make temporary stacks for testing.

Iím also going to test compression and vacuum, again.

Thanks for your advice.
I donít want you to think Iím one of those people who ask for advice and ignore it because it doesnít agree with my preconceived notions.  I know that you are an XS guru.
I also know that you canít accurately diagnose an issue via message board.
Iím taking all your advice to heart. Iím going to do plug chops. I still need to find my Colourtune.
Any and all advice given is of very high value to me.
It looks like I have a very busy weekend ahead.
Thanks for you help, and I hope you have a great weekend.
Now, Iím off to the parts store to get some more plugs.

1981 Yamaha XS1100H Venturer
2015 Yamaha SR400
1996 Ford Mustang GT (First and only owner)
1977 Ford F100
1974 Dodge Dart Swinger (Leaning tower of power)

Tom

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Whoa!!! I'm no guru, just an average joe that has done a few mods. Others know these bikes better than me.

I always use good used plugs for plug chops, the deposits seem to stick better.

And here from a while ago as this is an often asked question....

 

Plug chops are where you run the engine at certain throttle openings under load, in other words riding the bike, then cut the engine instantly coasting to a stop, and check the condition of the plugs, this tells you what your carburation is doing AT THAT THROTTLE OPENING.

So many people mistakenly take the bike out for a good fast ride, get home and take out the plugs to tell what their carburation is doing, all they have checked is the tickover coz its the last thing the engine did shortly before turning off the engine, if your engine is ticking over at 1000rpm it fires the fuel 500 times in a minute which means even 30 seconds of tickover will wipe any deposits off the plugs or add more.

An idea I've seen used is tippex a mark on the throttle body, with a corresponding mark on your handlebar twist grip rubber next to the throttle body, then wind open the throttle to full and tippex another mark, now you have a distance you can divide this into 1/2 - 1/4 - and 3/4 openings marked to use as a guide when riding. Do each plug chop separately at each different opening, ride for as long as you can at that opening then hit the kill switch, snap shut the throttle and pull the clutch in all simultaneously and coast to a stop, this has preserved your plugs condition at that throttle opening, take out the plugs at the side of the road to tell how your carburation is.

Altering your carburation is another kettle of squid :rofl: :rofl: :rofl: :rofl: :rofl: :rofl:


I never use Colourtunes, I don't set the tickover pilot mixture for best tickover, I set it for best acceleration from low revs. I don't ride at tickover. :rofl:  I was taught by an old racing bloke, racing bikes didn't used to have tickover at all (pretty much until fuel injection came along.) so tickover is the last thing I do.

It makes you look a tvvat but question everything!!


Tom, belligerent old tosser!!
Dazed and confused

xsalan

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Spot on tom.

bradster

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Theres a you tube video called basket case ,,the guy called andy fitted a set of mikunis to that bike . Well worth a watch an see how he set them up ..an indication of lean runnin carbs is the revs " hanging on to drop slowly " bigger carbs  slow air flow so bigger jets needed sometimes if theres no needle adjustment left .?....a head ache at times but once set  up its worth while ....

Plod

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https://www.youtube.com/watch?v=5eUnbVAp8hI link for 'Andys Motorcycle Obsessions fitting 36mil flatslides to his XS1100- hth - Kev
XS1100 2H9 Blue/White 1979

fortj3

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I installed the velocity stacks from the OEM airbox onto the carbs, today.
They seemed to like that. I guess I could make velocity stacks that allow installation of my pod filters on the ends.
I'm seeing some improvements.
I know. Plug chops. First, I gotta get it where I'm comfortable riding it on the road.

I wonder, just how restrictive are the factory Yamaha mufflers? I've thought about punching out the baffles, for testing.
I'm leaning heavily toward reverse cone mufflers with repackable fiberglass baffles.
1981 Yamaha XS1100H Venturer
2015 Yamaha SR400
1996 Ford Mustang GT (First and only owner)
1977 Ford F100
1974 Dodge Dart Swinger (Leaning tower of power)

Robjota

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You might find the official RS manual helpful in tuning these RS series carbs. They are designed to be easy to set up and can be done so.  Ive run these, also new for 12 years, 2 sets on Triples..
Have a read here..
You always set up the main Jet and work down, despite what anyone may tell you..  Have a read 1st.

They are notorious for chatter on idle, , its not a fault, just part of the design, as for blowing fuel back out the intake, this is common and has a name which escapes me..  The frame on my bikes is discoloured, less so with decent filters on of course.

http://mototh.com/files/other/carburetors/Mikuni-rs-manual.pdf

If you cant set it up, take it to a reputable Dyno guy who can.  Maybe ask Andy nicely if you can have his basic settings, forget needle groove, you need mainjet size although even that could be  10 out if yours is a std motor vs Andy's tuned motor. PIlot jet will likely be the same.
nb if you cant get any response from turning the pilot screw around where they should be, thats because the pilots are the wrong size.

The carbs need to be balanced properly as a first job, I think  3rd from left is the fixed carb and the rest are balanced around that but I could be wrong. they use a thin 12mm ring spanner and a JIS screwdriver. The eccentric nuts take a while to get used to.  SO hanging throttle in this case is quite probably your throttle balance.

You can disconnect your accelerator pumps for now to save squirting fuel everywhere. These are easy to set up, all together IIRC on a single screw as to when they start and finish squirting.

Im sure much of this is in the manual.

HTH
Rob
« Last Edit: June 10, 2019, 09:19:39 PM by Robjota »

XS1100UK Forum  |  Technical  |  Advice Needed  |  Topic: Mikuni RS36-D3K tuning help needed. Rough idle and stalling out on acceleration
 

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