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

[Dukeman]

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.

[Dukeman]

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

 

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?

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.

 

[Fula28]

Sounds like you need to check float heights first then , needle postion to work out where you are fueling wise. At 3k it's on needle circuit for sure and if it gets worse when hot it's fueling indeed.main jets don't come into play until 3/4-into full throttle.

[KATANAMANGLER]

You are too lean on the main jet. The plugs look lean to me. I have a 1230 with R336s with stacks and foam socks  and I run 130 mains and it's bob on.

Tell tale signs: A rich condition gets better the hotter the engine gets a lean condition gets worse. Backfiring through thr carbs is a lean symptom too.

[Dukeman]

Ok if its to lean, 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 for 2min and then started to farting again down low first and then  in all throttle positions. Again slowly got worse and worse.

Pulled the choke one click and diffidently better down low, not perfect but better. Could not find out higher up as I arrived home.

Once back home and sitting in neutral it will rev fine, sounds perfect.

Engine had pods which I changed to stacks would this require different jetting? also exhaust is different...I would have thought more restrictive.

New plugs after 20min ride on warm engine, spluttering home.

 

Edited August 30, 2017 by Dukeman

[KATANAMANGLER]

Start with the main jet. With the exception of the idle jet circuit the main jet has an impact on all other circuits. i.e. needle and main jet only.

First thing is first mark up your throttle with tape on the throttle grip and the throttle body. Then mark throttle positions as follows: Closed,  1/8th, 1/4, 1/2, 3/4 and wide open.

Try to find the point at which the fuel delivery is out ( forget revs think throttle position) Once you know which throttle position is at fault you will be able to tell which circuit needs to be adjusted.

If it pulls when on wide open throttle then your main jet is ok. This diagram shows you which circuits are active at each throttle position.

 

Could be you need to wind your mixture screws out in 1/4 turn increments if your idle circuit is at fault. You need to identify which curcuit is out and if you cant afford a dyno, marking tge throttle is the only way.  

[KATANAMANGLER]

Read this first

[Sheep]

If it is a race engine I would have thought the previous owner would have some info on what jets/parts etc he ran the engine on...It may give you some indication on what you have before stripping the carbs apart!

[nlovien]

symptoms described are inline with changing to stacks versus filters - i.e. leaning out, however before you do anything - recommend you remove the carbs then remove and inspect the idle screw tips ( before opening them up from their present position) - they are prone to leaving the tip jammed into the carb body port if slightly overtightened - i.e. no idle jet circuit flow

recommend this to anyone acquiring these carbs 2nd hand

if they are good then this is your 1st place - i.e. increase the no. of turns out - max around 3 1/2 turns - this will richen things up in the initial throttle / low rpm range but be careful, you have changed 2 key bits ( filter and ex pipe)  - there is no reason to expect any other parts of the fuelling to now be in sync i.e. be prepared to move onto the main jet

mind - if your going to get into the jetting to back off the accelerator pump whilst doing this

plugs - to get a meaningfull reading ref: mixture - you really need to be holding the engine load at the rpm / throttle opening  condition your investigating then hit the kill switch

[Jonny]

SOme good advice here!

Have you changed the exhaust from the race exhaust? Might be you need to rejet as the carbs were set up for that exhaust.

I'm running 155s in my 1230 using BST36s. Changing to velo stacks will make it leaner too. The length of the stack has an affect to apparently.

J.

[Sheep]

Just curious but how come the stacks can lean out the mixture??...is it to do with the venturi effect drawing more air in???...just asking as I may be getting some myself soon.

 

[Gixer1460]

Velo stacks - two theories - None and then added will potentially lean a mixture as the improved linear airflow will allow more inflow so leaning the mixture BUT conversely the improved airflow will allow better draw from the jet, so mixture should stay pretty much the same. Other feature is 'reversion air flow' due to opening / closing of valves - air has velocity and when stopped in the inlet, a pressure wave reverses pushing mixture backwards usually visualised as 'stand-off'. This can be contained by the ram pipes giving richer mixtures (sometimes) All varies with rpm as it moves torque peak around - short = best at high rpm, long for better low end power.

Edited August 31, 2017 by Gixer1460

[Dukeman]

I had one last effort before having to leave for my bike rally, I changed back to the pods and the bike was perfect UNTIL it got up to operating temperature. At this point I went home and pulled out the GSXR. Back now and will pull the carbs and follow the excellent advice provided here and report back.

I am still thinking it could be electrical the way it starts to miss in all rev ranges as it gets hot?

[nlovien]

On 31/08/2017 at 7:19 PM, Sheep said:

Just curious but how come the stacks can lean out the mixture??...is it to do with the venturi effect drawing more air in???...just asking as I may be getting some myself soon.

 

the venturi helps to speed up and smooth out the airflow - less turbulance = less back pressure (choke) = more potential flow

[Gixer1460]

2 hours ago, nlovien said:

the venturi helps to speed up and smooth out the airflow - less turbulance = less back pressure (choke) = more potential flow

Probably...............but totally unconnected with the quoted item, namely ram pipes / stacks, It is what it is generally and is fixed for all tuning scenario's.

[crashtester]

If it starts to miss when it gets hot, might be worth swapping the coils for a known set of good ones. I've encountered this problem a couple of times over the years.

[Gammaboy]

On 9/6/2017 at 0:41 AM, Dukeman said:

I am still thinking it could be electrical the way it starts to miss in all rev ranges as it gets hot?

That does sound remarkably like coils...

[Dukeman]

Good idea - I will do this except I dont have any spares.

Will start hunting.