Isolating the Throttle Bodies from Each Other to Defeat Port Robbing

I got inspired by Ian's posts on sorting out the 961 EFI, and his comments on port robbing. So today I pulled the throttle bodies off mine and plugged the passage between the two sides, as well as deleting the IAC valve. These are pictures of the throttle body before mods, showing the port for the IACV hose and how the two sides are connected.




I removed the fitting for the IACV hose and drilled and tapped the body for a plug. This is a picture of the body with the drilled and tapped hole, a rubber plug that I made from a stopper, and a screw to compress the plug. I did it this way because I wanted to be able to go back to the original configuration if necessary. All I would have to do is replace the threaded plug with a hose fitting to take the IACV hose.


I leak tested it afterwards, and there is no leakage between right and left sides. This is a picture of the finished product, with a tidier threaded plug.


I put the bike back together without the IACV and fired it up. After warming it up for a while, I adjusted the idle with the idle stop screw. It seemed quite happy to sit there and idle nicely at 1200 rpm. Now I just need to take a ride to see how it works on the road.

FWIW, I had already removed the cats and the narrowband O2 sensors. I'm currently still using the unlocked original SCS ECU, a modified Typhoon model. I will eventually go back to the newer 400 Delta ECU, like Ian is using, but I want to play around with the original for a bit first.

Ken

Watching with interest .

I'm running the power commander with the oxy sensors disconnected and cats removed on omex ecu.
Fueling for my bike is solely controlled by the PC so should be equal with both cylinders.
I have just plugged the iac hose and have set idle to 1200 on the butterfly's.


Would the hose between the throttle bodies act as a balance for vacuum variance with the iac blocked ??
I also have a Kawasaki versys 650 ,and a improvement is to install a hose between the throttle bodies to balance them out for slow running .

Cheers
Paul

Thanks Ken, so far so good! Paul I think some engines may benefit from a balance pipe others not. The Versys is a 180 degree crank and the Norton is 270 for starters.

Has anyone ever put carbs on in place of the EFI? Or is a aftermarket throttle body available?

iwilson said:

Thanks Ken, so far so good! Paul I think some engines may benefit from a balance pipe others not. The Versys is a 180 degree crank and the Norton is 270 for starters.

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Yes
True
But the norton has no separate adjustment for each throttle body .
At the very least it is going to balance vacuum between the cylinders at lower revs even with the iac valve blocked off .
My thoughts anyway
Cheers
Paul

True, but I can adjust the fueling for individual cylinders to account for any variance in airflow between each throttle body. Would be magnitudes better than the current situation. Which actually isn't that terrible once you've got the 'good' cylinder running nicely.

iwilson said:

True, but I can adjust the fueling for individual cylinders to account for any variance in airflow between each throttle body. Would be magnitudes better than the current situation. Which actually isn't that terrible once you've got the 'good' cylinder running nicely.

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My case is a little bit different , beacause the PC controls the fueling to the injectors.
Would be good to get a vacuum reading on individual throttle bodies with the iac balance tube open and another reading with it blocked off .
Possibly a test point on cone filters could be used as the throttle bodies don't have test points.

Can you control individual injectors or just globally with PC? Have you measured the AFR from each cylinder at idle? If not be interested if you could at a garage. Sample size of one at the moment is not representative!

iwilson said:

Can you control individual injectors or just globally with PC? Have you measured the AFR from each cylinder at idle? If not be interested if you could at a garage. Sample size of one at the moment is not representative!

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I will get back to you on this tomorrow ,
Might be time for the bike to go back to dyno for some info on the changes.
cheers
paul

Voodooo said:

Has anyone ever put carbs on in place of the EFI? Or is a aftermarket throttle body available?

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They were originally designed to use 39mm FCRs. I bought a pair off of Kenny Dreer thinking that if ever my electronics start playing up, I can rip the lot off and fit carbs!

WOW , The IAC blocking and hot engine butterfly idle adjust has finally gone viral !

Also , if you decide to keep the IAC blocked , you can use a throttle stop at the twist grip to keep the engine running while it warms up . This will make the mod be almost seamless and allow you to walk away from the bike when you first start it up ! Say shoot for 1300 to 1500 RPM with the the throttle stop on as you get ready to leave while its warming up ? Kind of like a fast Idle choke on a carbie !

Another question is what are you doing with the IAC plug ? Tape it up and leave disconnected ? Or a dummy load of some kind ?

TonyA said:

Another question is what are you doing with the IAC plug ? Tape it up and leave disconnected ? Or a dummy load of some kind ?

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My dads been testing reducing the sharing by only a very small hole.

Ever since I blocked my IAM the bike has ran perfect.... PERFECT!

Why don’t you guys measure each cylinders EGT (exhaust gas temperature) this would tell which cylinder is rich or lean.

Also, when running the megaphones you don’t use a o2 sensor. So how then is the ECU adjusting the injector pulse width and timing curv? Strictly from the throttle position sensor I believe?

Have you tried adjusting the throttle position sensor by loosening it and or elongating the screw mounting holes to fine tune the settings?

This is what I used to do on a early 1990s ford 5.0 before mass air sensors came and barometer.

I think its not adjusting it , and the port robbing is making cylinder 1 lean at idle only . This is how I understand it. Would blocking the passage between allow the AFR's to be closer to correct at idle ? Assuming that you are not using the IAC and going for the throttle stop adjustment .

TonyA said:

Another question is what are you doing with the IAC plug ? Tape it up and leave disconnected ? Or a dummy load of some kind ?

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I taped it up and tucked it away out of sight. I also plan to turn off the IAC function in the ECU, but haven't got to it yet. With the IAC and O2 sensors gone, the only idle control in the ECU is by ignition advance, and there might also be some improvement possible there. Probably some improvement possible in cold enrichment maps and such. I don't think we'll run out of things to experiment with for quite a while.

Ken

Well, so far it's looking good. I do have to hold the throttle a bit while it warms up, but that's not a big deal. I'm hoping I can eventually sort that out with ECU settings. I took a 50 mile ride this morning through the local canyons, and it still runs great at speed, but now I also have a nice, stable idle. And, the problem I had with it sticking at a higher rpm in corners is now completely gone. I'm very happy with it. Next step will be to try some of the fuel settings from the map Ian sent me from his dyno tune. Right after I get a new fuel hose, that is. I'm going to put up a separate post on the subject of the fuel hose coming loose.

Ken

Great news Ken, I'll send you the latest map I'm using shortly.

Just to clarify there are two issues/approaches being dealt with here.

1. Blocking off the IAC valve and setting the idle with the throttle position screw instead. The throttle bodies in this situation are still joined and as far as my testing goes cylinder 2 continues to steal fuel from cylinder 1. But a stable idle is still possible. If you have a bad IAC valve or just want to simplify your setup no problem. I'm still wondering if half the problems are due to the o2 sensors getting screwed up at idle due to the stealing.
2. Or as Ken has done - going full tilt, removing the IAC assembly completely AND blocking the pipe that joins the throttle bodies. This should mean a more stable idle as both cylinders can run with the correct AFR. You could then leave the o2 sensors in as they will take care of getting the fueling correct at idle. As Ken has a programmable ECU he can adjust each injector.

If you're going to block the IAC pipe then you may as well block the pipe that joins the throttle bodies as well.

The ECU btw uses what's called Alpha N mode for fueling (who comes up with this stuff I don't know). Instead of a MAP or MAF sensor to calculate the mass of air/oxygen entering the engine, it relies on the throttle position sensor (the Alpha part) and RPM (the N part). With this setup you do not want to play around with anything that may change the mass of air entering the engine. This is because the ECU has no way compensating for it, the map is developed around knowing that the throttle bodies will always flow the same amount of air at a given throttle opening. If you change the size of the throttle bodies for e.g. then the ECU's fueling would be incorrect. But with a MAP setup the ECU would detect the change in air mass and adjust the fueling accordingly.

It remains to be seen what effect blocking the pipe between the bodies has at normal loads - I wouldn't think much since the same mass of air is entering the throttle bodies, but we'll have to wait and see.

iwilson said:

Can you control individual injectors or just globally with PC? Have you measured the AFR from each cylinder at idle? If not be interested if you could at a garage. Sample size of one at the moment is not representative!

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Just spoke with Steve at powerhouse,
The power commander can be setup for dual map which will fuel each injector separately ,
He also suggested leaving the iac balance hose in place as there is no adjustment for the vacuum for each throttle body , but did say it will make little difference when the throttle is wide open.
This is a recommendation for the setup on my bike with the PC fitted and iac blocked .
Tony
I have left the iac plugged in and installed at this stage . But will look to remove and plug at the t piece in the future .

Cheers
Paul