Colourtune or rpm measurement for pilot screw adjustment?

[waddycall]

my recently acquired CB750 needed a carb strip and clean last week as it was running rough at tickover. Seems fine now, running really smoothly, but I'd like to make sure the pilot screws are set right.
My previous tuning experiences are on single cylinder dirt bike engines where a plug chop is dead easy. On this 4 cylinder lump it's not so straightforward so it looks like I either need to tune the carbs by rpm changes or with a colourtune kit. Any preferences either way? I'll get myself a carb tune gauge for synch too.

 

[brightspark]

I thought u had to balance the carbs with vacuum gauges

 

[waddycall]

I thought u had to balance the carbs with vacuum gauges

Balancing the carbs is the next step so I'll get a carb tune gauge for that. Mixture screw tweaking comes after that. Could take it to someone who knows what they're doing but where's the fun in that!

 

[Pete.]

Colortune is 40yr old tech or more. You want a wideband controller and gauge or datalogger.

But first you should make sure that your valve clearances are good and do a compression or leakdown check especially on an older bike then fit a new air filter and balance the throttles. No good trying to tune carbs if you don't know that the compression and clearances are good.

 

[roofman]

Just put the pilot screws to factory spec and that goes for mixture screws too as long as there not changed as with the mains included and you will be getting it as sweet as it will run given its age and carb complexity,then after a good ballance it should be at its best.

 

[waddycall]

Thanks chaps. I'll do a compression test and balance the carbs and go from there. I put the pilot screws back in their original positions but would quite like to check they're spot on. The Honda manual gives a procedure based on rpm changes at tickover but I'd need to get hold of a tachometer for that. The bike has hydraulic tappets and is unbelievably quiet. It's 20 years old and only at 15000 miles

 

[roofman]

Thanks chaps. I'll do a compression test and balance the carbs and go from there. I put the pilot screws back in their original positions but would quite like to check they're spot on. The Honda manual gives a procedure based on rpm changes at tickover but I'd need to get hold of a tachometer for that. The bike has hydraulic tappets and is unbelievably quiet. It's 20 years old and only at 15000 miles

has it got the CV carbs and what model is it...for some strange reason looking at your original post i had assumed it was an early K model

 

[waddycall]

Yep keihin cv carbs. It's a 97 f2v

 

[wookie]

Colortune is 40yr old tech or more. You want a wideband controller and gauge or datalogger.

It might be 40+ year old tech but it also happens to work, on a engine with multiple carbs how do you know which one is out of tune by sniffing the exhaust ? with the colortune I know which carb is at fault because I can see whether that cylinder's mix is too rich or too weak.

I'm not trying to be awkward, if there is a better tool than what I use I'm interested, but I fail to understand how sniffing the mixed exhaust helps me setup a multiple carb engine.

 

[Pete.]

If the carbs are in good service then you set them all the same and adjust them all the same, if they aren't you're wasting your time. You will never see a dyno guy tune a bike with a colortune, they just poke the wideband lambda probe up the exhaust. If you really want individual cylinder tuning then you can fit EGT sensors in the headers but for a basic check you can just idle the bike up to temp then use an infra-red thermometer to check the external temps of the headers. If they are all similar you can be fairly confident that all the cylinders are burning the same.

 

[waddycall]

Me being too picky?

Nope. I agree. Thanks everyone decision made.