Bikes running too rich? How can I adjust that?

[Jpich85]

I checked my plugs last night and they were really black which I think means it's running too rich, I've been having issues with the bike revving up the rpms so I took the carbs off last night ready for a clean, I wanted to know if there's anything I can adjust while I've got the carbs off which will lean it out more? I know I need a new jet kit but can't afford that atm so just wanted to see if I could get it a little better for now.

Cheers

 

[Gixer1460]

NO - simple answer. Engine stock or modded? If former why is it rich - if latter it usually should be lean unless someone has played but badly!

[Reinhoud]

You can't see on the spark plugs if an engine is tuned right, a lot of people see you can, but my experience is not. I've ridden quite a while with a A/F gauge.

The only proper way to see if it's tuned right is to use an A/F gauge.

Edited September 15, 2016 by Reinhoud

[Gixer1460]

2 hours ago, Reinhoud said:

You can't see on the spark plugs if an engine is tuned right, a lot of people see you can, but my experience is not. I've ridden quite a while with a A/F gauge.

The only proper way to see if it's tuned right is to use an A/F gauge.

But its a bloody good indicator something is amiss somewhere!

AFR Gauge won't differentiate between a duff plug due to over rich mixture / oiled up / ignition problem - its only a diagnostic tool.

[Jpich85]

It's a rf900 with the gsxr 750 head on, it's got pod filters and a none standard exhaust so I expect the set up isn't right, I appreciate any help. Thank you

[banoffee]

If you're new to carb setup this might be worth a read.

[Sheep]

Ive had no end of issues with my carbs but i reckon i am near enough there now...BUT while you are tinkering i would advise checking things like valve clearances,ignition,wiring etc while you are at it.Checks do not cost anything.I chased my tail over one issue only to find something else amiss...

[Jpich85]

Thanks for your advice sheep, it's driving me mad lol, I'm not sure if it's maybe a breather issue because the bike was running nice until I stripped the tank down

[teltwosheds]

On my old bike (not suzi) plugs were always black due to being set too rich at top end. They only ever looked right after a right good thrashing(whistles). straight through measured pipes, no filters pods etc

Edited September 16, 2016 by teltwosheds
info

[Sheep]

How far did the tank strip go??...could you have messed up the fuel tap perhaps?....mind you,with the open pipe and pods i would have thought the bike would err on the lean side.

[badgerkdd]

Can you not raise the clip on the needles a couple of notches? Thats all I did to mine when it was running rich. Thought that was the first thing to check? I'm ready to be educated if I'm wrong though 

[Legotoy]

Hopefully Jpich85 doesn't mind me posting this, but we're here to share knowledge so I thought people might like an update. We spoke, and the last time the bike was on the road it had an airbox and standard jets (112.5's).

It now has pod filters (no airbox) but still the 112.5's. I've sent him some bigger jets to try. Fingers crossed.

[KATANAMANGLER]

There are so many variables here. Changing things randomly without a sound and systematic diagnosis is going to lead to frustration and failure. I know this because I have done it many times. You learn the hard way. I'm still learning and I have to remind myself not to fall back into the bad habits of the eenie meenie minie mo method.

I'm dealing with an RF900 fuelling issue at the moment too as it happens.

1. I would always start with a compression test. Without good compression you are wasting your jets  ( just rule it out)
2. You have compression now check your spark. Start with new plugs. I have chased a fuelling problem before only to find I had a duff plug.
3. You have a spark and you have good compression, now you can start to look at fuelling.

There are 3 principle circuits on a carb. Idle, needle and main Jet. They overlap. The circuit or circuit combo are determined by the position of the butterfly which in turn is controlled by the throttle position. So the first thing you need to know is which circuit is too rich. This has to be done on a dyno or if that is not possible by plug chop. It's not about revs it's about throttle position. So if it is rich at closed throttle the idle circuit is at fault if it is rich at 1/4 throttle the needle and emulsion tube could be at fault. If it is rich at WOT then the main is too big. Float height can affect all of the circuits.

For example at wide open throttle the plug could show a dangerously lean condition but if the bike has a rich idle circuit and it is ticking over for a few minutes after a run the plug will give a reading for the last circuit in use and will mask any symptoms form the other circuits.

You have to also understand the adjustments that affect each circuit but first you have to identify which one is influencing the condition.

First thing I would do is get it dynoed and if I couldn't do that I would  plug chop it. If you don't know which circuit is out you will just be hoping to get lucky by making guesses.

 

 

[Madb]

Surely it would run lean if on standad jets?  Need at least 118- 122?

[KATANAMANGLER]

2 minutes ago, Madb said:

Surely it would run lean if on standad jets?  Need at least 118- 122?

Unless it was run lean and burnt a valve seat and the compression is down in which case it may appear to be running rich as a result of lower compression. Rule out the basics before changing anything.

[Madb]

Agree katanamangler but 112.5 are far too small for 750 head on 900. Hopefully no burnt valve's, eh.

[Reinhoud]

Ah, pod filters! That makes it a lot different. Start with about 30/35% bigger jets, and then see where you're at.

[Madb]

I were thinking along katanamangler's philosophy . Not a fuel probably as it would be running to lean. So possible  a plug swap.

[Jpich85]

Thanks everyone for your help, I've received some bigger jets today that legotoy has kindly sent me so I'm in the process of giving that a try first, I think it's a good place to start as like madb said the standard 112.5 jets must be too small, I'm still learning but man it really gets on my nerves sometimes, I had to leave it tonight because the carbs decided to leak after installing the new jets and giving the carbs a clean.

I do need a dyno sesh I think but I want to get it somewhere near if I can first