Carb Icing (again)..

[Waldorf]

Went out for a ride early this morning, and had some issues on Marranda's bike ('98 ZX6R). Through the slow speed corners from Toolangi -> Kinglake (well, they were slow speed in the fog and wet this morning ), the bike seemed to be bogging down at around 4.5krpm, and then it'd get up and rev ok. It also did it to me the other night coming down the Monash when it was bloody cold.

I thought I might have picked up some dodgy fuel, so I'm draining and flushing the tank this afternoon anyway, but I did the right thing and did a search and came up with "Carb Icing" as a possible answer. It seems to fit the symptoms right (in the fog early it was bogging down, but later on in the sun it seemed OK) I was interested in the following bit:

You probably did have carby icing, it's not a myth. All zx7r P1's and P2's were supposed to have a carby warmer fitted at the first service. They used the one that comes stock on the '97 zx9r. You should be able to see it, Its on the left hand side, next to the clutch slave cylinder. Its a coolant line with a little filter, about 25mm round and 40mm long, in it.
Becaue of the HUGE volume of the 7's (and kwakas in general) air box, ther is a large differece between manifold and Plenum preasure. Air ram works by increasing the plenum preassure the quicker you go. For wide open throttle in and out corners etc.. this isn't a problem. BUT, at 100km the plenum (ram air) preasure is relativley high and with the butterflies only open a crack means massive air speed through the venturi. This does cause icing on 7's. The carby warmer does improve things, but mine does it still on cold Ballarat nights, and blueflies (without the warmer) is even worse.
Because of the 7's intended purpose, hard wide open throttle track or twisty riding this wasn't anticipated as a problem. It only even happens to me on a cold free way, get to hills and use some throttle opening and it's not a problem.
The reason they left them off origionally is that the colder the aircharge going into the engine the denser the air is and the more fuel can be carried. Denser air and more fuel equals more horse power that the engines will make. 6's and 9's aren't as bad.

If I am getting carb icing, would blanking out the ram air ports help to alleviate the problem? Any other suggestions? (apart from putting her bike away and riding mine instead? )

[Head_Mechanic]

You can buy fuel additive to help with this problem. Best to let the motor reach running temp before ridding it. The more rpm you run the more it will ice up.

[Strika]

Blanking off the air ducts will stop it running full stop Macca! Mate they need air to burn that fuel!

What you need is to find a wrecked 6 with the carby heater kit fitted to it and buy the bits! It's the only way to fix it!

[Waldorf]

You can buy fuel additive to help with this problem. Best to let the motor reach running temp before ridding it. The more rpm you run the more it will ice up.

Hmm.. I did come across that additive mentioned somewhere. I'll keep it in mind. I'd been happily riding for 45 minutes or so before we hit the fog & cold and it started playing up.

Blanking off the air ducts will stop it running full stop Macca! Mate they need air to burn that fuel! What you need is to find a wrecked 6 with the carby heater kit fitted to it and buy the bits! It's the only way to fix it!

I didn't mean to block off the entire "smile" on the front.. Just the two tubes that seem to feed cold air directly at the top of the carbs (or do they serve another purpose too?).

Looks like I'll just have to stop riding the 6 when it's cold and get back onto the Zed..

[javaman]

I found that running constantly at 8000 rpm the carb icing dissapears. It makes a noisy and fuel-inefficient ride though.