Air Intake

**Bradleyrayner** · 01-30-2013, 10:56 PM

If a motorbike does not have a air filter on can that cause revs to be high? I have ordered a new one from ebay and waiting for it to come. Answers will be much appreciated.

**moilami** · 01-30-2013, 11:14 PM

Originally Posted by Bradleyrayner

If a motorbike does not have a air filter on can that cause revs to be high? I have ordered a new one from ebay and waiting for it to come. Answers will be much appreciated.

Hmm, maybe the revs won't become too high, but the air/gasolin mixture on the cylinder can become bad. Your engine can get too much air and too little gasolin for that air, meaning that your engine would run "lean". That in turn can make your engine overheat, which is bad.

(I should really go to a library and borrow some books about combustion engines. I have read those briefly last time about 25 years ago or so :D Would be cool to read of them in detail and refresh update the memories.)

**euphonius** · 01-31-2013, 02:59 AM

Say, Moilami, this is the internet age!

How Stuff Works -- Motorcycle Engines

A video from a H-D shop This video is inadvertently funny; he's got a great heap of Harley engine parts on a table and holds each one up as he describes its function. "...our air enters our intake port..."

cheers!

**Krasi** · 01-31-2013, 07:59 AM

Originally Posted by Bradleyrayner

If a motorbike does not have a air filter on can that cause revs to be high? I have ordered a new one from ebay and waiting for it to come. Answers will be much appreciated.

Yes, especially with 2-stroke engines - hence my first question in your other thread. And also advised you to check for air leaks with a starting fluid spray.

In your particular case I think your engine runs at high rpm, because you must keep the choke on. The choke usually is made to bypass the "pilot and main gasoline circuits" and squirts gas directly at the exit of the carburetor, enriching the mixture. Rich mixture eases cold engine work.

So having big air flow (because there is no filter to restrict it) + a lot of fuel (from the choke circuit)= open throttle (under normal conditions).

Still this is just a theory, based on the inputs you described.

**Lowi** · 01-31-2013, 11:00 AM

Put fresh fuel in ... there might be water in the tank.

**Bradleyrayner** · 01-31-2013, 06:09 PM

will water in the petrol make the revs really high???

**moilami** · 01-31-2013, 08:49 PM

Are you sure the throttle cable is not jammed or mechanism near the carburetor linked to throttle cable is not jammed?

**moilami** · 01-31-2013, 09:04 PM

Originally Posted by euphonius

Say, Moilami, this is the internet age!

How Stuff Works -- Motorcycle Engines

A video from a H-D shop This video is inadvertently funny; he's got a great heap of Harley engine parts on a table and holds each one up as he describes its function. "...our air enters our intake port..."

cheers!

Hmm, indeed Internet Age! People want to know everything of a subject with 600 words. Before internet that would had been brief first chapter introduction to the book and the author.

So, I still miss the "guide to tune combustion engines" tome, which left me with a pretty nice picture of a system called combustion engine.

I always say that if you want to know something, then get the most expert book you can get because that kind of book explain basics briefly but details lenghty.

**Lowi** · 01-31-2013, 09:26 PM

Originally Posted by Bradleyrayner

will water in the petrol make the revs really high???

Yes it will ... mine revved high and took around 10 mins to steady before I could ride it.

It was the same everytime I started it, I drained all the fuel from tank, fuel line and carb, put fresh petrol in and was fine.

Water had been getting in from a seal that wasnt seated correctly on the petrol tank.

Everytime it rained or I washed the bike water got in.

Try draining your petrol and put fresh in.