Topic: WD-40 Air leak test?

[Magpie]

I've been told I have a possible vacuum/air leak on my CB750K1. The idle won't settle down to a reasonable level. 2 of the 4 intake boots are new and the clamps are tight. I'll try Hondaman's washer solution on them too.  There's a post about using WD-40 to test for leaks but not a lot more information. Anyone know what this is about and how it works please - and thanks.
Cliff.

[Gordon]

With the engine running, spray it on the areas where leaks can occur.  If the idle speed changes when you do this then you have a leak.  I prefer to use aerosol carb cleaner, though.  It doesn't leave an oily residue like wd-40 does.   

[bwaller]

Other possibilites that can cause your problem, carbs out of sync, mechanical ignition advance dry & sticking.

[kayaker43]

Carb cleaner may remove paint. Most flammable sprays will change the idle speed if sucked in but I sure wouldn't want to slime up my motor with WD-40?

Try aerosol starting fluid (ether). I'm not sure if you can find it everywhere or whether its a cold climate thing, but in Michigan its common. It is highly combustible (duh), leaves no residue and won't damage paint. Just don't fog it so heavily that it gets sucked in the airbox and fools you. Use the extension tube and spray around the intake manifolds.

[eurban]

I for one would not spray anything as flammable as starter fluid on a hot engine.  My understanding is that a product like WD-40 increases the idle speed by momentarily blocking the air leak rather than providing extra fuel for combustion.  It is less volatile than starter fluid, shouldn't hurt paint and seems to actually be good for rubber parts. Wipe off the excess when you are done and the rest should burn off.  It would be my choice for such a test and just about everybody already has some. . . .

[CrisPDuk]

Eurban, spraying WD-40 on to a leak used to cause the idle speed to increase because it is a flammable liquid, and effectively caused the mixture to go rich momentarily.  Since they changed the propellant from LPG to CO2 though, it doesn't seem to work as well as it used to, either for leak testing or lubricating

I personally tend to use carb cleaner or brake cleaner, whichever I happen to have to hand, both of them do the trick nicely

[eurban]

Eurban, spraying WD-40 on to a leak used to cause the idle speed to increase because it is a flammable liquid, and effectively caused the mixture to go rich momentarily.

Probably so, but I have heard other explanations.  How would you know the difference?   The new formula might not be as good at plugging air leaks In my experience, both carb cleaner and particularly brake cleaner (acetone) are great at removing/damaging paint.  Maybe starter fluid isn't as dangerous as my commonsenseometer is telling me . . . . . .

[joeb]

Why did you only change two of the intakes you should have replaced all four and got new clamps you would have gotton better results especially if two of the intakes were already bad.

[Magpie]

I do have a complete new set but the 2-3 ones seemed shorter than the old ones when they are side by each. Maybe it's my imagination but it won't take long to change them out and check it out. I thought checking for leaks would be the first step though rather than ripping and tearing as I sometimes to first.
Cliff.