The bike idles normally but with a tiny touch of the throttle (slide moves about 5mm) it goes straght to full revs without building up through the rev range. As you said hondars it will need to be pressure tested. But although it sounds like an air leak I think its a problem with the carb because if it idles fine you would think it would work normally.

www.sherco-usa.com

that site tells you all the jetting etc.

If all the other work was done properly, about the only thing left is the carb.

Maybe the bike is mad at you for using chainsaw oil in it.

Have you checked for a restriction in the fuel line or petcock? Have you checked the screen in the tank?

Think it must be the carb, the bike run fine all of last year on chainsaw oil and my other two bikes were fine using it. I have checked the fuel and it seems to be flowing fine with no blockages.

Whatever it is, we are all very curious to know the truth about this very perplexing problem. I once had cracked cases under the stator plate on my '78 Husqvarna 250 which was easily found via the gasoline residue in the mag cover. It acted lean at idle, ran hot and eventually became hard to start. Removing the mag cover made the bike run worse. Hints for you Heathy.

Theres 2 likely causes of this i feel. The first is what happened to me some years ago on my Fantic. I got a casing fracture and the machine revved out of control when the machine was revved even a little. When I stripped it i could see a crack in the crankcase housing although i was amazed how small it was to have such a large effect.. As your machine siezed already, The stress at siezure could have caused this for sure.

The other thing is possibly excess fuel is also getting into the crank and not being burnt fully till u add some air by opening the throttle. The engine wont rev on air alone, it must have fuel as well obviously

If you get it pressure tested, let us know the results.

Edited April 3, 200521 yr by Webmonkey

I have just re read one of your previous posts and it says that the reason your machine seized in the first place, was due to this fault therefore, the first place to look is the carb and see if excess fuel is getting into the crankcase.

I inspected the crankcases when i disassembled the engine looks like it can only be the carb now, do eurocarb have a website or phone number.

thanks for all of your help everyone

Heathy

Like most people have been saying it sounds like an air leak and just because you have put all new gaskets on doesn't mean it is sealed, mating surfaces must be perfectly flat as well.

To give you an idea of how flat they should be and how engine builders do it Have a look here

If you want I made a simple pressure tester and I have got a spare carb just to make sure.

Send me a email if you want to come and borrow them.

Chris

Thanks for the link hondars.

Chris the reason I dont think it is an air leak is that the problem started before I took anything apart, and it happened by itself. When I put the bike back together I did clean all of the mating surfaces with a razor then I put a light coating of grease on all of the gaskets to ensure a good seal.

I was going to try to make a pressure tester but it would probly leak more than the bike. Where abouts are you from chris.

thanks

Heathy

I live just below sheffield

Have you had a read of that website page I posted

Chris

Also have a look at how to do a leak down test

Here

Hi chris, yea I read the page, thanks, It could be a leak in a gasket but I don't think it is because of the way the problem occured to start with. How did you make a pressure tester? I was going to use a bike pump.

For my pressure tester I turned a block of aluminium down so it was a nice fit into the inlet manifold, then I fastened a normal tyre valve on to it. The exhaut side needs blanking off as well.

I pump it up with the compressor (turn the regulator down tho), then you can use your tyre pressure gauge to check the pressure.

It should hold 8 psi for around 10 minutes.

You can buy gas leak detector spray, bubbles where there is a leak, this will show up all your tiny leaks if there are any.

Chris