Don't have any history for this engine, but it starts and runs well.

Really nice for approx the first 1/3, but isn't keen to keep going.

I don't think it's carburation as it runs so well at the bottom.

I'm going to check the timing first.

It's had a new plug with no difference.

How about disc valve timing ?

The engine originally was from an Aprilia, but is running with a SWM air box and exhaust. Don't thing either are part of the problem ?

Also don't think/hope that's it electrical, unless anyone has had similar experiences.

Thanks in advance.

Ross

Ross

Are you using that dodgy Aprilia carb ??

Would suggest you look at the main jet first. I have had a few that have tarnished so bad that the standard 95 opening is reduced to a fraction of that size and they wont rev out.

If that doesn't cure it, and its smoking a lot when you try and get it to rev out, it could be the disc valve crank seal or O ring....you can check the settings when you change them.

Martin

Hi Martin.

Thanks for the info, just checked timing and its well out, while I was in there I popped the cover on the big 6205 bearing and its completely dry.

So will replace that as well.

Its not smoking to much so hopefully its only timing. I will have a look at the main jet, not something I usually check as in the past they didn't seem to have a problem, must be this dodgy new fangled petrol.

Ross

Sometimes on the SWM rear exhaust box baffles can come loose.

It is noisy but check without the final exhaust on the bike.

Hi reggie

Thanks, but the back box had just had the baffles welded/riveted and had been used on another SWM just before fitting.

Ross

Are you running the Aprilia carb? A stupid question that I have seen done wrong a dozen times are the vent tube hose. Just remove all to check whle running.

Hi lineaway, using Aprilia carb for now, vent hoses are blocked at both ends.

Thanks

Ross

I do not understand what you mean in `blocked`?

Hi lineway

I have removed the small diameter pipe completely, and sealed each end so the system is redundant. (I am not referring the the carb overflows) The following pictures show the pipe .

Well, checked the timing and it was about this far out when strobed,

Thought I had cracked it, still the same. Cleaned the carb again, still the same.

Swapped it for one off an Arpilia (petrol screw type) sorted.

Thanks for all your help and suggestions, now all I need is another PHBH 26 FS carb.

Ross

Model not listed on their site Ross but these guys might be worth contacting http://www.dellorto....artsectionID=20

New carbs aren't as dear as I had expected.

Might be worth getting a bit brutal with the solvent to clear the passageways in the old one?

Edited December 18, 201213 yr by 2stroke4stroke

Dellorto Uk / Eurocarb will build the carb to your requirements,

a new carb will make a differance

Resurrection - as said, solved the problem by borrowing a petrol screw Dellorto from another bike and ran it till about a month ago. Decided it was time to replace carb and return the original to the donor bike when the new one turned up. I expected to notice a real difference between a brand new carb, and a 25 year old one. Virtually none, which was a pleasant surprise, and goes to show that they are/were very good quality. (this is contrary to the opinion voiced on a well known site, which claimed they wear significantly in a year)

Good news...

my bike came with a receipt for a new Dellorto, I was surprised how very reasonable the price was compared to, for example one new carb for a 1992 Suzuki GSXR750 of which they made hundreds of thousands Mikuni BST's

Well, checked the timing and it was about this far out when strobed,

timing 002.jpg

Thought I had cracked it, still the same. Cleaned the carb again, still the same.

Swapped it for one off an Arpilia (petrol screw type) sorted.

Thanks for all your help and suggestions, now all I need is another PHBH 26 FS carb.

Ross

Just checked timing on another "new to me" rotax, and the timing is almost exactly the same amount out. Is this the heel on the points wearing, or someone trying to calm it down ? Any suggestions.