High Revving - air leak - failed gasket

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loadedscooterist
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Tue May 01, 2018 8:13 pm

Its strange you talk about this but I hadn't checked but what I have done today is to get a new carb - a 22mm upgrade kit with manifold and filter etc so I want to discount the carb thing once and for all (and it will be an upgrade from 18mm). I will therefore have to make sure everything is tightened when its put back.

I have also got on order a new exhaust gasket and in the meantime am going to clean up the exhaust as there is no holes in it - just flaking paint and rusty and get it put back together with a new clamp as there wasn't even that holding it together.

As to the other potential issues / nasties - I will look into that once I have everything else put together and see where I stand once the initial things are done.

The very first job I am planning on is to clean up everywhere underneath as the engine block looks like its never been cleaned up - years of dirt (its really bad in between the frame). At least if I get things cleaned and get it started again I can at least see where leaks are etc. Further leak down tests to be done once its back together again.

Fingers crossed!

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ForemanBob
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Thu May 03, 2018 3:50 pm

The marks on your piston tell me that you have had heat seize issues or stuck piston rings... you need to take the top end off and check these out...

Anything else is putting lipstick on a pig, IMHO

johnny650
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Fri May 04, 2018 3:19 pm

the high revving is a classic air leak/lean mixture symptom .
My advice would be to remove the inlet manifold and remake the joint with a fresh gasket and apply a non setting liquid gasket both sides of the gasket like Threebond 1104 .That way you can at least eliminate an inlet air leak from the equation .

Next check that you are getting a good seal between the carb and the manifold . just cos the clamp is tight doesn't mean there is a good air seal necessarily. You haven't said which carburettor or inlet manifold is fitted but presumably it is the original 18mm Dellorto with 18mm inlet spigot .

As Martin and I have done already ,it would be a big improvement in performance to fit a 22mm small block inlet manifold with a 22mm Jetex carb . There are plenty of used items on ebay if you want to try it without too much expense. You will need to buy and try a few main jets and possibly a different atomiser and pilot jet but we can give you a good starting point and help with the tuning .

it is possible to buy or fabricate a sleeve to reduce the 22mm jetex down to fit your existing 18mm inlet manifold if you don't want to spend too much. I used a thin strip of plastic to wrap around my 18mm inlet spigot so that the jetex clamp could seal and be tightened

loadedscooterist
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Mon May 07, 2018 8:53 pm

Unfortunately postman plod decided not to bring my new gaskets and Jetex 22mm carb before the Bank Holiday so that left me cleaning and sorting out the exhaust. I decoked the 42mm clubman with caustic soda so at least I have not holes in that and got a lot of gunge out. The next steps for the exhaust are a full prime and a respray.

Once I have the new items in hand I will get everything refitted so good suggestion with the threebond. As I have very little history with this scooter its been a guessing game and a bit of a minefield since I bought it I have been sorting out bits one by one over the last few months.

The original manifold to the 18mm Dellorto with the spigot is still in place as far as I know. Nothing to suggest this has ever been replaced.

I am not sure what I am getting in terms of jetting until it turns up but will post up what I receive. As far as I know the engine is standard with a 42mm AF Ray speed exhaust so any help on settings would be really helpful.

BTW, I also agree with Bob that the top end needs to come off to get a better look at whats really happening but I do want to eradicate at least the carb issue and manifolds as a starter for ten though. This scooter has been a huge learning curve so its one step at a time for me.

I will post my progress once I have got a bit further with it. Thanks for all the feedback to the problem.

hendy
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Mon May 07, 2018 8:58 pm

Good work. You're right about trying to get your head round what's going on, but before long you'll be replacing the entire top end and packing the barrel to compensate for longer con rods and waxing lyrical about corrected compression ratios. You stink of it. :-)

Martin20
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Mon May 07, 2018 10:03 pm

loadedscooterist wrote:
Mon May 07, 2018 8:53 pm
Unfortunately postman plod decided not to bring my new gaskets and Jetex 22mm carb before the Bank Holiday so that left me cleaning and sorting out the exhaust. I decoked the 42mm clubman with caustic soda so at least I have not holes in that and got a lot of gunge out. The next steps for the exhaust are a full prime and a respray.

Once I have the new items in hand I will get everything refitted so good suggestion with the threebond. As I have very little history with this scooter its been a guessing game and a bit of a minefield since I bought it I have been sorting out bits one by one over the last few months.

The original manifold to the 18mm Dellorto with the spigot is still in place as far as I know. Nothing to suggest this has ever been replaced.

I am not sure what I am getting in terms of jetting until it turns up but will post up what I receive. As far as I know the engine is standard with a 42mm AF Ray speed exhaust so any help on settings would be really helpful.

BTW, I also agree with Bob that the top end needs to come off to get a better look at whats really happening but I do want to eradicate at least the carb issue and manifolds as a starter for ten though. This scooter has been a huge learning curve so its one step at a time for me.

I will post my progress once I have got a bit further with it. Thanks for all the feedback to the problem.
I am running with a 150 slide, 45 pilot, 50 choke and a 118 main jet. Tried with a 108 main to start, but it was not happy! Only bigger one I had handy was a 118 which I thought would be too big, but it runs really well with it, revving well through all the gears!
Hope this helps.

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