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Series 3 62 start up issue

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Series 3 62 start up issue

Postby jdevane5 » Tue Jul 12, 2022 1:57 pm

Just finished building a 62 Series 3 150cc and stuck a 175 piston and barrel on.

So started it up and it just would not tick over...
Tried the usual, air mix screw/ throttle tick over screw -Checked Choke was working correctly.

Got it kind of ticking over once warm and then al of sudden it really over revved.... to the point I thought it might go bang, hit the off switch -did not work, pulled the HT lead off and it still ran as I walked around the scooter...and eventually blocked the air intake...a crazy few minutes.

Anyway I'm guessing I have a massive air leak so will do the inner tube test over the manifold inlet and exhaust, soapy water.
I noted some carbon/ soot on the exhaust joint once engine had stopped.

What pressure do you typically put into the system to check?

Last question -Should I stick a bigger main jet in?? I had a look at the current one and think it was "108" -the original dell 'Orto carb.

Cheers
JD
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Re: Series 3 62 start up issue

Postby Storkfoot » Tue Jul 12, 2022 3:35 pm

Whilst an air leak test is always a good idea when building an engine, in this case, just fix the air leak at the exhaust manifold and start again setting the tickover.

Are you running an SH1/18 and, if so, how have you jetted it?
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Re: Series 3 62 start up issue

Postby gp200ts1 » Tue Jul 12, 2022 3:49 pm

Fix the air leak first. A bigger main jet will have no bearing on tick over as it only comes into play from 3/4 slide open.
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Re: Series 3 62 start up issue

Postby MickYork » Tue Jul 12, 2022 6:26 pm

The "inner tube method" is a good fairly basic test (hard to get the tube air tight on the manifolds).

Not a lot of psi required 5psi should be ample, with liberal amounts of soapy water.

Good luck and report back :)
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Re: Series 3 62 start up issue

Postby jdevane5 » Tue Jul 12, 2022 6:45 pm

So started to take a look at the issue and have a leak from exhaust manifold and manifold to silencer. Will fix both joints and have another go at tick over.

Not touched the main jet yet -And as mentioned in replies will wait on main jet tune until I get it moving...

I have a std air box and duct -How critical is it to connect the 1/4 " clear pipe to the bottom of the air duct and where does it go?
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Re: Series 3 62 start up issue

Postby hullygully » Wed Jul 13, 2022 2:20 pm

could need the pilot upping & slide to a 200 one bud
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Re: Series 3 62 start up issue

Postby Fast n Furious » Wed Jul 13, 2022 11:52 pm

I find it odd that it didn't stop once the plug cap had been pulled off, unless the piston is heavily carbonized?????
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Re: Series 3 62 start up issue

Postby MickYork » Thu Jul 14, 2022 7:41 am

After crashing my scooter, it was laid on it's side revving it's t*ts off. My "friend" ran over on pressed the kill button but to no avail. He then proceeded to rip the wiring out, CDI wires, HT lead, etc. the engine still kept running, after about 30 sec the engine died.

Afterwards we concluded that when the scooter laid on it's side it suffered from fuel shortage but not air flow, effectively copying an air leak. This in turn led to pre-ignition, whereby the heat retained in the cylinder head was hot enough to ignite the new, very lean, fuel. No spark required. The engine then ran out of fuel and cut out.

An air leak would match the posters original scenario.
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Re: Series 3 62 start up issue

Postby jdevane5 » Thu Jul 14, 2022 8:36 am

MickYork wrote:After crashing my scooter, it was laid on it's side revving it's t*ts off. My "friend" ran over on pressed the kill button but to no avail. He then proceeded to rip the wiring out, CDI wires, HT lead, etc. the engine still kept running, after about 30 sec the engine died.

Afterwards we concluded that when the scooter laid on it's side it suffered from fuel shortage but not air flow, effectively copying an air leak. This in turn led to pre-ignition, whereby the heat retained in the cylinder head was hot enough to ignite the new, very lean, fuel. No spark required. The engine then ran out of fuel and cut out.

An air leak would match the posters original scenario.



Would have to say my engine was pretty warm when it continued to run on after the HT lead was pulled.
I have also found a massive air leak at the exhaust manifold last night -So above statement/root cause does fit.

Now waiting on some Locktite 5990 and bought some uprated nuts for the exhaust manifold flange and also noted the Engine cowl was a touch condition with the exhaust manifold so need to modify the cowl slightly to clear the manifold next.

It was a freaky moment!
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Re: Series 3 62 start up issue

Postby Storkfoot » Fri Jul 15, 2022 7:28 am

When you are putting the exhaust back on, make sure the area around the manifold is properly cleaned up with degreaser. On a standard exhaust, I have never used a sealing compound but I do make sure that none of the joins are stressed.

I fit the ubend, then the silencer. If you cannot get the silencer to connect pretty easily (ie not being forced), then you need to look at a solution. The solution could be a new ubend or opening up the holes on the silencer. You may need to untighten the ubend a bit to see where the problem lies.

Standard brass exhaust nuts with M7 flat and spring washers are, in my experience, absolutely fine. I use the standard “copper sandwich” gaskets. Some of the others available are, in my opinion, not up to the job.

Lastly, don’t assume that the silencers and ubend supplied together are a good match. I have had to take off the supplied ubend and revert to old and rusty ubends in the past to get a good fit.
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Re: Series 3 62 start up issue

Postby Storkfoot » Fri Aug 05, 2022 11:40 am

Have you got to the bottom of this yet?
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