LCGB Forums

Morning All - 250 miles into running in a Stage 4 gp 200 lump, clubman & 30mm delly carb, open mouth. A;; going well, running rich but OK, just starting up to 1/2 throttle yesterday, after 10 miles or so, just started to lose all power, spit back out the carb horrendous, hardly kept going, had to nurse home at 5mph with next to no power at all. Today, old fuel out & new fuel in, cleaned carb, checked jetting, changed plug, checked ignition with taking the green wire out, getting a good spark and compression but will just not start, backfiring from exhaust, a couple of farts out of carb, oily residue in end of pipe now. I swapped another 30mm carb from another scoot and exactly the same. It's relatively new BGM stator in it, only about 10k mile on it. I've also

The only change I have made has been fitting a new kickstart piston and adjusting the kickstart to give me a full range of kick. Any obvious starters for 10 to check before I drop the engine and get into it? Happy to compile a checklist to work my way through but I'm thinking

Woodruff Key sheered (but i'm getting a good spark)
Stator shifted & timing out?
Stator packed in on way out
Blown Cylinder Head Gasket?

Thoughts & direction . corrective advice appreciated -- Cheers Granty

Head gaskets. They don't even qualify as a 'last resort' for a face-to-face joint. If the head is somehow spigotted to the barrel. then they can be used as a packing to optimise squish, but that's it.

Somehow, I've 'got by' building engines for over 45 years without them & never had an engine in with them fitted that doesn't seep @ least a little....

What was your squish? What head gasket thickness did you use?

Hopefully that will be the problem. Have you looked down the inlet to ensure the skirt remains?

As for woodruff key, did you lap in the tapers? If a key shears it is due to O E (Operator Error) but even that will not stop a spark being generated.

First port of call for me would be to check woodruff key; easy to do and symptoms suggest that it could be the culprit. Easy one to rule out.

Granty wrote:will just not start, backfiring from exhaust, a couple of farts out of carb, oily residue in end of pipe now.

Sounds like my tuned P2 very early 90's after a heavy seize on the Oxford ring road
turned out the fly wheel kept turning when the piston had welded itself to the nikasil bore

OK Guys -- wee update so far after 250 miles running in with no problem, just up to 1/2 throttle now, been running rich but that's OK, conked out & won't start
- Fuel changed out
- checked and swapped off a working bike plug, cap, lead, CDI
- Carb off & cleaned & swapped for working carb off another scooter
- Tested stator with multi-meter (readings good as per Sticky & others help)
- Flywheel off, woodfruff key good, stator has not moved or come loose
- Leak test done & solid
- Compression is good and the same as previous

When going through checks symptoms remain the same, wants to start, will fire but just die after seconds & will not rev out, couple of backfires.

- Only 2 x things left I think
1. Stator is breaking down under load
2. Top end off to find ??????????????????

The good money's on the stator !!!

When the engine stops running when it gets warm, it is quite plausible that there is a problem with the pickup.

A simple compression check first to confirm you have a reading greater than 75psi will point you in the right direction before strpping anything down .

Granty wrote:- Compression is good and the same as previous

will fire but just die after seconds & will not rev out, couple of backfires.

You say it backfires but if it sounds more like a wet fart then it could be blowing past the rings, As already said, get a compression tester, you foot isnt accurate enough

coaster wrote:

Granty wrote:- Compression is good and the same as previous

will fire but just die after seconds & will not rev out, couple of backfires.

You say it backfires but if it sounds more like a wet fart then it could be blowing past the rings, As already said, get a compression tester, you foot isnt accurate enough

Good Intel there, the backyard is a real sharp bang, no soggy farts to be heard here, loud, crisp job

Granty wrote:

coaster wrote:

Granty wrote:- Compression is good and the same as previous

will fire but just die after seconds & will not rev out, couple of backfires.

You say it backfires but if it sounds more like a wet fart then it could be blowing past the rings, As already said, get a compression tester, you foot isnt accurate enough

Good Intel there, the backyard is a real sharp bang, no soggy farts to be heard here, loud, crisp job

I don't think he was implying that you aren't a virgin.....

Any update??

gaz_powell wrote:Any update??

New stator fitted today and 1st kick, away. Although the stator measured up ok it must have been breaking down under load. Timing set and back in the game. The Ks to everyone for their help, G

I'm convinced that the pesky Lambretta CDI stator plate is the most unreliable part on the machine.
I've seen the bloody things fail from new before the bike got to end of my street.

Fast n Furious wrote:I'm convinced that the pesky Lambretta CDI stator plate is the most unreliable part on the machine.
I've seen the bloody things fail from new before the bike got to end of my street.

This one was in the scooter 6 year I think and had a few 1000 clicks on it.

Granty wrote:

gaz_powell wrote:Any update??

New stator fitted today and 1st kick, away. Although the stator measured up ok it must have been breaking down under load. Timing set and back in the game. The Ks to everyone for their help, G

Brilliant! Nothing better than when you know you've solved it