Symptoms of broken or bent reeds.

[Storkfoot]

Am I correct in assuming that poor starting and an inability to set tickover is a strong indication that my reeds at least need looking at? It also “misses” occasionally further up the rev range. Reeds have done 2000-3000 miles.

It’s a GT186. Carb is a Mikuni TM24 (replaced a PHBH30) but I suspect the other significant change was the exhaust - it’s now a Ron Moss avanti which revs quite a bit higher than the old early Mb/ bgm Clubman.

[Leotech]

If it's only a crack or split then yes, poor starting, no tick over, misfire type / rich jetting type sounds, maybe backfiring type symptoms at specific revs. I had this on a TS1 about 15 years ago and I was convinced it was the ignition breaking down. It wasn't it was a vee shaped split in the reeds, 5mm at the tip down to nothing at the fixed end.

If there is whole petal missing it will be impossible to kick start. If you get it revving high enough it will bump start and keep running at a very specific RPM, usually quite high as its got 360º inlet timing being a reed motor with missing reeds, You'll get loads of spit back so need to be revving high enough to overcome all the extra fuel. When the piston comes down towards BDC it forces the unspent charge back out of the inlet port (least resistance) rather than up the transfers.

About 4 years ago I broke a reed (complete petal ingested) on the way to Hawes one morning for breakfast, I managed to bump it on one of the big down hills and ride all the way home about 50 miles just keeping the revs up but it was very slow. I stalled it once but fortunately I was on top of The Pennies just near Ribblehead Viaduct so had a big hill to get the revs up enough to bump it.

Its worth a quick check before you start getting too carried away looking for air leaks etc.

[Rich Oswald]

Had exactly that today but starting was ok but needed throttle to keep it ticking over. Eight mile ride home gradually got worse, very lumpy running. Struggled home, changed a very oily plug. Kicked it up fine but on revving, two big backfires and a piece of petal spat out of carb mouth. LTH reed block with only 500 miles on it!

[Storkfoot]

Thanks for that. Some of what you say does resonate with what is happening here. It’ll start but rarely with the throttle closed. I also noticed that the bellows were getting more spit back than normal on a Reed valve engine but I managed to convince myself that this was just because I didn’t have it jetted right or the float was set at the wrong height.

The “missing” at high revs seems to almost mimic a slipping clutch but it is a 7 plate LTH which I have checked. An air leak test was done when the reeds were changed and there is no visible signs of a leak now.

This is the first set of reeds I have ever had go, probably as I do replace them quite regularly. Thinking about it, I did have a backfire whilst revving on the stand. Also, whilst the reeds aren’t that old, those 2000-3000 miles have been done at high revs mainly.

I’ll have a look next week and report back. It’s due to go on the dyno next Friday so I’ll need to get a shift on.

[hullygully]

can you sick a camera down there to confirm, Ive had same but mine was a sweaty push to mates garage

[Storkfoot]

can you sick a camera down there to confirm, Ive had same but mine was a sweaty push to mates garage

Another thing that has occurred to me. I did notice some orange “stuff” come out of the float bowl. It didn’t occur to me at the time but I used an orange coloured sealant on the cage. It all points to….

[Rich Oswald]

Changed mine, one petal was totally shot to bits. Any idea why this would happen in less than 500 miles?

[Leotech]

Changed mine, one petal was totally shot to bits. Any idea why this would happen in less than 500 miles?

The reed may be hitting something in the inlet tract, I have LTH reeds on 2 of mine and had no issues at all, not that that helps you in the slightest. My broken reeds were on another engine configuration.

Also jetting can cause reeds to break, too rich usually and ignition timing, too advanced.

[Rich Oswald]

Changed mine, one petal was totally shot to bits. Any idea why this would happen in less than 500 miles?

The reed may be hitting something in the inlet tract, I have LTH reeds on 2 of mine and had no issues at all, not that that helps you in the slightest. My broken reeds were on another engine configuration.

Also jetting can cause reeds to break, too rich usually and ignition timing, too advanced.

Only just been on the dyno so jetting should have been ok. Didn't appear to have been hitting anything and motor was tuned and built by a race tuner. Maybe just one of those things as I have an LTH on another motor which I bought second hand off Sticky and that's been fine.

Rich'

[Storkfoot]

Well they are not cracked or broken but they are looking tired.

I have put a torch behind it so you can just see that there is a noticeable gap on one side. Would the symptoms I mentioned in the opening post be solely as a result of this?

[Fast n Furious]

The 186 uses a reed valve from a very high revving kart engine and is not really suited for use in a lambretta. Consequently, they are known for breaking the top reed petals.
The recommended solution is to "double up" on the top petals.

[Storkfoot]

The 186 uses a reed valve from a very high revving kart engine and is not really suited for use in a lambretta. Consequently, they are known for breaking the top reed petals.
The recommended solution is to "double up" on the top petals.

I did double up on the top ones. It’s the bottom that has bent outwards. I’ll double up both sides when I replace them.

To be fair, this engine has done many thousands of miles here and in Europe. This is the first time I have had, by the looks of it, any problem with the reeds. That said, the Ron Moss Avanti exhaust allows it to rev higher than it has previously.

[Leotech]

The 186 uses a reed valve from a very high revving kart engine and is not really suited for use in a lambretta. Consequently, they are known for breaking the top reed petals.
The recommended solution is to "double up" on the top petals.

I did double up on the top ones. It’s the bottom that has bent outwards. I’ll double up both sides when I replace them.

To be fair, this engine has done many thousands of miles here and in Europe. This is the first time I have had, by the looks of it, any problem with the reeds. That said, the Ron Moss Avanti exhaust allows it to rev higher than it has previously.

I doubled up on mine that kept braking the reeds as advised, mine then broke on the side I didn't double up on, it lost a certain amount of "perzazz" in the low to mid power with doubled up reeds.

[Storkfoot]

My eyesight must be going I had doubled up on both sides. However, I have discovered today that there is a right way and a wrong way to fit the reeds. There is a cut out in one corner and these must be placed in opposing corners of the Reed block.

Edit: the cutout must be to the left on both sides. Perhaps this should be referred to when you buy Granturismo kits. I have never seen it in writing anywhere and I have had my GT186 for the best part of ten years.

[Fast n Furious]

Ooops.

[Rich Oswald]

My eyesight must be going I had doubled up on both sides. However, I have discovered today that there is a right way and a wrong way to fit the reeds. There is a cut out in one corner and these must be placed in opposing corners of the Reed block.

Edit: the cutout must be to the left on both sides. Perhaps this should be referred to when you buy Granturismo kits. I have never seen it in writing anywhere and I have had my GT186 for the best part of ten years.

There was a cut out on both sided on my LTH one's. Martin Cook's advice was not to over tighten the securing screws as it makes them open up prematurely. He said just barely tighten and use locktite.

Rich'

[Storkfoot]

My eyesight must be going I had doubled up on both sides. However, I have discovered today that there is a right way and a wrong way to fit the reeds. There is a cut out in one corner and these must be placed in opposing corners of the Reed block.

Edit: the cutout must be to the left on both sides. Perhaps this should be referred to when you buy Granturismo kits. I have never seen it in writing anywhere and I have had my GT186 for the best part of ten years.

There was a cut out on both sided on my LTH one's. Martin Cook's advice was not to over tighten the securing screws as it makes them open up prematurely. He said just barely tighten and use locktite.

Rich'

Thanks, Rich. That makes sense.

[martyn dwane]

There was a cut out on both sided on my LTH one's. Martin Cook's advice was not to over tighten the securing screws as it makes them open up prematurely. He said just barely tighten and use locktite.

Rich'[/quote]

i Have a LTH reed assembly, need to get some new reeds , any idea which ones fit ?

[Rich Oswald]

There was a cut out on both sided on my LTH one's. Martin Cook's advice was not to over tighten the securing screws as it makes them open up prematurely. He said just barely tighten and use locktite.

Rich'

i Have a LTH reed assembly, need to get some new reeds , any idea which ones fit ?[/quote]

If you just mean the petals then easiest thing is to get some Polini sheet and cut out your own.
This is the advice I got:-


When you mark them out just tape the old reed down onto the sheet of reed and scribe around the edge if the reed your copying. Use sharp scissors to cut the reed close to the scribed mark, then finish off with 400 wet and dry paper up to the scrobed marks.

I use a diamond burr on a dremel to make any holes for securing screws or any necessary indents depending on type of reed.

Rich'

[martyn dwane]

Thanks Rich