LCGB Forums

Looking for some advice really, and I know that you guys out there have most of the answers. I have posted on here before about my Mugello sx186 spitting lots of fuel/oil out of the open carb, 28mm dellorto - all over my panel and floorboard. I tried a remote filter but it just soaked it up and choked it but I do remember reading about people saying fitting a reed valve helps, so my question is:- What would I have to get done in order to have a reed valve fitted and how much is it going to cost me?

Fitting a reed valve requires modification to the inlet port and piston in addition to fitting the actual reed valve inlet itself. You could just bolt one on but I think that might not give the benefit you want. Scootering did a test like this with the LTH manifold some time back and If I recall, without the modifications it didn't make a lot of difference.

Currently your piston controls the inlet of fuel by opening and closing the port. Spit back is caused by too long an inlet duration meaning that fuel mixture is being pushed back from the crank case into the inlet and not pushed up the transfers into the bore.

When you fit a reed valve you want to have 360 degree inlet so that the crank is open to the inlet for the full rotation. Whether the mixture is pulled into the crank is controlled by the vaccum, negative pressure in the crankcase. Fuel shouldn't spit back as when there is positive pressure in the crankcase the reed valve closes.

The piston needs to have material removed from the skit on the inlet side either by scooping the bottom skirt or creating holes in the skirt to allow the fuel through or both. The inlet port itself can also enlarged since there's no requirement to use its size to manage the duration.

A reed inlet block will cost you about £100 - 150, depending on the source, and the modifications to the barrel and piston probably about the same again. It's not a difficult DIY job but you need to know what your doing.

I have done all of the above to my Ron Moss Avanti (225). I used a ScootRs reed manifold (might be difficult to find now) which required the fins to be ground back a bit in order to get it to fit but I think the LYH one might be better in this respect. I matched the manifold to the inlet port but didn't touch the port itself. I then made a tracing of an old TS1 piston to get the position of the 2 windows needed in the skirt and also the raised 'arch' in the bottom of the skirt on the inlet side. I drilled 2 15mm holes for the 2 windows and then used a Dremmel to take them out to the rectangular shape I wanted. The arch in the bottom of the pistom was roughed out with an angle grinder...very gently and finished off with a hand file. All sharp edges were removed with a file. It is possible that I will have lost a bit of high rev breathing and cutting a finger port above the inlet is still an option but for the moment it pulls like a train and is totally tractable right up to at least 65mph (gps) but I haven't wanted to push it until I've dialled the jetting in.

It can be worth getting a reedvalve fitted if more inlet timing is required, but is it necessary ?
There are a few tricks ive learnt when fitting muggy kits and you shouldnt really need one if its set up correctly?

My RT195 spits back a fair amount. MB now do a reed valve conversion which is about £160 for the parts and about the same for MB to do the labour to modify the kit to fit.
I have used a remote filter (Scoots RS - Atomic) on a standard GP air hose. To allow the accumulated oil to drain away then modify to add a drain, two methods.
1/ Cut up an old Presta bicycle tube and take the innards out of the valve. Leave about 5mm of rubber around the valve, poke through a hole in the bottom of your air hose, to create a drain like the old series 2 ones. I glue the rubber inside to the air hose and then fit the valve knurled nut on the outside to secure it.
2/ Or use a Lambretta cable adjuster, same process, grind down the cable adjuster head where the cable sits until it is flat, poke this through the air filter hose and secure with a nut on the outside.

Attach a length of rubber hose to drain away, about 6 inches so it hangs below your running boards.
I've just bought a breathe sweet and elbow, haven't modified that one yet.

good ideas above, but surely the carb will suck air in as well

a.lo wrote:good ideas above, but surely the carb will suck air in as well

That's not a bad thing, kind of what it's designed to do Different if it is after the carb but in front is fine.

Thanks for the feedback guys, Paul I am going to buy another remote filter and give your drain tube a go.

I've a small block Mugello 198 version always run it with a reed valve but just bolt on didn't modify the piston, it runs ok and is reliable but the reed valve certainly impacts performance. I've always wonderd if I should modiy the piston as coaster mentions in this thread. I've also looked on line and there's a video of how you do it and in it also says Cambridge sell the kit with a reed valve and an Imola piston which looks like they do, so long ramble but could I just swap the piston for an Imola.?

Spit back on a reed valve motor can be just as bad as a piston porter. This usually happens as a result of the reeds weakening with age, which delays their closure time permitting primary compression to flow back up the inlet manifold instead of up the transfer ports.
I recently fitted some dual-stage reeds to my 6 petal valve and find that I no longer have pools of fuel-oil on the floor boards any more.
Additionally,
The engine is much more tractable,
There is a significant improvement in the 4.5- 5.0K rev doldrum dead zone, which plagued this engine with my worn 4 petal AF reed valve.
I can safely run a weaker mixture.
The Fuel consumption savings are a welcome blessing.

Only got a 1000 miles on this so far but the prognosis looks very good.
Well happy.

Fast n Furious wrote:Spit back on a reed valve motor can be just as bad as a piston porter. This usually happens as a result of the reeds weakening with age, which delays their closure time permitting primary compression to flow back up the inlet manifold instead of up the transfer ports.
I recently fitted some dual-stage reeds to my 6 petal valve and find that I no longer have pools of fuel-oil on the floor boards any more.
Additionally,
The engine is much more tractable,
There is a significant improvement in the 4.5- 5.0K rev doldrum dead zone, which plagued this engine with my worn 4 petal AF reed valve.
I can safely run a weaker mixture.
The Fuel consumption savings are a welcome blessing.

Only got a 1000 miles on this so far but the prognosis looks very good.
Well happy.

I get quite a bit of spit back on my TS1. it has two stage boyesen reeds. It hasn't done a huge mileage, maybe 700, so I doubt they are worn.

What could cause this?

Fast n Furious wrote:Spit back on a reed valve motor can be just as bad as a piston porter.

Yes and in my case was considerably worse, infant worse than I have ever seen on anything before! Mine was down to poor setup though and once I found someone who knew what they were doing (Chiselspeed) it completely transformed it in every way and with next to no evidence of any spit back.

Indeed, poor carburation set up will exacerbate the issue. As will a carb that is really to big for the motor's level of tune.
What type of reedvalve are you using Dickie? 4 petal? 6 petal?
When you fitted the dual stage reeds, did you use or discard the original deflection plates?

Fast n Furious wrote:Indeed, poor carburation set up will exacerbate the issue. As will a carb that is really to big for the motor's level of tune.
What type of reedvalve are you using Dickie? 4 petal? 6 petal?
When you fitted the dual stage reeds, did you use or discard the original deflection plates?

I've got 4 petals it's an rd350 reed block with the plates removed. I now know that when I had it on the dyno, the pick up wasn't firing consistently and the power curve was consequently "jagged". It's never been back on a dyno since I fixed that. Do you think that could affect set up enough to cause it?

So... when you fixed your ignition did it make any difference to the carb performance?
I use 6 petal, Boysen dual stage reeds in a modified TDR valve with the stop plates still attached in a TS1/200. It made all the difference for me. Only rarely do i need to wash out the sponge RAM filter anymore.