can someone help me with a Lag issue?

OK, I am making a Tycoon and it is working great right now.

When I get into the tycoon about half way through the conveyor belts start to mess up

They start to slow down and pause some, like Lag...

It cause the blocks to pile up...

Now to stop this from happening I changed the drop time to increase the time between drops, just increased the cash of the drops

but no matter what I change the time to it still does the same thing.

How can I fix that problem?

all the code that I have works fine...

just normal drop code as well as normal belt code.. Nothing special.

Dropper code

wait(2)
while true do
	wait(2.5)
	local part = Instance.new("Part",workspace)
	local cash = Instance.new("IntValue",part)
	cash.Name = "Cash"
	cash.Value = 20
	part.CFrame = script.Parent.Drop.CFrame
	part.Size=Vector3.new(1,1,1)
	local nMesh = Instance.new("SpecialMesh", part) 
    nMesh.MeshType = "FileMesh" 
    nMesh.MeshId = "http://www.roblox.com/asset/?id=19059116" 
	nMesh.TextureId = "http://www.roblox.com/asset/?id=19059111"
	a = part
	game.Debris:AddItem(part,60)
end
if a ~= nil then
	wait(5)
	a:Destroy()
end

belt code

while 2 > 1 do
	script.Parent.Velocity = script.Parent.CFrame.lookVector*15
	wait(0.2)
end

any help would be great.... thanks!

Well, your code is fine, but as BestDeveloper said, it could be due to some viruses. Check in your game. See if there are any unnecessary scripts, that could possible create "Fire" or ReplicatedStorage. If you have any Free Models within your place, be sure to check those thoroughly. Here's a script that I made, to go through everything in Workspace, to make sure there is no "Fire". :

-- By Shawnyg

local count = 0

function ClearFire(v)
	for i,v in pairs(v:GetChildren()) do
		if not v:IsA("Model") and not v:IsA("Fire") then
			if v:findFirstChild("Fire") then
				v.Fire:Destroy()
				count = count+1
			end
		elseif v:IsA("Model") then
			ClearFire(v)
		elseif v.Name == "Fire" then
			v:Destroy()
			count = count+1
		end
	end
end

for i,v in pairs(game.Workspace:GetChildren()) do
	ClearFire(v)
end
print('This script has removed '..count..' fires!')