My Blaster recently started idling high/running lean, and I had to do a leak test to find the air leak. As it turns out there was HUGE leak between the carb intake boot and the reed cage... I couldn't get the engine to pressurise with a hand pump: All the air just escaped before I could whip out the soap water 
The cause of this was a warped intake boot, thanks entirely to the genius who owned the blaster before me: Over-tightening the bolts holding the boot on past the recommended torque (8Nm). Well past, since one of the bolts was SHEARED OFF as well!
Anyway, these are the steps I took to fix the problem:
(Step 0 - I'm assuming that you've already lapped or draw filed the gasket face on the cylinder intake, and that it's flat. If not, it can be done in a similar manner to the steps below.)
Step 1 - Buy a new intake boot. HAHA! JK I'm poor, so I had to make another plan.
Step 1B - Lap the rear of the reed cage. Make sure that the thinner-edged side that mates with the intake boot has at least a 3mm (1/8") flat surface all around. I used a 400grit piece of wet-dry sandpaper, with general purpose lubricant (WD40 or similar) on a piece of 10mm (3/8") glass to do the lapping.
Step 2
I fitted the intake boot to the reed cage, and traced around the reed cage with a marker. This let's you see where you need to flatten the surface down to... As you can see, there's only a very thin space around the rubber that will actually seal. The rubber projection on the right of the picture makes lapping the sealing face a bit tricky.
Step 3
Lap the gasket face of the intake boot. The rubber projection makes a figure-8 lapping impossible. The best I could come up with was a "half-figure-8" pattern as shown below. Use the whole edge of the sandpaper sheet and try to roll around the corners of the rubber projection as you go (trust me it'll make sense when you get there! ). The duct tape on the edge of the sandpaper has 2 main purposes: It holds the sandpaper in place, and also stops you from sanding away the corners of the rubber projection. Pro-tip: Run a razorblade or knife down the folded over corner of the sandpaper, to get it as flat to the glass as possible and also remove some of its abrasiveness at the edge. Hold the intake boot lightly on the top of the bolt holes, and turn the boot around every few swipes so you don't remove too much material from one side.
Step 4
Lap slowly and don't apply too much pressure! My intake boot was warped by about 0.5mm and time to lap was about 20min. You'll need to keep lapping until the sealing face shows light sanding lines all the way up to the edge of the rubber, for decent sealing. You've got 4 edges on the sandpaper, so don't be afraid to use them; rotate the paper when it starts getting clogged. You'll see 2 different patterns emerging, because you'll be attacking the boot from 2 different sides. Notice in the picture below how I rolled around the corners to try get the 2 sides as even as possible. It won't be perfectly flat, but it'll be close enough! (The camera flash makes it look worse than it is, those surfaces are actually flat enough that 1 swipe across the sandpaper can remove those lines )
Step 5
Apply your favourite brand of grey to the sealing face of the intake boot. I used Loctite 5699 RTV. I would prefer Yamabond, but unfortunately I need my left leg to change gears No need to slather the gasket maker on the rubber part of the boot: The new sealing face is around the edge. Spread the stuff thin around the metal parts of the sealing face, excluding the empty space shown. It helps to fit the boot before applying gasket maker, and trace around it with a marker so you can see where you'll need sealing.
Step 6
Stick it! and torque down to 8Nm using a crisscross pattern. Leave it to dry at least overnight before leak testing.
I've seen people recommend putting in an OEM gasket and applying gasket maker to both sides... but that seems pointless to me. If the gasket was going to do anything, then why bother with gasket maker too?!
Anyway, this saved me from buying a new intake boot, and after leak testing the engine was 100% air-tight. Hope this helps someone out!
The cause of this was a warped intake boot, thanks entirely to the genius who owned the blaster before me: Over-tightening the bolts holding the boot on past the recommended torque (8Nm). Well past, since one of the bolts was SHEARED OFF as well!
Anyway, these are the steps I took to fix the problem:
(Step 0 - I'm assuming that you've already lapped or draw filed the gasket face on the cylinder intake, and that it's flat. If not, it can be done in a similar manner to the steps below.)
Step 1 - Buy a new intake boot. HAHA! JK I'm poor, so I had to make another plan.
Step 1B - Lap the rear of the reed cage. Make sure that the thinner-edged side that mates with the intake boot has at least a 3mm (1/8") flat surface all around. I used a 400grit piece of wet-dry sandpaper, with general purpose lubricant (WD40 or similar) on a piece of 10mm (3/8") glass to do the lapping.
Step 2
I fitted the intake boot to the reed cage, and traced around the reed cage with a marker. This let's you see where you need to flatten the surface down to... As you can see, there's only a very thin space around the rubber that will actually seal. The rubber projection on the right of the picture makes lapping the sealing face a bit tricky.
Step 3
Lap the gasket face of the intake boot. The rubber projection makes a figure-8 lapping impossible. The best I could come up with was a "half-figure-8" pattern as shown below. Use the whole edge of the sandpaper sheet and try to roll around the corners of the rubber projection as you go (trust me it'll make sense when you get there!
). The duct tape on the edge of the sandpaper has 2 main purposes: It holds the sandpaper in place, and also stops you from sanding away the corners of the rubber projection. Pro-tip: Run a razorblade or knife down the folded over corner of the sandpaper, to get it as flat to the glass as possible and also remove some of its abrasiveness at the edge. Hold the intake boot lightly on the top of the bolt holes, and turn the boot around every few swipes so you don't remove too much material from one side.Step 4
Lap slowly and don't apply too much pressure! My intake boot was warped by about 0.5mm and time to lap was about 20min. You'll need to keep lapping until the sealing face shows light sanding lines all the way up to the edge of the rubber, for decent sealing. You've got 4 edges on the sandpaper, so don't be afraid to use them; rotate the paper when it starts getting clogged. You'll see 2 different patterns emerging, because you'll be attacking the boot from 2 different sides. Notice in the picture below how I rolled around the corners to try get the 2 sides as even as possible. It won't be perfectly flat, but it'll be close enough! (The camera flash makes it look worse than it is, those surfaces are actually flat enough that 1 swipe across the sandpaper can remove those lines
)Step 5
Apply your favourite brand of grey to the sealing face of the intake boot. I used Loctite 5699 RTV. I would prefer Yamabond, but unfortunately I need my left leg to change gears
No need to slather the gasket maker on the rubber part of the boot: The new sealing face is around the edge. Spread the stuff thin around the metal parts of the sealing face, excluding the empty space shown. It helps to fit the boot before applying gasket maker, and trace around it with a marker so you can see where you'll need sealing.Step 6
Stick it! and torque down to 8Nm using a crisscross pattern. Leave it to dry at least overnight before leak testing.
I've seen people recommend putting in an OEM gasket and applying gasket maker to both sides... but that seems pointless to me. If the gasket was going to do anything, then why bother with gasket maker too?!
Anyway, this saved me from buying a new intake boot, and after leak testing the engine was 100% air-tight. Hope this helps someone out!
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