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I’ve got this what appears to be leak coming from around the reed cage, will this https://www.motosport.com/boyesen-rad-v ... -X001-Y006 be the right part to solve that? It’s weird though I’ve sprayed starter fluid around it while the bike is running but no idle change.

My other question can somebody point me to the right gauge to measure the cylinder wall so I can size the correct piston for a top end rebuild. This is my first time doing this so I want to make sure I’ve got my ducks in a row and don’t blow the bike up with the wrong piston size.

Thank you guys and sorry for the noob questions

I have a genuine Mitutoyo dial bore gauge in inch sizing, I wish I had a metric version, but this will do just fine with the use of a calculator... Beware however that there are a large amount of what appear to be counterfeit metric Mitutoyo dial bore gauges on eBay and elsewhere for significantly lower prices than a genuine sells for.

I think your best bet for the money would be just to take the cylinder to any automotive machine shop or any machinist in general, or most good bike shops, and have them measure it for a small fee.
A good dial bore gauge will set you back $200. Perhaps the knockoffs will measure just as well, I have been using a Harbor Freight dial indicator and analog calipers for years, and the calipers I always compare to my genuine but very well used Mitutoyo and get basically the same measurements...

Clean all that dirt off and see where it returns.

Like said above, just take it somewhere if you are just doing it one time.

If starter fluid did nothing then you don't have a leak at that boot. Like KDXGarage said, Clean it off and run it and check.

I would check your cylinder wear while you're at it to see if a replate is on the radar.

KDXGarage wrote: 01:56 pm May 30 2025 Clean all that dirt off and see where it returns.

Like said above, just take it somewhere if you are just doing it one time.

Thank you, I’ve cleaned it and after each ride it always accumulates right here around the edge of the boot going into intake side. I find it strange however that when it’s running and I spray starter fluid around that flange there is no change in idle. It definitely seems a little wetter on the lower part of this. I will wash it today and ride tomorrow and observe it throughout the ride.

Chuck78 wrote: 01:33 pm May 30 2025 I have a genuine Mitutoyo dial bore gauge in inch sizing, I wish I had a metric version, but this will do just fine with the use of a calculator... Beware however that there are a large amount of what appear to be counterfeit metric Mitutoyo dial bore gauges on eBay and elsewhere for significantly lower prices than a genuine sells for.

I think your best bet for the money would be just to take the cylinder to any automotive machine shop or any machinist in general, or most good bike shops, and have them measure it for a small fee.
A good dial bore gauge will set you back $200. Perhaps the knockoffs will measure just as well, I have been using a Harbor Freight dial indicator and analog calipers for years, and the calipers I always compare to my genuine but very well used Mitutoyo and get basically the same measurements...

Thank you, so if I did buy this dial gauge I’m assuming having it in metric is better for this application? Good call on the machine shop I didn’t think about that.

Any chance your carb vent tubes are split open and spraying fuel onto the bike??

If this is the only time you see yourself messing with a dirt bike engine, let somebody else deal with it.

On the other hand, if you see yourself where this will be the first of many, I suggest you get your own precision measuring tools and do the work yourself.

Yes, precision dial bore gauges are nice, but the more common way is to use a telescope gauge and a 2 - 3" OD micrometer, or if you prefer metric, a 25 - 50 mm OD micrometer.

I haven't checked prices on these tools lately, but you should be able to get the set of telescope gauges, and the micrometer for about $35 each. At these prices, they won't be suitable for aerospace work, but for measuring cylinder bore wear, and piston skirt to cylinder bore clearance, they are all you need.

In these cases, the actual diameter measurements don't really matter. What you're really interested in is the differences in the cylinder bore measured in several places, and the difference between the cylinder bore and piston skirt diameters to get the clearance.

A typical telescope gauge set will let you sweep bores from around 0.5" out to around 6", or of course the metric equivalent. Then when you need to measure a larger or smaller bore, just get the appropriate OD micrometer.

Once you get used to using these tools, its surprising how often you'll use them.

And while you're at, get yourself a 0 to 6" vernier caliper. I prefer the conventional type rather than the dial or electronic type. No batteries to go dead or pinion gears to jump a tooth requiring setting the zero to some odd angle. I am using a vernier caliper that was new in the early 1960s and it's still going strong.

If you're wondering how to use these tools, youTube videos will show you how.

KDXGarage wrote: 01:11 pm May 31 2025 Any chance your carb vent tubes are split open and spraying fuel onto the bike??

That's a great point, as well as maybe a slight chance of an over-oiled air filter dripping oil down out of the airbox drain rubber check valve type piece and allowing it to splatter in that area by chance. More often, and over oiled air filter will lead the person to see a spot on the floor in their garage and think that perhaps they're shock is leaking... Been there! My buddy has done this repeatedly, and it was about the third time that I told him it's just his air filter, when he actually believed me...

Is your crankcase vent tube installed? It should run from the little bung behind the kickstarter up to the airbox.