Yt 175 base gasket delete

[92wrangler]

I suspected some piston slap in my 175, pulled the head and there was definitely play, blow by at the ring ends indicates excessive end gap, and I had alot of vibration and smoke. Crank felt good, wrist pin felt good, and Piston and cylinder look great, wouldn't hesitate to clean em up and put it back together. Planning on putting some cabers on it and throwing it together. I don't have any good measurements at the moment, I took it apart before work this morning and had to go. As far as 2 strokes go I'm more familiar with chainsaws so would blow by cause alot of spitback, and how do I I NJ ow if I need to replace the reeds? Also if I do a base gasket delete and have adequate squish how much effect is that going to have? Will my carb run out of adjustment, how will I tune my high jet or is that all taken car of with the idle. How much does the timing usually change after that? Any help would be great, this is all a bit different to me and yet the same. Thanks in advance.

[RubberSalt]

These will toast them selfs without that gaskets. 2 strokes die from air leaks. You'll actually want to do a leak down test after a rebuild with these. air leak = lean condition = melted piston.

As for the other questions, the port timing on these are very conservative. You've also got a massive amount of squish. Either make your own gasket or order 1. As for jetting, You can do a plug chop to confirm your jetting is spot on. If you switch to premix from the oil injections, you'll need to increase your jet 1-2 sizes. The oil injection on these are pretty solid if maintained. As for reeds, you can see if boyesen makes power reeds for these. I forced a set of blaster reeds into mine. Made a spacer at home, and ported the F out the intake to fit them. Nothing looked right, but was. Ran it hard for years.

Vibration on these are expected. The motors were designed for a 125cc set up, then had a 66mm piston slapped into it.

2 stroke jetting has 3 main circuits. Tune the pilot circuit then the main jet, then the needle clip

Idle Circuit: Idle to 1/4 throttle -> this is the pilot jet and your air screw
Mid range: 1/4 to 1/2 throttle -> the needle clip position and the taper of the needle.
Top end:1/2 to full throttle -> Main jet

[92wrangler]

I was planning on doing a gasket out of motoseal, it holds up great on my saws, metal on metal wouldn't do me any good. I'm planning on keeping it stock so ill be keeping the oil injection, though good to know, I may buy one to build down the road. I'll keep the reeds unless in need to change them, just want sure at what point the were condemnable.
As far as the carb goes, you lost me a bit. I saw the low idle adjustment and the idle speed adjustment but I didn't see anything else adjustable, could you elaborate on how its adjusted, or is there somewhere I could find literature on it?

[barnett468]

I suspected some piston slap in my 175, pulled the head and there was definitely play, blow by at the ring ends indicates excessive end gap, and I had alot of vibration and smoke. Crank felt good, wrist pin felt good, and Piston and cylinder look great, wouldn't hesitate to clean em up and put it back together. Planning on putting some cabers on it and throwing it together. I don't have any good measurements at the moment, I took it apart before work this morning and had to go. As far as 2 strokes go I'm more familiar with chainsaws so would blow by cause alot of spitback, and how do I I NJ ow if I need to replace the reeds? Also if I do a base gasket delete and have adequate squish how much effect is that going to have?

.

Why do you want to remove the base gasket, it will not change the performance enough to notice?

What is a "caber"?

What do you mean by "spitback"? If it has a specific problem, describe it in as much detail as possible.

To get a rough idea if the piston has too much play, simply take a piece of notebook paper and make a piece that is 3/8" wide x 2 1/2 " long, then fold it in half and turn your cylinder upside down then stick one end into the cylinder in the front then install the piston in the correct direction then try to push the piston past the paper. If it easily falls through, double the thickness of the paper and try it again.

If it easily passes the single piece of paper, it is definitely worn at least a little. If you can push it past the double piece of paper with just light force, it needs a new piston and probably needs to be re-bored, however, the top will have even more wear than the bottom but there is sometimes a small ridge built up in the top of the cylinder, and if there is, it can not be measured from the top using this method.

If the reeds are not laying flat on the reed block then they are worn and can often just be removed and flipped over and reused.
Post the results.

[RubberSalt]

The lengthy mating surface between the base studs wont hold up with sealant alone. They need a gasket in there. I tried that before. You can make a paper gasket for cheap. Buy gasket material at any auto store and cut your own. Lay gasket paper on the base of the jug (cut the holes for the liner to slide through). lightly tap the edgesaround the jug with a ball peen. This will cut a perfect gasket... Don't go gorilla and dent the base.

[92wrangler]

It would really just save me buying a new gasket, depending on original gasket thickness I would gain a little compression and make the squish a little bit smaller. Again, not by much but if it isnt going to hurt me I'll go for it. I removed the cylinder, and I have motoseal on my bench but I do not have a base gasket.
Spit back Is when fuel spits back out the intake. Not sure if it's due to blow by or not, or if it's normal but I have fuel in my air filter box. I saw blow by marks on the cylinder wall that seemed like a large end gap, I'll have to confirm with a feeler gauge later though. I will also measure piston tolerance and let yall know what I find.

[nmarciano19]

It would really just save me buying a new gasket, depending on original gasket thickness I would gain a little compression and make the squish a little bit smaller. Again, not by much but if it isnt going to hurt me I'll go for it. I removed the cylinder, and I have motoseal on my bench but I do not have a base gasket.
Spit back Is when fuel spits back out the intake. Not sure if it's due to blow by or not, or if it's normal but I have fuel in my air filter box. I saw blow by marks on the cylinder wall that seemed like a large end gap, I'll have to confirm with a feeler gauge later though. I will also measure piston tolerance and let yall know what I find.

With spitback i would check reed valve, could be worn out

Sent from my SM-J727U using Tapatalk

[barnett468]

It would really just save me buying a new gasket, depending on original gasket thickness I would gain a little compression and make the squish a little bit smaller. Again, not by much but if it isnt going to hurt me I'll go for it. I removed the cylinder, and I have motoseal on my bench but I do not have a base gasket.
Spit back Is when fuel spits back out the intake. Not sure if it's due to blow by or not, or if it's normal but I have fuel in my air filter box. I saw blow by marks on the cylinder wall that seemed like a large end gap, I'll have to confirm with a feeler gauge later though. I will also measure piston tolerance and let yall know what I find.

Why do you want to make the squish smaller, the small change isn't going to do diddly squat?

As rubbersalt mentioned, it's a bad idea to run it without a base gasket due to potential leaks.

A feeler gauge will not give you an accurate reading unless it is only around 1/4" wide, plus this is only a rough guide for clearance. Ideally, the bore should be measured at 3 elevations and 2 different clockings at each elevation to determine if it is tapered or out of round.

.

[92wrangler]

Ah alrighty, I'll go your route then, thanks for the heads up, it's never fun learning the hard way. I often do a base gasket delete when I'm building a saw but those top ends are much smaller and have the support.

[92wrangler]

Ok that was what I was thinking, what do you look for in a worn red valve? Do they just lack tension against their seating surface

[nmarciano19]

Why do you want to make the squish smaller, the small change isn't going to do diddly squat?

As rubbersalt mentioned, it's a bad idea to run it without a base gasket due to potential leaks.

A feeler gauge will not give you an accurate reading unless it is only around 1/4" wide, plus this is only a rough guide for clearance. Ideally, the bore should be measured at 3 elevations and 2 different clockings at each elevation to determine if it is tapered or out of round.

.

Well with chainsaws you can take away the base gasket to bump up compression. Maybe he was thinking it would be the same

Sent from my SM-J727U using Tapatalk

[nmarciano19]

Ok that was what I was thinking, what do you look for in a worn red valve? Do they just lack tension against their seating surface

Pretty much, in my yt125 i just flipped them. Ran it like that for a while, but a better option would be boysen power reeds. They arent that much think i paid 17 for mine

Sent from my SM-J727U using Tapatalk

[RubberSalt]

You can hold them up to the light and see a bit of air between the petals and the valve. If there is a tiny bit, and it starts easily, your fine. But to much and it'll get hard to start and the power will start to suck. It'll act rich.

[nmarciano19]

Ok that was what I was thinking, what do you look for in a worn red valve? Do they just lack tension against their seating surface

And while your at it check the exhaust port couldnt hurt to clean any carbon build up out

Sent from my SM-J727U using Tapatalk

[92wrangler]

Awesome, I think the piston and cylinder are ok, my ring end gap was .012 over max spec so I have some new ones on their way, clean everything up and send it, the reeds didn't show any gaps.