Bubbles in coolant with cap off at idle/blipping throttle

[JZ05220r]

I just put my stock cylinder head on yesterday for testing. I used a fresh head gasket and dried the sealing surfaces with a rag. I added coolant and used the bleed screw on the head to get the air out. I started it with the cap off and noticed some bubbles coming up. Figured it was just extra air that was still trapped somewhere. Today I rode for about an hour. I let the bike cool for 15 minutes and carefully removed the cap to double check. When I started the engine I saw more bubbles come up. Not sure how to test the cooling system for leaks. I did loosen one of the water pump bolts the other day getting it confused with the drain screw and lost a bit of coolant. Probably head gasket leak but im not sure how to prevent it next time. https://youtube.com/shorts/yv2vXcoK3xY?feature=share

[SS109]

Yeah, looks like a head gasket leak to me. I assume you used a torque wrench, torqued to factory spec, and then went all the way around head again and made sure they were to spec, yes? If so, either the top of the cylinder or the head mating surface isn't perfectly flat. Odds are it's the head as it's much thinner than the cylinder. I would send the head off to be fixed and correct the squish while you're at it.

[JZ05220r]

Yeah, looks like a head gasket leak to me. I assume you used a torque wrench, torqued to factory spec, and then went all the way around head again and made sure they were to spec, yes? If so, either the top of the cylinder or the head mating surface isn't perfectly flat. Odds are it's the head as it's much thinner than the cylinder. I would send the head off to be fixed and correct the squish while you're at it.

Yes I did use a torque wrench. Also it ran pretty good in 85 degree weather yesterday so I was pretty happy about that. If you ride it sorta like a 125 keeping the revs abut higher than a stock bike it really isn’t that bad. You just can’t twist the throttle too hard off idle because the torque curve has moved up with the porting. Thanks

[SS109]

I have to admit, I don't like a Fredette ported cylinder on a 220. Seems he likes to port them to run more like a 200 and you end up losing the low end torque that 220's are known for.

[JZ05220r]

[album][/album]

I have to admit, I don't like a Fredette ported cylinder on a 220. Seems he likes to port them to run more like a 200 and you end up losing the low end torque that 220's are known for.

I can see how it would be great for riders who like to stay on the pipe, keeping their momentum. For riders riders who won’t the best of both world I think the stock 220 cylinder porting is great with the correct bolt pms. I have a cylinder coming in the mail that I will have repaired and replated. For now I can manage with the stock head and frp porting. Theirs nothing wrong with the RB head but it seemed to accentuate the power characteristics of Jeff’s porting. Running the stock head seemed to smooth out the hit. Also there is a noticeable clean band on the outside of the piston which I’m told can indicate too much squish.

[SS109]

When you go back to the stock cylinder I would put the RB head back on. It really helps with low end grunt IME.

[JZ05220r]

When you go back to the stock cylinder I would put the RB head back on. It really helps with low end grunt IME.

That’s the plan. Also I’m not positive about this, but I remember both times I got the engine back from Fredette the first time after rebuild, and the second time after the crankcase leak was resealed the bike would run great for the first ride then start to run badly. Maybe the squish is too extreme and was exposed once the rings seated. I don’t know if that logical or not but it certainly ran better. I could tell he honed the cylinder both times based on the ring gap markings faded when I got it back the second time.

[JZ05220r]

Still bubbles not as bad but they are there. I ended up sanding over a flat glass surface. With a new head gasket the problem is still there. Looks like I’ll be having the head resurfaced professionally.

[SS109]

Bummer. Did you sand the head, the cylinder, or both?

[Molly's 70]

Have you pressure tested your cooling system for leaks?

[JZ05220r]

Bummer. Did you sand the head, the cylinder, or both?

I just sanded the head. I would think the cylinder should be fine as Jeff had it last year and wasn’t leaking with the RB head.

[JZ05220r]

Have you pressure tested your cooling system for leaks?

I have not and am unsure how to do it. I have done a leak down before I messed with the head and the results were great. I even checked with the cap off to make sure there were no bubbles.

[JZ05220r]

I sanded head down a second time, threw it on, bleeded the air out and ran it for while today. Noticed that the coolant level in the expansion tank went down about a 1/2 inch. It’s now at the low mark. I’m hoping it was just extra air. Next ride I’ll check again and if it’s below the low mark I guess I’ll know for sure.

[JZ05220r]

Well the site crashed and I lost a lot of the posts I made.

[Chuck78]

Same... bummer. I typed a VERY lengthy and detailed post last night about fitting a Lectron Billetron Pro carb. Haven't heard from the admins yet to see if any of the posts since June 16th are backed up anywhere. Crossing my fingers.

[JZ05220r]

Same... bummer. I typed a VERY lengthy and detailed post last night about fitting a Lectron Billetron Pro carb. Haven't heard from the admins yet to see if any of the posts since June 16th are backed up anywhere. Crossing my fingers.

I know hopefully they can update us.

[JZ05220r]

I did throw on another head gasket again today. I used the tusk aftermarket style. I haven’t checked for bubbles yet. I did decide to take it for a ride since I had nothing else to do. I don’t think it’s effecting performance anyways but I will still be sure to sort it out in the future. I did notice something while riding that has been a problem but I just haven’t been able to describe it in the past. When I accelerate and rev to mid/hi rpm and immediately bring it to partial throttle, the exhaust note becomes extremely pingy, sounds terrible and momentarily runs very rough. I went up on the pilot from 38 to 42. I decided I’d be better off going up a couple sizes considering how terribly lean it sounded and felt. It did not help with the issue one bit. Weird because when I do the same thing but go to fully closed I hear just the absolute minimal amount of pinging if anything. A situation where this happens is when I’m approaching a hill climb in the woods that becomes rough right after the terrain transitions upward. I come toward the hill ripping and once I start going up I have to dial back on the throttle considering how rough and rocky it gets. I don’t know what the heck could cause this but that can’t be right.

[JZ05220r]

I just checked and the bubbles are much much smaller now. I mean they are like a speck of sand so it clearly is head gasket related as I have sanded and sanded at the head between each head gasket I have tried and it’s gotten better and better each time. But still very unhappy with the way it is performing. I mean it’s good here and bad there it’s like it has 2 personalities while I’m riding. The pinging is very annoying and it runs extremely bad when it sounds that way. I have my carb sealed nicely, really not sure what I’m dealing with. I do not understand why it pings terribly when coming off full throttle to partial throttle and isn’t really a problem going to closed throttle. The only thing I could think is the power valve closes too slow when I don’t let off completely.

[JZ05220r]

I think the running issue could very well be kips related. I started it and revved it while monitoring the mover below the cap. It took a second before I was able to get it to free up and open. There is a slightly hang up I notice while it is returning as well. I have felt it by hand in the past disconnected from the advancer and it seemed ok but maybe not. Maybe some lapping compound would work well on all of the contacts if I choose to take it apart. Also the first couple minutes of warm up always feel like the power valve isn’t opening now that I think about it. I always considered that being the engine needing to clean out.

[Chuck78]

If it is power valve related, and it's hanging up and slow to close, it could be gummed up from premix oil and needing the valves dismantled and cleaned extensively...

That'd also give you another opportunity to do a final lapping of the head gasket surface. A sheet of glass is the common DIY method, but I'd do MDF countertop material + glass on top, then 220 grit rectangular orbital floor sander sheets is what I've used for 4-cylinder heads. With a single cylinder 2-stroke head, a large sheet of 220 wet sanding paper will be perfect.
Just a sheet of glass on a work bench surface I might be critical of the flatness of. Tempered glass is better, but tempered glass on top of thick mdf sheets and checked with a machinists straightedge and feeler gauges for flatness is the only way I'd trust it.

My "surface plate" that I use is a large chunk of stone countertop material that's milled perfectly flat and polished, checked with a Machinist's straightedge, + 220 floor sander sheets. I was a huge skeptic of this at first, and very critical of it on my DIY attempts, but the results really spoke for themselves when scrutinized under my critical watch.



When you let off the throttle and it runs badly as you say, is the running badly just all in the sound of the engine, or does it buck and misbehave, and act up as you roll the throttle back on to begin accelerating?