New kit, cylinder has a hole.

thaifoo

New Member
Aug 15, 2019
4
0
1
40
Hello. I bought a new kit off of amazon from bbr. It's the second kit I've installed but I'm still pretty new. This new kit got finished up yesterday and I test ran it for about 5 miles. Firstly, it wouldn't stay running unless I held the throttle open. I adjusted the throttle cable and it stayed running. Second it had hardly any power. After doing some searching and reading I was sure it had an air leak. I checked around the carburetor and while looking, I saw a leak on the cylinder itself. While running I can see it bubbling out of a pin hole. So I'm planning on contacting the seller on amazon and asking for a new cylinder, should I be requesting a new piston, rings, and gaskets too? Like a said I'm new and I'm not sure if all these things need to be replaced together. I took the head off and felt inside the cylinder and can't feel any cracks. BTW I'm running opti 2 70:1 for the first tank then 100:1 after that. I've done that on my pk80 with no problems. I've attached pics of the inside and outside of the cylinder.

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Greg58

Well-Known Member
May 1, 2011
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Welcome to the forum, from the first picture I take it is leaking between the fin above the intake. From the looks of the inside I would request a complete top end, looks like you had a lot of medal shavings or something hard in side the engine when you started it. The third picture looks to have some debris marks near the ports.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
6,782
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Los Angeles, CA.
Tiny flaws in the cylinder castings are very common & don't usually cause any real performance problems...
A 'air leak' will cause the idle to be way too high with no way of bringing it down by carb adjustments).
The tiny hole you have probably isn't affecting the performance (but will make your engine very dirty over time).

It looks like you burned up the chrome lining on the cylinder walls... :(



Also...I don't recommend using that oil for break in... use a standard 2-cycle oil at 32:1

Another thing to mention is that when you take off the head, you need to properly torque it back on (12 ft/lbs) or else you'll warp it & cause a leak at the head gasket!
 
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thaifoo

New Member
Aug 15, 2019
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Did you try to clean up the ports before starting it??
It's hard to tell from these bad pics, but it looks like someone tried to clean up the edges of the exhaust port??

I did not do anything to it. But this is the kit I ordered. Bbr probably did if they're the ones that opened the transfer ports. I tried to set up an exchange but amazon wasn't able to send a replacement so they just refunded my money. If I get new top end I should be good to go? Screenshot_20190818-091051.jpg
 

thaifoo

New Member
Aug 15, 2019
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As long as you get the same type piston that you have now and the port timing is the same between the two cylinders it should work.
Thanks for the reply. I finally had some time away from work and took the cylinder off. It feels rough on the edges where the transfer ports were opened up. Anyway, the intake is 40mm, I have a low hole piston, any idea on what I should be looking for to match the timing? Thanks


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thaifoo

New Member
Aug 15, 2019
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40
OK here's an update. Instead of starting a new thread I'll just continue the story here lol. I never got the issues squared away on the first engine, since amazon refunded my money I just bought a new kit. My plan was to just swap the engines out since I had everything installed already and maybe use the blackberry engine as a backup once I bought a new top end for it.

I bought a runwell pk80 that had some port work done and a few upgrades. It was on sale. I got it swapped over and it runs poor until it gets up to around 18mph then it runs great. So around 18mph and and up it has tons torque, and very responsive. It's faster than my other pk80. At low speeds it's jerky and I believe sputtering is the term. I have to give it wot to get up to speed and it's slow to get there. I combat this by feathering the clutch at low speeds but it still runs poor.

I ran 1/2 a gallon using opti 2 50:1. Now I'm running 100:2 with no difference. I know this can be a controversial oil to use and I admit 2 out of 3 motorized bikes that I've installed have ran poor. First one has around 150 miles on it and runs so smooth. I am new at this and it probably user error, but learning has been fun. So anyway, I had all new parts from the second kit, some are nicer, so I just went ahead and tried to troubleshoot. Nothing has helped. Here's some things I've tried.

Changed muffler and gasket. It had a leak at gasket.

Sprayed starter fluid where cylinder and intake meets. It revved up.

Changed intake manifold and gasket. Manifold that got swapped out looked like it wasn't perfectly flat.

Added o-ring to carburetor/intake

Changed throttle cable and grip. Reason is, I had an issue with the cable sticking.

Changed cdi, wire, and spark plug boot. Tried 2 different spark plugs, B8HS and stock runwell plug. B8HS came with kit as an upgrade but I would think that's too cold of a plug. Plug boot is ngk and wire is good stuff.

Changed fuel filter. First one had a leak.

Made sure tank had good flow

Tried both nt and speed carburetor.

Torqued head bolts to 12 pounds. Rechecked.

Moved clip up to top notch on carb needle. It has 4 slots, it was 1 down from the top.

It could very well be just running poor becauses it breaking in. It probably has 40 miles on it. I didn't experience this on my first pk80. But it did continue to start running better and better as time went on.


If it had a air leak, or loss of compression, wouldn't just run poor no matter the rpm? Like I said this is just happening at lower speeds/rpms. Any insight would be great. Here is a description of the kit upgrades that came with it. I'm using a 44t sprocket instead of the 41t.

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Maphew

New Member
Sep 3, 2019
5
12
3
Missouri
Hey thaifoo is there any play in your throttle cable? Maby tighten set screw a hair or 2. BUT most likely (just imo) its iether your fuel mixture or carb setting. If u have checked for all leaks then u have combustion, if it starts then u have spark, so all thats left is air/fuel and type of fuel used. I would drain the tank and refill with break in mix using generic 2 stroke oil. These engines DO run better longer with a little higher quality oil and fuel but break in period is just to get all the parts comfy with each other essentially. Then go to ur needle , I'd start dead center on the clip and go from there.
Here's a link that does a decent job explaining how to adjust nt carb and y. Hope this helps man!

https://motoredbikes.com/threads/nt-carb-tuning-basics.24867/