Slanthead Tuning

Junster · #1 06-10-2009, 02:43 AM

I've been doing alot of reading on 2-strokes, squishbands, plug orientation, compression. My motor is a zoom 80 with slanthead. It came with 2 thin headgaskets. Now that it is well broken in I have been fooling around with stuff. I had removed one of the head gaskets with no clearance issues. Leaned the needle all the way to the top notch with the clip. It was running pretty well at WOT but I had it too lean at mid so the second notch is best for mine. I also started having a pinging sound I thought maybe the piston was hitting the head. But I opened it up a couple times and it isn't. The problem was too much compression causing predetonation. I've gone back to 2 headgaskets and that went away. I tried higher octane gas but it really made little difference. Maybe once the cylinder gets worn one gasket will extend the life. I'm having good luck with a NGK b7hs cooler plug, seems like I have more low torque with the same top end speed. With the head off and the plug in the firing area is nearly centered in the compression chamber so I don't think mounting it either way would matter. It's running the best it ever has now. Still planning on a expansion chamber to give it a little more on hill climbs. I'd appreciate hearing what's working for you. Especially with aftermarket carbs. There's only so much you can do with the stock one. I been following the carb threads but haven't seen anyone really say ok this is the one. This is the carb I've been looking at. Anyone using this one?

49cc / 47cc Performance Carburetor / Carb Pocket Bike:eBay Motors (item 140322240326 end time Jun-20-09 07:39:12 PDT)

Goat Herder · #2 06-10-2009, 03:18 AM

I originally ordered a head from those guys. I to had a pinging sound as well with one gasket. Sad to say that motor sprung a bearing seal leak at the out put drive sprocket bearing seal. So now I am on a Zoom engine as well The bearing/seals look of a diff design than I have recently paid attention to. The Zoom engine was of a bit of a fit I was having and Knowing of entertaining Chinas The heads were not available at the time. So I ordered a complete kit. The original motor ran hella strong. I did re jet to .029 thousands on the carb. The new motor breaking in already runs much like the old one. No scavenging at all unless the engine is still cold once warmed up .............250 pounds I am 85 pound bike = If shifted right in one neighborhood block 30 plus miles an hour on a average day. I have a SBP j shaft too with some mods. They were not entirely necessary BUTT I am a big boy!

Junster · #3 06-10-2009, 03:36 AM

Goat Herder, Are you getting a gear whine, vibration, rattley noise from the clutch/drive gears? This is my only ***** with this motor. I can't seem to get it to stop but then I've heard all the brands do it? Does yours?

Goat Herder · #4 06-10-2009, 03:51 AM

Yeah I have personally seen six do it. Its like a unmatched Chevy starter for the shims wrong! Keep it oiled and wiped cleaned etc with bearing grease. I never saw one die. Yes the noise is annoying. Pamper things Keep it clean and oiled. It will change pitch on you quieter. It is what it is. Far as my experience never ever Brock that part. It just made noise. My prob was freak vacuum leaks , but I Truly beat the bujusus out of my stuff for playing. I mean at some point its working great if you just save some for tomorrow. Well ya get my signature LOL. I don't always practice what I preach. But somehow we should all care!

Rockenstein · #5 06-10-2009, 04:52 AM

Junster if you look at the attached pic and read the text the slant head design itself could be the source of the ping...reducing compression as you found out would help but that kinda defeats the purpose right. I've not seen the inside of a Chinese slant head, does it have a squish band or is it like what is pictured? Reason I'm thinking about your experience with the slant head is that my brother is getting a zoom slant head engine for his build and I as well was thinking of getting one at the same time for my next build. Maybe I'll order a couple spare plain jane heads just to avoid any headaches...lol

BTW I too find our little motors like the cooler plugs...I've been running a B9HS and it gave loads more grunt than a B6 or a BP6 and the cylinder head temps were much lower too than with the 6 heat range plugs.

Junster · #6 06-10-2009, 06:16 AM

It does have a squish band. Next time I have it off I'll take a pic. It's about a 1/4" to reduce the chamber area. As far as the compression it raises it pretty good. Just going with one headgasket on my motor instead of the two it came with made it too high. I'd totally tell you to try one. I am sold on the cooler plugs too. I have better power with them. Haven't tried a 9 yet but going from a 5 to a 7 was a very noticable gain in torque. I did wetsand and polish the chamber with mothers alum polish. I really dunno if it helped but I liked it.

Masterm222 · #7 06-21-2009, 12:16 PM

I just got my slant head and I also got the pinging at high rpms. Two gaskets fixed that but it seems I lost a lot of what I gained with the head change. I am going to try a cooler plug and one gasket. I also got some octane boost to add to my premium mix. Just can't seem to get the thing to rev up to 6000 consistently. One day it will run up to 33.3 mph (44t sprocket) and then the rest of the week it flattens out at 25mph with no more acceleration from 3/4 throttle to WOT!

I also got a spare jug so I could widen the intake and exhaust ports and swap without making my daily driver inoperable while I make the mods. Expansion pipe is here and ready to be modified to fit and I also have a shift kit to install on this bike. Some day I will have my other bike running consistently so I can ride it while I install all of these mods. It will either go 19 mph and sit there or scream up to 35 and sing! Three miles to work so I need some reliability as I don't like pedaling!

Goat Herder · #8 06-21-2009, 12:41 PM

The more compression you put to it sure you will have a little more power but the RPMs will diminish.

Masterm222 · #9 06-21-2009, 01:54 PM

Sounds like I should keep the two gaskets so I don't loose to much top end. I may still be running a tad fat so time to solder and drill a spare jet to slightly smaller. I also have carb issues that I may attempt to cure with a Mukini 18mm upgrade. What carb do you think is best for an upgrade?

All I really need is more parts to swap out! Some day I will be satisfied and just ride. Just passed the 400 mile mark on build #1 and the needle and seat quit sealing. When I take the bowl loose to change jets gas will leak. Just changed carbs to cure that.

donuts31 · #10 06-21-2009, 10:21 PM

Cooler plug, higher octane fuel, and less oil (32 to 40:1 should be fine) and richer mixture should eliminate the pinging. It did for 2 of my motors with the high compression head.