Help me get more power...

[jmden]

What can I do to this to get a noticeable increase in power?

That's a 6.0cc Fred Head on top and really need the cooling that gives. Maybe his new 5.3cc? Would that really make much of a difference?

The thing that works this the hardest is towing a 80-100 lb trailer up logging roads and such. That's what I need the power for.

SBP Jackshaft shift kit has all the lowest gearing. 30 tooth front chainring goes to a 11-34 rear cassette, so a pretty good range there (this is an old steel frame with 6 sp freewheel, so I spread the rear from 125mm to 135mm [Subaru screw jack worked great] and put on a modern sized wheel/axle with 7 sp 11-34 cassette--working great so far).

I've done some port matching. Not sure if there's a better exhaust that would make a huge difference without being some 4' long behemoth. Better intake/carb?

Also, something I seem to notice regularly is when I twist the throttle to full throttle, past a certain point, the engine bogs down. It's like it's getting too much fuel or too much air or something. Same thing with two different 'stock' carbs, so... Wonder if i could solve that if part of my power problem would be solved.

Any other thoughts?

Thanks!

Jon

Edit: deleted pic of sand dollar at beach. Not sure how that got in there...

 

[Dan]

It is Jon! Dang. Just apologised in your hello thread. Day started hard and then went bad from there.

But again, I really would suggest throwing a harbor fright cheapie possibly on your existing trailer. Ya got time and effort well into your China Girl and by no means am i as experienced with 2 strokes as most of the folks here. Last time I bought one it was one, generic kit and only one guy made aftermarket stuff for em.

And he went insane. Well, think most folks into this are half a bubble off. But most, to the good.

But just my thoughts. 10 years ago, you'd see around 15% of new builds were pushers. Don't see a lot anymore but there are some great threads with how2s.

Got me thinking about it. A beast-ard, 2/4 smoke composite unit. Quick and perky up front, and grunt pushing.


something like that

 

[BeastBikes]

I'm still very new to motorized bicycling but I would suggest trying a boost bottle on it. I bought one myself but haven't been able to try it out yet because im having trouble fitting everything on it.

Not sure if they are effective or not for your purposes but its a possibility. You could also try other spark plugs to see if one works better for you.

BTW how well is that speed demon exhaust working for you? Is the noise level tolerable and did it provide better power?

 

[crassius]

boost bottle does nothing except make problems in any motor without reed valves

if you are bogging because you aren't getting enough revs to get to the power band, then gear lower - otherwise you're probably rich and need to drop the needle lower into the slide

 

[Tyler6357]

I would recommend getting a different pipe, that expansion pipe looks pretty small. If you are going to use it, at least put a longer header on it, like around 12" to 17" long. Doing that should help your low end. Also, the .6cc head won't help your compression much if your squish gap is higher than .06". Try decking your cylinder until you get a squish gap of between .025"-.035". Also, I agree that bottle boost is a waste of money.

 

[jmden]

I would recommend getting a different pipe, that expansion pipe looks pretty small. If you are going to use it, at least put a longer header on it, like around 12" to 17" long. Doing that should help your low end. Also, the .6cc head won't help your compression much if your squish gap is higher than .06". Try decking your cylinder until you get a squish gap of between .025"-.035". Also, I agree that bottle boost is a waste of money.

Talked to Jim at sickbikeparts about his expansion pipe and I may be going that way as I'm realizing what you are saying, but I'm running a 20:1 synthetic oil fuel right now as part of the '3 tanks' break in and that may be much of my problem acc'd to posts here and sickbikeparts. He starts at 25:1 for break in and goes up to 40 to 50:1, so I need to get that stabilized and see what happens there, then I might be able to make headway on other potential issues that still exist.

Give me a quick primer on squish gap. Have done alot of work on this thing and have no problem adjusting this. Just need to fully understand the concepts involved. I had a 'race head' from bikeberry on here before this one that definitely made more power, but had very little cooling capapbility and for long uphill runs at lower speeds because of hauling a heavy trailer, I needed all the cooling I could get and the Fred Head seems to be the best at that. But definitely lost power with it because of loss of compression.

Had a boost bootle from bikeberry on here and it was nothing but trouble with vacuum leaks, etc. There's even youtube videos showing where the problems are from a long time ago. I figured they must have fixed these known vacuum leaks...well, they didn't. I had the same problems and had to return the thing.

 

[jmden]

boost bottle does nothing except make problems in any motor without reed valves

if you are bogging because you aren't getting enough revs to get to the power band, then gear lower - otherwise you're probably rich and need to drop the needle lower into the slide

So am finding that if I'm 'bogging', it seems to occur only under higher load like when going uphill. That's when I can't seem to go more than 1/2 to 2/3 throttle. Sound like anything in particular?

 

[Dan]

Always enjoyed and learned a lot from SBPs. Just saying.

And lots of good advice above, Jon. (just sayin)

Please do post how it goes!


Rubber side down Beodder!

 

[Tyler6357]

Talked to Jim at sickbikeparts about his expansion pipe and I may be going that way as I'm realizing what you are saying, but I'm running a 20:1 synthetic oil fuel right now as part of the '3 tanks' break in and that may be much of my problem acc'd to posts here and sickbikeparts. He starts at 25:1 for break in and goes up to 40 to 50:1, so I need to get that stabilized and see what happens there, then I might be able to make headway on other potential issues that still exist.

Give me a quick primer on squish gap. Have done alot of work on this thing and have no problem adjusting this. Just need to fully understand the concepts involved. I had a 'race head' from bikeberry on here before this one that definitely made more power, but had very little cooling capapbility and for long uphill runs at lower speeds because of hauling a heavy trailer, I needed all the cooling I could get and the Fred Head seems to be the best at that. But definitely lost power with it because of loss of compression.

Had a boost bootle from bikeberry on here and it was nothing but trouble with vacuum leaks, etc. There's even youtube videos showing where the problems are from a long time ago. I figured they must have fixed these known vacuum leaks...well, they didn't. I had the same problems and had to return the thing.

The Squish gap is the gap between the head and the piston when it's at top dead center. When the piston gets to the top the ignition occurs. Making the squish gap smaller will increase compression giving you more power along the entire throttle range. However, if you make it too small it will restrict the volume of fuel to the point where you will lose power. For these little engines a squish gap of between .025" to .035" is optimum.
The first thing to do is measure your squish gap. First your going to need some soft leaded rosin or acid core solder.

.050" Rosin Core Solder
.062" Rosin Core Solder
.093" Rosin Core Solder = NAPA Auto Parts PN # 777-1862
.125" Acid Core Solder = NAPA Auto Parts PN # 777-1857

You may have the right solder laying around, or at your local hardware store.

Basically you cut two small strips of solder about 1" long.

Give them a slight bend so they match the contour of the top of your piston.

Prep the engine so that the head is removed, the cylinder is installed, with the piston installed on the rod and the head gasket you intend to use in place.

Now:

Use some heavy grease and place the two bent 1" pieces of solder on the top of the piston.

Placement is important!

They must be directly in-line with the piston wrist pin, and they must sit on opposite sides of the piston. Place your two pieces directly in-line with the piston wrist pin so that one end of the solder piece goes right to the edge of the cylinder.

Once you have your solder in place, carefully rotate the crankshaft so that the piston is just below top dead center.

Assemble the head onto the engine without the spark plug.

Torque the head to the torque value you use (I use 15 foot Lbs.).

Make sure the clutch is engaged (clutch handle released) and grab the back wheel. Now rotate the crankshaft through top dead center, compressing the solder. It will be kinda hard to compress the soft solder, just pull the wheel up to run it through once.

Remove the head, measure the thickness of the compressed solder at its smallest point (usually the edge closest to the edge of the cylinder).

This measurement is the SQUISH GAP.

If the gap is bigger than 0.060" you might as well not even have a squish band in the head, and you are not going to get the MAIN benefit of the Fred Head, the optimized squish band. However, the Fred head will still provide you with superior cooling over a stock head. Those big fins really help keep temps down.

If after you have your measurement you decide you need to deck the cylinder, but have no idea how to go about doing it, I will walk you through a super low budget method I have used. All you need is a reasonably flat surface like a piece of glass about 1' square or larger, and some varying grit sandpaper.

 

[Tyler6357]

So am finding that if I'm 'bogging', it seems to occur only under higher load like when going uphill. That's when I can't seem to go more than 1/2 to 2/3 throttle. Sound like anything in particular?

You might try jetting down a jet size or 2. Is it 4 stroking??

 

[jmden]

You might try jetting down a jet size or 2. Is it 4 stroking??

I think it is. What I've been calling 'bogging'. Doesn't happen downhill, just when going up hill. And I'm talking quite slight up and downhill. Can go WOT downhill, but uphill, almost all the time, when I need the power the most, it starts bogging down when I estimate I'm at 2/3 or so and above throttle. I have to back off and hold the throttle as high as I can, but where it won't bog down and lose power.

I adusted the float arms so the float is sticking up 21mm from carb body when top part of carb is upsidedown. It was way lower than that so prob contributing to possible rich condition...? No change. Double checked slide-- functioning ok. If I take off the air filter--no change. If i turn on choke when at high throttle--it dies, so doesn't seem like lean situation. I just cleaned out my fuel tank a second time--no debris showing in clear sided KnM in line fuel filter. Getting great fuel amount coming out of line when disconnected from carb so vacuum in tank isn't issue. Everything looks clean in carb and can see through jet just fine. Just changed to 40:1 fuel ratio with hi quality synthetic scooter 2 stroke oil. Seems like it's time to change the jet. I have a bunch of them so, when I get a chance, I'll go down a size or two and report back. Might be a few days with Thanksgiving (Happy Thanksgiving all!) and all.

Thanks for the input here guys. I appreciate it.

 

[jmden]

The Squish gap is the gap between the head and the piston when it's at top dead center. When the piston gets to the top the ignition occurs. Making the squish gap smaller will increase compression giving you more power along the entire throttle range. However, if you make it too small it will restrict the volume of fuel to the point where you will lose power. For these little engines a squish gap of between .025" to .035" is optimum.
The first thing to do is measure your squish gap. First your going to need some soft leaded rosin or acid core solder.

.050" Rosin Core Solder
.062" Rosin Core Solder
.093" Rosin Core Solder = NAPA Auto Parts PN # 777-1862
.125" Acid Core Solder = NAPA Auto Parts PN # 777-1857

You may have the right solder laying around, or at your local hardware store.

Basically you cut two small strips of solder about 1" long.

Give them a slight bend so they match the contour of the top of your piston.

Prep the engine so that the head is removed, the cylinder is installed, with the piston installed on the rod and the head gasket you intend to use in place.

Now:

Use some heavy grease and place the two bent 1" pieces of solder on the top of the piston.

Placement is important!

They must be directly in-line with the piston wrist pin, and they must sit on opposite sides of the piston. Place your two pieces directly in-line with the piston wrist pin so that one end of the solder piece goes right to the edge of the cylinder.

Once you have your solder in place, carefully rotate the crankshaft so that the piston is just below top dead center.

Assemble the head onto the engine without the spark plug.

Torque the head to the torque value you use (I use 15 foot Lbs.).

Make sure the clutch is engaged (clutch handle released) and grab the back wheel. Now rotate the crankshaft through top dead center, compressing the solder. It will be kinda hard to compress the soft solder, just pull the wheel up to run it through once.

Remove the head, measure the thickness of the compressed solder at its smallest point (usually the edge closest to the edge of the cylinder).

This measurement is the SQUISH GAP.

If the gap is bigger than 0.060" you might as well not even have a squish band in the head, and you are not going to get the MAIN benefit of the Fred Head, the optimized squish band. However, the Fred head will still provide you with superior cooling over a stock head. Those big fins really help keep temps down.

If after you have your measurement you decide you need to deck the cylinder, but have no idea how to go about doing it, I will walk you through a super low budget method I have used. All you need is a reasonably flat surface like a piece of glass about 1' square or larger, and some varying grit sandpaper.

Thanks! I think I get what you are saying and thanks for taking the time to explain it. I've have several types of solder at home so will measure them with calipers and see if they are near enough to do the job.

What is the 'optimized squish band' of the Fred Heads?

I've got what I need to do the cylinder decking. Have no prob doing that if need be. Thanks. Just trying to ge this thing runnning like it should be.

 

[Tyler6357]

Just stick the solder to the piston crown with a little grease, as straight in the center as you can starting from the outer edge closest to the cylinder wall. The squish gap is tapered in the engines, as the curve of the squish band is a greater radius than the curve of the piston dome. So it will be narrowest at the edge of the cylinder, and progressively gets wider as it gets closer to the center of the head, therefore the smallest spot should be on the edge closest to the cylinder walls.

It's worth it to deck your cylinder if the squish gap is too large. The advantages of the squish band go alot farther than just improving performance. It makes the combustion process much more efficient, giving you better fuel economy. It keeps the combustion event contained in the center of the cylinder. When the squish gap is set properly, the gasses in-between the gap cannot be ignited so they help cool the cylinder wall and the piston dome, improving piston and cylinder longevity, and helps to prevent piston seizure.

The dynamics of the squish event effectively "squishes" all the gasses into the center of the combustion chamber so they are closer to the spark plug, and can ignite more completely. Rouge patches of un-ignited gasses in the cylinder that don't get ignited with the main charge lead to detonation. Effectively, the rouge patch of gasses ignites late, and the expanding flame front it creates collides with the expanding flame front of the initial ignition event. This is known as "detonation" and is incredibly destructive to engine components. And on top of all that, it's just free power, everywhere in the power band.

However, I also want to say that I suspect you will get a better performance upgrade and more low end power by changing your expansion chamber than by decking your cylinder. That thing looks almost useless. I put a sick bike parts expansion chamber on my first bike (see pic). I put a 18 inch header and picked up a lot of low end. However, I should say that the SBP pipe is NOT the best one out there these days. Remember typically the larger the chamber the better it will be.

 

[Tyler6357]

I think it is. What I've been calling 'bogging'. Doesn't happen downhill, just when going up hill. And I'm talking quite slight up and downhill. Can go WOT downhill, but uphill, almost all the time, when I need the power the most, it starts bogging down when I estimate I'm at 2/3 or so and above throttle. I have to back off and hold the throttle as high as I can, but where it won't bog down and lose power.

I adusted the float arms so the float is sticking up 21mm from carb body when top part of carb is upsidedown. It was way lower than that so prob contributing to possible rich condition...? No change. Double checked slide-- functioning ok. If I take off the air filter--no change. If i turn on choke when at high throttle--it dies, so doesn't seem like lean situation. I just cleaned out my fuel tank a second time--no debris showing in clear sided KnM in line fuel filter. Getting great fuel amount coming out of line when disconnected from carb so vacuum in tank isn't issue. Everything looks clean in carb and can see through jet just fine. Just changed to 40:1 fuel ratio with hi quality synthetic scooter 2 stroke oil. Seems like it's time to change the jet. I have a bunch of them so, when I get a chance, I'll go down a size or two and report back. Might be a few days with Thanksgiving (Happy Thanksgiving all!) and all.

Thanks for the input here guys. I appreciate it.

Yeah, it sounds like it might be running a little rich, try leaning it out a little with a smaller jet. The stock #70 jet is often times too rich for people who live closer to sea level like me. I'm running a #60 in my first bike and a #65 in the other one, both use the HT carb like you got but they have different pipes.

 

[jmden]

Yeah, it sounds like it might be running a little rich, try leaning it out a little with a smaller jet. The stock #70 jet is often times too rich for people who live closer to sea level like me. I'm running a #60 in my first bike and a #65 in the other one, both use the HT carb like you got but they have different pipes.

Well, just slipped in a .060 jet and no difference. If anything it was worse. Even losing power downhill and when clutch disengaged and go to WOT. Hmm... Looks like the stock jet was .065 using some wire drill bits to compare replacement jets to stock. Maybe I should try a .070...? Not the direction I thought this might go, but worth a try, I guess.

 

[jmden]

I have done some port matching on this thing but I can't imagine it's enough to make it need more gas...

 

[Tyler6357]

Well, just slipped in a .060 jet and no difference. If anything it was worse. Even losing power downhill and when clutch disengaged and go to WOT. Hmm... Looks like the stock jet was .065 using some wire drill bits to compare replacement jets to stock. Maybe I should try a .070...? Not the direction I thought this might go, but worth a try, I guess.

Hmmmmm, alright, I guess jet back up, you don't want to run it too lean, that will create too much heat followed by bad things happening. It's better to be a little rich than too lean. If it got worse when you changed it then I would go back to the stock one but you can try the #70 just to test. Make sure you get the engine warmed up and hot before making an analysis, most engines run slightly leaner after it's warmed up.

 

[jmden]

Hmmmmm, alright, I guess jet back up, you don't want to run it too lean, that will create too much heat followed by bad things happening. It's better to be a little rich than too lean. If it got worse when you changed it then I would go back to the stock one but you can try the #70 just to test. Make sure you get the engine warmed up and hot before making an analysis, most engines run slightly leaner after it's warmed up.

So I tried a .070 jet. Maybe a little better at letting me get to WOT. Then tried a .075--definitely better, but still not letting me get to quite WOT before losing power, so, threw in the big .080.

That bike has never pulled like that before! I was going up hills in the higher gears (has a SBP jackshaft kit on it so switching gears) with no issues at WOT! Wow...maybe my exhaust/intake port matching works...?

Still have the issue of it dying at idle when the engine is hot. Any ideas? I've messed with the different c-clip positions to no avail. What would cause an engine to die at idle when it's hot? I have the idle screw in all the way and can see the slide going up and down in response to the idle screw adjustment when I take off the air filter. So that's working, but adjusting this and the c-clip position doesn't seem to make much difference. Hmm..

Thanks.

 

[Tyler6357]

Hey, glad you figured out your jetting. It's unusual to need a jet that big for one of these little china girl engines but it really depends on things like the altitude and barometric pressure of where you live as well as the porting done to the engine. If the #80 works better use it!! The richest jet you can use and still get good performance the better it will be for the longevity of your engine. As far as the idle is concerned, usually idle problems are fixed by messing with the carb. Quite honestly, I haven't spent much time messing with NT carbs, I've been using an HT/ Dellorto Clone carb. The best advice I can give is to check your twist throttle cable and make sure it's springing back when you release it. Also, make sure that the slide is set low so that just a sliver of light shines through when it's at bottom throttle. Perhaps others here could better advise you on that.

 

[Dan]

Doubt this is terably Germaine but I have always had performance increases just cleaning well used carbs. And making sure the fuel filter is clear and not backwards. (Happens a lot. Works best as a pine tree being rained on and works poorly like a coffee filter)

A small but seemingly a constant contributing factor and just sayin'