loss of topend power??

bigben77

New Member
Jul 2, 2008
66
0
0
43
Edmonds, WA
Recently I have noticed a loss of power in the mid to high end prm range. Checklist of repairs done so far. ( did each repair seperatly with test rides between each.

burned ignition wires. replaced wiring with new and soldered conections.

ALL motor nuts and bolts tightened to proper torque.

carb cleaned and reasembled properly (thanks Norm for such detailed instructions)

needle set at stock location, second notch from top.

no air leaks.

new plug and wire.

fuel mixed @ 40:1

While looking at everything slightly disassembled I noticed scoring in the cylinder bore, could be from bad rings?

Also, the head gasket is slightly out of shape, inside diameter the edge of metal gasket is bent up a bit. could this cause a loss of comprestion?

Sorr, no pics at the moment?
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
235
63
up north now
Do you have any leaking around the head to cylinder joint? If not, the head gasket is not leaking.

How many hours on the engine?
How long have you run it at the too lean gas to oil mixture of 40 to 1?

Scoring in the cylinder will cause a loss of compression.
 

tyrslider

New Member
Sep 26, 2008
958
0
0
RainCity
I agree that seems a little oil starved w/ will cause scoring and too much heat will cause warpage/distortion of the bore. Rings can't stay seated throughout the stroke = loss of compression = loss of power. 32:1 premix is a pretty standard ratio on 2 smoke m/c's and it seems that's what rhe guys who know run on m/b's.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
235
63
up north now
32:1 premix is a pretty standard ratio on 2 smoke m/c's and it seems that's what rhe guys who know run on m/b's.
I will remind everyone that these are 40's tech piston ported engines with terrible loose tolerances. 32-50 to 1 are for modern close tolerance two strokes.

I wouldn't run any less than 32 to 1, preferably 24 to 1.
 

Goat Herder

Gutter Rider
Apr 28, 2008
6,248
11
38
N.M.
Thank you Bike Joe I had the same conversation just tonight, tun!s of miles on mine,4000 hella plus. They just refused to hear me , If not for the great info on this forum. Man I love you guys nothen but love, mine runs , the care and shared know how for checking is here!(^)
 

Goat Herder

Gutter Rider
Apr 28, 2008
6,248
11
38
N.M.
Mines been 24 to 1 since break in, mine is a bushed engine, I would run a bearing one the same! For those who don't know some ch have bushed piston bearings, others are needle bearing at the piston. Mines bushed Its Just Fine !!
 

Goat Herder

Gutter Rider
Apr 28, 2008
6,248
11
38
N.M.
Oh we carryed for our talkin 4000 miles,and this forum has my faith! God Bless Us All Lets fix some folks bikes!!!!!!!!!!!!!!!!
 

Pablo

Master Bike Builder & Forum Sponsor
Dec 28, 2007
3,664
5
38
Duvall, WA PNW
www.sickbikeparts.com
Before we get all wrapped around the 40:1, allow me to state - with certain oils (such as Saber) 40:1 is perfectly fine and will not cause cylinder scoring.

That said, no oil mix ratio will prevent scoring if your rings are failing or your engine has ingested a nasty. If this has happened it could explain your power loss. Does the engine have plenty of static compression?
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
235
63
up north now
Question Pablo....am I right or totally worng about the viscosity thing with 24:1? Does it help loose fitting parts or no?

I realize with a good oil you can run 40:1 as far as the piston goes, what about the bearings/bushings?

Same question when talking about dept. store oil and "pretty close" methods of measuring?
 

bigben77

New Member
Jul 2, 2008
66
0
0
43
Edmonds, WA
I'm slightly confused about mix ratios, 24:1 is how much oil per gallon of fuel??
my last gallon was mixed at 8oz oil per gallon as per instruction manual from seller.

I have since replaced head gasket and it seems to run better. I am starting to wonder about fuel cavitation now? time for a new fuel filter I think.

Can I replace my rod bushing with a roller bearing type? I have seen them on dax's parts pages.

I need more oil then...

Thank you all for your time and input.
 

Goat Herder

Gutter Rider
Apr 28, 2008
6,248
11
38
N.M.
:confused:I've never spewded any oil Or had to clean my spark plug, its allways been perfect brown color? Seems the rings need a good film of oil to me. Glad to see ya got the ch going its pretty common for the head gasket to get loose on a new build head bolts somtimes settle strecth alittle. If your are careful High temp permatex red gasket maker, I use a very thin layer on both sides of my head gasket, don't need much. Tack the head together gently pull it back off to see if too much was applyed, if its perfect bolt it down! I used this stuff on v8 hot rod custom headers they never leak!(^)
 
Last edited:

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
235
63
up north now
Can I replace my rod bushing with a roller bearing type? I have seen them on dax's parts pages.

No, they don't interchange.

I need more oil then...

No, you need less oil than you currently run. 24 or 32 to 1.

.................................
 

Pablo

Master Bike Builder & Forum Sponsor
Dec 28, 2007
3,664
5
38
Duvall, WA PNW
www.sickbikeparts.com
If the OP is running a low end oil at 40:1, then yes maybe drop it to 24:1 or 32:1, just to see. Yes more oil will make a better ring seal and protect the bottom end, but this statement is HUGELY general. Oils are different. I don't see some huge problem with running 24:1 with many oils if your plug is fine, you fuel:air is good. A tiny bit of smoke and pipe drool is not a problem. Again if you ever run Saber 24:1, you would absolutely know you are too oil rich.

Get it set at between 24:1 and 32:1, measure very carefully mix well. Use absolutely fresh RON/MON 87 gas without ethanol if possible. Drain all the fuel in the tank and use it your car. Add the fresh fuel, prime all the old fuel out of the carb bowl. Use a NEW spark plug. Take it on a hot run for at least 3-5 miles. This fuel variable should be eliminated.

Now let's solve the original problem. "loss of topend power"
 

bigben77

New Member
Jul 2, 2008
66
0
0
43
Edmonds, WA
Let me take a moment to go into better detail, At 25% to 50% throttle the engine has great power and torque. From 50% to I'm guessing 75% the "power band" seems to flatten out. Any more than 3/4 throttle the engine starts to stutter and sounds like an ignition miss, Schwinn wireless speedo says it happens at 26 mph. This engine and my riding habbits seem to like cruising at 20 to 25 mph. Let me also state that I'm pushing 300lbs!