what did you do to your motorized bicycle today?

GoldenMotor.com

Danschutz

New Member
Aug 19, 2013
392
0
0
Wyoming
Well, I took the bike out today with the SBP expansion chamber.

I dont know how I feel about it yet. I wasn't expecting the degree of quiet It has. it also falls on its face in low RPM at 3/4+ throttle input. once its kicks in though it has a great tone and finds its stride. Seems to have lost 6-9mph top speed.

I shortened the header on it and we will see tomorrow if i miss the rain if that helped
I just posted that my sbp exhaust gave me incredible low to mid torque, a real hill puller but I'm sure I lost some high end. I'm not certain high much I lost because I swapped out sprockets also.

The low end is so strong I can pull a pretty big hill by my house from a dead stop no peddling and about a ten yard head start with no issues.

Does your motor have any other mods?

Dan.
 

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
Recently installed the sbp exhaust and replaced the 44t sprocket with a 41t. My low mid power is unbelievable, there is a hill near my house that I test my bike on. The bone stock motor struggled about 15-17 mph with a top speed of 22 (unknown that i had a cylinder issue) then after installing the hi head, ported cylinder and notched piston I was sustaining 22 mph up the hill with a top speed of 31 while four stroking like crazy.

With the addition of the expansion pipe (and 41T sprocket) I can take that hill at 27mph. Here's the twist, I can only get about 28mph top end, tonight I hit 30 mph.

Cruising at 20-22 mph is hardly a chore for the motor right now and it gets there in a hurry. I can't believe I'm about to say this but you can feel it shove you right along. I rode with my buddy Brian and his very nice running Arrow 4.5 hp motor and was eating him up around the hills and leaving him in the dust up to 28-30 mph then eventually he catches and blows by me.

I added one 45 degree elbow to the Sbp kit so I'm guessing I need to shorten the pipe somewhere to get back some top end OR do I get a 36t sprocket?

Also upgraded the stock bolts on the sprocket, so much nicer lol.



Dan.
A 36T rear sprocket and a well tuned carb will likely get you at leas 5mph more on top end, the RT carb from dax is an excellent upgrade that makes a felt in the seat of your pants difference all the way around and will likely put you at 35+ mph on top end and a good cruise speed of 30-32mph maybe better jst depends how well balanced your engine is.

Map
 

Danschutz

New Member
Aug 19, 2013
392
0
0
Wyoming
Oops just noticed you have the RT carb...... so tune is well and get a 36t on the rear and enjoy the extra power and top speed........!
Shan,
The cylinder and piston mixed with a stock pipe and 44T on another bike was making 32 mph with me on it, nearly 33 actually. I figured with a 36 I would get more top end speed?

Im not super worried about this build because Im going to put forth more effort on the Dax motor but at the same time I want to learn as much as I can off this motor. My bud is running a 42T and getting 35+ mph and he is about 65 lbs heavier, Im light at 165.

I trust what your saying, Im just confused I guess. I was hoping the 36 would get me at a 35mph cruise speed. Im I asking to much?

As always thanks Map,
Dan.
 

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
Shan,
The cylinder and piston mixed with a stock pipe and 44T on another bike was making 32 mph with me on it, nearly 33 actually. I figured with a 36 I would get more top end speed?

Im not super worried about this build because Im going to put forth more effort on the Dax motor but at the same time I want to learn as much as I can off this motor. My bud is running a 42T and getting 35+ mph and he is about 65 lbs heavier, Im light at 165.

I trust what your saying, Im just confused I guess. I was hoping the 36 would get me at a 35mph cruise speed. Im I asking to much?

As always thanks Map,
Dan.
Dan
I was being conservative with what I said, I have gotten 38mph with a 36t and a mostly stock engine with well tuned carb and free flowing exhaust and you could very well see the same results.

Map
 

BonusParts

Member
Nov 28, 2012
168
0
16
SE-PA
I just posted that my sbp exhaust gave me incredible low to mid torque, a real hill puller but I'm sure I lost some high end. I'm not certain high much I lost because I swapped out sprockets also.

The low end is so strong I can pull a pretty big hill by my house from a dead stop no peddling and about a ten yard head start with no issues.

Does your motor have any other mods?

Dan.
My motor has cleaned intake an exhaust ports, they have been smoothed slightly enlarged, the combustion chamber is polished, head is milled down. .016 copper gaskets, NT speed carb,with air filter & .66 jet from SBP. ngk iridium plug, jag cdi and coil, accel 8mm plug wire.

Its on a 36t sprocket.

Oddly enough i've noticed that at low rpm it runs great on low throttle input, but at wot it just bogs. not four stroke, bog. Not sure what to make of it. I shortened the header, but it was rainy all day so no test yet.

I've maxed at 43.62mph on the 36t via GPS (MyTracks)

Recently (right before i hit the deer) it was about 39mph
 

Huffydavidson

STREETRACER/MANUFACTURER
Jan 29, 2012
1,076
4
38
st.louis,mo.
today I met the anesthesiologist and the whole medical staff that will be transplanting the Fred motor into the body of blue , she will be in room 66 C , the smokers unit.
LMAO laff
 

BonusParts

Member
Nov 28, 2012
168
0
16
SE-PA
today I met the anesthesiologist and the whole medical staff that will be transplanting the Fred motor into the body of blue , she will be in room 66 C , the smokers unit.
LMAO laff
Which fred motor did you get? I've got one of his engines BNIB in my basement that i keep pushing to the back of my parts stash. Idk why, but I just really dont want to run that engine. Something about my BS cobbled together grubee variant makes me happy. and FWIW my buddy has a fred motor on his bike, 36t and i still romp a few mph faster.
 

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
Oddly enough i've noticed that at low rpm it runs great on low throttle input, but at wot it just bogs. not four stroke, bog. Not sure what to make of it. I shortened the header, but it was rainy all day so no test yet.
By bog, if it just looses power and seems to be running flat while you are riding at top speed, it is tuned too lean. It needs a larger main jet.
(Note, a highly restrictive or clogged exhaust will cause this symptom too even though the carb is tuned correctly.)
Now that said, if you whack it WOT from idle speed and then it bogs that too is a lean condition but good luck tuning it out. The carb has no accelerator pump and it cannot accommodate large throttle input changes without temporarily leaning out.
 

BonusParts

Member
Nov 28, 2012
168
0
16
SE-PA
By bog, if it just looses power and seems to be running flat while you are riding at top speed, it is tuned too lean. It needs a larger main jet.
(Note, a highly restrictive or clogged exhaust will cause this symptom too even though the carb is tuned correctly.)
Now that said, if you whack it WOT from idle speed and then it bogs that too is a lean condition but good luck tuning it out. The carb has no accelerator pump and it cannot accommodate large throttle input changes without temporarily leaning out.
You absolutely confirmed my sneaking suspicion.... I had a feeling I needed to switch back to a .68 jet, seeing as both my crank and head compression have been raised some, that and I noticed it more after I installed the jaguar CDI. I perhaps didn't realized that I had equipped the engine to finally handle the potential of the small NT speed carb....

Well, back to jet seeking!
 

Cruise

New Member
Oct 2, 2013
150
0
0
Australia
I'll throw my bit in amongst you smart lot:
Is there something in being able to adjust the timing at all by gapping the plug?
I'm sure I read somewhere you can advance it by closing the gap, and vise versa.
If so it's another factor to play with.
 

CTripps

Active Member
Aug 22, 2011
1,310
1
38
Vancouver, B.C.
I'll throw my bit in amongst you smart lot:
Is there something in being able to adjust the timing at all by gapping the plug?
I'm sure I read somewhere you can advance it by closing the gap, and vise versa.
If so it's another factor to play with.
I can't really see how changing the gap by a few thousandths of an inch is going to have any significant effect on the millisecond(s) it takes for a spark to jump the gap. At a level beyond common measure there may be a difference, but to find it I'd suggest you get good walking shoes and turn right at the decimal point.
 

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
Cruise, electricity travels at 186,282.397 miles per second. Changing the gap on the spark plug a few thousands of a inch will not affect the timing.
Perhaps you were thinking of changing the gap on the points of a traditional points/breaker style ignition? Changing the gap on that will definitely affect the ignition timing.
 

Cruise

New Member
Oct 2, 2013
150
0
0
Australia
Thanks all for your diplomacy and light humour! I've played lots with cars but am new to these cool little motors. Now I reckon I'll leave that gap out of question.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
Cruise, electricity travels at 186,282.397 miles per second. Changing the gap on the spark plug a few thousands of a inch will not affect the timing.
Perhaps you were thinking of changing the gap on the points of a traditional points/breaker style ignition? Changing the gap on that will definitely affect the ignition timing.
I note that it may be the case that a larger gap could cause the spark to wait fractionally for the voltage to climb higher to jump the gap - in fact, a too large gap may cause the spark to wait forever.

Also, this may affect the quality of the spark in terms of its ability to start a good burn.
 

Huffydavidson

STREETRACER/MANUFACTURER
Jan 29, 2012
1,076
4
38
st.louis,mo.
Today rode this Dax engine for one of last time for a bit, at least until my New GT-2a frame arives YEA!!! BLUES GETTING Fred engine when the next rain days come. Until then we'll pray it rains like he!!. Finished custom tubing (1.25") fabrication and ready for the welder Monday morning. Ordered a bag of racing muffer repacking glass to repack the silencer and not compromise performance this massive expansion chamber !!!!