Why some motors run better than others

Quenton Guenther

Well-Known Member
Local time
10:53 PM
Aug 2, 2007
Outer Banks North Carolina
I have a lot of requests asking about "secrets" I use in some of my modified motors. Also at the top of the request list is "why is my 2008, faster than my 2007?", or "why is my 2005 easier to start than my 2008?", etc.
When I raced during the 60s, 70s, & 80s it became clear some motors just are better than others. I had 2 Ducati motors that were just outstanding, and much faster than the rest. When I was instructed by my sponser to build an extra "backup" motor, I spent a lot of time finding out why some of my race motors were so different. While some of my competitors resorted to cheating, I always ran legal motors [never even bored a single motor to 1st over]. After a little research, and a little thought, it soon became clear why some items made by man can be so different, it has to do with tolerances. If a company has a 5% tolerance rule it can translate as follows..... a 29" belt can be as small as 27.55", or as large as 30.45", a difference of almost 3 inches. In the case of Whizzer belts, I have seen the front belt vary from 28.75" to 29.25" [1/2 inch], which is only 1% tolerance [1% is considered to be better than average]. If you apply this rule across the entire motor, some will have the lifter clearance too loose, and some will have them too tight, and some just right. Some heads will have a slightly smaller combustion chamber, while others might be slightly larger. Some pistons and rings will fit tighter, while other will have a looser fit, and some just right. Some carburetors will have a smoother bore, while other won't. Some camshaft will "degree" better than others. Some flywheels will be closer to perfect balance, and some won't. Some valve seats will be cut lower than others. Some valves will weigh less than others. Some lifters will be longer, some will be shorter, some will weigh more than others. Some muffler inserts will be longer, some will be shorter, etc, etc, etc. Most of these differences will fall within the 1% tolerance zone.
It is possible to restrict the Whizzer motor by tolerances, and by the restrictor plate, and as long as it stays below the required speed, who cares which method is used. I myself perfer the motor be 100%, and let the restrictor regulate the top speed. If the Whizzer motor is brought into closer tolerances, it will run much better, much smoother, idle better, and start easier, but if restriced it will still meet the guidelines. A perfect example is the new aluminum manifold, I have only seen one that matched the intake port. Most are off by at least 1/8", and of course the restrictor plate [9.5 MM hole] reduces the flow so much, most don't think the manifold mis-match matters. Here are the facts, most of my motors are "stock", yet will out perform all [so far]other Whizzer motors [including a lot of big dollar so-called modified motors]. All most all of my motors use the stock exhaust pipe, muffler insert, camshaft, crankshaft, carburetor [26 MM version], stock piston & rings, flywheel, and stock clutches. The big difference is 0% tolerances. My front belt is exactly 29", the lifter clearance is exactly .008" exhaust, .006" intake, the head combustion chamber is exactly as designed [no sharp edges], the head gasket matches the head exactly, the intake manifold matches the port exactly, the carburetor matches the aluminum manifold exactly, the plug gap is exactly .025", the plug is spaced to fit the head exactly [indexed], the head bolts are torqued exactly to specs., the exhaust port is smooth [rought casting extrusions removed] to meet the requirements exactly, the belts are aligned to be exactly straight, etc, etc.
In other words, a little [or a lot] time spent on making your Whizzer motor exactly as Whizzer designed it can result in a lot more power [still legal as long as the restrictor is intact], much easier to start, idle smoother, accelerate faster, pull hills better, and just better over-all. And always remember "no 2 motors are identical", unless you make them so. This is true with GM, Ford, Chrysler, etc.
If you want your Whizzer to be the "best of the best" [like mine], simply invest some time to make it as close as possible to the current design specs., it is a lot of fun doing the work, there is a lot of knowledge to gain, and the final results will net a really great dependable "ride". And don't forget the Whizzer is a single cylinder 4 stroke [thumper] motor and will vibrate just a tad at higher RPMs, so be sure to loctite all the bolts & nuts [I suggest using loctite on all motorbikes, motocycles, ATVs, & scooters].
BTW, I don't suggest that my stock motors will out perform my modified versions, cause they won't!
Let me know if this answered everyone questions, if not, just ask again.

Have fun,
that is a great write up
and very informative...i know that the closer tolerances mean a quality product
however ive never put 5% ti the test with the belt for example
thats quite a difference and i wouldnt have considered that

Hey Quenton
You just told all the competition for next year at Dawson Springs how to give you a run for your money. Great post as per usual.

Hi Jim,
It makes it more fun that way. I plan to use the same motor next year with a different [almost stock] head, hows that for playing fair? I remember removing the head on my wife's Whizzer at Portland, IN a few years ago [just after setting a record on the "roller road"], and as the crowd grew around the bike, everyone was amazed that it was stock inside. Sure makes a lot of people wonder.
Have fun,