Project Triple Double Is a Test to Find a Dollar to Horsepower Ratio of a 200 Cc OHV Engine

Project triple double is a test to find a dollar to horsepower ratio of a 200 cc OHV engine, specifically a Chinese made clone of a Honda GX200. The name of the project comes from the question can I double the horsepower of this engine for triple the cost of the initial engine? So if my dyno finds the engine to have it’s rated 6.5 horsepower right out the box can I produce 13 HP for $540? The $540 is $159 for the engine plus $21 shipping multiplied by three.

The dyno test will be run on an inertia type dyno equipped with Performance Trends pro version software. Four test will be run as follows, bone stock out of the box, aftermarket air filter adaptor and header with modified jets, complete blueprint job and new internals for the block and head, and the final test will be conducted after modifying the carburetor.

Here is the list of parts.

Billet filter adaptor Paper filter Foam pre-filter Kwik link throttle linkage RLV header Dynocams valve springs Lash cap Exhaust valve retainer ARC billet flywheel ARC billet connecting rod with bearing Dynocams modified clone cam Flat top piston GX 160 head gasket High strength bolt kit Heavy duty chain guard

Total price is $530.28 including all shipping charges and 7% Indiana sales tax. Now that the budget seems to be met it’s up to me to see if I can find the power using basics learned in Small Engines 101. I know the task would be simple given some more money and I will make notes of that along the way. By the same token the power could be made with less money but this would sacrifice safety and the durability and reliability of the engine. The tests will be conducted using 87-octane gasoline (for now).

For now the document will have to be in this form. Doing a web layout is simply too time consuming for me to do at this time. Click on the links to view the photos.

The only thing needed to get the engine ready for it’s first run is to add fuel and oil and over ride the governor. I will completely remove the governor during disassembly of the engine. After removal of the air cleaner, blower housing, and fuel tank the first piece of the Kwik link is installed. The return springs will go toward the front of the engine.

Throttle Linkage

Warmed up and engine and did three runs recording data on the second and third full throttle runs

Run #2

RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600 HP 7.16 7.26 7.26 7.18 7.00 6.70 6.39 6.08

Run #3

RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600 HP 7.13 7.23 7.25 7.17 6.98 6.66 6.35 6.07

Remove stock exhaust and install RLV 5438C header

RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600 HP 7.92 8.04 8.09 8.05 7.93 7.47 7.05 6.79

Install billet filter adaptor, drill low side jet .024” and main jet .036”.

RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600 HP 8.41 8.63 8.74 8.79 8.76 8.64 8.51 8.30

Install ARC billet flywheel

RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600 HP 8.87 9.09 9.19 9.28 9.35 9.24 8.96 8.69

Here is a view of the engine at end of initial tests.

See the overlay of the above dyno runs. Notice the two bone stock runs are very close together.

Dyno Graphs

I am going to call my baseline peak horsepower 7.29 at 4300 RPM. Letting the software find averages for horsepower between 4300 and 4600 yields 7.27 HP for run number 2 and 7.30 for run number 3. Keep in mind that the 200 RPM increments of the small charts hide some of the details. So now the challenge is to achieve a solid peak of 14.58 HP over a 500 RPM range.

This is a little more than I expected given the small amount of experience I have with the blue clone engines. Honestly, I was thinking the power would be less than 6.5 HP. Perhaps this engines carburetor had a larger main jet than the last blue clone I tested. I measured this one at .028” diameter and if I recall I drilled the main on a blue one to .028”, tested, and then drilled it bigger.

Three very simple bolt on pieces along with a jet swap made a two horsepower increase. How will these combine with the internals to increase the performance?

When I removed the bower housing to exchange flywheels I used a timing light to find the firing points of each of the flywheels. Here is a photo of the ARC flywheel firing point. Notice the mark on the magnet in reference to the front leg of the coil. I placed a line on the coil to mark that point. Keep in mind the engine is running at 2000 RPM in this photo.

Firing point ARC

This shows the position of the stock flywheel firing point. The engine is not running in this photo. Both of the flywheels were firing at 24 degrees BTDC.

Firing Point Stock

With the engine disassembled it is time to look things over and come up with a plan. The first order of business it to determine how much material will be cut from the block and head. The base circle of the stock cam is .870” and the ground cam is .755”. The difference is the radii of those is .057”, this lowers the pushrod that amount and removal of that much material will put the rocker arms right back at the stock position. Deviation from that height will most likely not cause a problem and may actually help a bit.

Using an indicator setup I measured the piston to be .007” in the hole.

In the hole

I need to be mindful of piston to head clearance when setting this up. I am going to try to stay around .030”. Given the .017” or so existing clearance I am going to need to go to a thicker head gasket. The block will get milled to zero deck height with a flat top piston and the head gasket will be sized for the clearance.

I arbitrarily had picked .050” to be milled from the cylinder head. At this point that sounds like a good starting point.

After the head is bolted down I checked to see that there would be an even amount taken off all sides.

Indicating head

I measured the depth of the head between the valve seats to be .291” stock. This gives a reference to how much material has been removed.

Cut head

Using a CD case with a couple of holes drill in it and a syringe I cam up with a crude way to check some volumes. I used a dial caliper to measure the movement of the plunger in the syringe rather that try to read from the graduations on the cylinder. Put a bead of grease around the edge to seal in the water.

Piston cc's

Using the CD case and some other unscientific methods I came up with the following volumes

.010” head gasket .025 cc .040” head gasket 3.69 cc piston dish 3.5cc top of ring to top of piston .43cc .007” in the hole 4.28 cc cylinder head 20.0 cc milled cylinder head 15.5 cc

Combustion chamber volumes for some combinations are

Stock 27.8 cc Flat piston, 0 deck, thick gasket 24.12 cc Flat piston, .007 popup, .040” gasket 19.84 cc Flat piston, cut head, .040” gasket 19.62 cc Flat piston, cut head, .007 popup, .040” gasket 15.34 cc

Using a swept volume of 196 cc will put the compression ratios respectively at 7.1, 8.1, 9.9, 10.0, 12.8. These are some pretty rough guesses but it gives me some idea of which way to go.

The zero deck height piston, milled head, and thicker gasket seems to be in the area that I am looking for.

Using a ¼” die grinder with an egg shape cutter I did what I could with the ports. Basically blend the edges into the bowl and make the best short side radius possible. There really are not a lot of choices with the given port.

There is not going to be any fancy work on the valves and seats at this time. After I get some test it will be easy to remove the head and get a separate test on the effects of extra work in this area.

Both valves will get refaced at 45 degrees just to freshen them up a bit.

Grinding valves

The seats will just get trued up. I really can’t work on addition angle right now because I need to save the material to match the valves up at the next testing session.

Grinding seats

With the seats and valves mated up it is time to find the valve spring installed height. Put a spacer of known size in place of the valve spring and use an indicator to measure the travel of the valve until the spacer stops the movement. Add that measurement to the thickness of the spacer. I will be using exhaust retainers because they allow the use of lash caps. I found the heights to be .909” intake and .868” exhaust. Checking the intake valve with the intake retainer yielded .857” height.

Checking the springs that I have with those heights gives me seat pressures of 4 pounds intake and 11 pounds exhaust. Seams that .825” will give 18 pounds of seat pressure so shims will be needed to get to that point.

Making shim Checking spring force

First step on the block is to enlarge the oil return hole located between the lifters. I used a 17/64” bit.

Oil Return

With the rod and piston installed it is time to remove the necessary material from the top of the block. I should say at this point that the flat top piston and gasket was not in the original budget. I had to add the shipping on the engine to get that to fit. I don’t know how necessary it was but wanted to get it in there for future modifications to the engine. The plan was to go for zero deck height. After taking measurement and finding head gasket to be around . 046” I decided to go with .005” pop up.

Head Gasket Rod & Piston Milling Setup After Milling

After the milling I used a 45-degree sanding cone to knock the sharp edge off of the top of the cylinder. Just to help prevent damage to the rings during final piston installation. Measuring with a bore gauge if found the bore to be with .0005” at all locations. The clearance is in the .001” to .0015” range. This is typical as the block has been heat cycled a few times and the dyno runs. A very few strokes with the hone should even out the cylinder wall and give a nice fresh crosshatch. After honing a couple of passes with a flex hone will knock off any sharp peaks left by the stone hone. If I continue to work on the Honda style engines I will make a torque plate for use when honing.

Hone Flex Hone

The final preparations now include prepping a new set of piston rings, cleaning all part thoroughly, and finish up the crankshaft by lapping the flywheel and cleaning the crankpin with crocus cloth and lapping oil.

With the bottom end assembled the crankshaft endplay is checked. I noticed earlier that the endplay was small to non-existent. After removing and cleaning both of the bearings and using a new gasket the endplay checked to . 005”.

End Play

With the engine assembled a degree wheel is installed to accurately set the ignition timing to the stock 24 degrees and to check the cam timing. I couldn’t come up with a convenient holder to keep the indicator over the rocker so I clamped the engine to the milling table and used a magnetic holder. Seemed to work well enough. There was no card with the cam. DynoCams advertises 236 degrees duration, I was coming up very close to that and measuring .265” lift. I didn’t think there would be an issue with valve to piston clearance and checking it proved there was more than .120”.

Checking Cam

With the final assembly completed and 14 ounces Cool Power Light oil in the crankcase it is time for another round of dyno testing. After a short warm-up and break in period here are some more results.

RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600 HP 9.20 9.58 9.88 10.12 10.19 10.03 9.76 9.59 9.48

Adding 2 degrees of ignition timing and .039” main jet.

RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600 HP 9.30 9.67 9.98 10.19 10.25 10.22 10.17 10.16 10.22

On the initial run the engine just did not pull well through the entire RPM range. I did not try to re-jet or adjust at that time. I knew the engine would run better with more ignition timing and time would be better spent tuning at that point.

With both the 24 and 26 degree timing the peak horsepower still occurred at 4800 RPM, but with the higher timing the power stayed up better after that point.

If I had another header this would be a good time to try it. At some point I will try the header with it’s intended RLV muffler.

Now it is time to remove and disassemble the carburetor. I measured the smallest diameter in the venturi area to be about .612”. Once the cutter was centered I cut .005” per pass. At around .675” the cutter broke through the wall into the low speed jet passage. A bit of Magnum Steel two part epoxy remedied that issue. A flex hone was used to smooth things up a little bit.

Boring carburetor Cutting fixture Throttle shaft

The choke is removed, the throttle shaft and plate are thinned, and the screw has extra material removed. I checked this carb on my flow bench against a PZ 22, I can’t give exact CFM numbers because my bench only compares, and let’s just say there is no comparison. In the end this engine will be wearing a Walbro.

The carb work certainly helped. The engine accelerates very well up to about 7500 RPM’s were it seems to just be done. I tried main jets from .030” to .042” and the largest was the best. Would some more help? I think there may be some power left to tune out of this engine but not enough to make the ultimate goal of fourteen and a half horsepower. I don’t have a spare emulsion tube at the time but there may be a bit a power there.

At this point the best 500-rpm average is 11.43 HP. The final run peaked at 6000 rpm compared to the previous high peak rpm of 4800. Quite simply there is not enough carburetor.

The results with the modified carb are shown below. Notice the scale of rpm’s is different than the previous test.

RPM 5200 5400 5600 5800 6000 6200 6400 6600 6800 HP 10.82 10.91 11.10 11.29 11.31 11.23 11.09 10.97 10.84

Here is an overlay of the primary test. In ascending order they are:

BOX stock Filter adaptor, header, billet flywheel Millwork, piston, and cam swap Increase ignition timing +2 degrees over stock Bored and worked carb

Overlay graph

One point that needs to be made is the use of the fuel pump. While waiting for some parts to arrive I had modified an Animal intake to for this engine. I put a hose barb in the intake for pulsing the fuel pump. I have billet oil fill hole adaptors to pulse from the crankcase but the Briggs threads are not the same. I pulsed the fuel pump from the valve cover for the stock carb, from the existing hole above the baffle. With the baffle in the cover the fuel was very slow to come out of the fuel container. With the baffle removed it pumped quite fast. I wanted to come up with a better way because this method was keeping the engine from being vented. It was pushing out a bit of oil from around the valve cover. The cover and the gasket are not the highest quality but the point is there was pressure in there. And yes, it most likely was robbing some power. I now realize there is enough space to get a hose barb in the valve cover beneath the baffle. I will set the pump up in that fashion when I convert the stock carburetor to methanol in the future.

Really at this point I just can’t believe that ignition timing, valve springs, carb jetting, or any other tuning will gain what I set out to test. The initial power of the engine just made to goal too lofty. Still this is a great improvement as the overlay graph indicates and would be one heck of a fun ride on a kart or mini bike!!! If the engine would have produced the six or six and a half that I expected I would continue the experiment to get into the 12 hp range.

Well, actually I will continue the experiment, just without the budget in mind. I have already modified an Animal intake to fit the head and set up a new PZ 22 for methanol. The engine will also be getting 1.3:1 rocker arms, +1 mm intake valve, replacement exhaust valve, new valve springs and retainers, chrome moly push rods, two angle valve job, the timing will go up to 30 degrees, and the sparkplug will be an Autolite 3910.

The first thing I notice after removing the head is the nice color left in the head by the fire ring on the head gasket. This makes a very nice guide to blend the combusting chamber walls from the seat to the block-mating surface to help unshrould the valves a bit.

Step one will be to widen the inside diameter of the intake seat 1 millimeter. I ran the cutter to about the top of the valve guide. After the seat inside diameter was cut to .933” a die mini grinder was used to blend the edge where the cutter stopped and the short radius back into the bottom of the seat.

Valve seat boring

The boring left the 45 degree cut very thin. With a bit of 600 lapping compound on the valve I check the contact point of the valve and seat. It is near the inside edge of the valve but the seat is sufficiently large. I wanted to go with a three angle valve but experimenting showed it would be difficult to get the 60 degree cut in the bottom with the stones I have right now. Sure I could have redressed the 30 or 45 stone to 60 degrees then back to its original angle.

I cut the top 30 degree of each seat with a 1 1/8” stone until the stone was getting into aluminum on the chamber wall. I then made the 45 degree cut until it was the width I wanted. On both sides the 30 degree cut extends past the outside diameter of the valve. Using Dykem layout fluid helps to show the relations of the angles. One can see in the photo where the valves meet the seat. In the future I can reduce the size of the 30 degree cut, move the seat further out, and put the 60 degree cut on the bottom. At this time I do not have the means to install 5.5 mm valve guides. Since the valve seats need to be trued after installation of guides that would be a good time to complete the seat work. History with kart racing has proved to me that good valve guides are worth power.

Valve seat

The valve springs and shims that came with the ratio rocker kit measure about two pounds lighter than the spring setup already installed. For now I will stay with the 18 pound springs and shims. I do think the retainers are nice and I like the lash caps. The rocker arms are noticeably shorter.

Valve springs Rocker arm

With everything assembled I thought that tuning the stock carburetor for methanol would be worth the time. After the pilot jet was adjusted so that the idle was good and the engine would accelerate crisply from idle it was time to work on the main jet. About the time I thought I had found the correct main jet the methanol took its toll on the epoxy and let raw fuel seep through. I was just accelerating the engine against the dyno flywheel to about 5000 rpm to see how it responded without recording so there are no results. I do have a good idea on where to start with the jets (and the limits of boring) on the next carb though. After purchasing a new carburetor I may return to gasoline for a bit as hindsight says there may be a better way to go about gas tuning by adjusting the jets and timing together.

With the new carburetor reworked and set up with the jets from the failed first carburetor it is time to try again. The original carburetor was a good experiment on where the fuel passages are located and how NOT to set a brazing torch to patch a hole. I must mention that I went through the casting in two places with the second carb while grinding but they were repaired quite nicely with a brazing torch and aluminum brazing rod. I must add the replacement carb was a different manufacturer than the first and in my opinion may not have the performance potential of the original carb.

Here is a view of both end of the new carburetor and one of the patches. The other patch was at the low side jet area. These views represent just about as much material that can practically be removed from the venturi area. I could possibly have the ceiling raised a small bit after the addition of the aluminum on the top. The two limiting factors are is the wall at the pilot jet area and the ledge that holds down the emulsion tube on the bottom.

Patch Carb 1 Carb 2

The fuel metering circuits on these carb are a bit unique and there are endless possibilities to modify the relationships within the carburetor. Here is one thought to ponder, ALL of the fuel enters below the main jet through two holes in the side of the casting. The pilot jet is fed from the outside of the emulsion tube. It’s no far off now as the engine runs VERY well. If I had a choice though I would like to try to richen below 6000 rpm and lean out a bit from there on to a peak rpm of about 7400.

Stock Appearing Methanol

This test exceeds the original test goals in horsepower but I cannot say that the actual goal was met because the engine has the ratio rockers and the +1 mm intake valve. The rockers could be easily changed but there is no going back on to the stock intake valve.

Keep in mind that the stock appearing methanol carb was conducted after the following PZ-22 test. A RLV modified “square hole” muffler was used which would have increased the performance of the Walbro carburetor. Also the valve cover was modified to pulse the fuel pump from beneath the baffle. With some experimenting with the fuel circuits there can be some improvements with the modified stock carb.

The final test will involve testing a Walbro PZ-22 on methanol. This is a new carburetor with only the fuel nozzle, pilot jet, main jet, and float height set for methanol. I do not want to modify the casting as don’t want to make the carb out of spec for stock class Animal racing if this engine prefers a Tillotson.

The Animal intake can be made to fit the bolt holes and line up with the port quite well by elongating the mounting holes. The problem being that this placed the carb at a fairly steep angle. The testing was done with the carb in that position but I have since went back and cut the flange from the intake and welded it back at so that the carb will be level when on an angled engine mount.

Walbro Carburetor

With the PZ hooked up I did a pull up to 7000 RPM. After seeing the graph still going up at 7000 it was time to see some more. One more run to 7500 + showed it was still holding. Now install the RLV WKA stock class muffler for the final pull. The muffler showed better power all around. This engine sounded impressive, never skipped a beat, and asked no questions about going to a clean 8000+!!!!!

As a final test the ignition timing was increased to 34 degrees and the main jet increased by .004”. This seemed to help across the entire rpm range

Below are the results of the last runs and an overlay of the final run verses the best results of the modified original carburetor running gas and the original box stock test.

30 degrees timing .050” Main jet

RPM 6000 6200 6400 6600 6800 7000 7200 7600 7800 HP 14.70 14.86 14.91 14.90 14.94 14.93 14.82 14.01 13.58

34 degrees timing .054” Main Jet

RPM 6000 6200 6400 6600 6800 7000 7200 7600 7800 HP 15.11 15.32 15.45 15.52 15.61 15.60 15.41 14.61 14.26

Final run Final Overlay

Keep in mind there is some room for improvement with modification to the casting of this carb. Also this was my only attempt at jetting the PZ based on my experience with WKA stock class Briggs Animals. I simply removed a carburetor from a new Animal and reamed the nozzle, pilot & main jet, and swapped needles to my initial tune for those engines.

A post runs inspection showed the lash caps to have a bit of wear directly in the center. No real signs of heavy swiping. Head bolts and studs did not budge when checked with a torque wrench. The lash was reset using some blue Loctite on the stud.

Lash cap wear

At this point I am going to order a new clone carb and head. Hindsight is 20/20. Both will be only for the use of going back to revisit the original test.

In conclusion, is this a do it yourself project, probably not? This was my first attempt at blueprinting a Honda style engine. I have completed somewhere in the mid 200’s of engine new builds and/or rebuilds but only for 5 horse flathead and Animal stock class kart engines. That finances the tools, equipment, and projects like this, plus I will make a few bucks on this engine.

Front View Rear View

As for the original question, can the power be doubled? Honestly, maybe it can!!

I hope you enjoyed and check back later to see if there are any updates.

Thank you,

Travis Atwood [email protected]