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Evolution of a HotRod - Part 4 Carburetor (Read 1150 times)
DragBikeMike
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #30 - 07/08/21 at 01:51:23
 
Install a simple mudflap on the rear fender to help keep the dirt and water off the filter.  There’s never any crud in my induction system, so I think the mudflap and filter are doing a good job.
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DragBikeMike
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #31 - 07/08/21 at 01:52:50
 
Although the airbox still has a nipple for the engine breather hose, there’s no way to attach a breather filter.  A catch can assembly takes care of that.  Here’s one installed on an S&S carb setup.  You can use a similar catch can on the PWK installation.
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DragBikeMike
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #32 - 07/08/21 at 01:53:45
 
Once installed on the motorcycle, the cylindrical air filter looks professional (IMO).
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #33 - 07/08/21 at 01:54:28
 
All the factory components still bolt right up.  The ignitor box and decorative tins still attach to the airbox, right where the factory intended.  Now we’re talkin AIR FLOW.
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DragBikeMike
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #34 - 07/08/21 at 01:56:26
 
Right off the bat I could tell the difference.  Now it would pull past 7000 in third gear (all the way to 7300).  After a few test & tunes, it was time to see how it did against the stopwatch.  I achieved best performance with a #35 pilot jet, #142 main jet, and the needle clip in the fourth groove (rich).

Second Gear 4K to 7K: 3.24 seconds            0.42 seconds faster than flat-panel

Third Gear 4K to 6.5K: 5.77 seconds            0.87 seconds faster than flat-panel

Third Gear 4K to 7K: 8.85 seconds

Fifth Gear 3.5K to 5K: 5.65 seconds            1.36 seconds faster than flat-panel

Fifth Gear 3.5K to 5.5K: 8.70 seconds      1.56 seconds faster than flat-panel


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DragBikeMike
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #35 - 07/08/21 at 01:58:55
 
Progress.  Now it’s behaving like it should.  It’s measurably faster than the stock carburetor (second gear -.31 seconds, third gear -.76 seconds, fifth gear -.49 seconds), and it pulls well past 7K in third gear.

But…. would the stock carb have benefited from this new air filter setup?  Time to switch carbs.  It was a simple job to throw the stock carb back on, but tuning was another story.  It couldn’t get enough fuel.  Running the stock header, I had previously achieved best time with a 155 main jet and the special compound slide needle at +.08.   Now it would hardly run with a 155 main jet.  It was scary lean.  It ran best with a #200 main jet.
 
The bike felt good with that big jet and big air filter, but the stopwatch don’t lie.  Even though it felt gangbusters, had great throttle response, perfect idle, zero afterfire, the whole enchilada, it was slower than it was with the flat-panel filter.  We’re not talkin gross disparity, but it was measurably slower.  After numerous WOT pulls and much fiddling around with jets & needles & clips & spacers, it was apparent that it wasn’t gonna get any faster.  Something about that filter didn’t sit well with the stock carburetor.  I suspect it has something to do with the differential pressure across the diaphragm, but I’ve got no way to test that.

With the K&N RD-0710 filter the stock carb ran:

Second Gear 4K to 7K: 3.53 seconds            0.02 seconds faster than flat-panel
     
Third Gear 4K to 6.5K: 7.08 seconds            0.55 seconds slower than flat-panel
     
Fifth Gear 3.5K to 5K: 5.68 seconds            0.04 seconds faster than flat-panel
           
Fifth Gear 3.5K to 5.5K: 9.43 seconds      0.24 seconds slower than flat-panel

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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #36 - 07/08/21 at 02:00:52
 
Time to reinstall the PWK and try it with the Mac header.  That was a simple operation, no surprises.  The bigger header along with the increased air flow worked great.  Jetting remained the same.  Pilot jet #35, main jet #142, slide needle clip fourth groove.

The stock engine with K&N 3x5 cylindrical air filter, PWK carb, Mac exhaust header, and LCGP high flow muffler ran:

Second Gear 4K to 7K: 3.13 seconds            0.11 seconds faster than stock header

Third Gear 4K to 6.5K: 5.58 seconds            0.19 seconds faster than stock header

Third Gear 4K to 7K: 8.20 seconds            0.65 seconds faster than stock header

Fifth Gear 3.5K to 5K: 5.48 seconds            0.17 seconds faster than stock header

Fifth Gear 3.5K to 5.5K: 8.29 seconds      0.41 seconds faster than stock header


It maxed out at 6200 rpm in fifth gear (200-rpm increase).  It pulled 7400 rpm in third gear (200-rpm increase).  Based on the acceleration times, it’s obvious that the larger carburetor combined with the larger header improves overall performance.  
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #37 - 07/08/21 at 02:01:51
 
A carburetor installation wouldn’t be complete without a fuel economy test.  She went 63.3 miles and gulped down 1.14 gallons of 89 octane E-10.  It was an economy test, so I behaved myself.  It got 55.5 mpg.  Mileage decreased 9.5 mpg.  That’s a significant decrease in fuel economy.  I’m not sure what’s up with that.  I did the mileage run with the stock header.  I thought economy would be better with the small exhaust pipe.  I guess I will have to try again.  Maybe I can find a few more mpg with the Mac header.  I’ll let ya know.

Temperatures remain normal.  Cruising on the freeway, oil temp is usually around 210°F and cylinder head temp (CHT) is usually around 310°F.  When you start doing a lot of WOT runs, the CHT comes down a bit.

The open induction system doesn’t affect noise much.  Using my iPad with the NIOSH app, the noise levels at 1300/3000/4000 rpm are 66/78/79 dB.  Looks like the wide open airbox is 2dB louder at idle and 1dB louder at 3K.  It’s not any louder at 4K.  That seems acceptable to me.  It’s quiet.
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #38 - 07/08/21 at 02:09:03
 
This completes the carburetor portion of the project.  All it took was a little more air filter to get the budget mixer up to speed.  I think $28 bucks for the carburetor was $28 bucks well spent.  The jetting is dialed in.  That budget carb is so sweet I ordered a 36mm to play around with.  I’m curious how the two stack up.  These carbs might be an excellent solution for the folks who have a mixer that just spent the last two years with fuel in the tank and the petcock left on.  One of those beauties that look like the LaBrea Tar Pits.

Let’s take a look at the results using test data from the stock header setup (keeping the project simple &  cheap).  The setup includes a completely stock engine, PWK38 carb, K&N RD-0710 air filter, modified airbox, catch can, stock exhaust header, LCGP 2.5” resonator with baffle.

We have improved the overall performance of the motorcycle.  Carburetion is excellent but fuel economy is down by 9.5 mpg.  Backfiring has been eliminated.  Audible noise has increased a modest amount, but the quality of the exhaust note is more pleasing to the ear.  Compared to the box-stock motorcycle, third gear acceleration has improved by 4.71 seconds, and fifth gear passing acceleration has improved by 3.82 seconds (13.73 seconds if you run it all the way up to 5500 rpm).

I think that’s pretty good for such a small investment in time and money.  We haven’t done any major work; the engine hasn’t been opened up.  Most of us could accomplish these simple modifications for under $350 bucks.  The tests show that if you throw on a bigger header it will be a bit faster with no appreciable loss of grunt.

All the easy stuff is done.  We have picked all the low hanging fruit and kept a close eye on our bank account.    Now it’s time to start doing some open-heart surgery.  As I recall, the general consensus was camshaft next.  Part 5 will install a DR650 cam.

At this point, I have done 153 WOT acceleration pulls to dial in the different combinations.  There’s a little over 2000 miles on the engine since it was restored to box-stock configuration.  The old girl is holdin up good.  No leaks.  No ugly noises.  Not using any oil.  Zero oil accumulating in the airbox or catch-can.  It’s a solid motor.

I hope some of you find this project informative and can use the data I collect to help make decisions on your own project.  If you have suggestions or comments on my test methods, post a reply so we can discuss.   As mentioned earlier, if you have a particular component or modification that you would like to see included, let me know and we can collaborate.
 
Best regards, Mike          
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #39 - 07/08/21 at 07:04:09
 
Thanks for all your hard work and careful documentation!
The Chinese counterfeit stuff is crazy. Supposedly there are fake NGK spark plugs out there that fall apart.
Funny, because when I was growing up the Japanese were doing crap copies of Western stuff, now it's their turn to get bit on the ass.
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #40 - 09/13/21 at 15:49:10
 
I wanted to alert everyone about a problem I had with the 2" ABS elbow used to connect the air filter to the carb boot.   I've been testing a new engine and went to make an adjustment on the carb.  While removing the air filter I noticed a big crack in the ABS elbow.  The elbow was essentially crumbling in my hand.

This elbow is not under any stress, and it doesn't get hot.  I've been running it for a long time (since about December of 2019).  I guess the fuel vapors eventually break down the ABS plastic.  I picked up an ABS replacement just to keep my test program going and ordered a PVC 2" street elbow.  I have a sample PVC fitting soaking in gasoline to see how the PVC holds up.

Anyone else have any trouble with ABS?  Anyone else tried PVC?
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #41 - 09/13/21 at 16:47:11
 
I have a PVC pipe between my air intake and filter. I installed it mid June and there are no visible signs of deterioration. I heated the PVC with a heat gun to shape it to mate with the Uni air filter. I'll keep visually and physically inspecting it going forward.
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Gary_in_NJ
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #42 - 09/13/21 at 17:24:55
 
If a piece of the PVC made it past the Venturi, it would be a bad day
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #43 - 09/14/21 at 05:48:57
 

 If it is not high-density polyethylene (HDPE) it should decay from gas vapors.

 The rate of decay depends on too many variables to break down just for this application.  ABS I would expect to decay over time, but how much time depends on a lot of things.
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Re: Evolution of a HotRod - Part 4 Carburetor
Reply #44 - 09/14/21 at 10:58:25
 
Absolutely correct Gary.  A chunk of that ABS through the carb and it would have been a bad day.  Fortunately, all the pieces stayed in the elbow.  It fell apart when I went to remove it.

The PVC test specimen is still in the gas.  I haven't pulled it out but it looks OK.  Eegore, do you think PVC (white) will hold up better than the ABS?

Jdvt, thanks for the input.  Please let us know how your pipe holds up.  One thing I noticed on my elbow was a slight oily residue in the area where it failed.  I had been seeing that residue for several months but there was no crack that I know of.  It just seemed to all-of-a-sudden fail.
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