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bikesandcars

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..er I mean motorcycle intake manifold

I thought I'd try making a motorcycle carburetor manifold.

So far so good, but definitely a little sloppy because I don't have the tools I need. I haven't had a problem with the concepts / measuring, more just figuring out how to do the machining in my garage.

I picked up a 1.25" hole saw for drilling the manifold holes, but the mandrel I got sucked and the thing wobbled like crazy... making hole sawing very difficult. I was surprised at this because i got an expensive one.

I don't have a band saw either, so I used the sawsall to cut the 3/8" manifold flanges out... that was ok but not nearly as nice as a metal bandsaw would be...

all in all though, I might actually have something that works.

the concept is to use zx6r carburetors with the stock airbox, mounted at an angle so I don't have to remove the stock cross-bar..though I will have to cut a hole in the engine cover.

 
Looks like the proper length to get the tuning in the desired RPM for LeMons racing..

If increased rigidity is needed from a hole saw, weld the hole saw to the arbor. End of wobble.

If you're cutting these holes in a mill, get an end mill or shell mill near the desired diameter and use a boring head to get the hole size precise. There are circle fly cutters that work well in a mill too.


Bernice

bikesandcars said:
..er I mean motorcycle intake manifold

I thought I'd try making a motorcycle carburetor manifold.

So far so good, but definitely a little sloppy because I don't have the tools I need. I haven't had a problem with the concepts / measuring, more just figuring out how to do the machining in my garage.

I picked up a 1.25" hole saw for drilling the manifold holes, but the mandrel I got sucked and the thing wobbled like crazy... making hole sawing very difficult. I was surprised at this because i got an expensive one.

I don't have a band saw either, so I used the sawsall to cut the 3/8" manifold flanges out... that was ok but not nearly as nice as a metal bandsaw would be...

all in all though, I might actually have something that works.

the concept is to use zx6r carburetors with the stock airbox, mounted at an angle so I don't have to remove the stock cross-bar..though I will have to cut a hole in the engine cover.

Click to expand...
 
Dayton Tom said:
maybe you can shorten things up and keep it all under hood..

http://www.network54.com/Forum/1215...+the+bike+carb+conversion-----dial-up+warning-----
Click to expand...

I like what was done there, definitely more professional than I have the time, patience, or money for on this one.

My first mission is to get a basic steel manifold complete so I can prove the concept of motorcycle carbs and get the tuning right. After I complete the installation I'll have a much better idea of how to do it "nice". I like how he made spacers between the inner-carbs, something I would do for the next one maybe. I definately want to keep it short/tight, but need to use the stock air box.

From what I know: To do this cheap you need to use basically stock sportbike carbs, not aftermarket flat-slide racing carbs. Support for those stock units is very limited, and I think a lot of people make a mistake when they take the stock airbox off (modern sportbike (late 90's) carbs need that airbox to function properly).

I'll continue to post notes and pictures for you DIY'ers.

Bernice: It may not be optimal for HP, but I may have to take liberty shortening the tubes and introducing angles to the intake to get the initial model to fit, I'm going to see how it goes :)
 
Good start there.
You'll find, as I did, that it'll be hard to keep it all under the engine lid.
I found the most important thing (with the FCR's anyway) is to end up with the carbs mounted at the EXACT same angle as they would be on the bike they came from.
The mixture will go rich as the carbs are angled down. This can cause tuning issues.

I built 3, yes three different manifolds before figuring this out.

100_0136.jpg


But once the carbs were at the proper angle, they were quite happy and easy to tune.
 
kite63 said:
Good start there.
You'll find, as I did, that it'll be hard to keep it all under the engine lid.
I found the most important thing (with the FCR's anyway) is to end up with the carbs mounted at the EXACT same angle as they would be on the bike they came from.
The mixture will go rich as the carbs are angled down. This can cause tuning issues.

I built 3, yes three different manifolds before figuring this out.

But once the carbs were at the proper angle, they were quite happy and easy to tune.
Click to expand...

Thanks! as this is for Lemons I'm not worried about cutting out the deck lid to fit, so that takes much of the potential issue away.

Spot on about the angle, that's what I'm going for. The bowls are small in those carbs and float-level is critical... too much angle can really mess them up :) Now I wish I would have measured the engine angle in the car before I took the motor out...though I think I can get it close by just eyeing it up.
 
I think the engine sits at an 11 degree angle in the X. (someone chime in here if I'm wrong)
Find the PRECISE angle of the carbs as mounted on the bike.
Set your engine stand up accordingly and fab it.


I thought I could eyeball it too.........3 times :):):)
 
Cutter RPM

Bernice I suspect that when he was using the hole saw he was cutting at too fast of RPM. This job should be done in a mill or drill press with everything clamped down. Predrill pilot holes and then follow with the hole saw with pilot. RPM should be about 250 RPM or even a little slower. Cutting oil and steady heavy pressure is required. Most use too fast of cutter speed and the hole saw chatters and does not produce large chips but small filings.


TonyK.

Grimsby Ontario Canada.
 
Very possible, you are so correct about the tendency to run cutting tools way too fast which results in cooked cutting tools and instant work hardening of what is being worked on. The amount of force involved at the cutting edge and rigidity required to hold accuracy is easy to under estimate.

This work should be done in nothing less than a drill press or better, a reasonable sized mill. That trick of welding the hole saw to the arbor does help, but it is more of a band-aid than the proper solution.

Chatter is the usual signal that spindle speeds/feed rate or machine rigidity/set up is wrong. Not only does chatter results in a poor surface finish, it can do really bad things to the cutting tool.

Bernice


TonyK said:
Bernice I suspect that when he was using the hole saw he was cutting at too fast of RPM. This job should be done in a mill or drill press with everything clamped down. Predrill pilot holes and then follow with the hole saw with pilot. RPM should be about 250 RPM or even a little slower. Cutting oil and steady heavy pressure is required. Most use too fast of cutter speed and the hole saw chatters and does not produce large chips but small filings.


TonyK.

Grimsby Ontario Canada.
Click to expand...
 
Got it done/welded last night. looks ok, gotta touch up some welds and work the inner ports, but overall it looks good.

regarding drilling...I used a drill press at lowest speed, it was definately the crap arbor. My drill press hated the wiggle, so i ended up drilling pilot holes in the drill press and finishing the work by hand with my 1/2" drill.

I measured about 10 degrees for the engine too, then measured the angle of the float bowl and set the mounting plate... hopefully that does it.

clearance to the engine is great.

Note the color, I had it in the blasting cabinet (glass beads) for some surface-tension stress relief, and to clean it so I can spot poor welds (NOT a pro welder here).

here's a couple pics:



 
got it mocked up

Got the motorcycle carbs (1999 zx6r) mocked up.

Still lots of detail work to do, but it's actually getting somewhere

 
Looks great. Wonder what your mileage will end up being...

Likely doesn't matter does it? :)

Nice work. Keep the updates coming.
 
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