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1972 XLCH and dual edelbrock quicksilver carbs

Started by ethan, July 05, 2016, 02:39:25 PM

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turboprop

In the early '90s I was lured into running a dual carb dual runner setup on a hot rod 96" evo. It didn't work. Bike ran ok, but could never really tell (butt dyno) if there was an improvement. After a few years of running  and fighting with it, I was one of the first guys in town to use a local shop's new dyno. The numbers were horrible, the curves sucked. On the spot we pulled the dual carbs and put on a Super G, picked up a bunch of peak HP and the curves shifted around a lot. Much better. Those dual carbs looked cool, and sure fooled a lot of sheaple (including me). Luckily I was able to sell it before word got out about how bad they sucked.
'We' like this' - Said by the one man operation.

JW113

Quote from: drifter on September 27, 2016, 09:06:26 AM
In my recent research, if I remember correctly (there has been a lot of it), Harley put one carb on each cylinder on the XR-1000.  Compression, bore and stroke stayed the same but the advertised HP changed from 56 to 70.  You might want to explore what the Moco did to achieve that result.

Yes the XR had two carbs on the right and exhaust ports on the left. One interesting set up that I've seen a couple times is to use two rear heads, with the one on the front mounted backwards. This puts one carb and one exhaust on each side. Looks kinda odd, but evidently works well. Also seen two front heads used with carbs and exhaust on the right side, but looks like a plumbing challenge to me.

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

Hossamania

Yup, big old dual carbs sticking out look cool as hell, but a tuning challenge, to be sure.
If the government gives you everything you want,
it can take away everything you have.

turboprop

Quote from: drifter on September 27, 2016, 09:06:26 AM
In my recent research, if I remember correctly (there has been a lot of it), Harley put one carb on each cylinder on the XR-1000.  Compression, bore and stroke stayed the same but the advertised HP changed from 56 to 70.  You might want to explore what the Moco did to achieve that result.

Has been attempted by many. Extremely difficult. Special cams have to be made so R&D becomes expensive and slow. If dual front heads really offered an advantage they would be seen more at places like Bonneville and El Mirage.

The dual carb thing worked on the XR-750 race bikes because they operated in a very narrow RPM band. Their narrow bandwidth allowed the intake  and exhaust lengths to be individually tuned. Works well on the oval track in a narrow rpm band, horrible on the street.

FWIW, I had an XR-1000 many years ago when I was a kid. That bike would scream (relative for the day) , but was a turd at anything less than ¾ throttle. That was with stock cams and exhaust. My buddies on regular iron heads would typically beat me racing around town light to light. When the Evo sportsters came out it was time to replace the XR. Again, it looked cool, but in reality it wasn't that much faster.
'We' like this' - Said by the one man operation.

JW113

If you use two rear heads, with the one on the front flipped around to put the carb/exhaust on the left, you don't have to do anything with the cams. The intake/exhaust valves are then in the same place as a front head. Other than having to fabricate the exhaust and intake manifold, which most any fab shop can do, I don't see that it's difficult at all. You do need to machine the new front head to put a bolt boss for the rocker box on the spark plug side.

Can't speak to why you don't see more ironheads set up like that, but two cylinders sharing a single carb is a well known deficiency in the Harley Davidson V twin configuration. I am trying to think real hard how many other motorcycle manufacturers (with the exception of Indian (RIP) and Triumph) that have cylinders that share carbs. Almost every one made since, what, 1960 has had one carb per cylinder. The Japanese V twins, Ducatis, & Moto Guzzis all seem to run great with dual carbs, right?
:nix:

All that said, I've no plans to do this to any of my ironheads or HDs in general. Just speaking to the subject line of dual carbs on a Harley. Yes, it can be done...

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

turboprop

Quote from: JW113 on September 27, 2016, 09:13:36 PM
If you use two rear heads, with the one on the front flipped around to put the carb/exhaust on the left, you don't have to do anything with the cams. The intake/exhaust valves are then in the same place as a front head. Other than having to fabricate the exhaust and intake manifold, which most any fab shop can do, I don't see that it's difficult at all. You do need to machine the new front head to put a bolt boss for the rocker box on the spark plug side.

Can't speak to why you don't see more ironheads set up like that, but two cylinders sharing a single carb is a well known deficiency in the Harley Davidson V twin configuration. I am trying to think real hard how many other motorcycle manufacturers (with the exception of Indian (RIP) and Triumph) that have cylinders that share carbs. Almost every one made since, what, 1960 has had one carb per cylinder. The Japanese V twins, Ducatis, & Moto Guzzis all seem to run great with dual carbs, right?
:nix:

All that said, I've no plans to do this to any of my ironheads or HDs in general. Just speaking to the subject line of dual carbs on a Harley. Yes, it can be done...

-JW

How does the work for the pushrods?
'We' like this' - Said by the one man operation.

JW113

The bolt holes for the rocker boxes are symmetrical at the valves. They can be installed in either direction, i.e. can be flipped on the head to stick out the other side. You have to machine a boss to bolt the pushrod side of the rocker box to the head, and clearance the fins for the pushrod tubes. There used to be a guy out in Albert Lea MN named Ironhead Tom, was a fabulous head porter for ironheads, did some work for mine. Was also a  well known drag racer in the upper midwest. He is the one that told me about the flipped rear head set up, was on his drag bike I believe. Sadly, he passed away a few years ago.

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

turboprop

So you are saying to flip the head around on the barrel, and then machine the head and/or rocker box so that the rocker box can be inverted on the head?

Interesting.
'We' like this' - Said by the one man operation.

JW113

Use a rear head on the front cylinder. Flip it around so carb and exhaust spigots point out the left side of bike, it will bolt right on. Install rocker box to head in normal direction, even though backwards on head, it will bolt right on too. Except there is no boss for that seventh bolt on the right side between the push rods. Will need to machine head for that, and a little bit of clearance in the fins to clear push rod tubes. Oil line hooks up like usual. I think you also have to do some machining to the head for the oil drain back holes. No mods to the rocker boxes, no special cams needed. You now have plenty of room to mount two carbs, one for each cylinder, one on each side of the bike.

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

Jako1

The 2 carbs they thought would smooth out the air and fuel{S&S}
Tears later the XR750 and 1000 did that with 2 separate Delorto carbs{ might be off on the make}
Any way this was a different seat up
you can run 2 ft heads so the intakes support single carbs
Racing tuning trick by Jerry Branch and team
Nuff Said," Were Burnin Daylight, Lets Ride", {Sober 29 years}And Proud

JW113

Yes you can run two front heads, but that creates a couple problems. One, where the rear exhaust and front intake crisscross takes some funky pluming, it's pretty tight. Two, timing the cams for the rear cylinder with the valves reversed. All can be done, just takes some clever fabrication and engineering.

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

Jako1

XR1000, dual carbs street able 90 hp
Did not sell well
Dropped from the line
The XR750 is still alive today  :chop:
Nuff Said," Were Burnin Daylight, Lets Ride", {Sober 29 years}And Proud

JW113

I think the problem with the XR1000 was "one sportster for the price of two"...

Cool bike, never the less.

-JW
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

turboprop

I had an XR1000 and it wasn't all that. Evo sportsters with just a little bit of mods would smoke that XR.
'We' like this' - Said by the one man operation.

Hillside Motorcycle

Almost bought a NIB XR1000 once, but Ed is right, an Evo XL will run VERY well with minor work.
Scott
Otto Knowbetter sez, "Even a fish wouldn't get caught if he kept his mouth shut"

hbkeith

Quote from: Jako1 on September 30, 2016, 03:17:35 PM
XR1000, dual carbs street able 90 hp
Did not sell well
Dropped from the line
The XR750 is still alive today  :chop:
The Factory stopped making XR750 complete bike in 1980 , now all you can get is a skeleton engine

hbkeith

Quote from: JW113 on September 27, 2016, 12:58:47 PM
Quote from: drifter on September 27, 2016, 09:06:26 AM
In my recent research, if I remember correctly (there has been a lot of it), Harley put one carb on each cylinder on the XR-1000.  Compression, bore and stroke stayed the same but the advertised HP changed from 56 to 70.  You might want to explore what the Moco did to achieve that result.

Yes the XR had two carbs on the right and exhaust ports on the left. One interesting set up that I've seen a couple times is to use two rear heads, with the one on the front mounted backwards. This puts one carb and one exhaust on each side. Looks kinda odd, but evidently works well. Also seen two front heads used with carbs and exhaust on the right side, but looks like a plumbing challenge to me.

-JW
Jared Mees has one of his ( Kenny Tolberts) XR750,s set up kinda like this , they call it Frankenstein , he has raced CNC1  on it

Dave*M

I know this is a little old for a reply but I had a 79 sporty with dual carbs.38mm round slides with 2 front heads 4 5/8 stroker and v9 grind cams. I had tubes welded onto the intake ports and had an exhaust made up. The bike ran really well above 2500 rpm and was a kick start only.
It was reliable as well. The rocker box needed to have if I remember correctly 1 hole relocated and drilled out and that was it. Might have a pic or 2 still kicking around. Never had it on a dyno but would outrun an 80 inch shovel with no problem. Had it up and over 120 mph but don't know how much more as speedo was pinned. Did it once and never did it again.Took it on 3 trips that were over 1000 miles. Still wish I never sold it.

Burnout

March 06, 2019, 06:42:55 PM #43 Last Edit: March 06, 2019, 06:51:32 PM by Burnout
A real XR had special aluminum heads, magneto and ball bearings on the cams with a close ratio trans.

The XR750 was a track bike it's power band was next to useless on the street.

XR1000 was a wankers wet dream not legal to race street bike detuned and not really any better than a warmed up XL1000.
No good bearings on the cams and a heavy street frame a fuel tank that was too big and passenger foot pegs! 10" brakes that were way behind the times for 1984.

I used to dream of owning one, until I rode one.



They don't call me Ironhead Rick just because I'm "hard headed"

Hillside Motorcycle

Quote from: hbkeith on October 03, 2016, 04:56:11 PM
Quote from: Jako1 on September 30, 2016, 03:17:35 PM
XR1000, dual carbs street able 90 hp
Did not sell well
Dropped from the line
The XR750 is still alive today  :chop:
The Factory stopped making XR750 complete bike in 1980 , now all you can get is a skeleton engine


Those XR1000's were about 75hp..........dynoed several.
Otto Knowbetter sez, "Even a fish wouldn't get caught if he kept his mouth shut"