Author Topic: 1972 XLCH and dual edelbrock quicksilver carbs  (Read 2400 times)

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Offline turboprop

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #25 on: September 27, 2016, 09:22:27 AM »
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.

Offline JW113

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #26 on: September 27, 2016, 12:58:47 PM »
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

Offline Hossamania

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #27 on: September 27, 2016, 01:52:53 PM »
Yup, big old dual carbs sticking out look cool as hell, but a tuning challenge, to be sure.
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Offline turboprop

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #28 on: September 27, 2016, 02:15:21 PM »
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 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.

Offline JW113

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #29 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
2004 FLHRS   1977 FLH Shovelhead  1992 FLSTC
1945 Indian Chief   1978 XL Bobber

Offline turboprop

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #30 on: September 28, 2016, 05:24:07 AM »
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?

Offline JW113

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #31 on: September 28, 2016, 08:33:19 AM »
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

Offline turboprop

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #32 on: September 28, 2016, 09:00:42 AM »
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.

Offline JW113

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #33 on: September 28, 2016, 08:23:51 PM »
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

Offline Jako1

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #34 on: September 29, 2016, 05:05:08 AM »
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
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Offline JW113

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #35 on: September 29, 2016, 07:56:54 AM »
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

Offline Jako1

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #36 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:
Nuff Said," Were Burnin Daylight, Lets Ride", {Sober 29 years}And Proud

Offline JW113

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #37 on: September 30, 2016, 06:51:36 PM »
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

Offline turboprop

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #38 on: September 30, 2016, 10:44:52 PM »
I had an XR1000 and it wasn't all that. Evo sportsters with just a little bit of mods would smoke that XR.

Offline Scott P

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #39 on: October 03, 2016, 04:28:01 AM »
Almost bought a NIB XR1000 once, but Ed is right, an Evo XL will run VERY well with minor work.
Scott
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Offline hbkeith

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #40 on: October 03, 2016, 04:56:11 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

Offline hbkeith

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Re: 1972 XLCH and dual edelbrock quicksilver carbs
« Reply #41 on: October 03, 2016, 05:14:58 PM »
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