Dual Carbs?

Harp

New Member
Jul 3, 2008
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Hello I have been thinking about this for awhile but never had the
time to do this idea. I'm not sure if there is a thread already about this
but I was wondering if it would work out
if I put on
"Dual Carbs on the bike".
If I somehow spit the inlet and have two stock carbs attached.
And split the Throttle cable and have that split aswell.

I'm thinking I would increase my revs/touque due to the increase of
gas and air intake but not sure how everything else
would turn out.
Is it worth going with this idea and testing it out?
Or would it just be a No go type of project
 
Sep 20, 2008
1,668
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Clearwater, FL
web.tampabay.rr.com
I only see one throttle cable and one fuel line to one carb...am I missing something?
Yeah, You're right...I never looked at it that good. I'll have to call Howard and ask him if it worked.

The video was to show-off the engine test stand, so I don't know if they were just running on one carb to try out the stand or if they have ever run it on both carbs.

Knowing Howard he has probably ran it on both carbs...how well it worked...who knows.

Jim
 

CalgarysFool

New Member
Aug 30, 2008
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Along the same line as doubling up, I wondered if there would be any advantage in modifying the head to take 2 spark plugs. Some bikes, like BMW, have dual spark plugs.

I thought it might, for example better ensure complete fuel burn.

Say, I know just the guy who could machine such a cylinder head . . . (Jim?)

Brenton
 

Finfan

New Member
Aug 29, 2008
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Tucson, AZ USA
I know most of you folks are mad scientists of the highest order but I have to ask again, Why? We've got single cylinder 2-cycle engines here most of which are made with questionable QA standards. For what you spend modifying these engines so you can blow them up you could buy a motorcycle with more power than you'll ever get out of these things. Yeah I know I'm being a wet blanket but I just don't see the point. I'm all for accessories that make them safer or easier to mount and use but going for excessive power seems kind of pointless to me. .dd.
 
Sep 20, 2008
1,668
2
0
Clearwater, FL
web.tampabay.rr.com
Along the same line as doubling up, I wondered if there would be any advantage in modifying the head to take 2 spark plugs. Some bikes, like BMW, have dual spark plugs.

I thought it might, for example better ensure complete fuel burn.

Say, I know just the guy who could machine such a cylinder head . . . (Jim?)

Brenton
Good question...I have no idea. I could definitely make a dual plug head. The only thing: firing the second plug.

I don't know if it would require a second CDI? And then the question would be, would the mag power two CDI's? For long trips the benefit of redundancy could prove useful. A 2nd plug, wire, and CDI...for "get home" insurance.

I don't think you could bridge to a single CDI. It would seem that the spark would take the path of least resistance, and only one plug would fire anyway?

Maybe this will prompt some thoughts from others...Anyone tried this on a stock cylinder head?

Jim
 
Sep 20, 2008
1,668
2
0
Clearwater, FL
web.tampabay.rr.com
I'm all for accessories that make them safer or easier to mount and use but going for excessive power seems kind of pointless to me. .dd.
It is pointless:

These engines are mounted on bicycles that are limited in thier ability to handle speed and horsepower safely. There is nothing wrong with a few minor mods to improve performance through the RPM range...but yes a full blown fire breathing monster on a bike is silly.

Howard has a race car...Like most of us he likes messin' with things...he isn't planning on marketing this, he did it for grins.

Jim
 

tyrslider

New Member
Sep 26, 2008
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RainCity
So the reason to upgrade to more/bigger carbs is the requirement for more gas. If you haven't created that, then the only real advantage is, maybe, some top end (main jet). But to get that, you can't just put on 2 carbs, you got to rejet those carbs to jets just over 1/2 the volume of the current ones. 'Cause now theres 2.
You can put power to these motors:
the 1st thing to do is an expansion chamber/rejet. ex/chambers make 2 strokes Come Alive!
The 2nd thing to do would be to rebuild the crank/bottom end. Build it to spin faster and stay together!
The 3rd More Fuel/Compression! Piston, Mill heads/alter squish, Porting, More/Bigger Carbs and probably a new ex/chamber.
After all that you'll need to run anywheres from 92 oct unldd to 110 leaded depending on what you did to it.
You could Probably easilly double the HP of these chengines, Maybe 50% gain w/o much loss in longevity, but definitely at over twice the price.
Jim, I agree about the sillyness for the road, not to mention the bad press.
But I'm thinking it would be fun to have a class at Bonneville or velodrome racing or who knows? I'm building my 1st speed bike for experimental purposes, even unmodded velo racing would be a kick

.wee.
 
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Norman

LORD VADER Moderator
Staff member
Jan 16, 2008
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Heck its just the need for speed thing what about a chopping off a front bank of a v-8 and fitting it in the bike? LOL..wee. I see someone took my idea of backwards mounting the cylinder a little farther but 2 carbs is not for me too much of a pain I'd go bigger with a tillotson pumper carb or a zuma.
 
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Harp

New Member
Jul 3, 2008
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Thank you for all the replys.
I came to conclusion that I won't go ahead with the project.
Just guess I'll stick some more lights on it =P.
I've got a spare car horn...Lets see if that might come in handy .sno.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
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up north now
Along the same line as doubling up, I wondered if there would be any advantage in modifying the head to take 2 spark plugs. Some bikes, like BMW, have dual spark plugs.

I thought it might, for example better ensure complete fuel burn.

Say, I know just the guy who could machine such a cylinder head . . . (Jim?)

Brenton

I may be full of it, but in my experience, dual plugs are used for two reasons- One, to have dual ignition, proven to not be optimal on either plug. That is to say, the plug(s) can not be in the best place, and mostly used so if your first ignition fails, the second set will keep you from landing in the middle of a playground, or woods. (aircraft)
Second, two plugs, one wire, used to swith over to the "good plug" if you foul the first. (how good can a non sparking plug be if the one that was lit fouled? Who knows, the design went out in the 70's as far as I know.)
 
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Norman

LORD VADER Moderator
Staff member
Jan 16, 2008
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I want to add a little to the dual plug thing it is not for redundancy it was necessary because of the dia of the cylinder to get the fuel mix to light off properly. On aircraft engines you test the mags. before take off and will see a rpm drop of about 75rpm you do this by shutting off one mag then the other.
Now we have 2 10 cylinder 2000hp 2-strokes turbo charged engines 310rpm wide open that have dual ignition that isn't for the safety factor for flying its because of the 14" dia of the cylinder then the ignition fires the flame front can't travel fast enough to light off the fuel mix so it gets lit at two different spots to get a complete combustion and no knock which if a plug does misfire you can hear it outside of the building as a huge bang and if your inside the building say standing on the engine catwalk you will almost poo your pants it will scare ya big time.
Now there is a lot of pilots who think that you need dual ignition for flying with the old mags that can be true it cost tons of money to change things on aircraft due to the hoops you have to jump through to get something done. The modern electronic ignition on autos is almost fool proof and I've read where the home builts are and have been running electronic ignitions for years and I have one on my airplane that's been flying for 25 years 1 mag and one electronic ignition why? I too thought it needed dual ignition at the time but guess what the electronic failed once and the mag hasn't yet.
I can't tell the difference when going from the mag to the electronic so the dual wasn't necessary for the combustion thing just for peace of mind and lighting my pocket of about $350.00 back in 1982
So do we need dual ignition on one of these bike engines I'd have to say na.
Norman
 
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tyrslider

New Member
Sep 26, 2008
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RainCity
Norm you said front bank; i only needed one cylinder from a 6.0L V8 dual carbed and dual plugged. Since the piston is 4" across I think your right about combustion travel, lol. Suzuki DR 750 single motor in a 2000ish Yamaha TZ 250 chassis.
 

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donuts31

New Member
Nov 9, 2008
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Colorado
My 1988 Nissan Stanza 2.4L 4 cylinder engine had 8 sparkplugs. It was mainly done for emissions. I do know that one set of plugs did fire at a slightly different time from the other set feeding the cylinders.