Single Weber DMTL conversion

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DuncanV
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Single Weber DMTL conversion

#1

Post by DuncanV »

Hi Guys, I'm new to this forum and seeking advice. I have been through the Unique Carburation thread but not found a definitive answer so the mods can redirect my questions if necessary.

I have a GL1000 trike conversion I have done myself and it has run fairly well for 4 years since I did the conversion, mileage is 77k and mechanically it is sound. It was always very thirsty (25mpg), and the previous owner confirmed it when I met him at a show. It also rattled at idle and even though the carbs were balanced to perfection I deceided to convert to single carb using the existing plenum and fabricated inlet tubes.

The carb is a 32/34 DMTL Weber (NOS) which is about as simple as a Weber can be, no auto choke, no solenoids, blanked off vacuum pipes and mechanical second choke not to cloud the issue. It sits atop the plenum with a 10mm adaptor plate with no need to cut the frame or any other mods.


The bike starts well on the choke and revs well, as smooth as can be BUT only over 3k. As soon as it dip below 3K it need to be revived with a few pumps of the accelerator pump and so it goes on. The pilot jet is a 50 and the main jet is 120 in both barrels of the carb. The primary of the OEM carbs is 65 so I wondered if this is the problem as only one (small), jet is not supplying enough gas to, now, all four cylinders.

There are no air leaks and the fuel pump can clearly supply enough for 3k+ running. The cutoff is quite distinct and it could be the changeover between pilot and main jet but I don't have any useful carb information. If anyone has any thoughts on the problem I would be glad to hear it, it is disappointing to me as the conversion and the theory behind it is all good and I don't want a fire breathing dragon, (I have a Buell and Ducati Monster for that!!), I just want a reliable and economical engine
Present rides
'09 Harley Dyna Super Glide Custom FXDC
'09 Buell 1125CR
'00 Buell Cyclone M2
'97 Kawasaki Eliminator ZL600
'74 Honda CB200
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Whiskerfish
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Re: Single Weber DMTL conversion

#2

Post by Whiskerfish »

Welcome to the forum! Not my area of knowledge so hopefully one of the Single carb guys can help out.
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Sugs
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Re: Single Weber DMTL conversion

#3

Post by Sugs »

I don't normally like to send people to other forums, but classicgoldwings.com has a whole sub forum dedicated to single carb conversions under their Goldwing Customizing section, and a ton of information on the particular carb you are dealing with.
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gltriker
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Re: Single Weber DMTL conversion

#4

Post by gltriker »

I don't have anything to contribute towards your single carburetor set-up questions.

Let us see a few photos of your GL1000 trike? ;)
Cliff (74yrs ;) )

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RE: a thorough fuel tank cleaning
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'75 GL1000 home built trike; http://www.ngwclub.com/forum/viewtopic.php?f=30&t=39996
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ericheath
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Re: Single Weber DMTL conversion

#5

Post by ericheath »

Pretty good stuff here: http://tedperkins.com/weber_principles.htm

My unscientific, non-experienced guess would be a bigger primary to allow more transition fuel in.

The guys at Classic all seem to be pretty creative at making it work in a variety of methods. It takes a fair amount of reading and then committing to a plan that is hopefully reversible if it doesn’t meet your goals.

I hope you’ll post here how it works out. Even though single carbs aren’t everyone’s thing, I think there are lots here who still enjoy reading and hearing of how they work.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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ericheath
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Re: Single Weber DMTL conversion

#6

Post by ericheath »

It looks like you can adjust the transition amount with a screw. Maybe try that before a different jet.
97889DA9-5839-42E6-AB2B-F9D219A6214A.jpeg
97889DA9-5839-42E6-AB2B-F9D219A6214A.jpeg (211.11 KiB) Viewed 622 times
My limited experience with small two barrels has shown lots of makers use these transition ports to help the transition from the primary to where the main jet takes over. This pic makes it look like Weber used a few holes/ports but it’s the first I’ve seen where you can tweak the amount.

It gives me ideas for one of my “projects.”
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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taunusrainer
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Re: Single Weber DMTL conversion

#7

Post by taunusrainer »

Weber's tables recommend:
for an engine with only 1000ccm but with 82hp the carb should have a 19mm primary and 27mm secondary venturi
with corresponding jetting.
The 32/34 DMTR and DMTL have 25/27mm afaik. That's why it won't idle.
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ericheath
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Re: Single Weber DMTL conversion

#8

Post by ericheath »

Hitachi makes a progressive 20/26 Venturi two barrel. Used on early Datsun/Nissan models. It has 26/30 throats and had plenty of obstructions in it.lol Cheap, as in shoddy manufacturing, knockoffs on eBay for $75.

I have two begging for me to do something with them. They are smaller than a straight bolt-on to a 32/36 two-into-one adapter.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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taunusrainer
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Re: Single Weber DMTL conversion

#9

Post by taunusrainer »

Hi!
I found a Weber DMTL Haynes Manual Chapter. Pretty detailed. It is a pdf which I can send You if You want.
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