Single Weber DMTL conversion

This is where discussions of EFI systems, Dual Carbs, Single Carb mods and plans can be discussed and shared.

If you are working on or have a problem with stock carbs then your questions do not belong here, please post them in the Goldwing Tech Discussions Forum.

Moderators: sunnbobb, Neil, Forum Moderators

DuncanV
Tin Member
Tin Member
Posts: 14
Joined: Wed Jan 03, 2018 6:29 pm
Location: UK

Single Weber DMTL conversion

Post #1 by DuncanV » Wed Jan 03, 2018 7:52 pm

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

User avatar
Whiskerfish
President
President
Posts: 30971
Joined: Thu Feb 16, 2006 9:34 pm
My Album: http://www.ngwclub.com/gallery/v/wingmans/whiskerfish/
Location: Norfolk Va

Re: Single Weber DMTL conversion

Post #2 by Whiskerfish » Wed Jan 03, 2018 7:58 pm

Welcome to the forum! Not my area of knowledge so hopefully one of the Single carb guys can help out.
"Agreement is not a requirement for Respect" CDR Michael Smith USN (Ret) 2017
1975/6/7/8/9 Arthur Fulmer Dressed Road bike
1975 Naked Noisy and Nasty in town bike
and a whole garage full of possibilities!!

Psst. oh and by the way CHANGE YOUR BELTS!!!!

User avatar
Sugs
Silver Member
Silver Member
Posts: 625
Joined: Sun Aug 09, 2015 6:12 pm
Location: San Diego, CA

Re: Single Weber DMTL conversion

Post #3 by Sugs » Wed Jan 03, 2018 8:22 pm

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.
_______________________

'90 Honda CB-1
'79 Honda GL1000 Goldwing

User avatar
gltriker
True Blue Steel Biker
True Blue Steel Biker
Posts: 2855
Joined: Fri Sep 24, 2010 9:11 pm
Location: Baldwinsville, NY

Re: Single Weber DMTL conversion

Post #4 by gltriker » Wed Jan 03, 2018 11:51 pm

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

Keep your eyes and ears open and you'll learn something new, everyday. tumb2

New users please visit our "Shop Talk" for common tips and help: <---jdvorchak
http://www.ngwclub.com/forum/page/ST :oldies

RE: a thorough fuel tank cleaning
"And your carbs will thank you. They no longer live down stream from a sewage plant." -gregforesi tumb2
"Can't see the paint when your looking thru the handlebars..........." -Oldewing ;)
"I'd rather Ride than Shine" -RAT tumb2 Me Too!!

Cliff

'75 GL1000 home built trike; http://www.ngwclub.com/forum/viewtopic.php?f=30&t=39996
October,2017 BOTM :shock: https://nakedgoldwingsclub.com/forum/page/Welcome
https://www.youtube.com/watch?v=FVpommgI-M8 turn up your speakers volume YouTube video from April 12th, 2014

previous rides:
1953 H-D Servi-car, naked, 1969-1978 (serial#53G1559 committed to memory!)
1980 CB900 Custom (triked) 1997-2003 .... R.I.P.

User avatar
ericheath
Honored Life Member
Honored Life Member
Posts: 8120
Joined: Wed Jul 29, 2009 11:20 am

Re: Single Weber DMTL conversion

Post #5 by ericheath » Thu Jan 04, 2018 12:56 am

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

User avatar
ericheath
Honored Life Member
Honored Life Member
Posts: 8120
Joined: Wed Jul 29, 2009 11:20 am

Re: Single Weber DMTL conversion

Post #6 by ericheath » Thu Jan 04, 2018 10:34 am

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


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.”
You do not have the required permissions to view the files attached to this post.
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

User avatar
taunusrainer
Silver Member
Silver Member
Posts: 859
Joined: Wed Oct 04, 2006 2:57 pm

Re: Single Weber DMTL conversion

Post #7 by taunusrainer » Sun Feb 11, 2018 11:33 am

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.
1976 GL1000 test mule
1977 GL1000 in parts, rebuild in progress
1980 GL1100 Interstate

1969 Ford 17m 2.3V6
1976 Ford Cortina 2.3V6 (Propane)
1990 Mustang 5.0 7up conv.
1994 Volkswagen Polo (Propane)

User avatar
ericheath
Honored Life Member
Honored Life Member
Posts: 8120
Joined: Wed Jul 29, 2009 11:20 am

Re: Single Weber DMTL conversion

Post #8 by ericheath » Sun Feb 11, 2018 12:47 pm

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


Return to “Unique Carburation”

Who is online

Users browsing this forum: Rc67 and 1 guest