Dual Weber temptation

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Spanky
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Dual Weber temptation

#1

Post by Spanky »

Greetings everyone, this topic will serve as my introduction to the Club and a short rambling of the running/riding project I have acquired dubbed the "What-the-Heck Cycle."

I love old unique bikes(cars,trucks), factory just does't appeal to me very much so when I saw a GL1100 stripped down like an old Harley bagger my interest was peaked. Next thing you know its in my driveway. However the bike had "something wrong with the carb rack" so naturally I took this as an opportunity to do some minor upgrades.

I have successfully removed the carbs, fabricated my own manifolds (I am a certified welder with access to a CNC laser and CAD software, so that helped a lot), and grabbed two knock off Weber IDF 40s from eBay and got busy. The linkage consists of components from Summit in a cross-bar design. My first truck was a 1980 Datsun 720 that I had put a knock off Weber conversion on with decent success so I felt comfortable with the project. Plus I have read nearly every thread on this board relating to dual carb conversions.

After a quick sync (so much easier to sync than OE carbs) and minor idle screw adjustment I had it idling nearly perfect, all cylinders pull between 4.5 and 5.5 mmHg, throttle response is amazing, revs are really quick and snappy. Overall I was very happy.

Then I got to ride it (I also rebuilt the front brake calipers and MS, that took way to long but finally got it done and bled right). The maiden voyage was extremely exciting so long as I was accelerating or decelerating, with the throttle held steady it sounds as if one or more cylinders is trying its best to fire but just comes our in intermittent spurts... Pulled the plugs and sure enough cyl #1 and #2 are black and wet.

Also stopped and topped off fuel twice to find out I am getting HORRENDOUS fuel economy, like 18-20mpg bad. So this tells me something is extra rich? Black/blue smoke from the pipes occasionally when cold confirms this. I have good compression, all cylinders are in the 140s/150s. Fuel/air mix is definitely getting to the cylinder because it idles fine - so we have fuel and air, the only thing I am unsure about is spark or spark intensity/consistency.

Questions are:
Is it possible that the ignition system is failing cyl #1 and/or #2, causing wasted/unburnt fuel of that quantity? Or do I need to focus on tuning/rejetting?

I have swapped the coils and spark igniters back when the OE carbs were on it thinking that it may have had an ignition problem in the beginning giving the P.O. false trails to a carb problem, but everything swapped out alright between circuit for cyl 1/2 and circuit 3/4. And being factory replacement IDF 40s the carbs shouldn't need rejetting that badly...

It is certainly ridable, it just gets the same fuel economy as my 1-ton diesel, and makes uneven racket at constant throttle... Any suggestions?



BTW its got a 550CCA marine battery wired in the left saddle bag, starts really easy, not sure if that is effecting the ignition circuit negatively...
Also checked/set valve adjustment before starting the dual carb project, so that should not have changed.
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Track T 2411
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Re: Dual Weber temptation

#2

Post by Track T 2411 »

I have no experience with the Weber/knockoff setup, but I'd start by troubleshooting the ignition, being that it seems to involve #1 and #2, which share a coil. If it were carb related, it would seem to me that it should affect cylinders that share a carb. My 2 cents.
"I have no special talent. I am only passionately curious." - Albert Einstein

"He that is good with a hammer tends to think everything is a nail" - Abraham Maslow

"If you can't take the time to do it right the first time, how are you ever going to find the time to do it over?" -Unknown

Current Rides:
'Grumpy' - '81 Standard, now fully dressed.
'Layla' - '81 Standard w/dealer installed fairing and Hondaline bags.
'Scarlett' '76 'Survivor' nekkid as a j-bird!

Under Construction:
The 'Jalopy' '78-'79 Mash-up
'Quikie' '81 gl1100I back on the lift, project with the step-son!

In The Shed:
'81 gl1100I barn find aka "Josie, the farmer's daughter." (almost comatose build)
'77 gl1000, roller parts bike.
'82 gl1100I, 'Old Crusty' titled roller parts bike (free!)
'82 gl1100I, My first 'Wing, and an expensive lesson!
New2U Bike? Read Me.
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Easter
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Location: South of Houston 100 miles

Re: Dual Weber temptation

#3

Post by Easter »

Stock ignition (points condenser)? Maybe something going on there, but agree with Track T, sounds more like ignition. Could it be a heat related coil failure?
Bikes at present:

83 XL 600r with a 2004 XR650L engine
And a slightly worse for the wear BMW GS adventure bike awaiting repair
83 GL in process :IDTS:
Spanky
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Joined: Mon Dec 18, 2017 2:46 pm

Re: Dual Weber temptation

#4

Post by Spanky »

Last night got an extra set of spark plugs, ran the bike down the block to get it warm, came back pulled plug #2, found it black/sooty/dry; the neighbor said he could smell gasoline as I went by (I could smell a little too but my sense of smell is terrible, if I can smell it it's probably slap-your-granny strong) so of course running suuuper rich.

Checked spark with one of the spare plugs at idle:
With the bike running,
Pulled wire #1, hooked to spare plug, touched plug to valve cover -- got spark
Pulled wire #2, hooked to spare plug, touched plug to valve cover -- got spark
Pulled wire #3, hooked to spare plug, touched plug to valve cover -- got spark
Pulled wire #4, engine instantly shut off.

So this tells me #4 is doing nearly ALL the work at idle on the left bank, but I am indeed getting spark to all cylinders. So long as I don't foul the plugs by flooding anything the spark should ignite the fuel/air consistently, so something MUST be interfering with #2.

I got the snail gauge back out and checked the balance between cyl #2 and #4. Sure enough cyl #4 is pulling 5.5, little jumpy but 5.5, however cyl #2 is set like a rock on 3 and only adjusts with the use of the air bypass screw next to the idle adjustment screw.

Since the cyl #2 tested with good compression am I correct in concluding either the valve train is out of timing/adjustment or I have a vacuum leak somewhere around cyl #2?

Tonight I will take the cover off the pulse generator and make sure nothing is loose/missing and no wires have been pinched/melted. I am also probably going to take the carbs/manifolds off and look for gaskets I may have torn or krimped during installation.
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