GL1000 Weber single carb conversion

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DuncanV

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Hi Guys, I'm new to this forum and seeking advice. I have been through the Carb 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 so as 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
 

joedrum

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Ok ..I’ve got the same carb on my bike ....bad mpg means your way rich at low rpm ...and it’s flooding out ..is why it quits running below 3000 rpm ..on my bike the motor is a 1200 modified like a 1000 motor ..so it’s a stroked and bored out 1000 like motor ....so my jetting won’t apply to your motor ..but basic theory will ....the old is a smaller motor than a car motor this carb is used on ...the idle and off idle is a combine circuit ...for cars with power steering ...ac and so on ...on the other hand a oldwing motor revs at least twice as much as a car motor ...the rpm makes this a big motor out of it needing way more fuel jetting at upper rpm ....first off on my bike there is no choke on it ..my bike doesn’t need it ...second this is not a simple carb ...it’s a very good carb ...but it’s a epa infected carb probably ...probably has a power valve ..another epa junk piece that can’t be adjusted ...I could go on and on ..others have different opinions than me ...my bike has gotten close to 60mpg and averages about 48 to 50mpg ...it’s very powerful ..but as said my bike is a one of a kind bike ...on the carb I modified it to separate the idle circuit and off idle ..modded it to get more air to idle mix that’s adjustable ...in general the carb is way smaller jetting at low rpm than car set up ...and way bigger jetting at high rpm than car set ..the bike can pull the wheel off the ground in second gear ...and don’t play much with first gear ...it take some doing but I think the carb you have is great carb to have to start with ...
 

DuncanV

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Thanks for your input joedrum, I have read it but I am still confused. I took the original 4 carbs off because of crap mpg and put the single Weber on. I have not tried it on the road yet as I cannot get it to run on the slow running circuit of the carb, it will run above 3k just fine but as soon as rpm drops below 3k it can only be kept running by pumping the accelerator injector pump and I can see fuel going down the hole. Surely this means that it needs fuel below 3k. I know opening the flap draws more air in so it does weaken the mixture if it is too rich but adding neat petrol makes it richer again. I have stripped the carb tonight and it is is all clean, the only thing I found was the primary solenoid blank nut was loose but that has made no difference to the problem. I did wonder it the plug was cutting off fuel to the slow running circuit but it is flat ended and seems to leave clearance for fuel to pass to the 3 small holes just inside the venturi. I squirted carb cleaner down the pilot jet hole and saw it come out of the centre of the primary choke so it does not seem blocked. What size pilot jet would, say, double the amount of fuel available to the primary circuit, I don't want to spend a fortune on different jets so I need a ball park estimate. The carb is brand new so I shouldn't expect any internal problems.
 

kerryb

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Duncan, i don't have a single carb conversion, and I only know enough about carbs to rebuild mine and tune them. But I read carb threads and try to understand. So I propose an experiment to prove joe's theory or just add evidence to different pile of knowledge. When you pump the accelerator... ( I assume this carb has an accelerator pump like my keihins) you are opening the airway too, so that changes the air/fuel mix. This makes the engine run and covers up the possibility that Joe is correct when he predicts the engine is flooding at idle. If you suspect the engine needs more fuel, try squirting a little raw gas through the hole in the butterfly without adding any more air, if there is any improvement, you might be right, lf no positive change, then Joe might be right...it's already flooded.

"Stay curious my friend"...oh wait...that was supposed to be stay thirsty....
 

slabghost

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You might want to buy a set of micro drills for the jetting. If you open one too far you can always solder it shut a drill a smaller hole.
 

DuncanV

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Thanks for your advice kerryb, I will try this test but there is no hole in the butterfly to squirt gas through though. Also when the engine starts to die, if I open the butterfly to allow more air in without pumping the accelerator pump, it just dies. If I squirt gas in then it comes back to life.
 

joedrum

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Duncan ...early on in my build ..I had the same problem your talking about ...and my set up was leaking air in at the stock intake horns and the only way I got it to idle without dieing was to have choke plates closed and also the rpm was like 1500 to 2000 ..idle is the most hardest place for the motor to run and be dial in right ...and the smallest of air leak will keep it from idling ..using the choke plates to determine weather it’s lean or rich ...is the quickest way to find out what problem your having ...if it is lean ..my guess is it’s leaking air in before the carb ....Once I got things set up,where there’s was no air leaking in....things went the other way ....things got rich ...lol...hang in there ...pics would be great to post so set up can be seen ...there are just so many factors at this point that can cause the same results of not idling .....
 

DuncanV

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Thanks joedrum, here are a few pictures to show the conversion
 

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joedrum

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Nice work Duncan..... love the mods you did to the air box ....runners look great and seal up it seems ....carb hook seems great too nice spacer set up....its looking like air leak if it had one could only be stock intake horns ..but after looking at the work I’m thinking as you said earlier in thread it’s not leaking .....this is looking like a real Weber carb ...somewhat different than my Weber clone motor craft carb ....but it does seem to have the power valve ...I personally don’t see this as a good thing ..as it is a non adjustable thing ...my carb came fortunately without one ...and makes precise jetting difficult ....as vacuum operates it and it dumps in fuel when it opens....so we are talking a completely different carb here in some aspects ....they can be block not to work if you want ....but I’m kinda leaning towards bumping the idle up ...to see if that works for this carb ...for me it was get carb bits and drill by hand to change jetting ...send yourself broke buying jets ...be nice to have full set of jets on hand to work with ....on my carb the idle and off idle circuit had a fixed air bleed ...I never could get a good idle just changing gas idle jet ....long story short I had to mod the carb and seperate these two circuits ...before I got the plug color and mpg I was looking for ...i do not use heat in my system at all ...in fact I’m the other way ...my runners are insulated from the head heat ...much more power in a cool charge .....ive really had no icing problems people talk about since I got my carb dial in right in jetting and mods .....
 

DuncanV

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Thanks for your complimentary comments joedrum, gives me a real boost in believing in myself. I don't know what you describe as a power valve and where it goes on the carb. The only power valve I have experience of is in the exhaust systems of Yamaha 350YPVS or the Exup Thunderace and these are not linked to the intake at all. This carb does have an accelerator pump which pumps neat fuel directly in the primary venturi, the actuating arm can be seen in the top picture. I have found that Webcon here in the UK can supply jets so I have ordered a 65, 85 and 100 pilot jets for the princely sum of £11.75 (about $10) so I'll see what they do over the weekend
 

joedrum

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Yes that’s it ....ok the power valve is vacuum operated ...most of the carbs today are set up lean on cars and a power valve works to add fuel in along with what jets do ...I’m not thinking real clearly right now ...it adds fuel when vacuum drops and closes off gas flow in low vacuum ....or it could be the other way around ...lol ....to me it’s best not to have in the mix of trying to Jett the carb right ....it mostly an epa thing ...put on carbs to please the idiot regulators and control freak governments ..different motors have different vacuum spots and power valves are non adjustable and just total junk device ..making a carb good for one motor only ...but others here have gotten along fine with power valve ....my motor far from stock and completely different than you motor ...so if it was me I’d try things with power in place first ....hope this helps you understand ..I’m not a great explainer
 

Ansimp

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[url=https://www.classicgoldwings.com/forum/viewtopic.php?p=199326#p199326:2hpgfp37 said:
dan filipi » Fri Jan 12, 2018 11:33 pm[/url]":2hpgfp37]
Try little shots of ether at the joints. If there is a leak, engine will speed up immediately.
:good:
Even a spray bottle with a fine mist of water will work as well.
 

joedrum

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Shame there no pics allowed if your not a member there ....I’m thinking it’s different here
 

DuncanV

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Update on the problem for anyone who is interested. I checked for leaks with a spray and there was no change in the engine revs so it would seem that all is tight. I changed the pilot for a 65 jet and there was a slight improvement but then I tried an 80 jet. Much, much better, engine ran clean from 1200 right up to almost the red line, no stumble between pilot and main.It didn't pick up from idle very well so I changed the pilot for a 100. Better from idle, picked up well but I'm still not getting a good idle. Idles at 1300 rpm ok but if I adjust the throttle stop screw down any more it gets very rough. The idle mixture screw is 2 turns out which is a factory starting point and it doesn't make much difference if I screw it in or out. I can't decide if the idle relies totally on this mixture screw or the throttle stop screw. I.E does the flap need to be open a tiny bit to get a good idle or should it be firmly shut leaving the idle to the idle mixture screw alone. Any suggestions on the order in which the two adjustments should be made. I am waiting for an adaptor for my Colourtune so I can see the colour of the burn at idle, pilot and main stages and even if I have to leave the idle at 1200, it will still be rideable. One other observation is that the revs do not seem to drop back to idle as quickly as they used to do. Japanese short stroke engines drop back very quickly compared to British bikes and I wonder what this is indicative of. Any suggestions would be gladly accepted.

joedrumm, you can join ngw for free
 

joedrum

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Hi DuncanV ...I was a member there for yrs ...that’s a long story why I’m not a member there anymore ...I think I’ve mention to you that the secondary barrel on the Weber has an idle jet too ...my clone Weber had a fixed position for the throttle plate on secondary ....I was able to make it adjustable ...so at idle the mix screw doesn’t completely control,the idle the secondary idle jet is in play too ...gas can actually sit on top of the secondary plate and keep feeding gas in motor as this plate doesn’t move till about 2/3 throttle is made ...causing slow return to idle....so in effect you have lots of gas going to idle fed from primary barrel and secondary barrel also ...need to check your carb to see how the secondary plate adjust ...it’s sounding way to closed ....the primary plate adjust with the fast idle bolt on linkage ....sounds like you are starting to figure things out ...keep plugging away ...if the motor doesn’t instantly rev off idle you are still not right ...on my bike this type carb revs so much better than stock cv carbs it not even close in comparison...
 

DuncanV

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Another quick update, it seemed to get progressivly worse the more I tried and eventually I concluded that it was, in fact, fuel starvation. It took ages to get fuel pressure and often made the battery go flat trying to start it so I mounted a remote electric fuel pump in the right hand dummy tank, still no better.. In desparation I took the carb off, it was a NOS carb so it had never been on any vehicle so I thought there should be no blockages inside. How wrong I was, the float bowls were pristine as were all the drillings but the filter on the inlet was blocked solid with what appeared to be sawdust. I cleaned it all out but kept the crap that came out, when all the petrol had evaporated there was a dried, shrivelled lumpy powder, not sawdust. I had a scientist friend look at it and he said it was a fungus, grown in the petrol as a result of ethanol or 'green fuel'. After I cleaned it all out and checked the in-line filter, it started first turn and run as sweetly as a nut, it pulls well, ticks over and had lost the clutch rattle that comes with out of balance carbs. Result! Also I had a new season problem each year with my Buell Cyclone in that it ran like shit when I took it for its test each year. I would come back, strip the carb and find deposites like snot in the float bowl. Doing the same thing, I let the petrol evaporate and there was a white powder left, every time!! I now turn the petrol off at the end of a run and let the bowl fuel run dry and let the engine stall to empty the carb. This new bio-fuel with ethanol in it is horrible stuff for carbed engines so I always use super-unleaded in all my bikes now. Does anyone know of any product that reliably prevents ethanol making fuel go bad and stop it rotting rubber seals etc.
 
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