Carb Rebuild Complete - Dies on throttle

[oohsam]

Wowowow...Lots of replies. Let me address each one.

OK. The kit for your bike does show both stage 1 and stage 3 jets. With pods and performance exhaust you have a stage 3 setup. Here is what it showed for your 83 gs1100
4 Main Jet DJ132
4 Main Jet DJ138
You will need a set of 138 and a set one size up = 140 main jets to get started. I would install the 140 jets first as they are most likely to run well with your setup. Leave the primary jets alone for now. Start by only changing the main jets and setting the mixture screws. Once installed and running, Test bike. then adjust the mixture screws as I explianed earlier, test bike. It is important to make only one change at a time when tuning carbs, make the change and test the bike's performance after each change. If you do not achieve better performance after making an adjustment, go back to where you where before the adjustment. If it won't idle at all after you have made the mixture screw adjustments but runs well when on the throttle you may want to go the larger primary jet but I doubt you will have to. Once you have a decent running bike try raising the needles up one slot and test the bike, if it pulls harder, try going up one more and test bike, if the bike is slower go back the other way. Do this until you achieve the most powerful settings. If the bike bogs while on throttle after changing the main jets, test the jetting by reading the plugs as i explained earlier, Black and sooty = too large of a main jet.
Bone white = too small of a main jet Light brown + you nailed it! Move up or down in jet sizes 1 size at a time as needed. Those 140's will get you very close but don't be surpised if your bike wants 142's or even larger as pods and performance exhaust is the most free flowing setup for the street. it will depend on your engines overall condition wether it needs more or less fuel from your main jets.

Ok, I have ordred 140's and 142 main jets and will have a play. Thanks for the info, exactly what I was after

Just so you know: the 165s and 170s are NOT "main jets".

They are the "pilot air jets" that go into the carb intake throat at about the 8 o'clock position.


Referring back to one of your earlier posts about the bike stalling when throttle was applied: did you have any filters on at the time?
As you have seen, the jetting needs to be changed for the type of filter that you have. If you have NO filter on the intake of the carbs, the bike WILL stall, unless you have the carbs jetted for that situation.

When the bike stalled, I pulled the carbs off, and i had all #45 PILOT jets and 117.5 Main jets, but for some reason I put a 115 main jet on carb #3. So it was all mismatched. I replaced it all to #40's and #115's and the bike started (took a few tries), and i could ride it. Still doesnt feel 100% but it didnt bog out. Yes the pods were on.

Regarding ct480's post about lean jetting running hotter. VERY TRUE, but for synchronizing the carbs, you are not getting into the main jet, so your jetting is still controlled by the PILOT FUEL JET and the PILOT AIR JET making a mixture, which is then controlled by the IDLE MIXTURE ADJUSTMENT SCREW. Usually, those jets are left stock, although some DJ kits have a "correction sleeve" that is inserted into the air jet to richen up the pilot mixture a bit.

When you did your "full rebuild and carb teardown", did you replace the intake boots between the carbs and the engine? If you have a bit of an air leak there, it might account for your "hanging idle". I was going to do the standard suggestion of changing your intake o-rings, but your bike does not have them.

Yeah, the intake boots are new, there are intake Orings on my bike, which are also new I replaced them after I painted my engine long before I rebuilt the carbs

You are running a #40 pilot?? theres your problem. Dont assume that your rebuild kits come with proper sized jets
Put in the #45's and I bet your stalling goes away
EDIT: I looked it up and the service manual says a #40 pilot, but that is for a STOCK bike with airbox, a #45 would be a better choice.

The rebuild kit came with 115 and 117 main jets, as well as 40 and 45 pilot jets and 2 diff sizes of air jets (cant remember the numbers), but they were all basically Stock, and stock + 1 size up. So i have some room for testing.

I'm getting my jets from www.iwt.com.au in SA. $8.50 each for my pilots and mains and I just give him a call and get him to express post so I get it the next day. $9 is what he charges for express post.

He has a full price list on there somewhere so you should be able to see needle prices as well I would imagine.

Thanks pete, Just ordered 140 and 142 main jets.

My next plan of attack is the following :

1. Vacum sync (i got my morgan carbtune in the mail last night express post from QLD. Will try a vacum sync tonight.
2. Once vacum sync is done, I'll see how the bike runs with the stock jet setup (just for a benchmark) - will play with the mixture screws also.
3. I will then go up on the main jets (might try with the next size up 117.5 first), then i'll go to the 140's
4. I am going to order a Colour tune so I can see what spark colour I am hitting.

I'll be following CR480's trial and error method to see how it works for me.
I really appreciate the help guys. I really want the bike to be as easy to start as pressing the start button and just taking it out without having to fiddle with anything.
fingers crossed.

[Billy Ricks]

Did you pull the float seats? There are screens over the top of them that could be clogged if not.

[cr480]

I for one cannot clear this up for you. I don't have the ability to bench flow a set of carbs.

I do know the taper is different between the stock needles and the ones in the dyno jet.

when jetting for pods, what have 'you' done to increase the fuel supplied during part throttle operation? did you change spring tension on the slides?

Ok,thanks for your post. My answer may help clarify some things for many in this forum. Lets look at the length of the needle taper first. The machined area of the needles at their end is around .100 to .250 thousands of an inch and is tapered to match for better or worse the top of the main jet which is machined in a conical taper. The jet kits use the same type of jets that the carbs where designed to use. The only difference is the size of the orifice that the fuel will flow through. the top of the jets are machined with a taper that extends down to this orifice. Whether your jets come from dyno jet or the bike shop this taper is the same more or or less. Stock needles are machined at the ends with a best all around taper, not a perfect match as the same needles are used in many different applications. The jet kit needles are machined to specs that match the jets taper more precisely as they are destined for a specific application only and need not be a cure all spec. However, they are still not a perfect match because they need to work well with at least 2 or 3 setups IE stage 1 ,2 , or 3. this is why needles are adjustable in hieght. raising or lowering the needle places these tapered surfaces closer together or farther apart. The closer these two parts are together the leaner your part throttle response. Raise the needles and you get a richer part throttle response. In a fully mechanical carb setup the kit needles would be superior because you would have a more precise range that is tuneable. Thes carbs however have vaccum actuated slides. The vaccum of the engine against the rubber diaphrams pulls up the slides overcoming the spring pressure that is pushing back on them. The kits usually come with lighter springs. lighter springs will offer less resistance against the intake vaccum and open up the slides faster, this is why they tell you to drill the air hole in the slides, because regardless of spring pressure pushing down the slides can only displace so much air. a bigger bleed hole will allow the springs to have the desired effect intended. The effect is a faster revving engine if proper jetting is in place. But how much faster? It will provide a noticeable difference over stock. However and more to the point given the length of taper, the stock needles versus kit needles will only provide a millisecond of gain in the real world when you actually ride the bike. To go even further into it, you can run the lightest springs available and drill the slides accordingly to match them. But you will not achieve a faster rev " throttle response" than the engine is mechanically capable of. The limiting factor for how fast a gs engine will rev lies in the rotor weight. The stock charging rotor is made purposefully heavy. This mechanically limits how fast a motor will build rpm's regardless of your intake\ exhaust setup. if you are running a race setup with a lightened rotor these needles may be more beneficial to you. But a street application is all about the best performance you can achieve, on a budget, on average. So I am still lost on how needle taper will be a real comprimise in a street application. Can anyone clarify this for me? Thanks in advance

[oohsam]

Did you pull the float seats? There are screens over the top of them that could be clogged if not.

Replaced with brand new ones!

[rustybronco]

So I am still lost on how needle taper will be a real comprimise in a street application. Can anyone clarify this for me? Thanks in advance

I guess it all boils down to the rate of taper on the needles. if these carbs had an accelerator pump then you might not need a faster rate of taper supplying the additional fuel required when opening the throttle 'quickly'. again, testing on a bench or a dyno would be needed to suggest if there is an improvement when using aftermarket needles over factory needles.

I guess if you're satisfied with using the factory needles when re-jetting that's all that matters doesn't it?

[cr480]

I guess it all boils down to the rate of taper on the needles. if these carbs had an accelerator pump then you might not need a faster rate of taper supplying the additional fuel required when opening the throttle 'quickly'. again, testing on a bench or a dyno would be needed to suggest if there is an improvement when using aftermarket needles over factory needles.

I guess if you're satisfied with using the factory needles when re-jetting that's all that matters doesn't it?

Yes, your right, it is a matter of choice in the end. Thanks.

[pete]

My next plan of attack is the following :

1. Vacum sync (i got my morgan carbtune in the mail last night express post from QLD. Will try a vacum sync tonight.
2. Once vacum sync is done, I'll see how the bike runs with the stock jet setup (just for a benchmark) - will play with the mixture screws also.
3. I will then go up on the main jets (might try with the next size up 117.5 first), then i'll go to the 140's
4. I am going to order a Colour tune so I can see what spark colour I am hitting.

I'll be following CR480's trial and error method to see how it works for me.
I really appreciate the help guys. I really want the bike to be as easy to start as pressing the start button and just taking it out without having to fiddle with anything.
fingers crossed.

This sounds like a sensible order to do it in to me and is what I should've done before fiddling with my pilots.

Don't forget to separate step 2 into 2 steps... as in put the stock pilots back in, set mixture screws to about 2 turns out and see how that goes.

Then fiddle with the mixture screws properly doing the highest RPM method.

I can't wait to get stuck in with my Colourtune, but at the moment I just can't get the tuning time. You'd think being on holidays would mean lots of time to play, but it doesn't seem to be working out that way...

[KEITH KRAUSE]

The bike started right up and the hanging idle issue seems to have gone. I didnt need choke or anything to start up, took a few cranks and off she went.

When I put the bike in gear and throttle, the bike dies.

I am running pods but not the K&N pods.

I didn't read all posts. But based on your first post here you have the classic sign of fuel starvation.
I will first assume all your CV carb diaphragms are in good condition. A damaged diaphragm will not allow that cylinder to accept throttle. It will idle all day but not accept throttle.
Classic sign: If your bike will idle and accept throttle while in neutral but will stall if put into gear then you have a lack of fuel flow. Putting a load on the engine (trying to drive away) requires much more fuel than an engine under no load. But many things can cause lack of fuel flow. Because you say you've serviced the carbs and done the job right I'll assume all venting, petcock, fuel tubes are clear. A good job done on the carbs would also mean the float levels are correct and the float needle valves you have are operating as they should and not sticking in their valve seats. You MUST at least do a good bench synch however. The bench synch needs to be followed by a vacuum tool synch too but a good bench synch will allow the bike to run OK. Vacuum levels that are very far apart will of course cause problems but I doubt that poor levels would cause your stalling. If all the above is good then any fuel starvation would be where the jets suck up from the float bowl.
Pods require larger mains, richer jet needle adjustments, and larger pilot jets, at least. Many times the CV carbs need additional things to operate well such as restrictors for the air jets, increasing size (by drilling) the vacuum orifice to each diaphragm chamber, lighter diapragm assembly springs to improve throttle response, etc.
I'm thinking your jetting is far too lean. What are the stock main jet sizes, pilot jet sizes and jet needle sizes? What sizes are you running at the moment?

[oohsam]

ohhhh jets came in today!! w00t!
Time to tinker when I get home

[oohsam]

I have some updates my good friends.

I got my 140 and 142 main jets yesterday. Also got my carbtune the other week so I was set to install the new jets, and sync the carbs and see how it runs.

First up was to remove the carbs, remove the 115 jets and install the 140 jets...
I didnt even bother trying to sync it stock, thought I'd dive right in. Plus I hate removing the float bowls....lol

Started up the bike, needed the choke to get running, but it ran ok.
Played with mixture screws but found no real change from 2.5 turns so left it as 2.5 turns.
adjusted the idle screw to get it steady...seemed to idle nice.

Hooked up the carbtune (hard to do when the engine is hot, pain in the ass!!!)
this is what the sync looked like :O


...Not good (proof that a bench sync is crap)

Used Basscliff's guide to sync the carbs and this was the best I could get. Very happy with the result.



Took the bike out for a squirt, takes off fine, when i hit the throttle, it bogs down a little through the midrange. So I think that means I need a needle adjustment (thoughts please).

Bike returns back to idle no worries and is nice and responsive.

So I'm running #40 Pilot, #140 Main jet and the stock air jet (not sure of the number!)

Not sure if I should try it with a #45 pilot... I will remove the needles tonight and have a look at my pin adjustment.
Given that this was my result, what are your professional recommendations - with the pin adjustment? up or down?

I have my colortune arriving today so that will surley help get my mixtures right.

[BassCliff]

Hi,

Nice work on your carb sync. Yes, sometimes "close enough" is "close enough".

With the stock needles you normally have to raise them a notch. If you are not using the Dynojet kit then you'll have to shim the needles using small washers. The Dynojet kit needles have a special taper on the bottom and slots on the top to make the adjustments easier.

But you may want to perform some plug chops to check the air/fuel mixture at the different throttle openings. Then proceed as necessary.


Thank you for your indulgence,

BassCliff

[oohsam]

Instead of doing plugchops, cant I just the color tune?

I think my carbs come with adjustable needles

[BassCliff]

Hi,

You can't really see how each carb circuit is doing when sitting in the garage. Have a look here:

Plug Chops-Highest RPM Methods
(by Mr. tkent02 and Mr. psyguy)

CV Carb Tuning by Factory Pro

Also see the carb jetting tips at Motorcyclecarbs.com, Inc.

Mikuni Motorcycle Carburetor Theory 101 - from Ian Williams Tuning.

Thank you for your indulgence,

BassCliff

[oohsam]

Thanks Cliffe, read them all thoroughly!

Got home, thought I'd look at the color tune and see where my idle is.
It's sitting with a nice blue spark. When I rev it, the spark becomes orange (lean?) and it struggles around 3,000 rpm. So I think that means I need to adjust the Jet Needle.

Do I move the clip up or down?....

I'm unsure at this stage if I should increase the main jet to 142.5 and also increase the pilot jet to #45.
Will this require a resync with my carb tool?

[oohsam]

OH I also did a plug chop. Took the bike up the road, hit it full throttle, it boggged out again about 3-4000 rpm then kept going. Killed the engine and had a look at the plugs.
They looked a little on the black sooty side but were sort of tanned.
Really hard to tell....

I'm pretty sure its felt like it wasnt getting enough fuel. hmm