Carb Problems With A GS650

[Dano]

Hope someone can help. I have a few carb problems that I can't get resolved. I looked through all the archives and can't find no answers to help. I have 47.5 pilot jets, 125 main jets, great compression, no air leaks,new plugs, coils and wires. I can only get a top speed of 60mph, wide open throttle in 5th gear. If anyone could help, it would be greatly appreciated. Thanks

 

[frosty5011]

You'd have to look at the manual to be certain, but if all is stock (airbox, exhaust, etc), I "think" you should be running 110 Main jets, and 42.5 Pilot jets.

PS, that's assuming you're running 32mm BS carbs ('80 on up?)

 

[Dano]

It's a 83', 4-1 Exhaust, Emgo Pod Filters, the carbs are BS32SS Mukuni's. I am frustrated with it, Sorry I should have given this information when I posted before. It did have 110 mains and 42.5 pilots before. I changed both. There was no airbox when I got the bike and already had 4-1 and still ran like crap. Still any help is appreciated. Thanks

 

[earlfor]

Re: Carb Problems With A GS650

What color are the center ceramics and electrodes of your spark plugs?

Earl

Hope someone can help. I have a few carb problems that I can't get resolved. I looked through all the archives and can't find no answers to help. I have 47.5 pilot jets, 125 main jets, great compression, no air leaks,new plugs, coils and wires. I can only get a top speed of 60mph, wide open throttle in 5th gear. If anyone could help, it would be greatly appreciated. Thanks

 

[Dano]

They are brand new plugs. I checked them and they are still pretty white. Electrodes are clean.

Dano

 

[earlfor]

What do the old plugs look like?

Earl

They are brand new plugs. I checked them and they are still pretty white. Electrodes are clean.

Dano

 

[Dano]

They were blackened, and one had very very little spark to it.

Dano

 

[earlfor]

What year is your bike? Do you have the stock 4 into 2 exhaust, stock mufflers and stock airbox fitted with a filter inside it and the lid on it?

Earl

They were blackened, and one had very very little spark to it.

Dano

 

[Dano]

It's a 83', I got it from a friend, It has a 4 into 1, no airbox, I installed Emgo air filters, and don't have any of the stock stuff.

Dano

 

[earlfor]

OK, that means youre roughly 2 sizes over on the on the pilots and about 6 sizes over on the mains. You shouldnt have a problem with running lean at least.

The problem is you're sucking down too much fuel. Remove the carbs, turn the upside down, remove the float bowls and set the float heights to spec.
(I dont have a book for the 650, so I cant tell you the float spec height)
After that, your intake velocity is too high. Put a set of vacuum guages on the bike and with the bike at 1200 rpm adjust the throttle plate position to a vacuum level of 8 in Hg @1200 rpm. Adjust the idle adjustment knob between carb adjustments to always maintain 1200 rpm throughout the synchronizing process.

Earl

It's a 83', I got it from a friend, It has a 4 into 1, no airbox, I installed Emgo air filters, and don't have any of the stock stuff.

Dano

 

[KEITH KRAUSE]

Are you certain you have spark to all 4 cylinders?

 

[Dano]

First, thanks for the help so far. OK, The Clymer Manual I have says that the 2 inboard carbs should be set the same and the two outboard carbs should be set the same. Should they all be syncronized the same, or go by what the manual says. Also, what type of vacuum gauges do I need to use. Also, since the 47.5 pilot and 125 mains are too big, what size to you think would be good. Also, could it be possible I may be getting to much air with the Emgo pods. I checked the plugs and yes, I am getting spark to all four. Thanks for any help again in advance. Sorry for the delay with the reply.

Dano

 

[earlfor]

I've tried the setup Clymer suggests of setting the 2 and 3 carbs at 1/2 inch or so less vacuum than the 1 and 4. There is no difference that I can tell between the plug burns and no difference in performance or throttle response, so I dont bother anymore. All get set the same. You can get a mercury carb stix from cyclrecycle for about $40 and it comes with the correct 4mm adapters. http://www.newmotorcycleparts.com/interest.htm
(look under tools) I would try a carb synch with the jetting you have. It is only about a 2.5 increment over what I would consider optimum and you may get away with it. The volume of air the engine requires depends on the rpm. The amount of fuel you can flow depends on the jet size. The mixture depends on the intake velocity, or the strength of the venturi effect. The key is finding the appropriate induction velocity/vacuum level for your combination. Once you have the mercury carb stix, you will be able to set this precisely. That is the only way, as it is not something you can do by eye or ear. As a starting point with your setup, I would set vacuums to 8 in Hg at 1200 rpm

Earl

First, thanks for the help so far. OK, The Clymer Manual I have says that the 2 inboard carbs should be set the same and the two outboard carbs should be set the same. Should they all be syncronized the same, or go by what the manual says. Also, what type of vacuum gauges do I need to use. Also, since the 47.5 pilot and 125 mains are too big, what size to you think would be good. Also, could it be possible I may be getting to much air with the Emgo pods. I checked the plugs and yes, I am getting spark to all four. Thanks for any help again in advance. Sorry for the delay with the reply.

Dano

 

[KEITH KRAUSE]

I'd try 4 full sizes up on your mains. Whatever stock size is, try (20) more.
Go up one step (2.5) on your pilots. There's been no mention of adjustments to your jet needles. The stock needles (U.S.) are not adjustable, but some people try shimming. I still think a jet kit is the best thing to do.
In any case, you'll run way too lean if you don't raise the needles. A good carb synch is mandatory too.
When you say your bike won't go over 60 mph at full throttle, does fully opening the throttle make any difference as compared to having the throttle just a little open in top gear? What I'm asking is, does it still go 60 mph in top gear with just a little throttle? Does the bike idle OK, but won't accept more than a little throttle? I think there's something wrong with your carbs accepting vacuum or the throttle valves are sticking or not operating right. I would check all four diaphragms conditions (cracks or any pin holes) and see if they're seated correctly. It's very easy to install the diaphragm/spring assembly the wrong way. I would also check the jet needles while you're there and see if they have been installed correctly with any spacers, etc, in the correct order. Verify this with your manual. You can also see if anyone has raised the needles with shimming.
After checking all this, the needles need to be raised correctly by using a jet kit. Then do your synch.
Also, what other symptoms is your bike showing? To get up to 60 mph, is it stumbling, missing, hesitating?

 

[Dano]

Quick question before I get started with all this. When I got the bike from my friend, there was no Tach and I still don't have a Tach. Is there anyway of telling the RPM's with some type of gauge, well any other way to tell or is it best I got get a Tach. Thanks again

Dano

 

[Don Lobacz]

You have CV carbs and they need a vacuum differential behind the carbs to lift the slides. The pods have reduced that vacuum. The best thing to do is put the stock airbox back on and rejet slightly for the header. I sold a GS650 last year and it ran like a dream: fast, smooth, responsive. I'm surprised that others who have had problems rejetting CVs haven't jumped in on this thread. I may still have a 650 airbox sitting around somewhere, too.

 

[Dano]

It accelerates somewhat decent. The idle is fine. There is no miss or hesitation. It tops out at 60 no matter if it is full throttle or little throttle. Top gear, 60mph is as fast as it will go. Also, the needle jets have not been shimmed.

Dano

 

[Dano]

If you do have a stock airbox, let me know what you want for it. I really do need the stock airbox. I am having alot of problems finding any kind of parts for this bike in the area (southeast virginia). Thanks for the info.

Dano

 

[Don Lobacz]

You can check the diaphrams and slide action by blowing compressed air into that curved, oblong orifice on the top back of the carb throats. The slides should rise easily and consistently.

 

[KEITH KRAUSE]

You have CV carbs and they need a vacuum differential behind the carbs to lift the slides. The pods have reduced that vacuum. The best thing to do is put the stock airbox back on and rejet slightly for the header. I sold a GS650 last year and it ran like a dream: fast, smooth, responsive. I'm surprised that others who have had problems rejetting CVs haven't jumped in on this thread. I may still have a 650 airbox sitting around somewhere, too.

Thanks for jogging my memory Don.
Dano, when you install pod filters on a bike with CV carbs, you have to drill out the vacuum orifice leading to the diaphragm chamber. A jet kit gives you the drill along with the adjustable needles.
A CV carb will idle and accept MAYBE a little throttle if its vacuum is compromised or the diaphragm is failing. It will not accept any more throttle than just above "idle". That's why your bike tops out at 60 mph in top gear regardless of how much throttle you give it.
I knew it was probably a diaphragm/vacuum problem but forgot about needing to drill the vacuum hole. That's what makes forums good. You get everyone involved and one thing leads to another. Again, Don gets the atta-boy here.
You sound like you would be happy with a stock air box and just increase the main one full size to allow for the pipe and maybe a 1/4 turn or so out on your mixtures screws. Needle adjustments are probably not needed.