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Carb Part Question

  • Thread starter Thread starter HobieSun
  • Start date Start date
H

HobieSun

Guest
Hello,
I have a 1980 GS750L. It has Mikuni BS32SS carbs. When I first got the bike it did not run. I took the bowls off to take a look and there was something that I had never seen before. There is a (previously)rubber plug very close to the main jet. This plug was melted into the bowl. It looked as if someone squeezed silicone into the bowl. Two of them were completely melted, the other two were halfway intact(half-way melted) I removed the mess and cleaned it out completely. What (I will do my best to keep my composure) the $%$# are these plugs for and do I really need them? I got the bike running very well except for a voltage regulator problem. The only other problem that I am noticing is that this thing is eating gas. Now, I am trying to fix one problem at a time and I know the regulator isn't any good, I should get that in a few days. It could be possible I suppose that it could be related to the gas issue, but my main concerns are what the heck are those plugs and do I really need them. If so, what would be suggested to use?

Thanks for reading this mess.
 
Those rubber plugs are an emissions anti-tampering attempt by the factory.
They have to do that to deter you from changing the pilot jets. Not much work to defeat them, but it makes Suzuki legal.
There have been a couple guys here in the past that swore removing the plugs caused their bike to run funny. Most say they've had no problems. I don't argue with them but if you study an illustration of the carbs pilot circuit and its operation, you'll see that fuel enters through the main jet and then through the pilot jet via a side passage.
Removing the plug doesn't change how fuel flows to or through the pilot jet or effect the vacuum.
If you don't know what to think, simply replace them. They're easy to buy.
 
And poor gas mileage could be many things. Check basics first.
Compression, valve clearances, spark/ignition quality, clean electrical connections everywhere, clean carbs with fresh o-rings/floats adjusted, good manifolds/o-rings, clean air filter..
Check the jetting while you have the carbs apart to see if others have made incorrect changes.
 
Thank you,
I really didn't think that they did anything and to avoid what ever melted them in the first place I will just do without.
 
WE ARE TALKING ABOUT INSIDE THE CARB That little rubber plug is needed
the bike will not run properly without them
 
SqDancerLynn1 said:
WE ARE TALKING ABOUT INSIDE THE CARB That little rubber plug is needed
the bike will not run properly without them
Click to expand...
Lynn, how can the plugs effect carburetion? I know we're talking about the rubber tamper plugs that go over the pilot jets.
I've read a couple of replies like this in the past and after studying the illustrations and looking at this type of carb in my hands, I can't see how the plugs, installed or not, could effect operation.
A couple of guys claimed their bike ran wrong without the plugs. I don't see how. I think they had other issues and just blamed the plugs.
 
The rubber plugs are indeed NOT part of the emissions system. On BS series Mikuni carburetors, there are plugs over the pilot jet wells on SOME (not all) assemblies. Those that use plugs, either use the rubber plugs or some have metal plugs with orings. The plugs are in place to keep gas from getting into the pilot well from the float bowl. The reason is that there is a small hole inside the well that goes over to the main jet holder well and that is where gas for the pilot system is drawn into the pilot jet. If the pilot well (where the pilot jet screws in) is NOT plugged, the pilot jet is swamped with gas and the idle circuit will be drowned and it not only won't idle properly but the bike will be a gas hog! On BS assemblies NOT equipped with a plug, there is no cross passageway for feeding gas and if you plug those, you can't get the bike to idle at all. An example of this type of Mikuni BS assembly is the BS34 used in an 83-85 GPz750 (ZX750A). Unfortunately, the pilot well castings are identical and there is no good way to know if there is a cross passageway if you are uncertain except to put L shaped dental pick in the main jet well (with main jet holder removed) and poke around next to the pilot well to determine for sure. Last, it is common for folks to try and use silicon to keep the black press-in pilot plugs in place since they don't really want to stay in well if reused. You can purchase aftermarket (K&L) press in plugs. www.z1enterprises.com can get some for you or any dealer that sells K&L carb products. I think they come in packs of 6.
 
wiredgeorge said:
The rubber plugs are indeed NOT part of the emissions system. On BS series Mikuni carburetors, there are plugs over the pilot jet wells on SOME (not all) assemblies. Those that use plugs, either use the rubber plugs or some have metal plugs with orings. The plugs are in place to keep gas from getting into the pilot well from the float bowl. The reason is that there is a small hole inside the well that goes over to the main jet holder well and that is where gas for the pilot system is drawn into the pilot jet. If the pilot well (where the pilot jet screws in) is NOT plugged, the pilot jet is swamped with gas and the idle circuit will be drowned and it not only won't idle properly but the bike will be a gas hog! On BS assemblies NOT equipped with a plug, there is no cross passageway for feeding gas and if you plug those, you can't get the bike to idle at all. An example of this type of Mikuni BS assembly is the BS34 used in an 83-85 GPz750 (ZX750A). Unfortunately, the pilot well castings are identical and there is no good way to know if there is a cross passageway if you are uncertain except to put L shaped dental pick in the main jet well (with main jet holder removed) and poke around next to the pilot well to determine for sure. Last, it is common for folks to try and use silicon to keep the black press-in pilot plugs in place since they don't really want to stay in well if reused. You can purchase aftermarket (K&L) press in plugs. www.z1enterprises.com can get some for you or any dealer that sells K&L carb products. I think they come in packs of 6.
Click to expand...

Thank you "Wired" for chiming in here as a "Member". I was going to but refrained....

ghwrenchit
 
George, thanks for the input. I don't agree that the plugs are necessary to correct mixture/fuel amounts.
I don't work on as many carbs as you must, but I'm familiar with the passage through the main jet and then to the pilot jet. It shows up in any illustration.
Plug or no plug, on a carb that comes with them, the fuel will still be regulated through the pilot jet. I don't see how the plug missing would "flood" the pilot jet. A missing plug wouldn't compromise flow and I don't think, vacuum. If there was any effect, I can see where vacuum could be compromised (less) but that would cause fuel starvation, not a rich/flooding condition.
Also, the majority of past posters say they noticed no difference at all when running without the plugs. I don't base my thoughts on what they say, just my interpretation of the carb design. I mention it for info only.
 
ghwrenchit said:
Thank you "Wired" for chiming in here as a "Member". I was going to but refrained....

ghwrenchit
Click to expand...
By all means, add your thoughts. We're all learning here.:)
 
I've been told more than once that the purpose of the plugs is to draw fuel from the main jet port, which is the lowest port in the bowl. The reasoning I was given is that when the bike leans the pilot port being higher in elevation would effectively see much different float heights than the main jet port would. If I remember correctly, the pilot circuit is much more sensitive to float heights than the other circuits (which operate off the main port anyway).

Just what I've heard. That being said, I've neglected putting them in with no change in driveability what so ever.
 
Like I said, just study the carb illustration and read about the operation of this carb. Look at a carb if you have one. You can see how it works.
 
One other thing that kinda bothers me.
On a few occasions, George has made a point of trying to "improve" or correct some of my suggestions. I don't see him doing this to others. If you read some of his replies, it's obvious he's referring to me. Why is this? George? Is there some kind of stud carb guru thing at stake here? I'm not in a competition here.
I only try to help here. I'm not promoting a side business. I also don't step on others unless provoked. If I'm right, I try to pass the knowledge on. If I'm wrong, then I've learned something. I take pride in my suggestions. That's why it's easy for me to get irritated over what feels like being policed. I've noticed that you never reply again after I re-make a point about something previously talked about. You may come back because this sounds more personal, but it would be the first time.
I've read your posts because I might learn something too. I've kept quiet if I feel your advice is wrong. But if you say my advice is wrong, I back up what I said with more detail and that's been the end of it.
You recently joined a thread where I was helping with jetting for pods/pipe.
You said my suggestion to go from a 100 main jet to about a 120 was "way tooooooooo rich". You suggested a 7.5 increase. If you ever jetted that bike correctly, you know that's wrong.
You also said to keep the jet needle in its factory position. How would that ever work?
At another thread you didn't think my advice about adjusting the floats to factory spec's was worth the time. But float adjustment is a basic part of tuning.
You've also tried to impress people who may buy carbs from you or have you rebuild theirs, that you'll vacuum synch their carbs on a shop bike you keep. It might sound fancy and like "an extra" to some, but you and I know that vacuum synching carbs that will go on another bike is as silly as can be. Total waste of time. But you lead these people to believe their carbs are vacuum synched and ready.
See what it's like to be policed? Get off my back.
This reply reads worse than intended, believe that. I've read your posts and I appreciate what you share most of the time. I've often said to myself that I bet you're a good guy and would like to meet you one day. I've let people know that you work on carbs and maybe that gave you some business, I don't know. But I'm a bit tired of this stuff lately.
Like I said, I take pride in the knowledge I have and that's why this post. I'm sure you know what I mean.
 
Last edited:
If they were not needed ? why then would'nt muniki eliminate them to save a few pennies
 
HobieSun said:
Hello,
I have a 1980 GS750L. It has Mikuni BS32SS carbs. When I first got the bike it did not run. I took the bowls off to take a look and there was something that I had never seen before. There is a (previously)rubber plug very close to the main jet. This plug was melted into the bowl. It looked as if someone squeezed silicone into the bowl. Two of them were completely melted, the other two were halfway intact(half-way melted) I removed the mess and cleaned it out completely. What (I will do my best to keep my composure) the $%$# are these plugs for and do I really need them? I got the bike running very well except for a voltage regulator problem. The only other problem that I am noticing is that this thing is eating gas. Now, I am trying to fix one problem at a time and I know the regulator isn't any good, I should get that in a few days. It could be possible I suppose that it could be related to the gas issue, but my main concerns are what the heck are those plugs and do I really need them. If so, what would be suggested to use?

Thanks for reading this mess.
Click to expand...

Those pilot jet plugs are a much debated subject. I asked the same question months ago. Bottom line is no one really knows for sure as to their specific exact purpose. All I know is Suzuki put them there for a good reason. My opinion is they are plugged to minimise the possibility of ingesting bowl sedimant, which commonly plugs the pilot jet. I have a new set of plugs installed, and my 1100 runs perfect, as far as the pilot circut. Like Keith commented, they draw fuel from a passage linked to the main jet. So even with the plugs installed, the pilot jet can draw the needed fuel.
 
Road_Clam said:
My opinion is they are plugged to minimise the possibility of ingesting bowl sedimant, which commonly plugs the pilot jet.
Click to expand...

Good point, never thought of that. Another thought I had was is it possible that with the plugs installed, forcing the fuel to be drawn from the main jet, that when in any throttle position off idle, there is enough vacuum thru the main and needle, that in effect it shuts off the pilot curcuit?

ghwrenchit
 
It has always been my belief that they were there to limit how much gas could get to the pilot jets at a time. With plug in place gas would have to go thru a metered passage which would meter the flow, which would in turn make the engine suck gas through a more intended route. Without the plug the gas would be free flowing and not force correct atomization in the jets and passages in other parts of the carb. It probably wouldn't effect much more than the idling and fuel milage. I can't imagine leaving something out the the crafty Japanese intended to put there. Notice the post on the inside of the bowl, it sits against the rubber plug and keeps it in place, tightly. I'm sure a removable rubber plug was used because of the likelyhood of it getting plugged and needing removed and cleaned. The rubber plugs will melt if carb cleaner is left in the bowls in an attempt to get it running and then stopping after a no go. I've seen it many times.

Note, anything posted above is only an opinion based on what I have learned and infact may be wrong, what do you expect with free advice.
 
SqDancerLynn1 said:
If they were not needed ? why then would'nt muniki eliminate them to save a few pennies
Click to expand...
For the same reason they install those cheap metal caps over the mixture screws. They don't want you to change the mixture.
 
If the plugs are there to prevent tampering, why wouldn't they have used metel caps instead? The rubber plugs are far too easy to remove as an anti-tamper device. :?

They do, however, hide the pilot jets, so you overlook them when you're trying to clean the carbs! I think you can guess how I know that. :oops:
 
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