Questions from a newbie

[usin13]

Hello. I want to preface this by saying all the mechanical work I've done has been on a 1961 Ford Falcon, which couldn't be more different than a motorcylce engine. For instance, who puts 4 carbs on an engine???
Anyways, to the real questions.
I have read a lot of previous post and I believe I have an air leak, mainly do to sporadic RPM's on idle. I got my Clymer manual and was hoping it would tell me what the boots are so that I wouldn't have to ask, but it didn't. So, what are the boots that I'm supposed to check to see if they are leaking? I see rubber connecting the carbs to the engine and rubber connecting the carbs to the airbox, is it one of these sets?

Second, I am leaking gas from at least the first and fourth carbs. It is a very slight leak, but I am not able to tell where it is leaking from. I just know that I wipe off the gas, then I come back after it's been parked for a while and there is gas again. Where/How do I start to figure out where this is coming from?

Third, I am just curious as to what my RPM's should be when driving. I am used to dirtbikes, but not something the size of a 750. That being said, when I am going 45 MPH, I am in fifth gear at about 3400 RPM. Is that high? It seems to me like a 750 should be able to handle that with a lot lower RPM, however, I'm new to street bikes and could be completely wrong.

I probably have 40 more questions, but that's my big ones right now. I thank you ahead of time for the help. If anyone lives near the Neenah, WI (Green Bay, Appleton, OshKosh) area, let me know and I'll recruit you for some beer or soda (whichever you prefer).

 

[marvinsc]

You have Figured the Boots Out. Two Sets, Airbox to Carbs and Carbs to Intake. Several Carb Gurus here but I'm Guessing you have Floats sticking causing the Gas seepage. These Bikes Do rev High and Most of us wish We had a 6th Gear BUT they are Built to Rev and will handle it All Day. Welcome to the GSR and Enjoy the Bike!

 

[Guest]

What year and model is it?

 

[bwringer]

Here are the intake boots between the carbs and the engine, a common source of nasty intake leaks:

http://bwringer.com/gs/intakeorings.html

These photos and part numbers are from a GS850; your bike will look about the same if it's an early 8 valve 750, although the part numbers are different.

 

[usin13]

What year and model is it

What year and model is it

You know, I hate when I'm reading forums and people don't put in the year and model. Then what do I do, not put in the year and model. It is a 1977 GS750. Sorry.

 

[usin13]

Intake boot site

Intake boot site

That site is very helpful with the intake boots. It answers some questions I had. On the boot that connects to the air box, I'm not sure mine are seated on the carbs right. They seem a little off kilter. Also, can I just replace the clamps that are currently on the boots with hose clamps from a hardware store? I tightened the ones that are on there now as much as they will go and I can still spin the boots to the airbox which to me makes it seem like they are loose.

Good to know about the high rpm's, I thought it was just mine.

As for the leaking gas, I'm not sure if this would cause it, but I realized it's been on prime since I got it. I switched it to on last night, but it was rianing today so I did not check it. While that wouldn't be the cause of the leak, is that perhaps making more gas leak than otherwise?

 

[rustybronco]

Hello. I want to preface this by saying all the mechanical work I've done has been on a 1961 Ford Falcon, which couldn't be more different than a motorcylce engine. For instance, who puts 4 carbs on an engine???

A lot of car companys put multiple carbs on their engines, triumph comes to mind.
why is a car engine different? cylinders, head, intake, carb(s), ignition, fuel, compression, spark, timing, cam, oil, oil pump ect.

Third, I am just curious as to what my RPM's should be when driving. I am used to dirtbikes, but not something the size of a 750. That being said, when I am going 45 MPH, I am in fifth gear at about 3400 RPM. Is that high? It seems to me like a 750 should be able to handle that with a lot lower RPM, however, I'm new to street bikes and could be completely wrong.

car engines usually have an rpm limit of 5-6000 rpm, yours? 9-10,000 rpm! think range here. tooling down the road at 2-2,500 or 3-4,000

I probably have 40 more questions, but that's my big ones right now. I thank you ahead of time for the help. If anyone lives near the Neenah, WI (Green Bay, Appleton, OshKosh) area, let me know and I'll recruit you for some beer or soda (whichever you prefer).

next question?

too bad i'm not going to crandon wi. this year BEER AND BRATS yum!!!!!

 

[Jethro]

In an effort to make your wrenching more complicated, you have a vaccum operated petcock. That is, the fuel only flows when the engine is turning, due to a port in the intake manifold that harnesses the vaccum. The petcock has a diaphragm that opens when the vaccum begins. Often times the diaphragm fails and owners use the "prime" setting to run the bike. "Prime" is not dependant on vaccum, as it bypasses the vaccum function. So let's continue our journey towards the piston...

The fuel flows down the fuel line and fills up the bowls on the bottom of each carb until a float bulb raises to a ver specific point and pushes a tapered needle into the port that feeds these bowls. It may be that these needles or the seats that they close up are either dirty or worn. That would cause gas to continue flowing even when the bowl is full. But if we back up a moment, the vaccum line we talked about earlier could also be dropping fuel due to the faulty diaphragm. The vaccum port is in front of the carbs, so the floats wouldn't be able to shut off the flow of gas, it would just spill into the airbox and down the drain line.

So, you need to put your petcock from "prime" to "on" and see if it is still leaking gas. If it is, you definitely have a faulty petcock- so fix that first. If it is still leaking gas, you have faulty float valves as well.

 

[usin13]

A lot of car companys put multiple carbs on their engines, triumph comes to mind.
why is a car engine different? cylinders, head, intake, carb(s), ignition, fuel, compression, spark, timing, cam, oil, oil pump ect.

car engines usually have an rpm limit of 5-6000 rpm, yours? 9-10,000 rpm! think range here. tooling down the road at 2-2,500 or 3-4,000

next question?

too bad i'm not going to crandon wi. this year BEER AND BRATS yum!!!!!

No offense was meant to the multiple carbs. My entire mechanical knowledge stems from that 1961 ford Falcon, so I couldn't tell you about triumph or anything else. What is different to me is the way the engine sits. On my falcon, the carb sits right on top with a gasket. 6 cylinders use one carb where on the Suzuki each cylinder has a carb. Just completely different from what I know. You should have seen me debate the best way to check spark. I was worried that if I did it with the electric start, it would just start on the other 3 cylinders, and not knowing what kind of affect that would have on the engine. So, I have not yet checked the spark.

Should I start a separate thread to ask more questions, or just continue on this one? Want to follow the forum etiquette.

 

[usin13]

So, you need to put your petcock from "prime" to "on" and see if it is still leaking gas. If it is, you definitely have a faulty petcock- so fix that first. If it is still leaking gas, you have faulty float valves as well.

WOW!!
Thanks for the info. I will check it tonight as I switched to on last night and wiped up the spillage. I'll let you know.

 

[lord1234]

prime is an "unchecked" fuel flow...so you are basically flooding your carbs if you aren't running the bike at a good clip...your bike should practically NEVER need the prime setting....reserve or ON (preferrable only ON)

 

[usin13]

new problems just keeping it running

new problems just keeping it running

The good news: it looks like switching it to on did the trick. I don't see any more leaks.
The bad news: now I'm having problems with it starting and running. I have no idea if the two are related as I switched it back to prime and that didn't seem to help. I will tell you what I did.
I started it like usual by putting full choke and then pressing the button. It started fine. I lowered the throttle, only little by little as it will stall out pretty quickly if I try to go to fast. The lever was really stiff, so I loosened the screw on the choke lever. I was letting it idle to see how much I could open the choke lever before it died. Normally I can only open it about a third, but I thought that maybe with the petcock on, I could now open it more. At about half way, the bike died. I tried to restart and it just kept trying to go, but wouldn't catch. I choked it again and it still wouldn't catch. I had to give it gas while starting it to get it to start. Then once I got it going, I couldn't do much with the choke. If I tried taking it down a little the bike would stall. Finally I got it to sit at about 2200 rpm and I put it into first and started to drive down my driveway and it stalled. In order for it not to stall, I had to give it quite a bit of gas otherwise it just bogged down.

Did I do something with that choke lever? Is it just coincidence it is happening at the same time as switching the petcock to on?

Again, thanks for the help you've already given.

 

[Guest]

Check your petcock flow with vacuum applied.

 

[1150bob]

umm..are you out of gas?

 

[usin13]

How?

How?

Check your petcock flow with vacuum applied.

How do I check it?

 

[usin13]

Gas?

Gas?

umm..are you out of gas?

I was hoping that was the problem when it was happening but no, there is plenty of gas.

 

[rustybronco]

No offense was meant to the multiple carbs. My entire mechanical knowledge stems from that 1961 ford Falcon, so I couldn't tell you about triumph or anything else. What is different to me is the way the engine sits. On my falcon, the carb sits right on top with a gasket. 6 cylinders use one carb where on the Suzuki each cylinder has a carb. Just completely different from what I know. You should have seen me debate the best way to check spark. I was worried that if I did it with the electric start, it would just start on the other 3 cylinders, and not knowing what kind of affect that would have on the engine. So, I have not yet checked the spark.

NO offence was even thought i was just saying... they are one in the same as someone said suck squeeze bang blow.

 

[usin13]

Update

Update

This morning I went and started the cycle. It started like normal. I did full choke and slowly backed off the choke. Also like usual I can only get the choke about 1/3 of the way open. I drove it to work, which is about 30 minutes, with no issues. Unfortunately, I still have some gas leaking. Not as much as I did when the petcock was on prime, but still getting some. I think however I am going to start by replacing the intake boot o rings to address the sporadic RPM. After I do that, I will look at the leak. One thing at a time I suppose. I assume it is best to just get a solid idle first and then start working on the other issues. Is that correct?

 

[bwringer]

It's a VERY bad idea to continue riding a bike with possible intake leak or any lean running issues -- it can quickly overheat the engine and lead to some pretty gruesome engine damage.

I'd post photos of the horrible remains of my bike's original exhaust valves (damaged by intake leaks), but they're just too graphic for a family forum...

 

[Guest]

Take off your fuel line going to the petcock and put a temp one running to a bucket or something. Pull the vacuum line off the bike but leave it on the petcock. Suck on the vacuum line on Prime and it should run even when you remove vacuum. On run the petcock should only spew gas with vacuum applied to the line. If you get a mouth full of gas rebuild time. If you don't have good flow, rebuild time. You also need to check your float needle and seats because they are not shutting off gas flow.