surging, poor idle, fuel leaking from carb overflow tube

[prosnomonkey]

So, I just reinstalled the carbs after a full clean, o-ring replacement, and valve clearance adjustment. I am having the same issues as I did before I did this work.
Idle issue: when the bike is first started it seems to idle fine at about 1500 RPM, I get the engine warmed up and the idle moves up to 3-4K, go for a ride and it will stay at 6-7k RPM. I turn the idle down to 1500 RPM, ride around for awhile and then it will die at idle. Turn the idle back up to 1500 RPM and the circle starts again.

Surging Issue: Riding around I get on the throttle and the engine feels like it is bogging down, but as the RPMs go up it surges and the bike takes off. Cruising around trying to maintain constant throttle and the bike surges, then sputters, surges then sputters.

Fuel leaking: I finally get frustrated, go home and park the bike and fuel pours out of the overflow tube going to the right hand carb.

Where do I go from here?

Thanks in advance
Jeremy

[tom203]

Fuel leaking; do you understand petcock positions? if so, have you tested petcock to make sure it's working correctly (not allowing fuel to flow when bike ain't running) ?

Surging and high idle stuff: did you replace the carb boot o-rings (at head interface)? maybe your boots are leaking- lots of guys replace them and find that solves the surging and high warm idle.

[Agemax]

have you set all the float heights correctly?

[Steve]

..., go home and park the bike and fuel pours out of the overflow tube going to the right hand carb.

This is a neat trick, because your bike does not have "overflow tubes".

As mentioned by previous posters, the overflow issue could be bad inlet valves in the carbs or improper float height setting, and the surging/dying at idle would be your intake boot o-rings.

The solution to both problems is simple and relatively cheap. Get a set of o-rings at cycleorings.com, be sure to include the intake boot orings and the stainless bolts that hold the boots on. Rebuild the carbs. As you are dismantling the carbs, measure the float heights. If they are pretty close, get new inlet valves, too.

Also be sure you are familiar with the petcock positions. Lever pointing DOWN is the normal position, and should be there virtually all the time. If you are riding and exhaust the main portion of the fuel tank, rotate the lever clockwise so the lever is pointing forward for the REServe. In both of those positions, engine vacuum will turn the petcock on. When the engine stops, the petcock will be off. If it has been a long time since you last ran the bike (usually more than one or two weeks), you might have to rotate the lever anti-clockwise to the PRIme position. In this position, gas will flow regardless of whether the engine is running, and this might flood the carbs if the inlet valves can not seat properly to hold it back. Do not leave the lever in this position for more than a minute to minimize the risk.

.

[prosnomonkey]

The petcock seems to be fine, I left gas in the tank when I was cleaning the carbs and the petcock in the on postion, no gas ever leaked out. As shown in the Mega-Welcome and carb rebuild tutorial (THANK YOU BassCliff!!) I replaced the o-rings (cycleorings.com is a god-send) at the boots on the engine side of the carbs, but not the boots themselves as they are still soft and pliable. The boots on the airbox side were replaced with new ones. I didn't measure the float height as I am not really clear on how to do that but the carbs appeard to have never been taken apart so I assumed (please shoot me) that they were still the same as when they came from the factory. If I don't have overflow tubes, what are the two tubes sticking out of the carbs next to where the fuel inlet T's? and why is gas coming out of the right side one?

I will begin researching the float-height measurement and start tearing into the bike again.

Any other ideas?

Thanks for the help!

PS I do really appreciate how simply you guys can explain things!
Jeremy

[tom203]

Those tubes look like the vent hose fittings -look at this link part #68

http://www.alpha-sports.com/spst/1980%20GS450L/05.htm?q=suzuki-parts

Not sure why they are shown angled down (on my bike they go up)- so yeah, if fuel is coming out of that fitting, your bowl(s) have overfilled ; so you got float seat problem... but even with bad float needle seats, it should only dump a little fuel when bike is shut OFF as a good petcock stops fuel flow.
Did you remove and replace the o-ring or gasket on needle seat valves?

[Gorminrider]

..it sounds like you are confusing the "carb bowl vents" (these allow air into the carb bowl -otherwise, it'd be airtight and no fuel would get in) with the vacuum line, that goes from the right carb's manifold up to the tank (when the bike is running or even turning over with the starting motor, the manifold pressure created by sucking pistons+valves sucks a valve at the fuel tap and allows fuel to flow)

anyways, as above-check the float level and seats sounds to be main issue...right now, gas is slopping around in the air passages of the carb so the engine is getting all kinds of gas all the time-pretty scary

[prosnomonkey]

Steve - I was referring to the part that Tom203 mentions. Mr. FlamingChainsaws calls it an overflow tube in his Rebuild tutorial, so that what I thought it was.

Anyway, I'm going to check the float height level tonight, but I have a question: On this page BassCliff shows how to measure the float height, but is he measuring from the side of the bowl or from the bottom?

Thanks
Jeremy

[Agemax]

measure it from the float bowl gasket mating surface, without the gasket, to the top of the float, with the carb inverted

[prosnomonkey]

So I measured the floats and they were off by about 3mm, that seems to have fixed the gas leaking out of the vent tube. Took the bike for a ride and it doesn't bog down during acceleration, but when I try to cruise at a constant speed, the bike sort of surges/dies/surges/dies. From what I've read, this sounds like an airflow issue, but I've replaced all the o-rings and boots. The one thing I haven't done is try to tune/sync the carbs as I don't have a carb sync tool. Going to go to the auto parts store and see what they have that might work... local place rents tools and they may have something I can rent. Anyone have other ideas as to why this surging occurs?

Thanks
Jeremy

[Agemax]

you could try bench synching the carbs, if they are way out it would help a lot, but wont be perfect

[tom203]

Step by step....

Run with petcock in "PR" spot and see if "surge/die" stuff changes- you do have air filter element in, right??
Skip the carb sync tool for now- a decent bench sync gets you pretty close, so get it running nicely

DON'T forget to put petcock back in "ON"

[prosnomonkey]

Ok, so the way I understand it is that a bench sync gets both butterfly valves set the same and left with about a paperclip sized space opening. This just mean they are set the same, so do I then adjust the throttle screw (the one between the carbs) back to the valves are completely closed? Or do I leave the space there and install the carbs? So far I have left the space there, installed the carbs and started the bike, it idles at almost 5k RPM in this place. Do I then turn the idle screw back to adjust the idle, or do I start fooling with the Fuel adjustment screws on each carb?

Thanks
Jeremy

[prosnomonkey]

nevermind, I re-read the bench sync tutorial and figured it out

[tom203]

Yes, it doesn't take much throttle plate opening to let revs go sky high! Thanks for update and keep posting- others will learn from your problems.