Symptoms related to holes in diaphragms?

I've been having the worst time getting my bike to run good (1980). After performing the dead cylinder method and using a diy manometer, the bike idles great. Even revs well and returns back down quickly (or normally, i guess).

Whenever I take it on a test run, the first 5 minutes are amazing. After that, it all goes downhill.....

The main problem, is that most of the time the bike's idle will jump up to 4-5000 rpm...Sometimes it will come back down after maybe 10 seconds, lately it just stays up that high. A few times, it even goes higher....to the point where I just have to shut off the bike.

I tore apart my carbs again, this would be the 3rd time in that last 2 weeks. I've done a thorough cleaning job, and replaced the floats. but I decided to look closely at the diaphragms. Sure enough, there are a few holes the size of pin needles.... Maybe 2 or 3 on each carb. Tiny little holes that you wouldn't see unless looking at the right angle with a light.

Obviously i need to replace them. But Is this the source of my problems? could this be causing the random high revs?

Hey, Newest. Not familiar with that model, so just taking a stab in the dark here.

Poor fuel delivery, when fuel drops low in the bowls can sometimes cause hi idle.

TCI timing issue. Possibly TCI going bad, or electrical condition causing TCI to falsely enter advanced timing mode. Thinking vibration-induced intermittant connectivity either at the sensor, internal to the TCI, or power/ground to TCI. Some older threads here also cover weak trigger magnet issues.

Pinholes in diaphrams usually only cause mid-range throttle issues, where the diaphrams receive enuff vacuum signal to pull the slides up...

As the bike warms up you develop an air leak. This air leak leans out the mix and causes the high idle.
I might suggest once riding it till it starts to act up and check for air leaks.
Leo

I really do think a air leak might be the cause. But I don't know where? I generally let the bike warm up for a good time, sometimes bring a fan to help cool the engine while it synch it.

What is the best way to check for leaks?

You say you replaced the floats..................are they the correct floats, and the correct setting?

1980G carbs used brass floats, and should be set at 27 mm. 1981 to 1983 used plastic floats, and should be set at 22 mm.

As in all carbs, the correct float level is very important.

Well...its kind of a story.....But basically....

The bike is a 1980, when I opened the carb, there we're plastic floats that we're not the correct ones for a xs650. Never seen them before, so I ordered the plastic ones. And set them to 22mm....

Could the float height be the cause of it? i'm getting ready to tear it apart again....i'll double check...

One of the things I did notice on my test run (and previous test runs)....is that "rarely" one of my float bowls will flood. It has only happened less than 4 or 5 times. Usually the left one, but yesterday it was the right one. I'll turn on the petcock and fuel will come gushing out of the front (I usually take the air filters off to get a better look).

I've read this (correct me if i'm wrong) is the float needle improperly seating...Usually i'll take the carbs off, remove the float bowl and look at the float needle. 100% of the time that fixes it. Sometimes (like yesterday), if I fiddle with it, or try to ride without that carb, the issue will fix it self....probably has something to do with the vibration of the road.....

Do you guys think this could be related to the random high revs?

NewestOnTheBlock said:

One of the things I did notice on my test run (and previous test runs)....is that "rarely" one of my float bowls will flood. It has only happened less than 4 or 5 times. Usually the left one, but yesterday it was the right one. I'll turn on the petcock and fuel will come gushing out of the front (I usually take the air filters off to get a better look).

I've read this (correct me if i'm wrong) is the float needle improperly seating...Usually i'll take the carbs off, remove the float bowl and look at the float needle. 100% of the time that fixes it. Sometimes (like yesterday), if I fiddle with it, or try to ride without that carb, the issue will fix it self....probably has something to do with the vibration of the road.....

Do you guys think this could be related to the random high revs?

Click to expand...

Its not normal for the bowls to overflow like that. The float needle should have a viton tip; is it in good condition? The float valve itself should have a rubber O-ring; is it in good condition?

Yes, if the float level is not being controlled, then that could give the high revs you are seeing.

Well, I have looked at them before and they "looked" fine. but obviously it has been a issue.

Why is it though, that it would only act up when i'm ridding? synching/adjusting when idling is completely fine, its completely fine for the first few minutes of a ride. But then everything goes downhill from there?

Also, I have recently replaced my carbs boots with new ones.......

I feel like it could be a air leak? but I can't find it if it is? (unless someone recommends a way to check for leaks...)

But then again, this issue has been going on for the same amount of time as the float overflow issue...

EDIT: come to think of it though.....the carbs don't always overflow and spew fuel.............but the bike always has a random high rev issue............

EDIT: is the float valve/needle something where a issue still can exist...but not be visible? aka.....can it cause my random high rev....but not overflow/spew fuel??

I just couldn't help myself......

I'm too lazy to read the thread so;
Have you sprayed carb cleaner while it's running to check throttle shaft seals?
Have the orings on the float valves been replaced?
Screens still on float valve bodies, new fuel lines?

BWHAHAHAHA how do they remember the names or do they number them with ear tags?
If you don't want the mess of an aerosol, a vacuum leak will pick up propane also. Just remember to only crack open the valve a little and close it when through.

The orings on the float valve do appear to be "old" they don't seem nearly as flexible and plump as o rings should generally feel. Guess its time to order new ones... in the meantime i'll try the other solutions...

You can use most any liquid to check for air leaks. WD40, Carb cleaner, Brake cleaner, even water.
Set the idle as low as you can. Spray plenty of the liquid around where you suspect a leak.
The fluid seals the leak for a short time. This effects the idle.
Leo

ive given that a try....unfortunately ive had no results.....the only time the idle was affected was when i sprayed it directly into the carb intake...u know where u would connect the air filters.

it did drop the revs...but i feel with such a direct spray it should of happened?