Surging RPMs When Choke Is Set

[84_KZ550_NewB]

84' KZ550-F2

This only happens when the engine is cold and its warming up...
I pull the choke to start it up in the morning. I let it warm up for a few minutes to 5 minutes. With the choke pulled all the way out, the RPMs seem to go up and down. But when its warm and the choke is pushed all the way back in, the idle is fine. No problems there. It just goes up and down in RPMs when the choke is pulled. Why would it do that? And also what is the RPMs suppose to be at when the choke is all the way out?

Thanks
Jay

[herk]

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[NoTyme]

Originally Posted by 84_KZ550_NewB

84' KZ550-F2

This only happens when the engine is cold and its warming up...
I pull the choke to start it up in the morning. I let it warm up for a few minutes to 5 minutes. With the choke pulled all the way out, the RPMs seem to go up and down. But when its warm and the choke is pushed all the way back in, the idle is fine. No problems there. It just goes up and down in RPMs when the choke is pulled. Why would it do that? And also what is the RPMs suppose to be at when the choke is all the way out?

Thanks
Jay

I have the very same issue. After going thru the carbs and sealing the tank she runs great except when cold at idle. She seems to surge from about 1100 up to about 3000. Once warm it stops... I am trying to find out what I missed.
I am not sure where your idle should be set at but mine is set between 1100 and 1200.

[brown recluse]

It sounds like the carburetor problems. Check and see if there is any air getting in around the carbuetor intake side. While the bike is running spray starter fluid around the carb intakes. If the rpms go up, then there is an air leak.

Otherwise, your carbs may be out of sync. You make a simple carb sync tool by following the directions here: $1.55 Carb Sync Tool by Marty Ignazito

[coppertales]

One of my bikes does that but I am too cheap to buy a new set of intake boots. It goes away once warmed up................................................ ...........chris3

[NoTyme]

Originally Posted by brown recluse

Check and see if there is any air getting in around the carbuetor intake side. While the bike is running spray starter fluid around the carb intakes. If the rpms go up, then there is an air leak.

Tried the starter fluid today and I did not find any rise in engine rpm. I did again adjust the pilot jets and ended up with one screwed 1/2 turn out from where she was set. I'll try a cold start tomorrow and see what I find. Damm thing idles so nice when she's warm.

[brown recluse]

... Maybe your air filter?

[NoTyme]

Well I do have a bran new air filter that I just installed this spring. I did see a good deal of improvement from the re-adjustment of the pilot jets (one side did change about 1/2 turn). I am going to do a bit of research and see if I am adjusting the pilot jets correctly, but this morning she started, never stalled and surged just a bit for the first say 60 seconds or so.
I got to say I am close to havin' her right on...

[brown recluse]

I've read of a way to adjust the pilots that you might want to try. While the bike is running, slowly turn the pilot screw in until the bike starts to bog down. Then start turning the screw back out, counting the turns. The bike should get back to normal, then bog down again. Take the number of turns from the in point to the out point and divide by two. Turn the pilot back in that number of turns.

[NoTyme]

Man I hate to say this but one carb would not stall the motor when I had the pilot jet screwed all the way in... I would if turned out but not in... Looks like I need to pull out the screw and see if the o ring is bad...

[NoTyme]

NewB
Sorry I hy jacked your post. Have you been following any of this?

[NoTyme]

Ok, I thought I would post an update.
I really got things screwed up now. I have been thru the carbs twice, and it boils down to the floats being out of adjustment... and I am not sure how to adjust them. The manual just doesn't make sense to be (can'
t grasp it).
Can anyone clarify this for me???

[brown recluse]

There's a lot of others who are better at carbs, but I'll try. The others will be along to correct me in a minute. The float should rise as the carb bowl fills with gasoline. Once the float reaches a certain point it lifts a needle that stops the gas from entering the float bowl. The thing that needs adjusting is the tang. The tang is just a little metal tab that pushes the needle up. If the tang is set too low then the bowl over flows with gas. If the tang is set too high, then the needle rises too soon and there's not enough gas in the bowl to feed the engine.

Adjusting the tang is just a matter of bending it. Setting the float height is difficult to get exactly right. It varies some but most of the time, the gas level when the float cuts off the gas flow should be about 5mm below the top of the bow. Confused yet?

[brown recluse]

Let me know if you need more explanation or pics/diagrams.

[NoTyme]

Originally Posted by brown recluse

Let me know if you need more explanation or pics/diagrams.

Yes, I am confused...
Heres the deal: I have been thru my carbs 3 times, and after the initial cleaning of the carbs the bike ran much better. I still had some surging issues and tore them down again and even pulled out the floats and upon reassembly I swapped the float valve needles. Now the bike stalls and has poor throttle response. I have checked the high idle, choke is synced and pistons slide easily. The only other think I can think of is that after removing the diaphragms I could not get them back as tightly as they were when I pulled them out. I assumed that years in the groove made them a nice tight fit but they are nowhere as tight in there as they were… I did try the diaphragm test, and they would hang up maybe 1 out of 6 or 7 times... I thought that was close enough for me.
The float adjustment is the only thing I can think of that I have not checked, and yes I am not sure how to go about that adjustment. I see nothing in the manual... and I bet your gonna tell me to pull them off one more time...

[NoTyme]

Holy S**T!!! Dealer says the Vacuum piston is $108 each... Time to part out this machine if thats the case.

[brown recluse]

Don't give up hope just yet. You can test the floats without removing the carbs. If they are out of adjustment, however, you may need to remove them unless you can get the carb bowls off without removing the entire set.
Check the thread here: A simple fuel level gauge. for pictures

Your bike needs to be level to do this test.
On my bike, I can hook the clear tube to the drain at the bottom of the carb , turn on the gas (Prime) and open the drain plug. Hold the tube alongside the carb body and it should show you the gas level inside the bowl.

I can send you another diagram if you p.m. me your email address.

(Just to be sure, you've already checked plugs, plug wires, coil, cracks in the carb boots and synced the carbs, right?)

[NoTyme]

Originally Posted by brown recluse

On my bike, I can hook the clear tube to the drain at the bottom of the carb , turn on the gas (Prime) and open the drain plug. Hold the tube alongside the carb body and it should show you the gas level inside the bowl.

I can send you another diagram if you p.m. me your email address.

(Just to be sure, you've already checked plugs, plug wires, coil, cracks in the carb boots and synced the carbs, right?)

Let me get this straight: You remove the black hose from the bowl drain and replace it with clear? Then just hold up along side the bowl, open the drain and the gas will rise in the clear tube and give you the gas level in the bowl? I gotta try this...

[brown recluse]

That's the way on most carbs that I know of. Basically, you are filling the carb bowls up until the float raises up and engages the cut off. The clear tube connected to the drain bowl shows you how high the fuel got before stopping.

The link I posted is for older 400 twins, In that particular carb, the clear hose had to connect to the drain screw hole, but on other carbs the clear hose connects to the drain.

[NoTyme]

Originally Posted by brown recluse

Setting the float height is difficult to get exactly right. It varies some but most of the time, the gas level when the float cuts off the gas flow should be about 5mm below the top of the bowl[/b]. Confused yet?

If I am reading the chart 8.18 correctly, my fuel level is very low. I measured from the point where the bowl and carb body come together and I have a fuel level of -.5" on one side and -.6 on the other. That's a good half an inch below the point where the bowl and carb body meet.
If I am reading the chart correctly the gas should be up to the top of the bowl, or just above it...
I also pulled my plugs and found them to be fouled up and this tells me the carbs were running extremely rich after re-assembly.
Does this makes sense?

Oh, I should also say that I just connected the tube and opened the drain on the carbs, and did not mess with the linkage: carbs are still on the bike.