Idle issues

[haggis905]

I did do a bench sync before the install, Jimg. That's what I was thinking also, that somehow I was off, but I followed the instructions for doing a bench sync from the Suzuki Service manual I have for my GS750 (came with the bike), and from the information that I have read in the GS forums. I could take them in and have them synced at the Suzuki dealer, but what would I learn then?

This weekend I am hoping to be able to check the timing and get a compression read and use the vacuum sync tool to see how far off they are.

[jimg]

I did do a bench sync before the install, Jimg. That's what I was thinking also, that somehow I was off, but I followed the instructions for doing a bench sync from the Suzuki Service manual I have for my GS750 (came with the bike), and from the information that I have read in the GS forums. I could take them in and have them synced at the Suzuki dealer, but what would I learn then?

This weekend I am hoping to be able to check the timing and get a compression read and use the vacuum sync tool to see how far off they are.

If the problem is in the carbs, the only other thing I can think of is the choke setup. Part of the choke valve's purpose is to open a bleed hole underneath the slide diaphram so the slide can't raise, at least on my 1980 carbs.

You might check and make sure the cable is allowing the choke valves to return all the way in. You might also check the choke rail to make sure everything is set correctly, i.e. the set screws are in the depressions that make sure they are aligned.

The choke setup could explain the high idle and bogging.

[haggis905]

I checked the choke valves and they move in and out perfectly, same as the old carbs. I didn't remember this until reading your post, but I was having the same exact issue with the original carbs that I rebuilt. Except those were really gummed up from gas being in the bowls, etc. for many years (the gas that came out of one bowl was green, and another was deep orange in color). The replacement carbs are in good condition, but I still cleaned them thoroughly.
The choke moves smoothly and if applied when the engine is running will increase the rpm's dramatically.

[jimg]

I checked the choke valves and they move in and out perfectly, same as the old carbs. I didn't remember this until reading your post, but I was having the same exact issue with the original carbs that I rebuilt. Except those were really gummed up from gas being in the bowls, etc. for many years (the gas that came out of one bowl was green, and another was deep orange in color). The replacement carbs are in good condition, but I still cleaned them thoroughly.
The choke moves smoothly and if applied when the engine is running will increase the rpm's dramatically.

I'll be honest, other than motor issues the only thing I can think of is that the slides are not raising when you open the throttle.

This sounds funny and complicated but its really pretty easy, except for removing the carbs again.

There is a wide and narrow opening in the carb throat on the airbox side. It is at the top of the throat on my carbs. Air moving into this opening is what causes the slides to move. If you blow into this the slide will move upwards. It doesn't take as much wind as starting to blow up a balloon. Give a real good puff and you'll hear the slide hit the top.

Then, on the butterfly side, you'll find a small hole in the carb throat between the butterfly and manifold. If you open the choke, air will flow throw the slide diaphram and out this hole. With the choke open and you blowing into the air opening, put your hand over the throat on the butterfly side and you should feel the air come out. With the choke open it takes a lot more air to get the slide to raise! Close the choke and the air should cease flowing out this opening.

If this works ok, then something else is wrong!

[haggis905]

Thanks, I will try that tonite when I get home and post the updated information. I have blown gently into that opening before and all diaphrams rose quickly, but I have not checked with the choke open.

Thanks

[haggis905]

I tried with the choke open and sure enough, I felt air passing through without restriction. When I closed the choke and did a normal exhale into the narrow opening, the slides hit the top immediately. I guess it is back to the drawing board....

Is there a way to change the butterfly settings on carb #3? I noticed that on the new set there is a wide opening, yet on the old set the butterfly is almost completely closed. I am going to replace #3 and then do my bench sync and see if there is any change in the situation.

[jimg]

I tried with the choke open and sure enough, I felt air passing through without restriction. When I closed the choke and did a normal exhale into the narrow opening, the slides hit the top immediately. I guess it is back to the drawing board....

Is there a way to change the butterfly settings on carb #3? I noticed that on the new set there is a wide opening, yet on the old set the butterfly is almost completely closed. I am going to replace #3 and then do my bench sync and see if there is any change in the situation.

The setting on #3 isn't something I've ever had to mess with. I'm not even sure what would cause it. I'd have to rip into my spare set to see.

If the butterfly is open that could explain the high idle, but I don't think the total bogging, but I really don't know since I've never experienced it. Out of sync carbs can give real flat spots coming off idle but eventually pick up steam. Out of sync usually makes it hard to get it to idle at a low speed.

[KEITH KRAUSE]

If you're positive you've bench synched the carbs correctly, then you have an intake leak.
You mentioned before that a PO used silicone/sealant on the manifolds.

[tconroy]

I just got done siliconing my intake boots a minute ago. As I took the carbs out of the boots one of them tore a little so i hope this fixes it otherwise its all new ones and a week to get them after ordering. Do they come with the sync screws or do ya keep the old ones?

[bradleymaynar]

Do they come with the sync screws or do ya keep the old ones?

Best to hold on to them JIC! Besides, if they end up becoming spares, you never know what GSR member may need them!:-D

Brad tt

[tconroy]

I just got back from the dealer and bought new intake boots and they dont come with the sync screws.I thought it would be best to go new rather than silicone and have to do it all over again in a month.I dont like the thought of sucking silicone into the cyclinder and causing more problems.This was decided after a just silconed the old ones and it looks like crap!Parts will be in next friday!!!!!!!A week without riding bums me out.......good thing its cold!!!

[KEITH KRAUSE]

Buying the new manifolds is the right thing to do.
Others may say they've had varying success, but using silicone is a mickey mouse fix to be honest.
Apply some hi-temp bearing grease to the new manifold o-rings and if you replace the PITA stock Phillips manifold screws with Allens, torque to about 6 ft/lb.

[KEITH KRAUSE]

Also, as I said earlier, if your carb synch has been done correctly, then the new manifolds/o-rings, installed correctly, will fix your problem.
Looking back at the last sentence of your last post, you said a week of no riding bums you out... but another week of tinkering and trying to fix the problem without fixing it would be worse.

[tconroy]

your right Keith, I also believe that silicone is "mickey mouse" and shouldnt be done.Replacement is not cheap but having the silicone sucked into the engine would be far more expense.And your right again,A week of not riding is well worth another week or more of tinkering.This should be my last "down time event" which means I will be riding when the "warm up" comes.Its really cold here in K.C. right now anyway,so I picked a good time to be down.Do you know the size of the allens to replace the old phillips screw with.I think its 6mm but I dont know what the thread pitch is.I will take one to home depot and see if i can match it.

[KEITH KRAUSE]

I can't give a positive answer to the bolt size/thread pitch for your model.
Take one in and compare as you said. Don't know about your area, but they're easy to find where I'm at. I haven't gone to Home Depot to look for metric hardware but I'd imagine they have them. I know OSH has them, Do-it Center, and lots of hardware stores and most MC parts shops.