I know this topic has already been discussed at nauseum but,

After cleaning my carburetors, polishing the throats so the clunk test is so fast it's like a magnet is pulling them down, the jets are open, the enrichment circuit is clean, adjusted the float levels and vac synced the carbs on the bike.

It idles great, revs great, but comes down too slowly (eventually it comes down to idle). I did the propane test thinking I might have a vacuum leak but there was none. The throttle butterflies come back immediately when I release the throttle. I had a spare rack of carbs so I cleaned those and put them on. Same issue. What have I overlooked? I haven't checked the valves but compression was really good. Could tight valves cause this issue? and wouldn't tight valves cause compression loss?

Thanks!

 

A "floating" idle drop can also be indicative of an over rich fuel mixture. What do the plugs look like and have you run a Colortune across the cylinders?

 

The plugs are brand new and I haven't run it very long. How long should I have to run the engine before it makes a signature?

 

I'm afraid I don't have the definiative answer to that. The idea is that you should be able to see, within a few hundred miles, tell-tale signs of engine operation. There is also the plug-chop method whereas you run the bike out to your favorite long flat stretch and open 'er up. Hit the kill switch and coast to a stop and pull the plugs to view their condition. Tan to dark tan is desireable. Sooty black and you are running too rich. White insulators indicate a lean condition.

 

Mine used to do the same thing. It had sat on one side, probably for years, the carbs were badly out of sink and I also think that a couple of cylinders probably flooded because with the bike on its side the floats wern't able to close the fuel inlet needles and gasoline seeped by them untill the carbon deposits had gotten saturated with fuel causing the engine to run oddly, #1&2 cylinder pilot jets were plugged nearly solid and with the engine fully warm #1 liked to run with the idle screws nearly 6 turns out. and #4 carbon or fuel fouled very quickly, and it ran best with the fuel enrichment (choke) circuit partially open. No vaucum leaks either.

Here's what I did; I tore them apart and with a tourch tip cleaning file, (the smallest in the kit) some .028 hobby wire and a can of gummout spray I cleaned out the pilot jets untill I could see daylight through them and the wire would pass through smoothly, without binding. I blindly reamed and cleaned the pickup tubes they screw into untill the hobby wire bottomed when pushed it into them in all four carbs. I took out the the idle mixture screws and the O rings and repeated the procedure. when I inspected the mixture screws I noticed that a couple had marks on them where someone had screwed them into bottom too tight so I took some #400 grit wet sand paper and some gummout and I polished them as best as I could without removing too much metal, then reassembeled them with new gaskets, I used the wire as a feeler gauge and bench set all four throttle blades at .028" and on mine at least #s, 1, 2&4 carbs are set seperately the #3 thumb screw gets turned when the other 3 are in sync with #3. The float hinge pins were bent & binding too. I hammered them straight untill lined up with a straight edge metal ruler and polished out the nicks and dings by hand with #400 grit 'till they were nice, pretty, and straight.

When I started it the idle speed was way too high but I just used the thumb screw to turn it down since it adjusts all 4 carbs together. I rode it about a square mile at low to moderate speed to make sure it was warm enough then I fine tuned the carbs mixtures to best lean idle, 2 1/2 to 3 turns depending which carb it was and I did notice there was a vacum leak but not where most people would look but in the the fuel petcock diaphram, and also a minor fuel leak in 2 of the three positions, not reserve, (I take the blame for that, I accidentally put $3 (1 gallon) of e85 in it, (I also had to replace the fuel hose too) now it will start without the choke in less than 5 seconds if the air temp is over 70* It will sit and idle without much more than an occasional burble at around 1100 rpms. Vacum is very good and will pull smoothly from a rolling stop from idle speed in 1st or 2nd gear.

I know some will cringe when they read this, its like using the manual as a door stop, but hey, its a 29 year old bike and I had neither the tools or money to do it the way I know it's supposed to be done. It worked for me. It took me 3 trys to get it right. I'd rather ride than walk.

 

Good call on the torch cleaning tools,works like a champ.

 

I #57 on the mains the first and second time and was running lean on #1,2 & 3 cyls the first time, then just # 3 the second time but after I modified the airbox and swapped out the internal air filter for the automotive style external (hi flow conical) and modified the exhaust I reamed them all out with #56/55 tip cleaners and its actually a little faster on 87 octane and gets better mileage too than 89 octane, but it runs cooler on 89. Daytime temps hae averaged around 100* here in slow poke Oklahoma, so I use 87 around town and fill up with 89 before doing any highway riding over 10 miles, I try and keep her around 5000 rpms on the highway. In fact I'm going to OK city tomorrow (180 miles round trip) so I will also do a mileage check.

 

Wow. Padre, you could give Macgyver a run for his money. Thanks for sharing that with us -- I was seriously considering buying a torch tool yesterday.

So today in northern California, it was really hot (we've been having a very cool summer -- the vintners were complaining about moldy grapes). the bike had been sitting while I read all your great advice and pondered about tearing into my carbs for a 4th time.

I got out today, forgot to put the choke on and wham, it started right up, idled perfectly or nearly so. I got on rode around and it had fixed itself! Seriously, no issue with the throttle coming down anymore. The last couple of things I did before I gave up was to take all of the intake plugs off and replace them with 1 inch pieces of vacuum hose with a screw in it and fix a small hole in the 4-1 exhaust pipe header under the engine. The weird thing is it was still having the issue after I replace the intake plugs or I would have thought that did the trick. What is it, the hot weather? It ran great today, super strong with the header and the seca 650 engine. I wish I could take credit for it but I'm happy to give it to you all for posting all those great ideas! You're the best.
Thanks everyone!