Topic: Idle/pilot screws keep falling out +Pic

[MT_CB750K8]

I just got my 750k8 up and running and twice now I have been out on test rides and lost my idle air screws.  First #3 fell out and I was left with the spring on the transmission so I limped home on 3 cylinders.  The second time #2  screw fell out on the highway I lost some power, then when I stopped to turn around it stalled.  I found the screw sitting on the transmission but the spring was lost so I screwed it in and limped home again.  Is there a trick or tip to solve this very annoying problem?  I would hate to loose the adjustment and just lock-tight them, but I don't have many parts left from the carb rebuild.

Also on ride #2 (30miles) I found that the sides of the engine at the head gasket are seeping oil.  I am using Rotella T SAE30, is this the reason??  If not is there anything I can do other than replace the gasket?

Any help would me great.

Oh and here is a pic of the bike, still need to do some buffing.
So far I have rebuilt the carbs, tune up, removed Vetter fairing, crash bars, and luggage rack, rebuild front brake, 530 18/48 chain sprocket change, blade fuse holder, repaired cracked side cover, repaired seat (gorilla glue is the best!!), full fluid change, and scrapped 30 years of grease and dirt off everything. 

By the way all of the above jobs were completed with the help of the archived threads, thank you all.

[scondon]

   It is kind of odd that they would be falling out like that. The spring tension should hold them in place very well unless your initial setting is backed out too far. Besides the spring there should be a rubber o-ring and washer in each passage and if these are missing it might affect spring pressure. If the o-rings are missing you will have air leaking in and have to back these screws out even further to get decent mix, compounding the issue. Stock setting for these screws is 1 1/2 turns out from fully seated. At this point they should still be recessed inside the carb body just a bit(screw heads either flush or below the lip of the hole).

   And for future reference those are "fuel" mixture screws(77-78 750 carbs). Earlier carbs had the "air" mixture screws. Turning your screws in decreases the amount of fuel in the idle fuel/air mixture. If you're having to turn these screws past 2 turns out in order to get enough fuel in your idle mix then you most likely need to remove and clean the pilot jets and related passages.


Bike looks pretty nice. Congrats on the good work:)

[eurban]

I have never known these screws to back out on there own so I would guess that you don't have them assembled correctly or you had them turned way to far out.  On  the screw you first put on the spring, then the tiny washer, then the oring.  When you gently tighten them down to full seat you should be able to feel their tiny tip poking into the bottom of the carb bore on the engine side.  As scondon says, back out 1.5 turns from there for a baseline. . . . . .Maybe your screw threads are f'd up?  I hope not . . .

[MT_CB750K8]

I am guessing that I must have misinterpreted fully seated.  I was turning them until they give me resistance then backing off 1.5 turns.  They are all assembled correctly rubber o-ring, washer, spring, then screw.  The jets were also cleaned when I tore the carbs down.  Also finding out they are fuel screws makes sense because I have been carbon fouling plugs constantly.  I'll try turning them in further and see how that goes, right now when I go 1.5 out they are about one turn or so out of the carb.

[eurban]

You have to seat them completely and then back out 1.5 turns.  Don't reference off of the distance out of body of the carb or anything like that.  Turn them in until that won't turn anymore, but be gentle about it.  I typcially set them to baseline with the carbs off of the bike and where I can confirm that the screws are fully seated by feeling the screws needle end poking through the carb bore.  Hopefully your threads are clear and you will be able to complete seat all the screws before backing them out.  . . .Just checking, did you pull your pilot jets out and clean them properly?

[mystic_1]

To give yourself a better idea of what it feels like, take out one of the screws and reinstall it without the spring, o-ring, and washer.  Then you'll know that any resistance you're feeling is from the screw itself and not spring pressure.  Run the screw in until it stops, take note of how far in it went, then remove and reinstall it with the spring, washer, and o-ring.

mystic_1

[MT_CB750K8]

Well adjusted the screws 2-3 turns out from fully turned in earlier today and it idles great, runs at highway speeds fine, and best of all the screws didn't fall out over a 40 mile ride.  But what I have now is a serious bog right off idle.  So from a stop I had to rev to 3-4k to move.  So I adjusted the screws almost all the way out again and it ran just well enough to get back home.  I also noticed that when the screws are adjusted in to about 2-3 turns out when it is warm it revs like crazy when the choke is pulled, if tuned correctly shouldn't it die if choke is pulled at operating temp?  I pulled the plugs while still at the leaner setting and found them to be a nice brown with a small amount of white specs on top.

I have the stock air box on and my pipes are also stock but have a few baffles rusted out and almost sound like straight pipes.  I am curious if I need to rejet or is something else the problem.  I used Keyster carb kits to rebuild them initially.

Also I did clean the pilot jets during my initial carb breakdown, they were removed and tapped back in place.

[eurban]

2-3 turns is not very precise and it is likely too many turns out as well.  If you have essentially a stock bike, the baseline setting should be more like 1.5 turns out.  From this baseline, you really should tune the settings to the bike. One option is to follow the factory procedure which essentially involves adjusting the mix screws for max idle speed at a given throttle setting.  Changes are subtle and the stock tach isn't really accurate enough though.  You could also try moving all the screws in 1/4 turn increments in or out (from a baseline of 1.5 turns)  and then go out for a test ride scrutinizing idle / off idle performance.  Overall you will need to actually determine when the screw is fully seated and then back them all out a precise amount.  When the system is functioning correctly, small changes in the position of the screws make a noticeable change particularly when you get to the sweet spot.
You also may have malfunctioning / nonfunctioning accelerator pump.  Pull the air filter assembly, whack open the throttle quickly and look to see whether or not you have fuel squirting towards the engine from the small brass nozzles located at the bottom of the carb bore next to the choke plates.