Topic: Stumble on take off/ Oil pressure light

[CafeWild34]

Well I've been working on this stumble problem for a couple days now with no luck. I have a stumble upon take off, it is only in first gear. I can switch to any other gear and slow down to almost stopping and pull the throttle half way and the bike responds beautifully with no stumble. But for some reason when taking off i can not get rid of it.

Ok now for some info about the bike. It is a 1975 cb550k, I have a stock air box with a stock air filter. My pipes are a four into two home made concoction. I think the headers are from a cb550 and i know the mufflers are from a cb750. I rebuilt the carbs with all new jets (stock sizes). The needle clip is in the third position from the bottom. I have tried many positions on the idle mixture screws from almost all the way in to 2 full turns out. The bike is idling at about 1100rpm. I believe the bike is running rich because the tips of the spark plugs are always black after a ride. I will attach a pic of them from after my most recent ride. I have stock coils and a hondaman ignition. I ordered a uni filter because the bike is running rich i have heard these can help lean it out a bit. I have adjusted the points, valve clearance and synched the carbs.  Im sure I'm leaving something out but thats all i can think of.

The oil pressure light has only come on during my most recent ride. After about thirty of forty five minutes i noticed the oil pressure light would come on during the stumble during takeoff, but as soon as the bike took off it went back off. Then close to the end of my ride, about five minutes after the light first came on, the light would come on when slowing to a stop and coming to an idle and would stay on till after the stumble. Also the stumble became more pronounced when the light came on. When i got home i checked the oil and it was good, if anything it is a little over full, but not by much. I changed the oil and filter about two weeks ago. the oil is Shell Rotella 15w-40.

I thought maybe i should raise the needle clip from the third from the bottom to the fourth from the bottom, but don't want to do this if some one thinks it won't help. If i'm leaving something out please let me know. Thanks for any help you can offer.

[CafeWild34]

Forgot the pic of the plugs. Don't know if it even matters but here they are.

[lucky]

Here is a clear statement of facts.

1975 CB550K.
Stock air box stock filter.
Cb550 headers four into two, and CB750 mufflers?Not sure what that is, Need photo.
Needle clip middle position.
Idle jet size?EDIT #38m
Main jet size?EDIT#100mm
Mixture screw 1 turn out.

Several unknown facts including:
We do not know if the floats are set correctly.

The plugs look rich.

I would not expect the plugs to look rich with this set up, but since I do not know what size the jets actually are, all bets are off.
Also the clip position on the needle should be counted from the TOP not the bottom.
 

[CafeWild34]

Well I just pulled the carbs to check them and the main jets are 100 and the slow jets are 38. I set the float height when I rebuilt them about a month ago or so but I will check it since I have the carbs off anyways. The mufflers say hmcb750a hm393 if that helps. I will get a pic of them tomorrow. You can tell they were welded up by someone. The mixture screws aren't two turns out any more I was just saying I've tried just about everything in between 2 turns out and almost all the way in. I reset the to one turn out. If anymore info is needed I will be glad to oblige.

[dave500]

what wires and caps have you got?stock coils?100/38 should be fine in this bike,go over your timing,get1/4 spot on with 2/3 with a strobe,if the carbs have cruddy emulsion tubes youll get this effect,got an air compressor?the oil light is a different issue,,most likely just needs a new sender switch.

[CafeWild34]

I have some red ngk wires with the caps that came on them I will get a pic of them also. Yes I have stock coils. I will check the timing when I get up tomorrow. The emulsion tubes is actually the reason I pulled the carbs off (easier than I thought). The first one I looked at had a little crud on it but it didn't seem to be blocking anything but you never know I will go through the rest of them tomorrow. What do you think should I move the clips up a position while I have them off? Or reclean the carbs first and check timing and go from there. I don't have an air compressor, it's on my list of tools to get.

I actually just read your way of bench synching, Dave 500, and will be doing this tomorrow also. I had done a bench synch the first time I went through them but think I did it wrong because I had a heck of a time getting the idle down. But anyways I will get back at it tomorrow. Thanks!

[dave500]

youve got the carbs off so remove any and all brass you can and clean it better than a tax dodger,the clip in the middle should run fine,the 100/38 jetting should also be fine,im thinking as you have the carbs off do a very good clean,,did you not remove all the emulsion tubes the first time?you shouldnt have to remove the carbs again after this time!have you compressed air?this makes all the difference,,spraying carb cleaner only wont cut it,,you need to blast all those galleries through with a storm of compressed air every which way back and forth a few times.

[bollingball]

If no air compressor at least get a few cans of air at Wall Mart in the computer section or a 10 gallon tank and fill it at the service station.

Ken

[lucky]

Well I just pulled the carbs to check them and the main jets are 100 and the slow jets are 38. I set the float height when I rebuilt them about a month ago or so but I will check it since I have the carbs off anyways. The mufflers say hmcb750a hm393 if that helps. I will get a pic of them tomorrow. You can tell they were welded up by someone. The mixture screws aren't two turns out any more I was just saying I've tried just about everything in between 2 turns out and almost all the way in. I reset the to one turn out. If anymore info is needed I will be glad to oblige.

Thanks for retrieving that information Cafewild.
Did you use a float gauge or measuring ruler for the floats?
I hope you did NOT use a plastic tube and set the float level 2mm from the top edge.
Then the float bowl would be too full, and you would have rich looking plugs all the time. Almost all of the /honda motorcycles have the float bowl about 3/4 when the float is adjusted with a float gauge or steel ruler.

[CafeWild34]

No i didn't clean the emulsion tubes the first time. Honestly i didn't even know they were in there until i was already done and started researching this problem. I will have to use the cans of air or take it to my dads house and use his compressor. When i set the float height i made a homed tool that i learned about on this site using an old hard or floppy disc. I think i will buy the tool for this just to be sure.