well now i have carb problems please help if you can

82 750

bike was running fine before. however it had at least one bad float valve/seat as it would trickle into the cylinder.

I also had previously repaired cracked boots, which I replaced with the reproductions which we have found out tent to be not that great.

I only changed the float valves. seats and they work.

I have the floats set to 4mm below the seam, that's as close to 3mm I could get. previously though the bike was running (back before I got in there) on almost 12mm below. also on the floats I mounted the carbs at the same angle as on the bike which I saw to be 80*, and while on the bench they did not overflow and seemed to seal and hold fuel in the bowls.

stock jets 120 main 40 pilot, stock needle.

new plugs gapped .030

synced with YICS tool perfectly synced.


biggest problem is the idle, idle adjustment screw is all the way out butterflies are closing as far as possible. visually confirmed this, but it wasn't to idle high, like 2200. and once good an warm the idle likes to creep up.

current mixture screws 2 turns out, before taking them apart they were set at 4 turns. the only way to bring the idle down is the lean it out. if I bring it down to 1 out its more normal, but my plugs were turning white fast. and had hanging revs from blipping throttle. if I increase mixture it increase the idle revs.

I don't understand how my butterflies can be so closed and yet the bike revs higher and higher.

if I use the choke, which I believe is enrichment ciruit, RPMs will increase, if I go full choke on hot motor it bogs for a second then revs to the mood, this is while sitting still.

on the go if I add choke it really dogs out. as far as driving around it is very nice. if the idle could be solved I would be happy with it.

I don't think I have any vacuum leaks, I sprayed started fluid everywhere around the carbs, headgasket, spark plugs, practically sprayed the whole motor. no change in rpms. and I don't hear a vacuum leak. but maybe im missing something.

cold start today, required the use of the choke which would be normal, idle slow then when warm kept kreeping up.



so if I keep leaning it out the idle gets better but never normal where I need to use the adjust to bring it up. but it seems this bike is getting extra fuel it shouldn't while the throttle is closed than it should.

please help if you can, thanks

anyone have ideas?

I should also add a the same time I adjusted my valves, intakes all 0.005 exhaust all 0.008

 

Units please.

 

thousandths of an inch.

 

I think you set the fuel levels too high. The carbs are supposed to be level and square on the bench when measuring fuel height.

Setting the fuel levels

 

Your bike ran. It did not run fine.

The float tang can be adjusted to make the carb over flow prior to it shutting of the fuel. Adjusting it to 3mm should be possible.

This is some of the problem. To wet set the rack should be level both side to side and front to back.

Idle at 2200 is too high.

Gary H.

 

So the the first thing I should try it's reset my floats keeping them square.

High floats can cause this problem? Thinking it's overflowing into the cylinder? It is it because it's too high it somehow affects pilot circuit?

 

Imo yes.

Gary H.

 

Fuel levels being too high can cause the mixture to be too rich, or even overflow into the crankcase. Too low and the mixture can be too lean, or the bike will stall under braking.

Specifications and procedures are given for a reason; to ensure that things work as intended.

 

im in the garage right now and quickly setup my mount to be square all around and took some levels. maybe im not even holding the tubing right, you tell me please. but it looks like all of them are high, some even above the bowl into the carb body.

pics are not very accurate as to the levels as holding the phone and all that but a representation of what im seeing.

 

Yep, those are too high.

 

well we know these are wrong.

what are the odds this is causing my issue?

im going to fix them now. might not be able to run it tonight

 

Use a sharpie to put a 3mm mark on the carb body. Adjust the tang in minute increments to make the bottom of the fuel curve hit that mark.

Gary H.

 

Too high fuel levels will cause a runaway idle.

Gary H.

 

thanks for the replies so far guys.

I don't expect you to give me numbers from this, but do we agree this is a step in the right direction? by my measurement that's 3mm to the bottom of the meniscus.

the sharpie idea is great, I will do that

 

That last pic looks good. You have a little wiggle-room. Anywhere from 2mm to 4mm is good, but exactly 3mm is best if you can manage without going insane first.

 

Or your eyes popping out your skull cause at first glance the meniscus was spot on but then you lowered the tube to let the fuel rise and settle and now the @#! $& level is off again.

Gary H.

 

they are all now at 3mm the correct way.


think ill throw them in.

 

+1. Looks good to me.

Gary H.

 

well gang I appreciate the late night session.

carbs are on, it runs. im at 2.5 turns out. and I started with the idle screw all the way out. I had to crank it in a good bit for it work.

and the choke is working like it should.

not tuned at all kinda late for all that, but I am feeling more confident about it. obviously it hasn't come up to temp yet, didn't run it long enough, but I must be about 1/3 to 1/2 way in on the idle screw. giving me adjustment either way.

suggestions for mixture screw settings?

before I did all this I found the carbs at 4 turns out. thoughts?

 

The 2.5 turns out you have now is a good start. You will need to read the plugs or use a Colortune plug to dial them in. It is rare to need to go more than 3 turns out.

You'll want to do a running synchronization of the throttle plates once you have the idle mixture set.

 

status update, we might be out of the woods or very nearly the edge of the forest.

tonight I went through and tuned it. it acted normal and responded to adjustments the normal way. I synced them again with the YICS tool install, required a bit of extra idle with that in. mixture set at 2 plus a little extra, it seems happiest here. it was bit boggy at 2.5 and much worse at 3, 2.25 was close then a little less.

synced, I have 177mm of Hg at idle, slightly low from spec of 180. it is idling well at near as I can tell 950-1050 I don't really trust the tach that much, but its smooth and sounds normal. no hanging revs, no bogging. cold start requires choke. warm/hot start does not. rode around like 50 miles pulls well comes to a stop with out dying and holds idle when cold/warm/hot.

so im pretty happy over all.

HOWEVER

after taking the YICS tool out I had to dial down the idle to a point where it is basically all the way out. so I can go no lower at this point and that bugs me. plugs after 50 seem pretty normal, maybe not enough time to tell. alos the mixture screw adjustment this time around was not so drastic in how it affected idle, which I would say is more normal.

so do I worry about it? not sure what to play with next.

I will have to ride it more to really tell if it will hold these settings. it is rideable at least, seems pretty normal over all.

 

I've got mine set so that it idles at 1200 RPM when hot (after a good ride). That seems to be the sweet spot for making cold starts easy and not idling too high when fully hot.

 

I believe stock is 1050? It seems happy at the moment, I might play with that a bit. I'll keep the gang posted

 

Stock is 1050, set as soon as the machine is able to run without the choke. The idle speed will increase as the engine gets hotter.

 

For fun I think I'll use an external tach and see what this thing is really doing

 

Sounds like it's ok for now. Tweak as you go. If you fret over it it'll eat you up. Keep a eye on things until you have it dialed in the way you like and enjoy the ride.

Gary H.

 

palyed with it more, i dont even recall what settings i have now. i did a bit of ride and tune. it is finally happy in all aspects. never had a bike that was this much of a buggar to get dialed in. cold start, choke, cold idle, hot hidle, high revs, mid range, no hanging, no loping or dropping. all that jazz where it should be. went 400miles plugs look healthy. used my photo tachometer for fun, my tach is about 200rpm fast. my idle is set to 1077 as close as i could get, which shows about 1200 on the gauge.

so i am offically calling it good and wont be fidgeting anymore with this for as long as possilbe