CARB TROUBLE....

[LA Mike]

Here is the particulars:

1993, yoshi slipons, uni pods; Carbs: 115mains, 40pilots, dynojet needles 2nd groove from top

Will fire right up, idle fine at warm up and operating temp, blip throttle test fine.

It will surge when riding 1/4 - 1/2 throttle and you have to power though the gears for it not to surge. Also when coming to a stop and pulling in the clutch you have to rev it or it will die.

This is what my brother is telling me whats' happening, he and the bike are in PHX,AZ, Should I have him raise the needles? or is the float level causing this? any suggestions.

Thanks,

LA Mike

[andyb]

Things I'd look at

new fuel
chain tension and condition (tight spots?)

After that

carb synch check
dirty pilot circuit
half a turn more out on the idle mix
bigger pilots

The last two are out if the bike has run well at some point without altering those since.  If he just bought it and it's doing this, then they're in the running, but they seem to be rational sizes.  How far out are the mix screws, how big is the air jet?  

Chains with tightspots make a surge nearly impossible to diagnose, so that's definitely the first thing to check.  Going between fuel brands can also give you some wonky effects.  If you're unsure of the condition of the various tuneup bits, it's probably wise to get those set properly now to make sure that you're at a good starting point (spark plugs and such).

If you're at a standard 2-4k cruising speed and it's doing it at a steady throttle, it's almost assuredly not the needles, because they're not doing much at all at that point.  Half throttle is accellerating pretty hard!

[racerrad8]

Mike,

Vacuum leak behind intakes, bad cap(s) on intake brass nipple(s), cracked intakes...Vacuum leaks will cause all of the problems you describe as well.

Randy - RPM

[SlowOldGuy]

Sounds like fuel level too high to me.  
Maybe bad floats?
At the least, measure the fuel level.
How do the plugs look?
I sent you new o-rings for the intakes, right?

DavidR.

[LA Mike]

I sent you new o-rings for the intakes, right?

DavidR.

Yep, put the new o-rings on the intakes when I had the bike. The intakes boots looked good very minor cracks were the metal hold the carbs, I could not see any cracks on the inside of the boot so I don't think it is sucking air that way.

He is using caps that he picked up at pepboys w/o any clamps but they fit very tight. I'll tell him to spray WD40 on & around the boots to see if the idle changes.

LA Mike

[rhubarbray]

If you blip it at idle does it hang and come down slowly or drop below idle and then come up? My `88 1200 comes stock with 42.5 pilots. Double check with Dynojet and see if it`s supposed to be a 40.
Beyond that I`d agree with the other guys and check the fuel height/float level/carb sync.  A common problem is the o-rings holding in the fuel needle seat cracking and splitting letting in too much fuel.

[andyb]

Did this bike just go from LA to AZ?  If that's a big elevation change, that'll start ya out with some problems....

If you blip it at idle does it hang and come down slowly or drop below idle and then come up?

Will fire right up, idle fine at warm up and operating temp, blip throttle test fine.

My `88 1200 comes stock with 42.5 pilots.

Isn't a US model then, which came with 37.5's and different needles.  A 40 should be appropriate for the mods on that unless it's at a crazy elevation or has other tweaks not listed.


Big part of the puzzle to me seems to be that it's not idling once fully warm, but it starts and idles ok?  It's too fat then, and the blip test is being passed when it's cold.  Float level won't cause this type of running unless it's way, way out (as a leak would be).

[fj1289]

Here is the particulars:

1993, yoshi slipons, uni pods; Carbs: 115mains, 40pilots, dynojet needles 2nd groove from top

Dynojet doesn't change the pilot jets to richen the lower throttle settings - they use a smaller pilot air jet (stock is 155, Dynojet uses 144). 

What pilot air jets do the carbs have in them?  (They are located on the air filter side of the carb - on the left side)  If it has the Dynojet 144 pilot air jet, then the 40 pilots will be too rich.

Chris

[RichBaker]

I have a '90, put the DJ kit in many years ago, including the PAJs.  A couple years ago, I had let her sit for several months because I was going thru all the bodywork and doing some other minor fixes. When I got her back on the road, the pilots were clogged, could'nt get them clean. So, I got a set of 40 pilots for her, because I have never liked cranking the mixture screws out to 3-4 turns..... I prefer them at 1-2 turns out. The 40s put my screws at 1 1/4 turn out, +-about 1/8 turn..... right where I prefer.
Since I'm in Tucson, similar climate and altitude as Mike's bro, I'd say they'll be just about right.....

1st thing that came to my mind was a clogged fuel filter.....