Topic: any carb adjusting tips for 77?

[the_genrl]

im usually a lurker but i need some advice.  i have a 77 750k and at least once a season i have to adjust the fuel idle screws (which is fine, im not #$%*ing about that).  however, i am #$%*ing about the #1 and mostly #2 carbs.  they are nearly impossible to get to and i usually end up not adjusting them.  i guess i have big hands or the wrong tool or something.  right now i use this piece of 22guage sheet steel folded in half.  ill post a picture if there is any interest.

anyone have a secret to reaching that #2 screw?

[eldar]

No real secret. You either fumble with it or you can get a carb adjusting tool from motion pro. the head is bent at 90 degrees and you turn the handle like a screw driver. jcwhitney has em for $25.

[the_genrl]

hmm thanks for replying and bringing this tool to my attention.  guess its off to ebay again lol

[bowhunter]

I've used a short piece of thick rubber tubing about 1/8 in.  in diameter. The screws need to be free of oil and grease or the tube will slip. Force it onto the screws and it makes a nice handle.Remove them when you're done.
 I keep short lengths of it in my toolbox for when adjustment is required.

Bowhunter

[jesusno2]

best cure for those carbs for us who live at seal level or close to it is to drill the slow jets to a 38 or 40 I personally like these carbs alot. Unfortunetley if you mod the bike any, tuning them can become a real headache i've seen i have a bunch of little tricks to help make these cabs work as good if not better than a set of mikuni's properley modifyed they real work good.

[flatblack]

i have a bunch of little tricks to help make these cabs work as good if not better than a set of mikuni's properley modifyed they real work good.

Care to share?

fb

[jesusno2]

Well mainly the pilot circuit is what is mainly their biggest down fall, and the fact that the needles are non adjustable, in all the carbs i've seen anyways. alot of guys condone against drilling jets but on these carbs ya don't have many options i have found these "press in" pilots in a number 40 in xl 250 carbs but drilling them to a #40 is way easyer than trying to find 4 xl 250 carbs not to mention cheaper. shimming the needles up with tiny 2.5 mm washers makes a huge inprovement i have a few different thicknesses i can play around with i've also turned tapers on the needles so shimming is not needed as much. it make alot better midrange power and is almost a must with anykind of induction change. adjustment on the accel pump works wonders too increasing the shot, again depending on what your engine needs i ran a set of these carbs on my 836 for a while and i have ran 29mm smoothys too. and honest truth, i like the instant power ya get with the accel pump carbs but the smoothys seem to pull a tad harder at wot so its kinda a no win situiation only differece is their is alot more accel pump carbs avaliable the 29's and alot cheaper alternative. i would not expect to see these on a big cc sohc but on a mild 750 or 836 they work quite well as long as you have the paticence with them and are willing to put in the time to get them working the way honda should have. Honda had good intentions and they knew these carbs worked well but once again the good old EPA stuck their foot in the door so they had to lean the crap outta them to pass emmision standards of the day. I live at sealevel and when thess carbs are stock alot of times i have found that having the choke fully closed until the engine has reached full temp is not uncommon.

[flatblack]

Interesting.  Both my '78 750K and my '79 650Z are lean machines; full or partial choke for several minutes before they'll idle well.

Once I get past some other bike and "life" challenges, I'll go sleuthing.  Thanks!

fb

[eldar]

I think you need to explore the idle circuit more. You turn that mix screw out and it will get rich fast. Does not take much either. The 77 carbs still have the adjustable main needles but the 78 does not. And while the idle jets are press in, the mains are just as swappable as any other carb.

[chung]

What year was that XL250?

[eurban]

Here's a few thoughts on the 77/78 pumper carbs.  First off, don't waste your time with carb performance tuning till your carbs are actually functioning properly.  The pressed in pilots in these 30 year old carbs are almost always to some degree clogged.  So pull them out with a gentle twisting motion and really clean them. Can you run a single strand of copper wire thru them?  Are the side holes clean.  Do a reality check of the level of fuel in the bowls.  Connect clear tubing to the brass overflow nubs, drain the fuel from the carbs, mount the carbs level in a vice, tape the tubing up high along the carb bodies, fuel up the carbs, open up the drain screws and observe the level of fuel in the tubing.  This is the actual level of fuel in the bowls and they should all be exactly the same and just around even with the bowl to carb body joint.  Visually confirm the function of the acellerator pump.  Remove the airbox and look for a nice squirt of fuel towards the engine from each brass nozzle (located on the bottom of the carb bore near the choke plates).  The needle jet ("bushing" that the main jet needle slides in and out of.  Has a distinct impact of just off idle performance)is an overlooked part in the carb rebuild process and after 30 years can be crudded up and worn.  Same goes true for the main jet needles.  You can actually buy a new set of main jet needles specced for the 77 models (I got mine from David Silver Spares) that have muliple slots for needle height adjustment.  These come with new needle jets.  This will cure performance issues related to wear and contamination of these parts and will give those with the 78 carbs the option of raising or lowering their main jet needles with clips. . . .As to perforamnce tuning, stock #35 pilots are more than adequate for my 78K 836 cammed with pods and stock exhaust.  I drilled a set of pilots to aproximate #40s but these were too rich.  I currently have a stock set of 35s in and idle fuel mix screws are set at about 1 1/8th turns out and the power is excellent.  The dynamics of carb tuning is alot more complicated than always simply throwing more fuel into mix.  Do yourselves a favor start with the stock 35s and adjust the fuel mix for best off idle power.  If power keeps increasing as you turn the screws counter clockwise till and you are at about 3 turns out then you need larger pilots. While I found that my pilot jets were large enough for my application, I did need to increase the size of my main jets (about 125s now) and raise the main jet needle up a bit.  Overall, performance is excellent with these carbs particularly the immediate throttle response they offer.  Sure a set of 29mm Keihin CRs or Mikuni smoothbores might give you the most power at WOT but how much time do you actually spend in those conditions??  Hope this helps someone . . .

[eldar]

It always amazes me how people are so used to the earlier carbs and have the wrong ideas on how to tune the later carbs. These things are so adjustable that I think people give up and go right with the rejet option.