gt550 later model carb setup and tuning book?

[chance johns]

so ken at knk tells me i need this book to properly tune these carbs. he says he'll order this book for me. months and months and months later he says its unavailable. which is fine. ken is an extremely knowledgable and helpful guy when it comes to these bikes.

do i need this book? is this bike available online or does anybody have this book? can somebody give me the proper steps to set these carbs up? it seems somewhat standard, but ken insists these are the most complicated carbs to set up and if you dont do everything perfect from step 1 they will never run right.

ive never had this bike consistantly running right, so id like to be thorough and do everything 100%.

[Suzukidave]

Ian has you hooked up http://www.oldjapanesebikes.com/mraxl_G ... cover.html" onclick="window.open(this.href);return false;

[chance johns]

so i found some time to get into this, and im still not clear on some things.

-the manual in the link is missing some pages.the images go from 4-4 to 4-10 in the disassembly section

-i have found 2 different specs for jet sizes for the gt550 which is the one i should have (74-75)

-the manual says to tilt, i assume in your hands, the carbs 10-30 degrees and then measure the float level.
do they really intend on this to be done by hand and you to adjust the floats to the hundredths of an inch?
is the point of tilting the carbs to have the float tab to barely touch the float needle? with a small precision ruler the hundredth of an inch can change drastically by how high or low you look at it.

-ken at knk stressed doing everything 100% and the carbs needing alot more than just standard carb adjustments and setting up. but as i read the manual it seems somewhat standard. there are only 4 pages of adjustment instruction.

-there are nipples on each of these carbs. what exactly are they for? i assume they share mixture or vacuum with each other. what needs hooked up with line? i have one side of the carbs hooked together with line, and the other side i have the nipples capped off.

- i dont understand what the "night side" of the carb means in reference to the dent on the throttle slide (valve). it seems the throttle slide can only be put in one way

-why are the throttle valve arms so specifically spaced to each other?

-what is the needle jet groove and the needle jet dowel pin

-do the boots make an air tight seal? or are they just dust covers? (one of mine is ripped) i plan on replacing it regardless.

i dont have a return cable. is this 100% necessary? what does a return cable really do?

what needs adjusted?
-mixture screw
-float level
-cable tension
-throttle stop screw
-throttle valve rods
-valve arm spacing?
anything else crucial i am missing?

thanks for any help coming my way. i felt like i could handle the setup of the carbs but then knk made me doubt myself, and i respect his opinion and i want to make sure everything is correct.

[chance johns]

oh yeah, AAALLLSO i am installing a new key switch to my gt750. it had a pep boys cheap switch when i got her. the new switch has 4 in a wire connector and 2 loose wires. the diagram i have accounts for the 4 in the connector only. what should i do with these 2 extra wires?

[tz375]

They are just carbs and to me that means they are just the same as any others though they are different - if you follow me.

Yes 30 degrees or so that the float tang just starts to press on the spring pin in the float valve. Tolerances are +/- 0.5mm but up to 1mm is OK and yes, it is a pain to be that precise.

Needle jet pin:
There's a small pin in the bottom of the carb body that locates the needle jet in correct orientation for the spray bar and air bleed. It must point the right way. They rarely fall out but it's worth checking. The groove can be seen in Pic #4.9

I think that the carb bodies are all the same so they all have that vacuum connection, but only 1 is used and the others are capped off.

Synching those is a PIA because of the linkage etc but no different to say a SOHC 750 Honda.

[chance johns]

could you elaborate on the vacuum hose orientation. between carbbodies

[chance johns]

how do you think they intend for you to measure these gaps? the bore is curved so it seems a feeler gauge would give you inaccurate results. but then i realised that in the picture it shows the bottom of the two measuring points sitting higher than the bottom of the bore, possibly over compensating for flat/round issue of the gauge/bore.
but then i was thinking, that measurement would differ depending on the width of the gauges. im just a little confused and i want to make sure i got this right.

[Suzukidave]

For the top measurement a proper sized drill bit layed in the carb till the slide contacts it and the bottom picture they just want you make sure the the slide is completely out of the bore at full throttle .

[chance johns]

so i just did the carbs . test rode the bike. and IM STILL having a reoccurring issue. i have my idle set at 1500 rpms, and it will drop a cylinder when at idle and sometimes die. i have to rev it at idle to keep it going. ive been thru the timing and points and coils and boots and ive been thru the carbs A BUNCH. the chambers in the pipes are busted up but i just repacked the baffles (which didnt dampen the sound AT ALL) what else should i be checking for? other than that the bike seems to be doing good. ill know more when i give it a longer ride. there were definitely a few things i straightened out when going thru the carbs this last time.

a couple possible things to note:

-i havent compression tested it.
-i had to chase the threads in one of the pilot jets and tapped SLIGHTLY deeper than the other two.(before this happened the bike had the same problem)
-the pilot jets might be from a rebuild kit.(i dont remember 100%)
-i dont have return cable(whats the point of this anyway?)
-i havent synced them with the manometer i own but i did set the throttle valves within spec via .9 mm drill bit , in the closed position (i have synced them in the past with the manometer and had the same results.)

how can i tell which cylinder is dropping off at idle? to pin point a possible issue?
it doesnt drop off completely it will intermittently go in and out and sometimes just go out and die.

i think i have good motul in the oil tank but probably low octane ethanol fuel

i dont know how to adj the mixture screw. i know where it is and i set it to spec but i dont know how to tell if its doing something one way or another. i know that with a single carb or dual carb its easy to hear a consistant "rumble" by turning the screws in and out. i just feel like its much more difficult to hear consistencies in 3 and 4 carb bikes.

an issue i had before was one of my condensors was going ,causing a cylinder to drop sometimes and i replaced it both oem nippon condensors and it seemed to do good. maybe its happening again. why would they be going so quick? the points plate cant be getting that hot from the factory, could it?

ok i thinks that it. its been a frustrating 3 years with this bike! i paid way too much for it ive done alot of work and paid alot for parts and such for it. ive never had it consistently running properly. i would like to sell it and have a nice stock example of it.(its a chopped cafe custom, i know...i know...i wouldnt do it again in 100yrs) but then i wouldnt learn anything!

[chance johns]

oh yeah.
also i cant read the numbers on the main jets. i can read of em partial of another and none of the middle .
if somebody replaced the jets at some point the kit comes with 3 95's

[tz375]

Suggest that you do a compression check just to be sure that is not an issue.

When you had the carbs off, did you use a can of carb cleaner to spray through each and every orifice and did you get a good clean jet out of the pilot jet discharge hole on all 3 carbs? Were the spray patterns similar for each circuit for each carb?

I would strongly recommend new genuine Mikuni jets in the pilot and main jets.

What did you say was on the filters - stock OEM airbox and filter or pods?

[chance johns]

new pilot jets. i had to extract the old ones they were stripped and i couldnt get them out to know i properly cleaned them.

stock airbox. my problem i feel, has to be in the carbs. ive spent money on parts and repaired and adjusted the crap out of these carbs.
i must be missing something??

i am 99% sure i cleaned every orfice . i had them in a sonic cleaner the time before this one.

ill order mains and do a compression check.

please. any more suggestions? any body selling some carb bodies on here?

[Suzukidave]

Is the battery topped up .. i know a low charged battery will cause a engine to drop cylinders . If the battery is good maybe check the battery voltage to the coils with the switch on but the engine not running , i have seen where poor connections in the wiring and ( or ) main switch can drop battery voltage by several volts to the coils .

[tz375]

Good call Dave. You know the way it works. When you are 100% sure the problem is carburation, there's a 99% probability that it's actually electrical.

If the battery isn't holding a charge it may drop too low at idle and drop cylinders.

[chance johns]

yeah, i pulled it from the charger and put it straight in. ive checked the resistance in my coils and wires and boots. but not voltage to the coils from the battery.