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Discussion Starter · #1 ·
hey all
great site you have here
i see a ton of knowledge and am trying to suck it up as quickly as possible
anyways i just got a 95 thunderbird and it had been sitting for 5 years with gas in it
so i pulled the carbs and let em soak overnight
well when i pull the throttle cable it looks like number 1 and 2 butterfly valves dont open all the way number 3 doesnt budge at all, is it just stuck with old varnish or am i missing something? it looks like 2 and 3 might open up before 1 because of the spring assembly attached to the cable but that doesnt make sense to me? anyways thanks in advanc guys
aaron
 

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Did you separate the carbs from the mounting bracket or leave all three mounted together? It sounds like the throttle shaft is not assembled correctly.

Stan
 

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Cleaning the carbs isn't difficult but it's one of those time consuming and exacting jobs that's a PITA.

You'll need to do some disassembly but don't separate the carbs from each other -- just remove the top and bottom covers on them.

Use zip-lock bags and a magic marker as you disassemble. Mark the bags as you put parts in them to denote which carb the parts came from.

When disassembling the top and bottom covers, use only enough force to break the screw loose and don't loosen it further on the first pass then move to the screw diagonally across from it and loosen it the same way. Loosen and remove the screws in a couple of steps, working diagonally, to prevent warpage of the covers.


The bottom cover is the float bowl where most of the gunk will collect. Clean the float bowls with solvent (carb cleaner, brake cleaner, whatever) one at a time as you remove them. When they're clean, bag them and mark the bags.

I'm not 100% on the Mikuni carbs but I'm pretty sure you remove the floats and float valves by pressing the pivot pin out of the float hinge. Use a paper clip or similar to press out the pin. Again, clean and bag the parts and mark the bags.

Once you've removed all the carb bottoms and float assemblies, start on the top covers.

Under the top cover you'll find a rubber diaphragm and slide with associated parts (needle, spring, etc.) Clean and bag these parts and mark the bags. Make notes or diagrams of where the various parts go!

Be careful with the diaphragms! They're fairly fragile and if you tear them it gets expensive. Also, some solvents may cause the diaphragms to swell so it may take 24 hours of air drying until the return to normal size for assembly.

Clean the slides with solvent. The lubrication for the slides is gasoline spray from the carb, so they can get pretty varnished up.


When you've got the tops and bottoms off the carbs it's time to remove the jets. The brass used in carb jets gets brittle with time, so wet the jets with solvent and let it soak in before you try to remove them. That will provide a bit of lubricant and reduce binding.

I highly recommend that you use gunsmith's screwdrivers for this and select the size of the screwdriver carefully. The gunsmith's screwdrivers have hollow ground parallel blades that exert an even force on the jet slots. Conventional (taper ground) screwdrivers have a wedge effect that can damage the jets and may break off the brass.

Also, worn or wrong-sized screwdrivers will damage the screw heads so pay attention to your tools!

Once you've got the jets out, examine them carefully against a strong light with a magnifier. The jet bores should have a clean, machined look. If the bores look kind of 'fuzzy' or 'organic' they need a solvent soak and cleaning.

I use a short piece of stranded copper wire for this since the copper is softer than the brass and won't scratch it. Strip back about 1 inch of insulation and use the end of the wire like a brush. Separating one or two strands from the wire will let you poke the strands through the bores and loosen any varnish chunks there. Soak and scrub as required until the jet bores are clean.

Once the jets are cleaned up and bagged, you need to decide whether to remove the EPA plugs so you can reach the mixture screws. I don't have a clear picture of the Mikuni carbs in my head, so you'll have to get the location from someone else.

The sticking butterflies will usually clear with a blast of solvent and some manual encouragement. Blast them, and wiggle them and they should loosen up. The throttle bar is normally lubricated by the fuel in the carb so varnish can build up on the shafts.

At this point you're probably OK to reassemble the carbs and try them out.

Don't use any thread locker mixtures on the carbs!

When you're replacing the covers and tightening them, always work diagonally from screw to screw and tighten in steps to avoid warping the covers. The Mikunis only have two screws on the float bowl so don't over-tighten them or they'll leak.

I believe the diaphragms have a lip that fits into a groove in the top of the carbs. Put all the diaphragm/slide parts back together and lower the assembly into the carb body. The diaphragm lip should drop into the groove. If you've gotten solvent on the diaphragm it might expand and not fit. Let it air dry for 24 hours and try again.

With a fingertip, tap the diaphragm lip into the groove. It should fit smoothly and lay flat. Then insert the slide spring and place the cover over it making sure that the cover is centered over the spring. Press down the cover vertically with one hand until it's in place and insert the screws finger-tight working diagonally from screw to screw.

Tighten the cover screws in steps and take care not to over-tighten!

When it's all back together, manually push the slides upward and let them slide back into place. Do this in pairs and note that the slides all have the same resistance to compression and return at the same speed. If one is noticeably faster than the others, you may have a leaking diaphragm. If one is noticeably slower than the others it may have a kinked spring, blocked vacuum port or grunge in the slide guide.

If you have any questions or problems, ASK! :wink:

Jim
 

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Discussion Starter · #4 ·
thanks guys, you rock, hopefully ill get this put back together soon enough
see you on the road
aaron
 

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Discussion Starter · #6 ·
the gas tank looks fine, i emptied it, put some carb cleaner in it and swished it around, and it came clean. really didnt look that bad to start...well my new question is what happens if you separate the carbs and put them back on in a different order? will this hurt performance? i know that many times the center (#2) uses a different jet than the others. why is this and would it mess it up if that jet was on a different cylinder? i cant think of a reason but im new to this. thanks again.
aaron :???:
 

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my new question is what happens if you separate the carbs and put them back on in a different order? will this hurt performance? i know that many times the center (#2) uses a different jet than the others. why is this and would it mess it up if that jet was on a different cylinder? i cant think of a reason but im new to this. thanks again.
You shouldn't separate the carbs, but since you're asking the question, you probably already have... :-D

The biggest issue there is getting everything to line up again so that the linkage and butterflies don't bind. The next issue is replacing the seals on the plumbing so you don't drip gas everywhere.

If you haven't removed the butterflies and shafts then it's not a problem -- they'll only go back together one way.

The jetting on the Classics models is the same for each of the carbs, so no problem there.

If you need hands-on assistance, let me know. I'm only a few miles north of Austin.

Jim
 

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Discussion Starter · #8 ·
actually i had a friend run it through his cleaner and he reassembled them in a different order...i was trying to get it all back together today but i was waiting so i didnt install them and mess something up, thats a huge relief they can go back as is, the butterflies all open smoothly together now...the throttle adjustment is not in the middle but it still points to the left (oh well) ill go finish putting it all back together and start her up!
thanks a thousand
aaron
 

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Discussion Starter · #9 ·
i put em back together but i didnt get a rebuild kit
so i went to open the petcock (excitement) and the #1 cylinder pissed all over me
think theyre overtightened or i need to use new gaskets?
if they are overtightened am i out of luck or do i just need to back em out? im pissed...she did start though...she sounded beautiful, it was great. thanks again, again.
aaron
 

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Discussion Starter · #11 ·
well i pulled the float bowl that was leaking and loosened then retightened the screws. i opened the petcock anxiously and no gas came flooding. so i was quite excited and started the bike! well it ran fine for 5 seconds and then the bowl leaked all over again. is it a good or bad idea to use gasket in a tube there? i realize not on the inside but what about where the old gasket was? oh and after it ran for a minute or so a bunch of grey / white smoke came out. it only did it once but it seemed to be alot. i started it afterwards and it didnt do it anymrore. i also noticed on the airbox side of the carb the black valve on 2 and 3 were shaking a bit but 1 was solid. is that bad? how should i lube the choke assembly? it seems very tight and doesnt always close back right away. man i have alot of questions. thanks guys. youre worth every penny i dont have to pay a mechanic.
aaron
 
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