‘75 GT550 carburetor questions

[pgb123]

My bike won’t keep running unless I keep the choke on. And even then, I have to keep the throttle open a bit to keep it running. When I change gears, it often shuts down. Since it sat for several years, I’m pretty sure I have to take the carbs apart and run the parts through an ultrasonic cleaner. So, First question I have is what parts will I definitely need to have on hand. Surely gaskets. What else? And where in the States can I source the right gaskets, etc?

Thanks in advance, as always.

[GTandcbr]

Hi.
Your running problems are almost certainly caused by blocked jets within the carb in particular the pilot jet and circuit. IMHO you are doing the right thing by getting them cleaned ultrasonicaly as the carbs have internal passages which are difficult to access. As regards what you need to buy, apart from the float bowl gasket there is a gasket on the main jet and on the float needle valve but these rarely need replacing and come with the new jets. It all depends on how much you want to spend and what needs replacing. I would strip the carbs examine the jets and look for obvious damage. Deffo replace float bowl gasket and then see how it runs.
Here is a link to the carb manual in case you dont have it
http://www.3cyl.com/mraxl/gt/manuals/su ... /cover.htm" onclick="window.open(this.href);return false;

[jabcb]

The pilot jets are pretty cheap, so I’d replace those too. The pilot jets are stamped near the threads. The Mikuni symbol will be there if they are genuine. It looks like a box in a box. Beside that will be jet size number.

The float bowl gaskets & pilot jets are standard Mikuni parts. Will be a little cheaper to get the standard parts rather that getting the parts via the Suzuki part numbers.

[pgb123]

Thanks for the replies.

I had a hell of a time figuring out which gaskets and pilot jets to order. Ended up ordering VM22/210 size 25 pilot jets and VM/103 gaskets. Is there a list or chart of the correct Mikuni part numbers somewhere?

[sportston]

Thanks for the replies.

I had a hell of a time figuring out which gaskets and pilot jets to order. Ended up ordering VM22/210 size 25 pilot jets and VM/103 gaskets. Is there a list or chart of the correct Mikuni part numbers somewhere?

Gaskets are the same on many VM models. The pilot jets you ordered should be ok I think. Just check the amount of holes they have in them with the originals.
You can get Keyster recon kits which will give you everything you need at a reasonable price, but their jets are not always the correct size for your model. The gaskets would fit, as will the float needle etc. but check the size of the jets and throttle needle before you fit them.
Don't forget to very carefully set the float level upon rebuilding the carbs.
Take your time rebuilding and synchronising the carbs carefully and methodically and hopefully you will only need to do it once.

[jabcb]

Your carb specs are in Service Bulletin Specification-6: http://www.ozebook.com/compendium/techb ... %206-9.pdf
Size 25 pilot jets are correct for the stock setup.
Pilot jet VM22/210 should be correct — that’s what I’ve used in other Suzuki VM carbs.

Suzuki part 13251-33110 & Mikuni VM30/103 are identical. That’s correct for your bike.

Mikuni part descriptions are shown on:
http://jetsrus.com
https://www.mikunioz.com/product-catego ... ilot-jets/

[GTandcbr]

I'm sorry I would give Keyster a very wide berth there are so many bad reports. Just get Mikuni they are worth the extra money and your engine will thank you

[GTandcbr]

.

[pgb123]

Your carb specs are in Service Bulletin Specification-6: http://www.ozebook.com/compendium/techb ... %206-9.pdf
Size 25 pilot jets are correct for the stock setup.
Pilot jet VM22/210 should be correct — that’s what I’ve used in other Suzuki VM carbs.

Suzuki part 13251-33110 & Mikuni VM30/103 are identical. That’s correct for your bike.

Mikuni part descriptions are shown on:
http://jetsrus.com
https://www.mikunioz.com/product-catego ... ilot-jets/

Thanks for the links. That's helpful.

[pgb123]

So, got the carbs off the bike. May have lost the little spring behind the choke lever, even though the manual said to be careful of that! Still have the ball bearing though.

I've only taken the first carb apart so far. It was surprisingly clean inside considering how long the bike sat. Noticed that the pilot air screw was screwed all the way in. Could have something to do with how the bike ran, no?

I have just a couple of questions at the moment. First, do I need to tap out the needle jet before putting the parts in the ultrasonic or can I just leave it in? Also, can I put the rubber hoses in the ultrasonic or should I avoid that? Same with the carb floats?

When putting back together, the manual says to pump Suzuki Super Grease C into the column where the throttle valve shaft goes and to the bearing surfaces of the shaft. Can I use something like this? https://www.autozone.com/greases-and-ge ... 561696_0_0" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

How do I pump it into the grease fitting? Apologies for the question, I've just never done anything like this.

[sportston]

So, got the carbs off the bike. May have lost the little spring behind the choke lever, even though the manual said to be careful of that! Still have the ball bearing though.

I've only taken the first carb apart so far. It was surprisingly clean inside considering how long the bike sat. Noticed that the pilot air screw was screwed all the way in. Could have something to do with how the bike ran, no?

I have just a couple of questions at the moment. First, do I need to tap out the needle jet before putting the parts in the ultrasonic or can I just leave it in? Also, can I put the rubber hoses in the ultrasonic or should I avoid that? Same with the carb floats?

When putting back together, the manual says to pump Suzuki Super Grease C into the column where the throttle valve shaft goes and to the bearing surfaces of the shaft. Can I use something like this? https://www.autozone.com/greases-and-ge ... 561696_0_0" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

How do I pump it into the grease fitting? Apologies for the question, I've just never done anything like this.

Yes that grease would be fine. You use a grease gun to pump it through. Rubber hoses in the ultrasonic solution? No, I'd replace them.
Yes you can tap out the needle jet, but make sure to keep the brass locating dowel that will be forced out when you drift the jet tube out. Be careful what you use to drift the tube out. You must take care not to damage the threads that the main jet must screw into. You will need to re-insert the brass dowel when you reassemble. I suggest you tap it in gently with a centre punch.
Carb floats can go into the ultrasonic but you will need to weight them down. Check them for any signs of leaks (if you hear sloshing when you shake them, replace the float).
Make sure you remove every jet and component from the carb body before you pop them into the bath.
Get your ultrasonic bath nice and hot before you put the parts in. Only clean for the recommended interval. Leaving them in too long will discolour them and the cleaning solution will start to eat into the metal.
Once removed from the bath, thoroughly rinse them clean, then spray them with WD40 or similar to prevent corrosion (failure to do this immediately may lead to further carb problems).
Good luck

[pgb123]

Rubber hoses in the ultrasonic solution? No, I'd replace them.
Yes you can tap out the needle jet, but make sure to keep the brass locating dowel that will be forced out when you drift the jet tube out. Be careful what you use to drift the tube out. You must take care not to damage the threads that the main jet must screw into. You will need to re-insert the brass dowel when you reassemble. I suggest you tap it in gently with a centre punch.
Carb floats can go into the ultrasonic but you will need to weight them down. Check them for any signs of leaks (if you hear sloshing when you shake them, replace the float).
Make sure you remove every jet and component from the carb body before you pop them into the bath.
Get your ultrasonic bath nice and hot before you put the parts in. Only clean for the recommended interval. Leaving them in too long will discolour them and the cleaning solution will start to eat into the metal.
Once removed from the bath, thoroughly rinse them clean, then spray them with WD40 or similar to prevent corrosion (failure to do this immediately may lead to further carb problems).
Good luck

Many thanks for the reply. I'm only using Dawn dishwashing solution and an auto dishwasher rinse aid as a surfactant in the ultrasonic bath, so I'm wondering if the rubber hoses would be damaged from that? I didn't run them through yet, so should they be replaced anyway, just as a matter of course?

Can I just leave the needle jet in? I don't see a brass dowel in the parts manual. I'd rather not mess with it, if I can just leave it in. But if it should come out for a thorough cleaning, then that's another story.

I did run the carb bowl and body through the cleaner and left it out to dry for the day. Will it still need the WD40 treatment considering it was only cleaned with dishwashing soap?

I apologize for my ignorance! First time doing any of this.

Thanks again!

[Dave Robbo]

i always leave carbs to the experts but will tackle most other things.

[pgb123]

K. Answered my own questions. Hoses survived u/s bath. Needle jet wasn’t difficult to get out (using a chopstick). Dowel pin was obvious once it was out.

So now, how in the world do I get the melted gooey black mess that used to be carb boots but now is all over the mixing chamber top, the jet needles, the throttle valve rods, the springs, the throttle valves, my kitchen sink, my hands ... ??

[Alan H]

Slowly, thoroughly, and eventually. Horrible isn't it?