i have a 1982 Yamaha XT 550 and right when i get it to about 65mph it starts bogging down as if it isnt getting any gas. when i let go of the throttle it kicks back in and starts accelerating again until i get it back up to 65mph. is it possible that it has a governor on it?

No governor.
Was the bike sitting for a long time with old gas in the carbs?

oh okay. no it has about 1000 miles through the engine since i got it

Clean the carb thoroughly....I've experienced this more than a few times with an assortment of bikes

Sounds familiar...I have been going through the same thing on my TT600. I have tried a tonne of tests to find the answer. It ended up being jetting issue in my case but there are lots of things on these bikes that can cause it.

Read the last few pages of this for potential ideas, tests and solutions
http://www.thumperta...t=922836&page=7

Mine does the same thing If I run through the gears I can get it above that in 4th gear but around 60mph It does the same thing. In magazine tests [ I bought 5 different 1982 magazines featuring it] top speed is listed at 99 mph when the weather is right it will run right up to 80 mph [that is fast enough on knobbies with drum brakes].

Nope, I've had mine at 85 and felt like it would keep going beyond that. Found out later the tire is only rated to 81mph.
God looks after fools and small children. Depending on whom you ask, I fall into both columns.
Do you have any issues running it near red line in any other gear? It should pull to 7K, but with the old mechanical tachs, stop at 6500, it may not indicate accurately any longer.

jpaulbills, on 03 October 2011 - 01:54 PM, said:

There was a secondary carb fuel starvation problem in the ’82 model, that was corrected in the ’83 model.   There was a kit available to correct the problem if I remember correctly.  Do a search, you will find some info.  


Not saying that is your problem though…. don´t know.

GU520, on 15 April 2012 - 01:30 AM, said:

I often wondered why the only thing that changed on a bike made for only two years was the carb. Now I know.

Smacaroni, on 16 April 2012 - 07:39 AM, said:

I I read that it was to reduce backfiring on decel who knows it was 30 years ago I read through repair bulletins from Yamaha and did'nt find anything related to it either

Glad I stumbled across this. I'm having exactly the same issues but mine come in at around 4000 revs. I find that if I accelerate gently, it is almost OK, but if you open up and cane it it just coughs and splutters. I think it's to do with the secondary carb. Do you think it's worth taking the carb off and sending it off to a pro to overhaul? I wouldn't have a clue what to do with carbs. If it isn't the carb, what else could it be? Maybe valve clearance or something (I could be making a fool out of myself by saying that, I'm a 2 stroke guy, much simpler, no valves).

I posted in the jetting thread about this and one question I asked there was if you activate the secondary carb by pushing the lever to open the butterfly valve, when in idle, the engine just dies abruptly. Is this right?

The first thing I would try is a good thorough cleaning. However, you sound like that would be really intimidating, so instead, follow the hose that feeds the secondary carb. On the right side of the bike is where you'll find this and it's a simple tube, sometimes has a spring on it, running from the bottom of the left side to the center of the right side.
Pop it off, use a boxed end wrench or socket to remove the exposed brass jet.
Soak it in carb cleaner (parts cleaner, brake cleaner will also work), then blow it out with compressed air. The hole in the center of the jet should be much larger than when you started. Avoid the temptation to stick anything in it, you've got the most expensive, hardest to find jet I've ever had my hands on, you don't want to screw it up by stuffing things in it.
Re-install the jet, reconnect the hose. Fire it up and take it for a ride.

Thanks for that. I will try that when it eventually stops raining (assuming it does).

I had a look at the pipe. I pulled it off from the main carb (real easy to pull, no clips) and fuel came out. I pulled it off at the intake on the secondary carb (again, very easy, no clips) and fuel came out of the pipe.  I have added a couple of pics of the carbs from both sides so you can see the pipes. I also add a 3rd pic of the exploded diagram and I've pointed to a fuel pipe connecting the 2 and wonder if that could be blocked as well?

Edited by pete63, 23 April 2012 - 10:10 AM.

The jet doesn't have an elbow. At least mine doesn't. I think a PO did some customizing.
I'll get you a photo in a few days.

Yea, I believe you are right. The pipe in one of the diagrams goes right up and in. Makes me wonder if the right angle is affecting the flow in any way?

EDIT:

Ok, I've looked into this a little further and after studying the parts manuals I've found out the exploded carb pic above is for the XT550J. The J doesn't have that fuel pipe, it has the one I pointed to in the diagram. Mine is the carb from the 550K (which I assume is the later version?) and it has this parts list exploded diagram which shows the fuel pipe in question.

I'm a little bit worried now that the different intake nozzle (right angled one) may mean that the PO has altered the thread so a standard won't fit anymore. I'm hoping not as I can get the nozzle and jets (only 2 left apparently??) at great expense (70 euros) but wouldn't like to find they no longer screw in!

Edited by pete63, 23 April 2012 - 11:30 AM.

pete63, on 23 April 2012 - 11:04 AM, said:

I was thinkin' since you're across the pond that "normal metric pipe threads" may be available at a hardware store and they might just screw in.
If the carb is hosed, just buy one off ebay. You can use the old one for spare parts and as a model to reconstruct the ebay one during the cleaning process.
The carb is the only thing that changed on this bike and I would suggest buying the 1983 version from what I've read although I don't  have any hands on experience.

Smacaroni, on 23 April 2012 - 11:59 AM, said:

It's an import from your side so should be the same as yours. Came over in 92 according to the V5.

No, I mean the pipe threaded into it, not the bike.
But that's good to know if there were any differences between the US and UK XT550, it's not on that bike.

I'm actually starting to think that this is a bit of a "frankenstein" bike. Things on the bike seem to be from different models. Not really a problem, the bike looks good, and works aprt from this fuel starvation problem. I looked on ebay and there were 2 carbs for sale from the XT550. They looked the same but were different to my carb. The plot thickens.