Timbuckets-
I have had both problems with my TT600--bad CDI, evidently not advancing and the slide sticking in the secondary carb--both gave similar, if not the same, symptoms as you are experiencing. Power was severely lacking. The exhaust note was flat, excelleration was sluggish and you couldn't pay the front end to come up. lol I fixed the sticking slide and it was better but still not right. Then, I tried a different CDI and that was the ticket. Night and day difference.

As far as carb "sync" on these dual carb machines; there really isn't any, at least in the sense of multi-cylinder multi-carb engines.
On the above style engines, the synchronization consists of setting all of your carbs to draw the same amount of vacuum at idle, essentially setting the slides (or butterflies) to be closed the same amount and (hopefully) open at the same rate.

The sync on the dual-carb Yamaha (as well as any dual-carb single) consists of setting them up to have the secondary open at the proper time and be fully open when the primary carb is fully open.
I haven't had very good luck setting them up as the manual says. Basically what I do is make sure the secondary butterfly is wide open when the primary is wide open. Also, I make sure the butterfly is level or flat at wide open, not farther than that one way or the other as it will impede on air flow.

timbuckets said:

Having the butterflys out of sync and operating in an overlapped sequential fashion on a single plenum or cylinder increases the air velocity and thus pressure difference in the carb throat at idle and just off idle throttle openings.  Thus providing more consistent fuel feed and atomization at idle and partial throttle, while allowing greater volume a WOT.  You get the advantages of both under and over carburating a motor simultaneously.

Once you start thinking of the carbs on a single plenum or cylinder in a sequential manner, then you realize that the needles and jets of each carb don't even have to match.  This gives you even greater control of fuel metering across the throttle range.  This is how many (most?) 4 barrel automotive carburators work.  Acting more like 2 overlapped sequential 2 barrel carbs than a single 4 barrel carb.

Drawing more more air/fuel through one valve as opposed to the other should not be a big issue.  Swirling of the air/fuel charge as the piston drops and then compresses should prevent pooling or an uneven distribution of atomized fuel.

Long day of in the garage:

-Played with the carb. I did a vacuum test and it tells me that the bike is running to rich or too lean (thanks-very discriptive). The needle was reading 0-10 inHg but bouncing on every stroke.  I did a measurement of the float level. I should have done this the correct way with the tube rather than calipers on the float. It was WAY out.I have it set now to ~7mm. When I put the carb back together I noticed that the 2nd are carb slider was sticking. I loosened the 2 screws and repositioned it until the slid did not stick any more.

- I decided to check oil again and found that it was low, again. This did not make sense to me as I should be well over the amount of oil in the engine. I decided to check to procedure in the manual and found out that I should be checking the oil when hot. Well, when its hot I have WAYYYYY too much oil in there . I'm so embarrassed, this is likely the cause of my oil leaks (too much pressure & volume). Hopefully it okay and I did not permanently bust any seals or the crank case joint. I really don't want to go back in there...man I feel stupid

Prognosis is that its running better! Defiantly not 100% but better. Top speed is not 100km/h, runs cooler and I have better acceleration (still cannot lift off ground). This makes me think that its not the CDi but rather the carb. I have to play some more. I want to pull the plug to see what it looks like now, do another vacuum test.

Am I correct in thinking that the needle in the secondary carb will only lift when the bike is running (vacuum pulling it up?)

This is so cool man. I just picked up a '84 TT600 for 80 bucks and am starting the teardown process as well. It will be my first full rebuild and im so pumped to see all the support for this bad ass bike. I will definitely be following along as you go. Thanks, cant wait for your next update.

JohnnyJugulur said:

Dang JJ! I can almost afford that one! If you find another for $80, ride it over to Indiana for me and I'll give you $80 and buy you a beer

I checked the vacuum again last night and it was bouncing again but not as bad...not sure if this is even a good test. I figured I would give it a try since I had the tool on loan and in my garage. I pulled the plug again and it looks better. Still a little bit of soot on the edges but the center is clean and the side/top electrode portion is clean and looks good. I was thinking of swapping CDIs but I want to run it for the week first to see if it improves (some times these things just need to be run). I will swap it next week when I get a chance.

So again, its running better. It will do 100Kph (60 mph) but it will not lift the front up (its close though). It runs cooler than before. I get to ~5.5K or 6K RPM and it stumbles (fires 40 out of 50 cycles, stutters the rest).

To Do list:
-Move my needles down 1 or 2 settings, test
-swap CDIs, test
-Jetting, test
-New pipe, test

Johnny - Good luck with the tear down. This bike is pretty easy to work on and getting parts is not horrible. Feel free to post up if you have any questions

you're  getting close! mine was doing the same. changed the cdi to(wayne gums) ran good. was the tt cdi bad or was it not compatible with the xt stator? i guess i need to put the tt cdi back on to settle this.

ZRXER----it was nice meeting you in somoa. we had a great day as we won! nice drag strip also.

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I did not try the CDI yet. I want to ride this week and I was worried that pulling out all the wiring would mess something up again. I will try one day when I know I will not be riding it for a while. I think its just clip in but  but there is the 3/4 extra wires for the lighting circuits. If the TT CDI is the answer I will have to tap into power somewhere else for these 3 circuits.

bergman501 said:

Nice meeting you too! And Wally. Very cool to put a face to an on-line name.

You guys won?! Excellent! Congratulations!!

Well its been almost a month and I’m still stumped and very frustrated. I still cannot get this thing to run better than 5000RPM. It pulls relatively well up to 5K, may not be the TT600 legend that I hear of but its not a slug. When I hit 5K (sometimes 4.5K, sometimes 5.2K) it immediately stumbles like its getting no gas. It goes from sounding/running fine to lurching in 1/2 second, no transition. Rolling off the throttle its fine again. Here is what I have been working on all with little impact to the performance:

• Swapped the XT600 CDI for TT600 CDI. Ran the same. I would doubt that both CDIs are crapped out in the same way with the slow circuit fine and the high RPM circuit fired– note that besides the extra wiring needed for lighting, this is drop in replaceable
• First loosened then removed the decomp lever (fitted with a spare with the end ground down). Yes it’s a beast to get past the compression portion of the stroke but once I have lined it up it still starts in 1-2 kicks
• Checked the pick-up coil signals (out from stator) to make sure that both signals (12deg and 36deg) were operating properly
• Checked coil resistance and spark – In spec with a big blue fat spark
• Checked the plug after running – rich at lower end (its fine at lower end so this is okay with me for now) but lean at upper end (you can see this on the upper electrode of the plug). See pic below
• Check flow out of fuel tank – runs freely
• Checked flow out of float bowl to secondary carb – runs freely
• Checked and re-checked float level. Used calipers on inside first, then checked with carb in vise, then checked with carb on bike
• Checked for leaks in intake boots with carb cleaner. They look perfect. I may not have done a good job checking this, I may try it again
• Opened carbs- cleaned again & verified that the CV carb is opening and closing okay. This carb is a little slow on coming down**
• Reset the carb sink so that the secondary opens earlier

I’m still stumped – any suggestions?

Still need to check:
• Re-test carb intake boots
• ** I read that on some of these the spring for the CV carb is too weak to return the spring correctly. You apparently need to wight the CV slide with a washer...Is this true?
• Purchase a new spark plug cap – does anyone have the #?
• Purchase a set of raptor carbs?

Hey Tim,

Your plug looks like it was dipped in black paint! Have you ensured that the sync on your carbs is absolutely dead on or that your intake manifolds are alright (sorry, I haver read the past posts for a while)? Also, to big of a main jet will make that happen every time. I did some experimentation with jetting and if it was just one size too big, it wouldn't rev past about 4000 RPM without running terribly.

If you tested 2 CDIs I can't imagine that both of them would identically be bad. Seems like it would be too coincidental.

I agree that the bottom ring looks black & rich but that is usually an indicator of the low RPM condition.

Look at the upper electrode and center core/lower electrode. They are white and clean. This area is usually associated with hi RPM. Its running lean here. I can also tell from my exhaust pipe that the engine is running hot.

Am I wrong?

they say with unleaded gas you can't read a plug like in the old day's (leaded gas) plug looks fine with a little oil burning. my exhaust feels hot also just sitting. out on the road or trails it is not noticeable.

well, I give up..my TT my is up for sale..Got a few others that I'm into now and 'don't feel like messing with the title thing.

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Really

Did that jetting kit ever work out for you?

I never put it in..Its on C.L. but I havent had any real replies to it yet..May just keep it after all..who knows.

Well, it's gone..made a little money off it to boot..gonna put tires on the Jeep with the money..Good luck everyone with there old school TT and XT's..Maybe someday I'll get another one, but it'll be an XT for sure..

Well...I think I may have actually figured it out. Just in time for winter :foul:

Looks like Thesyk and Bergman are right. I cannot read the plugs like that and its rich, like really rich, but I think only on the CV carb (which is why it runs okay at lower RPMs).

I put a long hose on the overflow pipe for the float bowl and ran it up into my helmet. Then went for a ride. While the bike was hitting the "wall" I would suck on the hose to create a pressure drop in the float bowl reducing the amount of fuel entering into the CV carb. While doing this I could temporarily exceed the 5k RPM roof.

Jetting kit is on order from 6sigma and we will see how this goes. Hopefully I can get some riding in before the snow comes (and maybe a bit after )

Other winter projects:

• repaint plastics
  
• Dye the tank using the method I suggested before
  
• bleed the shocks and setup suspension
  
• new gasket for stator side (I have a small leak)
  
• new clutch cable
  
• install some bark busters
  
• figure out a solution for my muffler
  
• re do wiring with better connectors (posi-loc?)

A thought just came to me Tim... Have you checked to ensure that the fuel line connecting the first carb to the 1/2 carb is completely tight? I remember that one of the problems I had was that since the line was not "tight" onto the little nipple-jet, when the butterfly opened up, no fuel flowed into it because of the vacuum leak created by that line not being tight. Even if it's not tight, it won't leak... It'll simply create the effect of sucking a drink out of a cup with a crack in the straw. Little or no fuel to the 1/2 carb which can sound like the CDI not working. I put a zip-tie on mine and it was just fine!

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Interesting...I have had the hose on and off again so many times, maybe its getting too loose. It may not be my issue but it could be contributing to the issue. I will try the zip tie thing tonight