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Discussion Starter · #1 · (Edited)
VIDEO: rough tw

Hello all. Sorta new here. I recently fell into the TW world when using a 2001+ front end swapped onto a 1976 Yamaha DT400 (then ultimately went a somewhat different route). But it got me interested in these bikes. Then I came across a ROUGH titled project near me and couldn't say no.

It was missing a handful of parts but I figured a little elbow grease, couple bucks, and patience would do the trick. I busted most of the rust and replaced what was too far gone. For reference: I could stick my finger through a rust hole in the tank (shoutout to reddave for selling me a replacement!). And the header was rusted completely off, leaving the "collar" rusted to the cylinder, which was a bitch to remove.

But even after the costs of parts and effort (and a broken ez-out in a snapped exhaust bolt) adding up to negate the "good deal" I thought I got, I am still struggling to get the thing running right.

Hoping some of the TW vets could send any tips my way to help me get this thing on the road. Its close.

Key details:
  • 1990 rust bucket TW with 22k on the clock
  • It sat outside for some time. Had not run for ~15 years.
  • BUT previous owner did the marvel-oil-in-the-cylinder-trick to seal it off. And it worked. Cyl is in decent shape.
  • 110 psi compression (good, not great?)
  • Have solid spark (unrelated: new battery)
  • Fresh lightly oiled air filter
  • Carb was missing so I ordered a cheap rough carb off ebay needing rebuild (im cheap and would rather spend labor than $). Cleaned in ultrasonic cleaner. Then cleaned with aerosol carb cleaner and little brushes. New diaphragm kit, & some new bits but also kept some old bits. stock main jet (I forget the number now but I confirmed on the web it was stock... 128 I think)
  • The oil was sludge. Bike is on its second oil change and the new oil is still instantly black after running it for like 2 minutes. I did not open the cover and blast the whole gearbox with brake cleaner, probably should have done that instead of wasting fresh oil.
  • Valves: viewing window to be centered on the line NEXT to the "T"... On the compression stroke. Intake set to ~ .003 inch exhaust set to like ~.005.
  • No change in RPM when spraying starter fluid around the intake/carb
  • Mixture screw @ 2.5 turns out

Symptoms:
  • When cold: On full choke it SCREAMS. Half choke it yells. No choke and it whispers. There is no in-between.
  • Quick opening throttle = it briefly bogs. But with feathering the throttle, you can overcome the bog to rev it.
  • Then when its warmer, the above changes. Can barely get it to run off choke at all. Unless I really raise the idle set screw. On choke it is all over the place. Keeps dying, inconsistent behavior. Dies on throttle twist. RPMs are high one minute then drop wayyy low (like in the video). Seems to do it's own thing.
  • The engine itself sounds ROUGH. I am aware these bikes are born noisy little engines. But there is a higher pitched rattle - almost sounds like a loose washer is shaking around somewhere. But I don't think its external, it sounds internal. About 80% sure of it. Also sounds slightly rough on the bottom end too, like general metal on metal clang-y... Guessing that could be the sh*t oil build up - or I could just be not used to the noisy TW engines.

This has got to be at least two separate problems. 1 of which is the carb, but I do not know what /why. I used new pilot jet. So unless there is still build up in the carb passages out of sight, I'm at a loss. Air leak in the choke assy??
The engine noise I am also completely unsure about.

***
Aside from this bike, a bulletproof '92 DR350 is the only other 4-stroke I've owned, and never had to mess with it. The rest have been 2-strokes. So I'm still not yet accustomed to all the extra moving parts when trying to bring a bike back from the dead.

Thanks in advance for any input!
 

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I recommend a #34 pilot jet. The #31 is just too lean in my opinion.
The chinese knock off carbs on eBay and Amazon for under $40 are good. I'm running one on a TW200 and a TTR225. As good or better than the factory carb.
 

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Discussion Starter · #3 ·
I recommend a #34 pilot jet. The #31 is just too lean in my opinion.
The chinese knock off carbs on eBay and Amazon for under $40 are good. I'm running one on a TW200 and a TTR225. As good or better than the factory carb.
Thanks for the advice. I will check out a 34 pilot.

I saw plenty of knock off CV carbs on amazon but assumed that wouldn't necessarily work on my '90 with the old style carb. I couldn't track down any knock off old style carbs.
 

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Thanks for the advice. I will check out a 34 pilot.

I saw plenty of knock off CV carbs on amazon but assumed that wouldn't necessarily work on my '90 with the old style carb. I couldn't track down any knock off old style carbs.
Never mind about the pilot, it's for the later model carb. I didn't realize you have the older style. I know nothing about those.
 

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I would check the chain tensioner. It might need to be adjusted. Later models are automatic but yours needs to be adjusted manually.
 

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Another thing you might try is to squeeze your cdi box. I’m having similar issues on my 87 which is known to have cdi issues. Apparently a lot of mechanical seeming issues can be caused by a bad cdi. If you squeeze it with a c clamp or something to put pressure on it and bike runs smoother the box is junk. Also the newer style carb that can be had in a cheap 30$ Chinese version actually runs pretty good on the older bikes, only issue isn’t big but airbox boot may be more difficult to put on and cables need to be routed to other side of carb… pretty easy.
 

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Discussion Starter · #8 ·
Wow, lot of good info here. Thanks everyone!

Check the rear shock, Dan! There is a spacer/washer that can rattle around inside the spring and make that exact same sound.

I found a rattling gremlin.
Bingo! Dave this is great, thanks so much. That's gotta be it! Its funny I said I was 80% sure and not 100% for a reason :ROFLMAO:haha ..knew there's a chance I could be mis-attributing the location. I will check this later today.

@littletommy & @Mud - Thank you as well. I just ordered a chinese CV carb to give it a try, and later today will see if the CDI squeeze has any effect.

And I'm going to check out how to adjust the chain tensioner, I take it you all probably have some good instructions on the site here somewhere.
 

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Discussion Starter · #9 ·
Adding some pics and details on my progress - for posterity

Can you guess where the tank rust hole was located underneath?:LOL:
Tire Land vehicle Vehicle Wheel Vehicle registration plate


Soaked each rim in 3.5 gal of evaporust. For the rear rim, I used a strong trash bag in a 55gal trashcan. Put the rim in. Poured the evaporust in. Then took misc water bottles and small capped recyclables and stuffed them in between the spokes to take up space, thus raising the level of the evapo rust to get more coverage. Still didn't cover the whole thing so after soaking one side, I flipped to the other side... Front rim: same deal but it doesn't fit in a trash can so I used an aptly sized carboard box as the container (still with the strong trashbag). Cleaned em off, then hit the whole deal with rattle-can clear coat. I'm pretty happy with the results. Rust will come back over time I'm sure but this works for now.
Wheel Tire Automotive tire Tread Locking hubs


For the header that rusted completely off - I just used a dremel and SURGICALLY cut a slice and remove a good bit of material (to eventually allow space for it to bend). Then made another slice about an inch away. Eventually I removed enough material & one section was thin enough were I was able to hit it with a flathead & hammer (without touching the cyl) and bend it in on itself. And it then separated from the cylinder. Unfortunately I snapped an ez-out in a exhaust bolt which sheared. Rookie mistake. Don't know what I expected with the ez out. So that had to be completely drilled out with carbide tip dremel bits. PITA! hence why one stud is larger than the other..

Wood Automotive tire Bicycle part Gas Cameras & optics
 

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Is pilot jet a nice clean clear round orifice?
How many turns out is the idle mixture screw?
Is the new diaphragm lifting the slide?
 

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Thanks for the advice. I will check out a 34 pilot.

I saw plenty of knock off CV carbs on amazon but assumed that wouldn't necessarily work on my '90 with the old style carb. I couldn't track down any knock off old style carbs.
You can easily adapt the newer style carb to the older bikes. Search this forum there is a guide or two.
 

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Some of the running symptoms sound like an air leak. Make sure the carb boots don’t have any cracks. You might have to get new ones if you switch to a new-style carb anyway. From the video mechanically it doesn’t sound too bad.
 

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I've got two suggestions:

1. This is gonna sound dumb but make sure there isn't anything blocking the intake on the air box. More than one of us here has used that 'handy little space' near the battery to stuff some document or other crap.

2. Once yer tired of playing with the junk carbs just get a Nibbi pe28mm https://smile.amazon.com/gp/product/B076C5PV3W/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 You will need to replace the boot from the airbox with one for the 2001 and newer model TW. It is about 1/2 inch longer and the carb is a single cable so either use what ya have or switch out the throttle grip to a single. Either will work, just having one 'empty' guide on the OEM throttle looks 'funny'. For PIX look here 1999 TW - Upgrades Now with Pictures!
 

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Discussion Starter · #15 · (Edited)
UPDATE TIME

The verdict:
@reddave called it - there is a loose shock washer which was the cause of the high pinging rattle. For now I stuck a big glob of grease in there to hush it down. Will probably put a makeshift rubber washer in there as a longer term fix.
@littletommy was right about the tensioner. It was backed out almost all the way for some reason, maybe previous owner did that before storage or something. Also the intake valve was in spec but exhaust valve was out of spec. So between the chain tensioner and the valve adjustment, the engine itself no longer sounds like shit!!
• And everyone who suggested trying a cheapo chinese carb was right. Slapped it right on, it started right up, and now it purrs like it kitten. No erratic behavior anymore with high then low RPMs. Now it idles & revs more or less like I would expect it. Or at least good enough for the time being.

VIDEO: not-so-rough-anymore tw

THANK YOU EVERYONE FOR YOUR INPUT. This thing was becoming a little bit of a headache. It was only intended to be a backup/loaner bike for short trail rides, so I really did not want gray hairs from it. So I appreciate the help with being pointed in the right direction.

Time will be the test for how long the cheapo carb holds up. But I am going to use it for now. Thanks for the tip @Hazcat about the Nibbi, I will keep that in mind if/when this carb gives me trouble.

I will post a follow up with pics when it's all buttoned up and out on the trails 🤘
 
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