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Discussion Starter · #1 ·
I have stubbornly waited to post this question for years now in hopes that I could diagnose this problem myself by searching the forum. However, I am running out of ideas! My '87 runs good - but it cannot take WOT at low RPM's or the bike dies. If I roll the throttle at a moderate speed everything is fine. When going from idle to WOT the bike dies, but if I quickly release the throttle the engine comes back to life. Holding the throttle open kills the bike. A very good friend of mine and a lifelong mechanic worked on this bike before I acquired it. He has informed me that this bike has ALWAYS behaved in this manner. Here is a quick video...



So here is what I've done so far...

cleaned carburetor passages and jets with guitar strings and carb cleaner
replaced the Valve Seat set and Diaphragm set
installed missing splash baffle plate
installed missing mystery o-ring (Help with photo of carb innards)
replaced both intake boots
replaced petcock/fuel filter, fuel line
tried larger/smaller main jets
tried smaller pilot jet (ordered a larger one)
all manner of pilot screw adjustments
cleaned all electrical contacts

While this work has helped the bike runs better, nothing has had ANY effect on the real problem. Being that it is a 1987 model - could this problem be an electrical component? Bike runs good at speed so I don't think it's the CDI. I did the freezer test which provided no change at all. This problem is killing me on steep, rough jeep trails when I need power at low speed! So who has an idea of what I should try next???
 
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What size pilot jet is in it now? A larger one might help.

I have two 87's and if I snap the throttle open the engine dies especially if cold, not so bad if hot. I have #40 pilot jets.

Your other choice is getting a carb with an accelerator pump on it. That should solve the problem.
 

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Discussion Starter · #3 ·
It's got a stock size 40 pilot jet in it now. This issue happens at all temps, even when warmed up fully. I really want to keep the factory carb if I can. However, a Mikuni pumper that would bolt up easily would be hard to argue with.
 
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From idle to about 30% throttle, only the pilot jet is in the equation – from 30% to full throttle both the idle and the main jet come into play

My money is on an imbalance in the air mix – which incidentally, seems to also be the only thing you haven’t commented on

Sure, taken up the rev gently and it’s fine – but whack it open and it bogs – classic air problem ……
 

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Discussion Starter · #5 ·
Sorry I forgot to mention I have replaced both intake boots with factory Yamaha parts and extensively sprayed carb cleaner everywhere looking for a vacuum leak. I haven't found one. Got a freshly cleaned and lubed UNI filter installed. Bike also behaves the same with no filter installed. What else should I check?
 
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You said you passed some piano wire through the pilot jet -- you did that the long ways?

A buddy had the problem as you described and the problem ended up being what looked like a very small piece of sand plugging the pilot jet. It was almost clear so it was hard to see. Once gone it ran fine.

Circuit component Technology Auto part Electronic device Passive circuit component
 

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Discussion Starter · #7 ·
Yes, I ran it through all openings in all directions, elime. I used a magnifying glass and a LED flashlight to inspect it as best as I could and everything's clear. Carb cleaner sprays evenly through all ports of the pilot jet. I also tried a brand new 38 pilot jet, which had no effect on the issue.
 
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Discussion Starter · #8 ·
New factory #42 pilot jet installed today with no effect on the issue. Can anyone suggest a comprehensive vacuum leak test procedure? Maybe there is a spot I'm missing? Electrical suggestions, anyone?
 
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Air filter not over treated, rung out well, intake leak somewhere, mixture screw, all electrical connections checked and clean, Battery up to par? How's the valve adjustment? New plug? Timing? Chain tensioner? Wear and tear and the timing not quite perfect anymore due to chain stretch?

Gee, what else is there?

Have you tried 3 or 4 ounces of Lucus Deep Clean Fuel Cleaner? I think it is better and faster acting than Seafoam personally.

I had a 87 that ran perfectly, very fast for what it was. Old Ronnydog (one of lizrdbrth's old buddys) told me put a 42 in mine, so I did. I think I had a 112 main in it, 2 or 3 washers on the needle jet and 2 and 3/4 out on the mixture screw all said and done. Perfect at 2 thousand feet elevation. It's not the CDI.



Not Related, but had to add it when I thought of him...
***RIP Russ, I think of you often brother. I checked on little GinaMarie about a month ago, she's doing great bro, really great!! But I'm sure you can see that from up there. I love you brother and can't wait to give you a big hug in heaven some day.... You'll be one of the first guy's I'm looking for too!! I can't believe it's going on 8 years since you left us already.
 
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Discussion Starter · #11 ·
Do a carb swap with another tw owner and see if the problem remains.
I don't think a lot of members out here in CO are running the old TK carb! I'm pretty sure it is the carb at this point. I'm going to have another go playing around with different jet sizes and mixture settings.

Timing? Chain tensioner? Wear and tear and the timing not quite perfect anymore due to chain stretch?
This could be a possibility, LT. Admittingly, I have not checked the timing yet. The bike runs absolutely great otherwise. I will also double-check the timing when the weather is permitting! I kind of gave up on this issue last year - I put it out of my mind and just went riding instead! Russ was before my time here, however, I have read many of his posts that have been extremely helpful to me in gaining TW knowledge. I know he is missed, and I know his contributions here continue to be greatly appreciated by us newer members.
 
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I don't think a lot of members out here in CO are running the old TK carb! I'm pretty sure it is the carb at this point. I'm going to have another go playing around with different jet sizes and mixture settings.



This could be a possibility, LT. Admittingly, I have not checked the timing yet. The bike runs absolutely great otherwise. I will also double-check the timing when the weather is permitting! I kind of gave up on this issue last year - I put it out of my mind and just went riding instead! Russ was before my time here, however, I have read many of his posts that have been extremely helpful to me in gaining TW knowledge. I know he is missed, and I know his contributions here continue to be greatly appreciated by us newer members.
That guy is a big big reason tw's have developed to the point they are now he knew everything, absolutely everything. He impressed me for sure and I kind of looked at him as a mentor for myself on the Forum. When I run across his posts, would you believe I still give him likes. haha

Would have loved to have met him, I've met Gina Marie and she's such a nice girl, a real trooper.

Bro check your valves and all that other stuff, in other words a full tune up. The carburetor is always the last adjustment you make. What altitude are you running at? Did any of my settings come close to where you are at now?

You'll get it yet bro, hang in there. 87s fastest year evermade!! (y)
 
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Just looked up your altitude, are you really at almost 10,000 feet?



What did you guys do to Kenny? He's died a hundred and twenty six times now...
 
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Discussion Starter · #14 · (Edited)
Haha! Currently base camp is at 9,060ft, LT! But I almost always ride up in elevation. Right now I'm running a #110 main jet, #40 pilot jet, and zero needle shims. I played with different shims but it didn't affect the issue I was pursuing. It's a bizarre issue to me. I've seen a lot of shitty running small engines, and they always bogged when gunning the throttle from idle, but they always "caught up" and continued to rev. I have not experienced an engine completely and quietly cutting out like this before - and this engine runs very well aside from this small issue.
What did you guys do to Kenny? He's died a hundred and twenty six times now...
I think he chose a more "serious motorcycle" and rode off a cliff, then took a bath in the Devil's Punch Bowl...
 
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Haha! Currently base camp is at 9,060ft, LT! But I almost always ride up in elevation. Right now I'm running a #110 main jet, #40 pilot jet, and zero needle shims. I played with different shims but it didn't affect the issue I was pursuing. It's a bizarre issue to me. I've seen a lot of shitty running small engines, and they always bogged when gunning the throttle from idle, but they always "caught up" and continued to rev. I have not experienced an engine completely and quietly cutting out like this before - and this engine runs very well aside from this small issue.


I think he chose a more "serious motorcycle" and rode off a cliff, then took a bath in the Devil's Punch Bowl...
Brother Dave, this is totally fixable. Yes, it's a lot of work, but only change one little thing at a time or you will be dazed, lost and confused and never get it. But First... everything else. Carb is always the last thing in a tune up on a well warmed up bike.

Just curious, what did the plug look like? Rich or Lean? Those carbs will always be a little slower acting than a slide. When the weather gets better, check all the other stuff first, then do the carb. Don't stress over it, you'll get it. Does your bike have the canister on it? Are those lines ok? And plugged off for sure?

Do you have that little nipple on top of the intake manifold? I had an idea. Not sure how you could really vacuum test it, you would have to block the airflow off after the rear boot at the airbox, and you will always be losing some air past the rings or valves so it won't hold vacuum, but maybe you could put air into that nipple and listen very carefully and hear a leak (hiss) going towards the airbox? Just a thought.

Do all the other stuff first.
 

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Discussion Starter · #17 ·
Nope! The bike still does the same thing it always has. I have learned to deal with it, for now. However, a 229cc six-speed engine is on deck for installation and I am still interested in resolving the issue. I have played with the float bowl adjustment with no change in condition. Also, still unable to detect an air leak of any kind...
 
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