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'90 XT600E, how often do starter plungers (choke) fail?

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hello all,

ok, got my xt600e running pretty good and I'm down to one final issue (I think all of this is a related issue).

SETUP: 1990 XT600E, stock jets, supertrapp exhaust, stock everything else, carb(s) cleaned just a few days ago (fresh gaskets/o-rings, carbs stripped and all parts dipped in cleaning solution for 45mins, all parts dried and blown-out with compressed air), mixture at 2.0 turns out, supertrapp at 8 discs, no sign of rich or lean (supertrapp discs are clean with a slight brown color, no black carbon, no white scale, as supertrapp says... perfect), NGK spark plug with textbook color (tan to light brown, supports claim of no rich or lean condition)

ISSUE 1: when I start this bike for the first time, I pull the choke plunger out, and fire it up. it always starts right up. but it may only run for about 20 secs or so and dies. this goes on for about 3-5 mins, then it will stay running until warm, push in the choke plunger and away I go...

ISSUE 2: when this bike idles, there is a surging effect that happens. it also surges in the lower gears up to about 40mph... then she runs perfect up through 70+mph without any issues what so ever. during the idle, when it surges, I can hear what sounds like a gasp for air. I tested this theory by shooting compressed air into the intake. the RPMs rose, idle sounded perfect, and no surging in the idle while extra air was applied.

THOUGHTS: I think both of these issues are related to the starter plunger (choke). so how often do these things fail? during cleaning, it looked alright. spring was in good shape (appeared to be). bike may have sat for some time (found evidence to support, just bought bike a few weeks ago, so no history).

any comments or thoughts?

oh, and if you guys think I'm on the right track, is there anything I can do with the plunger besides replacement?

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got the new starter plunger today. well that wasn't it... it improved things a little, but not a cure. it did lessen the number of times I have to restart the bike before it stays running. but it didn't help the surging idle. any ideas?

a new condition in my running has been a few days running rich, then a few days running perfect. this is with no forced changes by me.

I want to check the air pilot, but can't find it in any of the carb diagrams. where is it?

Edited by HiTechRedNeck

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How's the rest of the engine? Compression, leakdown test, valve lash all OK?

Surging idle can be an intake leak - check the manifolds as they can dry rot after a while.

Good luck!

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How's the rest of the engine? Compression, leakdown test, valve lash all OK?

Surging idle can be an intake leak - check the manifolds as they can dry rot after a while.

Good luck!

I adjusted valve lash when I did the carb cleaning. all the valves where too tight, I set them to factory spec (I have the 90+ service manual). I meant to do the compression test, but wasn't able to find the right adapter (to my gauge) at the time... looks like I need to make a point to do it. I will do a leakdown test also.

I've checked the intake boots, but I will check them again. I thought intake boots affected the entire power band? this machine runs perfectly on the highway. doesn't miss a beat and has good passing power.

this is my primary transportation and work vehicle. I put about 140+mi on the clock during a work day (not every day). 5 days week before last, 3 days last week and 3 days so far this week. other than that, misc running around town locally. highway speeds are usually 70-75mph, occasionally 80-85 if I'm passing someone. basically, my avg day is leave the house, 40mi commute to next larger city, ride around city with usually 10-25 stops for less than 5min each, and then commute back home. I'm getting a consistant 40-45mpg. after I've been on the highway (even if just going across town) the bike runs without surging for a little while. basically, it runs better warm/hot. the weather here are been pretty constant 40-55. outside temp doesn't appear to affect the issue. there is less than 100ft change in elevation during any time that I ride. I do occasionally get into some foothills (may +300ft), but elevation doesn't appear to change anything. the local elevation is 150ft above sea level (valley).

that brings a thought to mind... the guy I bought the bike from used it to volunteer with the forest service in san bernadino. is there something he may have set up for elevation that I need to check? when I cleaned the carbs, I checked the primary and secondary jets sizes, but I didn't pay attention to anything else.

to further that comment... I bought this from a guy in southern CA. I'm in central CA in the valley. when I bought the bike, it was running way too rich. I tried to adjust the carb, but there was too much varnish and carbon buildup to effect good results. that's when I decided to pull the carbs and check everything I could. everything I found in the carbs, suggested that the bike wasn't used that much. (with only 27k mi on a 20yr old bike... that made sense) I didn't replace any diaphrams. they all looked good to me. I replaced the bowl gasket, and all external hoses. all new clamps. I reset the mixture screw to 2.0 turns (was at 3.25 turns by prior owner). I reduced the supertrapp discs to 8 (prior owner was using 10, what the pipe comes with). replaced plug. checked stator, battery, plug cap and coil to service manual specs. replace bad battery. everything else checked out within spec. while cleaning carbs, I found trash in the fuel pickup screen (carb), so I added an external filter between petcock and carb. the rest of the carb cleaning went perfect. everything cleaned up well in the carb dip, and I saw no evidence of blockage when I was blowing every port out with my compressor. jets and meters went back in spotless. everything was removed from carb bodies.

I worked on the carbs for 2 days, so I didn't rush anything. bike fired right up after everything was done, ran for a few moments and then this surging issue came up.

I'm working today, but either tonight or tomorrow I should be able to do a compression and leakdown tests. I will report what I find. any other ideas are welcomed.

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sorry I haven't posted anymore about this... over the weekend the front sprocket & nut come off... I'm ok. the sprocket came off as I was coming to a stop at a stoplight... so no injury or damage. I got lucky.

anyway, no one has the nut in stock, so my bike is out of commission until the ordered one gets here.

back to my idle issue, I was playing around with the intake boot clamps and my idle improved. I now suspect the clamps to be my problem. I'm going to replace them and let you all know.

but give me a few days... ordering everything.

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well, replacing the clamps improved, but didn't solve. now, another issue. I noticed that my new (clear) fuel filter is not filling with fuel (a little less than half full) while the engine is running. so I have a fuel delivery issue now...

I know that the tank, petcock, fuel filter, and line are all free of debrit... since I can take the line off the carb, put it in a cup and open the valve... I get full flow of fuel. the problem has to be in the carb.

so, I'm going to pull the carbs off again... and this time, I will write-up (w/pics) of what I'm doing and identify all the parts and adjustments. I will be starting a new thread for this... so stay tuned in...

also, any ideas are helpful and wanted...

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I would be thinking air leak as well. Have you tried blasting brake cleaner, starter fluid, etc at the area between the carbs and cylinder while the bike is idling? Same for the intake tract between the air filter and the carb. If the engine rpm picks up when you do this, it will show a small air leak in the intake, whichwould explain the surging idle, and the gasp as it dies. This is a common problem on the XT350, but I'm not too familiar with the 600. Does your carb have an adjustable needle? Raising the needle a clip position can effect those small throttle positions as well.

Psycho

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...Does your carb have an adjustable needle? Raising the needle a clip position can effect those small throttle positions as well.

Psycho

yes, the 600 carbs are just like the 350 carbs. the needles are adjustable. that brings up a good question... what is the stock position for the clips? I will be sure to check what they are set to.

yes, I've went looking for air leaks in the intake system, but found nothing. I used a variety of sprays just to make sure. found nothing.

I've removed the carbs tonight. but I didn't do anything else. I'm going to remove the boots and check the o-rings in the morning before I begin tearing down the carbs again.

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The needles aren't adjustable on the 350, but you can shim them with very tiny washers. Not sure what the standard clip position is for your bike. You had mentioned it seems like it's running rich.

Could the air filter be over-oiled, making it rich at small throttle openings?

Also, while its idling, try adusting the fuel screw out a 1/2 turn at a time and see if that makes the idle smoother. Do this with the bike warmed up and idling, just keep opening 1/2 turn at a time until the idle raises and is steady. Then adjust about 1/4 turn from there until it's idling at it's peak and you can dial the exact rpm you want with the idle adjustment. I'm guessing 2 turns is pretty lean, and you need more along the lines of 3.5 with otherwise stock jetting. (Wasn't the previous owner at 3.75 turns?) This is definitely the case with the 350's.

Psycho

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took apart the carbs... my replacement o-rings didn't hold up to the gasoline... black rubber particles all over the place.

also, the needles are not adjustable except by shims. no clip adjustment (sorry, I was wrong). looked up the numbers stamped on the pins, and everything in these carbs are stock. so it's all down to adjustments. I started re-dipping the parts tonight... 45min each dip. will get the rest done tomorrow and begin checking each port with the air gun. this time around, I'm replacing all rubber fuel and vaccum hoses.

I removed the intake boots from the head, took them down to yamaha with me and got a mechs opinion as to condition. on his recommendation, I will just replace the o-rings and re-install them. also, I will have all new clamps on the intake system.

I had plans today to test compression, but my tester doesn't have the right adapter... so I will try to find one tomorrow.

air filter... didn't know if I over oiled it or not, so, I degreased, cleaned and air/sun dried it today. I bought a can of spray oil for it and will apply just before installation. any tips on how much?

you asked about the mixture setting... I was under the impression that anything more than 2.5 turns was too much and re-jetting was required. as it turns out... the mech I spoke with asked the same thing you did, and didn't see any problem going as much as 4 turns out if the setup called for it. I'm going to make note of the total number of turns capable in my carb, then I can insure that during adjustment, I don't go too far. other than that, I won't limit myself to so few turns... thanks for asking about it. it set me straight.

will keep you guys posted.

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I wouldn't go much more than 4. Much beyond that, and I would think you'd run the risk of it vibrating out all together. Opening up that fuel screw makes up for a lean pilot (I think that's the right term, could be idle jet). I doubt you will find a richer pilot to put in. I haven't found one for the 350...

Psycho

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ok, this problem is gone... here's what I found...

carb dip (cleaner) - I thought this stuff evaporated off the parts... so on my first cleaning, all I did is wipe key locations dry. what I found on taking the carbs apart this time is that the clean stuck around... and mixed with the gas... destoryed all my o-rings in the carbs... so this time, I dipped the parts, then when they came out, used a heavy duty de-greaser and water to clean the cleaner off... then a combo of wiping and compressed air drying... a much better result.

enricher diaphram - last time, I left this in because the holding plate/valve is mashed into place... this time, I took it out... carfully.... glad I did, because it had a ton of trash behind it. result - not matter what, if it comes out, take it out... better cleaning, and no having to do it over... lol.

needle shims - if you want the carb stock, regardless of how the prior owner had it, follow the parts install order in the service manual... the prior owner had the stock shims in a certain way that didn't match the factory manual order. after talking to my some-what friendly yamaha dealer, I put the parts back in just as the manual says... result, everything works and adjusts as it should... lol, go figure, yamaha knows how their bike went together :thumbsup:

well, got it all back in, installed the tank, and fired it up. fired on the first shot (mixture at 2.25 turns). idle was smooth and strong. I was very happy. no stalling, no surging... just smooth. I began making mixture and idle speed adjustments... took it for a run around the block... no surging during low speed... all my problems are gone.

so, now I'm just making micro adjustments until I get everything just right. overall, my pace was slow, so I'm happy with the cleaning and glad I didn't get into a hurry. but I didn't follow the instructions (service manual) and that costed me having to do this cleaning again. as soon as I realized that the carbs were stock (jetting and needles) I should have followed the bible (service manual). lesson learned, and I will follow the book next time.

thanks for all your inputs.

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