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Makotosun

LT2100 woes and troubles

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LT2100 woes and troubles was created by lt2100

Greetings,  stumbled across this forum while working on a '72 LT2 100 I recently acquired in non running condition.  The previous owner had it for at least 20 years and supposedly ran before being stored for a long time.  The top end had been redone years back (receipts from 2007) , bored over and new piston and rings.

I purchased the bike for $400 as is to tinker on and hopefully get running to introduce my 14 year old son to the wonderful world of vintage motorcycles including the repair and maintenance aspect.   I have some small engine repair experience, and have revived old bikes, mopeds, outboards, etc.  Definitely NOT an expert however. just a tinkerer.   Bike was all there, decent overall shape, no spark, compression felt good via the kickstarter and the "blow the thumb off the sparkplug hole" test.

Initially there was an aftermarket coil on the bike that did not quite match the bolt holes for the original coil. I tried a NOS coil from ebay but it arrived damaged, while waiting for a replacement, I ordered a EMGO universal 6/12v coil from amazon, as well as replacing the points and condenser.  The emgo coil only lines up one bolt hole also.  but after it and the points and condenser, there is a nice healthy , happy bright spark.    I have tried both the aftermarket coil, and now another NOS replacement, and neither of those will produce visible spark when swapped for the EMGO coil..   Not sure why. 

Adjusted the timing (stator is stationary , only points gap is adjustable) by eye / matchbook, close as possible to 1.8 btdc.  There are timing marks on the flywheel and case corresponding to 1.8 btdc

Rebuilt the original 20mm mikuni carb with a keyster kit ( I have now read that their jets should not be trusted and the original brass is preferred. so i swapped back in the main and idle jets so far from the orig. carb.   Even after all this and fresh 25/1 premix the bike wont do anything other than a few coughs and whisps of smoke out the exhaust,  not even a stumble.  Have tried starter plunger in, out , no throttle some throttle ,, full throttle, nothing,

Kicking the engine over feels like good compression for a 100cc. or so I thought,   But i just bought a cheapo compression tester from harbor freight, and get the following (bad?) results.  - first kick 40 psi. second kick 70, 3rd kick 90 4th kick 110.  

At this point i'm in all the way and ready to redo the top end again, gaskets, crank seals , whatever it takes to get this beast running,   Have had moments of pulling my hair out and trying to find the nearest local cliff to roll this thing over.  But I will persist and make it run!!   Hoping the community here can give me some input and confidence I need to see this thing through.  The forks, chain , brakes, sprockets, all seem good, bike seems to shift correctly, and in pretty good cosmetic condition for the age, I really feel like it wont take much to get it back on the road. 

Anyway thanks in advance for any input.  Really appreciate places like this and should have probably just started here before pulling everything apart.

C
25 Feb 2024 05:25 #1

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Replied by lt2100 on topic LT2100 woes and troubles

forgot to mention a few things, - the carb is definitely pulling fuel, with hand over the inlet there is strong suction, and the plug is wet with fuel after kicking over, I have tried manually squirting premix into the carb, directly into the cylinder etc, and nothing except for a few coughs and whisp of smoke.

Also- a real mystery, when i took off the reed valve to take a peek, One side of the reeds was actually two layers, one layer was close against the valve cage, the other was floating up kind of like a flap on your shoe if that makes any sense. When i ordered a nos set of reeds, the ebay listing said two reeds, but low and behold, three reeds arrived, one individual one, and two layered sandwiched together (on initial inspection the two stacked appeared as one, the same way two flat razor blades might stick together. but easily slid apart between my fingers. . I looked everywhere online and could not find any info regarding the sandwiched / stacked reeds. So this is a total mystery,, I carefully installed two of the NOS reeds and stored the 3rd one.
25 Feb 2024 05:36 #2

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Replied by Sneezles61 on topic LT2100 woes and troubles

First, welcome! There are many very good folks here that know these enduros thoroughly.
Sounds like ignition system. Cleaning the points faces, check all connections from the points up to the spark plug. Be sure the isn’t a wire shorting to ground. All these are a part of a spark killer.
Sneezles61
25 Feb 2024 05:57 #3

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Replied by Schu on topic LT2100 woes and troubles

Welcome to the forum!
I wouldn't worry yourself over those compression readings. Those values per kick are what I get on most of my small cc bikes, and you climbed above 100 so it should start and run.
I would install new crank seals as my next step. You could also try removing the exhaust to see if it will start without it. The exhaust can get plugged up and restricted enough to prevent it from running. If it starts without it, then you can place the entire pipe in a nice hot fire and burn it clean. Lots of smoke involved in that process, so be aware. I live rural and typically toss it into a nice hot bonfire!
Schu

CT1B, CT1C, JT1, JT2, DT360A, GT80B, DT100B, DT125B,
DT175B, DT175C, DT250B, DT400B, Z50, SCR950

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Last edit: 25 Feb 2024 06:38 by Schu.
25 Feb 2024 06:10 #4

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Replied by Knutco11 on topic LT2100 woes and troubles

I've never worked on the 100's, so I will tread lightly here. The reed valves you are describing has me baffled. but if it was both like that originally, and the new ones you got, I suspect there is more to the story! Hopefully someone here can chime in on that. I also think that compression reading sounds ok, don't worry there. I would ohms test the ignition coils. You may be able to find a service manual for that bike here. Lots of good resources on this site!
25 Feb 2024 07:37 #5

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Replied by Ht1kid on topic LT2100 woes and troubles

Greetings from Tennessee 

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  points gap should be.015 thou. Did you use a new spark plug did you use oem points or Chinese points. I 
 used them one time and they didn’t work well.Daikhi is a good brand Also change out your brake shoes 50 yr old can delaminate 
Last edit: 25 Feb 2024 08:49 by Ht1kid.
25 Feb 2024 08:39 #6

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Replied by MarkT on topic LT2100 woes and troubles

Sounds like you've discovered the bad new ignition coil many others have run into.  Sad thing is if you had the original coil it was probably still good.

If you have the points just opening at close to 1.8 mm BTDC and a spark, you're good there...  timing is set by points gap as it sounds like you already know (so you don't gap the points with a matchbook cover or anything else)

I had an LT2 as my first real motorcycle.  On the new reeds it sounds like seller just didn't notice they were stuck together and you got an extra.  Old reed sounds like maybe Boyesen or something.  (it would have been fiber instead of steel)

I spent MANY hours trying to start my LT2.  From what you've said. my guess is it's simply flooded.  It would happen every time on mine if I forgot to shut the petcock off overnight.  Can be a real bear to clear.

Plugs would sometimes spark outside the engine but not run.  Make sure gap is 0.020 min to 0.024" max.  And try a new plug.

(Another thing that can happen is the crankcase floods with autolube oil when the bike sits a long time...  which could have pushed out a crank seal.)

Also make sure kick starter is tight on splines and pinch bolt is tight.  I never had issues but some people have stripped the splines on the LT2/LT3.

Shutting fuel off completely (make sure petcock shuts off!) and pushing bike in gear (ignition OFF, spark plug REMOVED) with a towel over the head can tell you how bad it's flooded and with what.  Spitting liquid fuel smells like gas obviously and will evaporate from towel.  Oil will not evaporate.  We lived on a slight hill so we'd push it to the top of the street, and with a friend's help, push it in gear with throttle wide open until it stopped spitting fuel out of the plug hole. And then maybe one more run down the street.  Plug in, ignition on, and hopefully it would start.  If not, we'd repeat. 

(Another trick I used was to remove the gas tank and spark plug...  Piston at BDC...  then I'd lay the bike on its side and then flip it upside down and let it sit a few minutes.  Cycle the kick start a few times by hand to help blow the fuel out, flip it back over and it would almost always start pretty easy.  I had to stop using this method when my mom figured out where all the brown spots on the lawn were coming from

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Good luck...  and again, it's probably nothing at all serious that needs any more money spent...  maybe a good spark plug.

 
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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25 Feb 2024 10:04 #7

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Replied by Knutco11 on topic LT2100 woes and troubles

Did you get oem stainless steel reeds? And did the reed cage have reed stoppers on top of the old reeds?

Reason I ask, I put boyeson reeds on an rt3 360 reed cage.  I remember per their instructions, the reed stoppers could be removed, in conjunction with using their reeds. 
The oem stainless reeds i believe rely on those stoppers, but ive never tried to find out what would actually happen..  too worried about engine accidentally ingesting metal parts.
Last edit: 25 Feb 2024 13:15 by Knutco11.
25 Feb 2024 13:04 #8

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Replied by lt2100 on topic LT2100 woes and troubles

Wow , thanks everyone for the fast and thorough input. I really appreciate it.

Regarding the exhaust, when i took it off of the bike for the first time it weighed a ton. Followed advice found online, plugged the engine side with a potato, then filled pipe to capacity with lye based drain cleaner and let soak overnight , lots of thick black crud poured out afterwards. Flushed with degreaser and let it dry completely and it feels much lighter now and seems to flow freely. . I will throw it in the next backyard bonfire to really clean it out.

Definitely agree on the crank seals, I will track them down online, partzilla has been great and I did find the service manual listed here.

About the reeds - both old and new sets are stainless, the previous "double stack" was installed with the reed stoppers in place. I can only hypothesize that the previous owner also tinkered with it and may have gotten stuck together reeds perhaps from the same ebay vendor, and mistakenly installed two on one side.. I saved the 3 that were on the bike, and the one extra new one, I will take some pics tomorrow. That one really, really confused me, as I assumed that the double reed must have been intentional , but could not find any information whatsoever regarding two reeds being stacked or laminated. They were definitely not fiber reeds . identical to the ones i received from ebay .

Testing the ignition coil values has been confusing and bewildering, I dont really understand how to test the secondary i guess. as the values were all over the place. This is in an unheated outbuilding so perhaps the temperature could be a factor, could also be my multimeter or more likely, user error. Can the primary and secondary coils be tested off the bike or do they need to be grounded? The universal coil I purchased was supposedly similar impedance specs to the oem one. Here is the "oem" coil that arrived damaged, then when a replacement arrived, still does not produce spark - ebay .com/itm/225325658594 And the universal coil that ended up producing visible spark - amazon .com/dp/B00230959C/ref=pe_386300_440135490


Not sure regarding the chinese vs oem points, here is the set i ordered - ebay .com/itm/352927651900 the condenser did say made in japan. Just bought a proper set of feeler gauges, so I will recheck the point gap. I did get a new plug however I could only find a B8HS-10 locally which appears to be the identical plug to stock but with a 1.0 mm max gap? I have the B8HS that came on the bike and have tried both with no luck, I will properly gap both plugs with the feeler gauges and retry.

Mark T , you raise a really valid point regarding the flooding, I did dump a lot of premix down the carb and probably flooded the hell out of it trying to start. I rigged up my most powerful electric drill to a 18mm socket and was able to crank the engine via the flywheel . Tomorrow I will take the exhaust off and the plug out and crank it to see what comes out..

About trying to fire it without the exhaust installed, holy hell, wouldnt it spit fire??? I didnt dare! but if you guys insist, I suppose I will get out the ear protection:)

Thanks again for the encouragement!! I really am looking forward to making this thing run!
25 Feb 2024 18:17 #9

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Replied by Knutco11 on topic LT2100 woes and troubles

Only benefit I could see twin reeds having is making a low output engine more responsive? Less air would flow, that much is certain. But if there is a certain amount of reversion that happens before the reed seals, two would make it seal quicker. Sorry alot of people pry think im kicking a dead horse, but it's strange that both old and new were like that? What are the odds of the old set coming from the same seller?

I'd like to say, I doubt this will have any affect on your engine running right.  More of a curiosity for me at this point.
Last edit: 26 Feb 2024 08:42 by Knutco11.
26 Feb 2024 08:31 #10

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