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TOPIC: 1981 dt 125 and 175 at it

1981 dt 125 and 175 at it 04 Oct 2018 21:37 #1

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So as you can see I have been working away at the 2 bikes I decided to get the 175 going first .The guy I bought it from said it ran when he got it but he tore it all apart because of low compression .When I got all the pieces home I had a quick look at the cylinder it had a few marks below the ports but nothing obvious to cause low compression . Then I looked at the piston it looked really good too mmn? I grabbed the rest of the bits and pieces all looked ok till I grabbed the head gasket . Right on the compression ring there was some damaged something must have got crushed in there .Long story short I threw it back together with a new base gasket and another used head gasket .stomped it a few times and got it to fire on spray then it ran although not very well .I had quickly gone through the carb and adjusted the float level and checked the needle and seat the level was way out .looked for daylight through the main and idle jet and called that close enough 150 main jet was installed .I ran it with 20 to 1 mix of gas and oil so she smoked badly I swear I saw spiders snakes and various other creatures exit the tail pipe but it may have been the smell of 2 stroke oil that made me delusional .Here is where I am at starts quickly on spray runs good wont idle with the idle screw turned right in .My thinking is plugged idle circuit bad reed cage or poor primary compression due to bad crank seal oh did a compression test 115 psi which I figure should be enough to run
n one of these beasts looking for input as to how to proceed from here?

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1981 dt 125 and 175 at it 05 Oct 2018 15:57 #2

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I see no reply's after being posted for almost a day ? On my other questions there were all kinds of reply's Where do I go from here ? Is there anything in particular these bikes are known for as far as problems leading to not idling go ? .Am I wrong in thinking the compression is high enough that it should idle well ?From what I have rear 90-135 is ok to run? pls experts let me know what you think

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1981 dt 125 and 175 at it 05 Oct 2018 17:16 #3

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I think i would look at the idle circuit first, not just the jet. Today's gas is pretty bad on carbs, there are a number of carb rebuild posts on here by others. Try the search feature. Hope this helps. Most of what you have listed as potential problems are available on older posts.

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1970 DT1-C Grand Prix race bike
1970 DT1-C Dirt bike
1968 Honda CL90
1971 Honda Sl 125
1973 Honda CR250
1974 Honda MR-50
1966 Triumph Tiger Cub
1967 Moto Guzzi V700

1981 dt 125 and 175 at it 05 Oct 2018 18:35 #4

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I'm not a fan of compression tests as meaningful... that said, 115 should be enough.

How does it run other than idle? Have you ridden it? If so, how far? (Could simply be "loaded up" from sitting... bottom end might have a lot of oil.)

Rare to have a reed issue.

You usually can't clean the carb enough times.

How is the air filter?

Exhaust could be plugged.

Pressure/vacuum test is always a good idea... some prefer to just replace the seals.

Posts with pictures and/or videos always get more responses... without them only you can see what you're looking at and experiencing.

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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

1981 dt 125 and 175 at it 06 Oct 2018 03:14 #5

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It was running with the air box removed no battery installed .It ran for 20 minutes the last time I ran it has sat for a long time .I would have thought running for that long would have gotten rid of any loading in the crankcase .how easy are the seals to install can it be done without removing the engine ? I have bought some seals for it .

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1981 dt 125 and 175 at it 06 Oct 2018 06:10 #6

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No need to remove engine for seals.

You have to ride not just "run" to clear out loaded up engine.

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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

1981 dt 125 and 175 at it 06 Oct 2018 06:13 #7

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Seals can be done with the motor in the bike.

How did you clean the carb? Not being facetious, but you really need to strip them down of everything, then soak in a quality cleaner (I prefer Berryman’s non-California formula), sometimes for several days. Seriously. Pilot jets are notoriously easy to have a clog.

If it runs and doesn’t rev well, check the pipe. Pull the silencer and see if it revs freely. I had a mouse nest in my 400 which stopped it from revving. Acted just like it was loaded up in the cranckcase.

If you can get it running, upload a video to youtube, then link it here. Hard to diagnose without actually hearing it run.

Good luck!
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No Good Story ever started with a Salad . . .

1981 dt 125 and 175 at it 06 Oct 2018 12:33 #8

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Ok will try sorry not the best video

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Last Edit: by speedbuff.

1981 dt 125 and 175 at it 06 Oct 2018 14:40 #9

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Video is fine! I think I'd start with cleaning the carb.

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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

1981 dt 125 and 175 at it 06 Oct 2018 16:26 #10

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Went through the carb again found a plugged choke passage in the bowl .At least I believe that's what that passage was? It doesn't look like that jet can be removed.drove it down the road after adjusting the shifter .runs great zips through all the gears and lots of power I think from what I remember
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