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1980 MX175 Compression reading

  • turdferguson
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1980 MX175 Compression reading was created by turdferguson

Hi y’all, what kind of compression should I be seeing on a1980 MX175?  Can get the bike to run and idle after a couple kicks but after about 3-4 minutes it dies and won’t start again.  Took a reading this morning and got about 130.  Plug had some oil on it. Stock carb (rebuilt) 130 main jet, boysen reeds, E3 plug, all seals replaced.  Blowing a lot of smoke, running premix until I get the tank and oil pump hooked up.  Ran last night, took the reading this morning.  What’s everyone think?  Let me know if you need more info on the config!
Last edit: 02 Oct 2022 18:00 by turdferguson.
02 Oct 2022 17:50 #1

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Replied by MarkT on topic 1980 MX175 Compression reading

How does it run when you ride it? Or are you saying all it does is idle?

It sounds like it's just loaded up and needs to be ridden.
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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02 Oct 2022 21:19 #2

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Replied by RT325 on topic 1980 MX175 Compression reading

Compression sounds good. Might've just oiled the plug but wet oil should wash & dry off. Burnt on oil different story as shorts out. try a 'clean' dry plug & take the revs up & give it a good clear out on & off high revs if it will. Possible 'but unlikely' that it's pushed out the right side seal & let trans oil in bto the crankcase as that lets it smoke beyond description but would hardly run & be all hollow in the power--gaspy & underpowered & need full song to run--if at all. Left seal out behind the mag would just go all hollow but not smoke more than usual.
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02 Oct 2022 21:24 #3

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Replied by turdferguson on topic 1980 MX175 Compression reading

That’s encouraging but the Bike it still in the get it running stage before I move onto get it ripping. Wish the video upload feature was working here, can I email it you?!?! 

thanks!
02 Oct 2022 23:22 #4

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Replied by AirborneSilva on topic 1980 MX175 Compression reading

You can upload video to youtube then post here.
1976 DT400C
1981 DT175H
1972 DT2 250
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03 Oct 2022 03:00 #5

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Replied by RT325 on topic 1980 MX175 Compression reading

Not sure my email would have the grunt to download a live video without fiber internet where i am. Youtube seems the way to go then just link it to the site. I've managed to handle that myself a few times--impressed myself haha.
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03 Oct 2022 03:44 #6

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Replied by turdferguson on topic 1980 MX175 Compression reading

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Last edit: 03 Oct 2022 06:05 by MarkT. Reason: Insert video
03 Oct 2022 04:57 #7

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Replied by Tom P on topic 1980 MX175 Compression reading

That sure is smoking a lot, I'll bet you have a bad right side crank seal, and it's sucking in transmission oil. Same thing happened to me when I was first fixing mine up.
03 Oct 2022 07:50 #8

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Replied by Ht1kid on topic 1980 MX175 Compression reading

What premix ratio and kind of oil are you using?
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03 Oct 2022 08:01 #9

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Replied by turdferguson on topic 1980 MX175 Compression reading

I replaced all of the seals.  Hoping it’s just residual oil in the case.  I soaked it big time with PB several times over the rebuild so I’m sure there’s that and the oil that leaked in there prior to the rebuild!  

Running a HEAVY premix for the first start.  Using Lucas 2-cycle.  Will be hooking up the factory oiling system today. 
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03 Oct 2022 08:50 #10

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