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TOPIC: 78 DT400 Engine/ carb

78 DT400 Engine/ carb 05 Sep 2018 17:54 #1

  • mbakula
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I just started teardown of my 1978 DT400 that was in storage for 30 years. I have the top of the cylinder off and started trying to remove the carburetor but have run into an issue and that is I can not get to the lower right allen bolt to remove due to a line that is in the way. I have attached a pic of it and would appreciate assistance on what to do next. I don't have an allen wrench short enough. to get this last bolt out. I alos have the rubber sleeves loose.
Any assistance on my next steps would be greatly appreciated

Thanks, Mike
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78 DT400 Engine/ carb 05 Sep 2018 18:13 #2

  • RacerClam
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Remove the carb from the rubber mount first

Rich
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racerclam

78 DT400 Engine/ carb 06 Sep 2018 14:47 #3

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So are these hoses going to the carb that UIO can pull off as I do not see that they may be screwed into the carb.
Thanks, Mike

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78 DT400 Engine/ carb 06 Sep 2018 16:01 #4

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thanks, that worked. I have the cylinder ready to come out I think, But I have the piston frozen in place due to it just sitting. I have been pouring WD40 around the piston and I have lightly tapped the outsides with a rubber mallet. Are the any suggestions on my next step??
Any input at this time would be greatly appreciated

Thanks, Mike

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78 DT400 Engine/ carb 06 Sep 2018 16:13 #5

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there is a small gap at the bottom of the cylinder should I try it put a wedge in?
Mike

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78 DT400 Engine/ carb 06 Sep 2018 16:32 #6

  • MarkT
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mbakula wrote: there is a small gap at the bottom of the cylinder should I try it put a wedge in?
Mike


No. Not unless you want to almost certainly turn the engine into scrap.

Get some liquid wrench or better penetrating oil than WD40.

How far is the piston down the cylinder?

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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

78 DT400 Engine/ carb 06 Sep 2018 17:08 #7

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Here are a couple of pics. Not as must rust as expected. should I tap on the top of the piston as well?
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78 DT400 Engine/ carb 06 Sep 2018 18:27 #8

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Have you pulled off the ignition cover to see if the flywheel is not all rusty?

Often you can beat the piston down with a block of wood to break it free... yours is all the way down so that won't work.

What I would do is cut a block of wood just long enough so that with the block in the cylinder you can get the head on, but not all the way and be able to get the nuts on the head studs. Then slowly and evenly tighten the head studs which will force the down piston out of the cylinder a little at a time.

Once head is all the way down against the cylinder remove it and put a wood shim or folded rag on the block of wood to space the head back up a little again. Tighten nuts carefully and evenly again. Repeat until cylinder is off.

Don't force anything! Go slow. Keep head parallel to cylinder while tightening head down onto studs. Slow and steady. Patience.

An alternate to using the head would be to bolt a heavy steel bar across the head studs to press on the block of wood.
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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

78 DT400 Engine/ carb 06 Sep 2018 18:31 #9

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Whoa... wait a minute... first thing is to make sure you've loosened the cylinder nuts... I can see one down inside the circled hole. Make sure all are completely unthreaded before attempting to remove the cylinder.

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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

78 DT400 Engine/ carb 07 Sep 2018 11:44 #10

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Yeah, they all are still in but unbolted they lift out some with the socket but just can't grab them. I tried using a magnet but they must be stainless .
Mike

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