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Dt3 manifold insulator

12 Feb 2020 20:14
Dion
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Dt3 manifold insulator #1
Hello,

Working on a dt3, and was running fine until the other day. Initially, I was having some power loss, now the engine doesn't want to stay running. I think I might have found the problem or at least part of it.

I attached a photo, this part is called the manifold insulator? Sits between the carburetor and the cylinder intake joint. It's about .2" thick. First, I don't think it's sitting flush and air is escaping. Also the diameters of the two parts do not match up.

The insulator inner diameter measures around 1.36" or roughly 34.5mm. The carburetor inner diameter is 27mm or about 1.06", and the o-ring ID is about 1.3125" or roughly 33.3mm. So the insulator is not fitting over the o-ring, and that doesn't seem right to me.

Other insulator's on ebay I'm finding for a dt3 seem to have the same dimensions. Feeling stuck at the moment. I was thinking about attempting to make my own part. Appreciate any help I can get on this.

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12 Feb 2020 21:56 13 Feb 2020 02:10 by RT325.
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Dt3 manifold insulator #2
Welcome from NZ down under, any further under & we'd fall off!!. I hate to start the ball tolling by saying i don't think that's the problem or A problem as looking at the pics i'd guess some of the Oring is contacting the insulating block. also--if it's been running ok up until recently then i can't see 'that part' turning faulty overnight. Video would be good if possible or a bit more info on describing as best you can exactly how it plays up. Thanks for the detailed measurements on the spacer though. I'm wondering if they run the same spacing block on the 250 & 360 [yamaha saving money lol] as by memory the 360 carb is 32mm. Actually i'm running one on my DT1 but that's another story. Now you have the carb off, have a good look through it & replace the tiny Oring at the base of the needle jet where it sits into the bowl as has to seal 100% so no fuel bypasses the main jet [side mounted main jet]. At least make sure it's got good tension when you slide the bowl on if you don't have a new one. Problem though sounds more like points closed right up over time & need a scratch & opening to about 15 [no more]. If the carb tiny Oring was faulty it'd act like its drowning on full throttle, & your description doesn't sound like that. See how ya go. Oh, & exhaust baffle & spark arrestor down in the tail if original will affect top end plenty if really clogged up, but doesn't sound like your problem. good luck [now i've confused things].

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13 Feb 2020 01:01
Gr8uncleal
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Dt3 manifold insulator #3
Prepared to be shot down in flames here, but I'm not sure the part that you show is an original Yamaha fitment. My RT2 doesn't have one and it isn't shown in the Yamaha parts manual.

If the 'o' ring is in good shape, bolt the carb back on without the gasket that you show and see if that makes any difference. If the 'o' ring is jiggerered, then you can still get new ones.

As RT325 said, your issue might lie elsewhere.

Good luck.

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13 Feb 2020 01:14 13 Feb 2020 01:14 by Mauser.
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Dt3 manifold insulator #4

Gr8uncleal wrote: Prepared to be shot down in flames here, but I'm not sure the part that you show is an original Yamaha fitment. My RT2 doesn't have one and it isn't shown in the Yamaha parts manual.

If the 'o' ring is in good shape, bolt the carb back on without the gasket that you show and see if that makes any difference. If the 'o' ring is jiggerered, then you can still get new ones.

As RT325 said, your issue might lie elsewhere.

Good luck.

I agree why would anyone have two sealing faces? the "O" ring should provide a perfect seal between the carb and the mating surface, you should be able to look across the carb face and see the "O" ring sticking up slightly, if it's not then you needs a new one......

Yamaha RT2 360 ~ Honda XR650R ~ Yamaha DT175MX ~ Kawasaki KH400

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13 Feb 2020 02:14
RT325
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Dt3 manifold insulator #5
Gr8uncleal, that shoots my 360 spacer theory down haha. Good to learn something new every day.

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13 Feb 2020 03:27
RT325
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Dt3 manifold insulator #6
Just looking on Partzilla at DT2 & DT3 then RT2 & RT3 & can't see the spacer shown on either lol. I give up--going to bed. Link there to start from www.partzilla.com/catalog/yamaha/motorcy...linder-head-cylinder

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13 Feb 2020 04:40
mike8162
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Dt3 manifold insulator #7
My DT3 has the insulator. There is a gasket between the manifold and insulator and the o ring seals the carb side. It is shown in the air cleaner diagram. I presume it is to insulate the carb from the heat of the cylinder. I'm guessing that these bikes being air cooled can generate enough heat to cause problems in the carb.
Cheers
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13 Feb 2020 05:21
MarkT
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Dt3 manifold insulator #8

mike8162 wrote: My DT3 has the insulator. There is a gasket between the manifold and insulator and the o ring seals the carb side. It is shown in the air cleaner diagram. I presume it is to insulate the carb from the heat of the cylinder. I'm guessing that these bikes being air cooled can generate enough heat to cause problems in the carb.
Cheers


You are correct that it's to insulate the carb from engine heat. Air and water cooled engines... even those in cars and trucks... almost always had a phenolic spacer or sometimes a very thick gasket to insulate the carb from the heat of the engine transferring through the manifold. Rubber boot manifolds in later years provided the insulation.

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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13 Feb 2020 05:37
Gr8uncleal
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Dt3 manifold insulator #9
Yes, with you now.

Silly me for thinking that it would be shown on the carb or cylinder parts page!. :Ugh

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13 Feb 2020 13:00
Dion
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Dt3 manifold insulator #10
Mike do you recall the insulator sitting over the o ring? I'm wondering if I have the wrong size part here, or perhaps the carburetor ID needs to be wider than 27mm. I'm missing that gasket! So that might help some of the issue here.

Appreciate all of your thoughts on this. RT325, thanks for tips on power loss.

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