1978 CB750A, bringing it back..

amc49

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If the ethanol in fuel answer was yes then the idle jet hole size is such that they tend to clog when the ethanol makes the fuel dry up faster. Bike then won't idle, no fuel. Those holes are like .013" or so in size and they can still have fuel in them even if carb is drained, capillary action keeps them with a drop of fuel covering the opening. It then dries and clogs the hole.
 

Medyo Bastos

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Agreed; take the the jets out out and blow carb cleaner through them. From the inside out works better for me when cleaning jets. I prefer the walmart brand supertech carb cleaner the best. A little bit goes a long way.


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wingedwheel

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I am also looking for the countershaft oil seal. The part # is 91203-393-003. It lists as a 32x64x13. I found a 32x64x10 that I replaced it with but I’m seeing oil leaking out when I run the engine and I’m highly suspect of that being the culprit. Anyone know where to possibly get this NLA seal?
 

amc49

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That seal may be complicated by having to match with another one if like the DOHC is, the two fit together then create an oil chamber that supplies the big output bearing with oil. The illustrated parts list seems to show one like that.

If your distance collar has wear on it the seal being new still cures nothing. The collar as well can leak on the ID where the seal has no impact.
 

wingedwheel

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I don’t think it’s different than the SOHC, just a different size? In any case is there an odd parts supplier that I might get lucky with?
 

amc49

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I for one would not know.

https://www.partzilla.com/catalog/h...750a-a-750-hondamatic/top-clutch-countershaft

Pic there of '78 automatic shows both seals, parts 28 and 30. They work as a pair. On the DOHC it was always a problem, one time you would get the entire two piece affair and other times they only sent the outer part of it. On the DOHC they snap together to make one part. Can't say on the automatic.

There is also a part 29 seal that is not picced and who knows what that one does? Your X13 and X10 thing is likely a thickness of seal issue, one is 1/8" thicker than the other likely.
 
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wingedwheel

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Yes AMC49 that is the only difference. I totally missed that inner on the diagram(I think) and I see it is still available. I wisely ordered two of the outer I found I think the issue is I have to split the case to get the inner out.
 

amc49

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Clarity of the issue is not helped out by the way Honda does things there. You wonder if the different seals are because they changed something there and you just need one of the right one. I had fits with DOHC until I figured out what they were doing there, it helped to have one of the seals fall apart in my hands too, to be able to recognize the two parts separately. While the DOHC is not an automatic SOHC, Honda tends to make changes that sometimes show across different product lines, it being part of the evolution of things.
 

wingedwheel

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Yes I had a parts guy tell me that this bike uses parts and pieces from other models. Almost like they had something they wanted to try so why not just throw it on this odd man out machine. In hindsight I do remember looking at that seal and I actually have it in the drawer I was just reluctant to split that case when everything was apart. Now it looks like I have no choice. Outsmarted myself once again.
 
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