Author Topic: Carb work  (Read 1919 times)

Offline mattsz

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Carb work
« on: January 18, 2019, 02:02:47 PM »
I'm beginning to think about my carbs.

The PO says everything was running fine when the bike was stored, but I know the bowls weren't drained and the fuel dried out.  I opened one carb up, it doesn't look all that bad, but some attention is needed.  Here's a post with a couple photos attached, nothing too surprising there:

http://www.sohc.co.uk/index.php/topic,17461.msg150591.html#msg150591

And here's a couple more (click to zoom).  The float valve seat's o-ring is typical of the rest of them in this carb, dried out and cracking apart.  Obviously, all new o-rings needed:

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The float valve - showing signs of age, but I can't feel any texture or ridge at the seat with a fingernail, and the spring action is smooth.  Ok to try out, or should I just go right with new?

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Float bowl screws: 15 all the same, one different...  ::)

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The jets and brass bits all seems pretty clean, so I'm hoping I can reuse them.  Of course, things could be different in any of the other carbs!

Offline mattsz

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Re: Carb work
« Reply #1 on: January 18, 2019, 02:39:35 PM »
Regarding the choke lever action: there's a slight amount of play in the linkages between each carb.  With full choke, all the plates are closed, of course.  As I rotate the lever to reduce the choke, the #1 plate rotates right away - but there's a slight lag before the #2 plate begins to move.  Same with #3, and then #4, all "cascading" as I rotate the choke lever.  As a result, when the choke lever reaches the limit of its travel, the #1 plate is noticeably "more open" than the #4 plate, with 2 and 3 in the middle somewhere.  You can see that condition in this photo:

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Is this ok, or should I be looking at trying to adjust the linkages to equalize them?

My initial plan is to try to clean the carbs without separating them, and reassembling with new o-rings (definitely) and jet, float and seat parts (maybe) to see how it goes...

Offline taysidedragon

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Re: Carb work
« Reply #2 on: January 18, 2019, 03:00:15 PM »
Yeah, use the adjuster screws to equalise all 4 butterflies so they move together inline. Don't forget to tighten the locknuts afterwards. 😉
Gareth

1977 CB400F
1965 T100SS

Offline Nurse Julie

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Re: Carb work
« Reply #3 on: January 18, 2019, 03:21:58 PM »
Be careful with the threads on the float bowl screws, they strip for fun due to being so fine and old alloy. I got Graham to helicoil all 16 of mine when I refurbed my carbs.
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

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http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline mattsz

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Re: Carb work
« Reply #4 on: January 18, 2019, 03:26:03 PM »
Be careful with the threads on the float bowl screws, they strip for fun due to being so fine and old alloy. I got Graham to helicoil all 16 of mine when I refurbed my carbs.

Thanks for the warning!  But... assuming you're talking about removing them - how does one be careful with them?  Apply penetrating oil and hope it soaks in before trying to remove the screws?

Offline Nurse Julie

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Re: Carb work
« Reply #5 on: January 18, 2019, 03:35:05 PM »
You could try penetrating oil but experience has taught me that how ever careful you are removing the screws, its when you put them back in the problem occurs. You jut get that very 'loose' feeling on the end of the screwdriver but by then its too late. Remove the screw and the thread comes out with it  :'(
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline mattsz

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Re: Carb work
« Reply #6 on: January 18, 2019, 03:37:18 PM »
You could try penetrating oil but experience has taught me that how ever careful you are removing the screws, its when you put them back in the problem occurs. You jut get that very 'loose' feeling on the end of the screwdriver but by then its too late. Remove the screw and the thread comes out with it  :'(

Ah, ok... I wondered if it was an initial "removal" problem, where the screws simply bring the threads with them...

Offline Nurse Julie

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Re: Carb work
« Reply #7 on: January 18, 2019, 04:22:05 PM »
The removal of the screw is ok as you have the leaf spring pushing the bowl down, so there is little or no tension on the screw thread. When you re fit the bowls, you are having to push against the leaf spring, whilst trying to do the screws up. I always put 2 screws in at opposite corners of the bowl and just nip them up to take out some of the tension and then pop the other two screws in.
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline andut

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Re: Carb work
« Reply #8 on: January 18, 2019, 05:11:30 PM »
I'd recommend that you try using the original needle valves.  Just give the needles and the seats a bit of a polish and replace all of the o rings and then take some time to make sure that you get the float heights correct. 

Whilst you're in there, it's also worth checking that the jet sizes are std to get an idea if someone has been in there before you in which case you might want to think about checking needle heights.

Also check that both jets and the emulsion tubes are clear - make sure you check the cross drillings in the idle jets and the emulsion tubes. 

The choke flaps are simple to adjust to make sure that they're all fully open.

And as Julie mentioned, buy yourself a helicoil kit for the float bowl screws

Offline mattsz

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Re: Carb work
« Reply #9 on: January 18, 2019, 05:32:03 PM »
Thanks guys!

Is there a specific resource which would show me specifically, on these carbs, what parts are what and where they go... the jets and float valve and such I know about, but what about the different passages?  I'm looking to dismantle the carbs enough to replace the rubber bits and clean everything as best I can, but without separating them, which means carb cleaning spray and compressed air.  And probably some degreaser for the exteriors...

Offline Rob62

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Re: Carb work
« Reply #10 on: January 18, 2019, 06:16:45 PM »
Regarding the float bowl screws, sure use penetratong oil if they have been stood a while, but if you’ve already removed them once its too late for that. Make sure the screws are clean and if they look shot (threads or screw heads) replace them... Most importantly when you refit them just give them a gentle nip and avold overtightening. You could use a bit of copper grease on the threas to prevent any further damage but shouldn’t be necessary if you don’t overtightening. Good luck 😄

Offline mattsz

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Re: Carb work
« Reply #11 on: January 19, 2019, 07:48:41 PM »
I opened up the rest of the bowls today, no issues.  All screws were only just barely more than "finger tight."  I had a moment of panic when I removed one of the carb top covers, and felt the screw dragging and grinding a bit, but it turned out to be the split washer turning with the screw and scraping the top of the alloy cover.

All four bowl interiors looked about the same - dirty, but dry and powdery, not sticky or varnish-y.  Two of the float pins were a bit bunged up, though, and gave me a bit of trouble - one had been gripped with pliers at some point, and had some tooth gouges, which I polished out enough to be able to reinsert it easily.  The second had one end that was slightly bent, and so it didn't want to budge. But I freed it up and tried to straighten it out a bit, not sure if I really improved it, anyway it goes back in enough and I can remove it again.  Either way, all four floats pivot with no restriction.

All four have a 75 main jet, and a 40 pilot (slow?) jet, per spec.  Are there any other numbered items I should be on the lookout for?  The Honda Service Manual quotes a spec of "Carburetor Setting mark: 054-A".  I can't find any other reference to that.

It seems like most of the "tutorials" for carb disassembly include disconnecting them, which I was thinking of not doing initially.  I'm having a hard time deciphering what steps are for separating the carbs, and what steps are just for dismantling interior parts for cleaning, especially for the upper parts (everything in the float bowl is obvious).  Anyone have any suggestions for where I might go for clarification?  Are there multiple grooves in the needle?

Offline taysidedragon

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Re: Carb work
« Reply #12 on: January 20, 2019, 01:27:10 AM »
If you don't split the carbs you can still remove the throttle slides with the needles attached to them. The needle has several grooves. If I remember correctly the standard position is 3rd groove down for the circlip. It's clearly shown in Clymer or Haynes manual.
Gareth

1977 CB400F
1965 T100SS

Offline mattsz

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Re: Carb work
« Reply #13 on: January 20, 2019, 02:57:10 AM »
If you don't split the carbs you can still remove the throttle slides with the needles attached to them. The needle has several grooves. If I remember correctly the standard position is 3rd groove down for the circlip. It's clearly shown in Clymer or Haynes manual.

I have both.  Interesting that the Honda service manual doesn't mention the needle grooves...

Offline Clem2112

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Re: Carb work
« Reply #14 on: January 20, 2019, 09:51:39 AM »
Honda didnt want anyone messing with the mix !

 

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