SOHC.co.uk Forums > CB350/400

Gummed up Carbs and modern fuel

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florence:
My carbs were stripped and cleaned, set up and balanced in 1995 and they have been running well ever since.  I think any changes in fuel must be negligable because I have not had the problems you describe.  I am sure the variable here is your carbs which you are addressing. 

If a bike needs to be laid up it is good to drain the carbs completely.  When the big end failed on my CB350K in 1995 I took the carbs off, drained them and they lived in a box for fifteen years.  Recently, I rebuilt the engine; I simply rinsed out the carbs with petrol, put them on the bike and it fired up after about four kicks and runs fine.

Yoshi823:
As on the 500/550 fours i'm sure that the 'O' rings that seal the inlet rubbers to the cylinder head...#108 on the fiche...
http://www.cmsnl.com/honda-cb400f-england_model14639/partslist/E01-1.html

...do perish & cause all sorts of headaches for people trying to find the problems with fuelling.

exvalvesetdabbler:
Since my last post I have has 3/4 of a success.

After making sure that the tool tray cover was well clear of the air inlet last weekend it seemed to run a little better. This evening I put some new plugs in and went for about a 10 mile jolly around town (mix of urban and dual carriageway).  I now have 3 very clean plugs and one completely black one . At least this gives me something to work with now. It certainly  starts to pulls well in the higher gears once the tacho gets above 6500. At 8500 its willing to go more but I'm not at this point.

I'm going to whip the carbs off again and see where the differences lie. I'm convinced that a bit of crud has been missed somewhere or the float tang isn't hitting the needle square on.  I'm not sure how critical that is other than if it's too far out the float drops too far and the needle drops too far and gets stuck.

So the plan for this weekend,

Change coil and plug cap on #3 pot (leads won't reach to swap 2+3 over)
bung in the best of the float valves from my junk box in #3 carb (just looking for a difference to what I have now)
check small passage ways on #3 carb
valve clearances on #3
leakdown test if I have time.

This leaves the question of whether the pilot jet in #3 is the wrong size so i'll swap it with one from another carb to see if the problem moves with it.

Since all of the float valves and jets were new genuine Honda a couple of years ago, I'm finding it hard to believe that they would be the wrong size or duff.

I'm using D8EA plugs at the moment however I remember dealers putting D8RESL at one time.
I know that the R means it's got a resistor in it but I'm not sure what the other differences are. These D8EA's must be a good 15 years old but new plugs shouldn't go off in storage should they?

What plugs are you guys using?

Regards
Dave.

PatM:
Dave

A thought just occured to me- it wouldnt answer the problem completely- is your seat clear of the air intack? are the rubbers in the seat-base stilll servicable? if you take the air cleaner box cover off and theres a heap of difference- that would  explain something?

For me today

Points
replacemnt speedo

..then think of somewhere to ride it to.. :D

Happy tinkering!


PatM

K2-K6:
Mostly all heat range 8 for NGK plugs on Hondas of this era that I've worked with as it covers most things you use it for.

Very few times but 7s for concentrated low ambient temp running and maybe short journeys as it allows you to get off choke sooner and still run cleanly.

And 9s for concentrated high speed / high temp running to prevent the plug tip from going overtemp and possibly causing pinking.

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