carb cleaning

[F5 Dave]

Hmm, they did a compression test presumably? Not saying they are wrong, but I'm naturally suspicious, sometimes it is easy to hone down on a suspected cause (which I might well be doing now) but if it is fouling plugs I wonder how much blowby would be produced as a result?

[rwh]

Hmm, they did a compression test presumably?

Not yet; they've only had it for a brief check. It goes back for real on Monday.

Not saying they are wrong, but I'm naturally suspicious, sometimes it is easy to hone down on a suspected cause (which I might well be doing now) but if it is fouling plugs I wonder how much blowby would be produced as a result?

I'm obviously inexperienced in this area, but doesn't blowby mean that more is getting past the rings than it should, implying that there's something wrong with the rings, bores or pistons? Anything that's causing plugs to foul (incorrect mixture or lack of spark is it, right?) couldn't cause that, could it? Though perhaps the other way round - lack of compression could cause bad combustion?

Richard

[F5 Dave]

Yeah it could, but that would tend to indicate that 2 cylinders had ring problems & the others didn't. Comp test should show that up. Interestingly my RF showed better compression on the cylinders that were fouling, but I think that is irrelevant.

If there was oil getting on the rings then it would leave an oily residue & blow blue smoke. If it blows a bit of black smoke when revved hard then that can be normal or tending rich.

All I'm saying is if you have the bike I'd swap the carb plastic slides & emulsion tubes to the good sides try the bike for a couple of days to see what happens to the plugs (swap plugs as well would be good). If it still fouls then forget what I've said & entrust in the shop. Also look to see if the plastic slides (runners that the slides slide on) are worn near the bottom.

I'd also check the float valves are ok if haven't done already. (Can't remember rest of thread)

[tri boy]

Has anyone checked the spark plug cap resistance value?
Quite a lot of plug fouling/cylinder "drop out" can be traced back to this fault.
Plug cap resistance should be around 5-8k ohms.
Quite a few suzi's were diagnosed with oil fouling leading to top end overhauls, when the real fault was a $20 plug cap.
Worth probing with a multi meter.

[F5 Dave]

Std they are ~12kohm, but this is still ok, when they fault they are about 40-100k. Of course they are double coil so measuring from cap to cap will net about 40k from saggy memory. Take them off if in doubt.

I found one on mine like this & thought ahhh! But didn’t help, just a red herring that wasn’t helping the cause either.

[SILVER SUZI]

I may be a bit late with this. I have an 89 Gixxer 750 (it has the same model carbs) and had a similar problem. The cause was a very small tear in the diaphram. It requires replacing the diaphram. I'm waiting on a price for new as this has happened before so I'm guessing four new ones is the way to go. It's easy to check, you don't need the carbs out, just the tank off and take the tops off the carbs. Take out the diaphrams and work your way round them streching them slightly so any holes show up. It's quite amazing how similar your symtoms sound, like a miss that you can't put your finger on but you know it's there.
Hope this comes in time and hope it helps.