fuel problem with 1 carburettor

Issues with balancing, jets, filters, etc
Pete
Posts: 16
Joined: 05 Sep 2017, 01:24
Location: Perth, Western Australia

fuel problem with 1 carburettor

Post by Pete »

Hi all,

I think that I have a problem with the fuel mix on carby #4. I checked the plugs last weekend to find plugs 1 to 3 a nice grey colour but number 4 is black and sooty, not oily. This tells me that #4 is putting in too much fuel. The mixture screws are all the same (3 turns)

Any tips on what to look for?

Cheers,

Pete
Current Stable: 1991 Kawasaki Zephyr 750 C1, 1972 BSA Thunderbolt 650
==============================================================
Departed: 1978 Yamaha 250 Special, 1980 Yamaha SR 500 Single, 1984 Honda VF1000F, 1982 Yamaha XJ650 Turbo
hugojose
Posts: 161
Joined: 05 Sep 2017, 00:43

Re: fuel problem with 1 carburettor

Post by hugojose »

Assuming your don't have some build-up in the air passagages.......the fuel level controlled by the float also determines how rich or lean. Fuel level could be checked by clear tubing with carbs in bike.

,,,,,,,,,,
Freddy
Posts: 695
Joined: 06 Sep 2017, 11:06
Location: Sydney Australia

Re: fuel problem with 1 carburettor

Post by Freddy »

Also check all the 'choke' slides and the choke 'valves' are fully free and returning to completely closed. Gunk can build up around the mechanism and prevent everything from working properly.

Personally, if you have a doubt, pull em out and give ever thing a good service. My guess is its probably been ages, perhaps never, since they were done, so a good service won't hurt. Can't speak for other models, but getting the carbies in and out of a 750 is actually a very easy job if you know the 'methodology'.
Pete
Posts: 16
Joined: 05 Sep 2017, 01:24
Location: Perth, Western Australia

Re: fuel problem with 1 carburettor

Post by Pete »

Yep, I’ll take them out tomorrow and give them all a good clean to see what is going on.

Thanks for your advice.

Cheers,

Pete
Current Stable: 1991 Kawasaki Zephyr 750 C1, 1972 BSA Thunderbolt 650
==============================================================
Departed: 1978 Yamaha 250 Special, 1980 Yamaha SR 500 Single, 1984 Honda VF1000F, 1982 Yamaha XJ650 Turbo
Freddy
Posts: 695
Joined: 06 Sep 2017, 11:06
Location: Sydney Australia

Re: fuel problem with 1 carburettor

Post by Freddy »

Pete wrote:Yep, I’ll take them out tomorrow and give them all a good clean to see what is going on.

Thanks for your advice.

Cheers,

Pete
Give it a compression test if you have (or can borrow) the gear. I know you said it look sooty not oily, but it wouldn't hurt to have an insight into the mechanical condition. May just tell you everything seems solid, which is still valuable to know as there sort of things are often a process of elimination.

Don't be tempted to replace anything in the carbies with non genuine parts. The bowl gasket and idle mixture screw o-ring are the only thing I'd ever use out of non genuine 'overhaul' kits. There is a tiny o-ring in the bottom of fuel mixture screw, if you not familiar with the setup. Easy to loose. The idle adjust screw arrangement from outside in is screw - spring - tiny flat washer - tiny o-ring.
Pete
Posts: 16
Joined: 05 Sep 2017, 01:24
Location: Perth, Western Australia

Re: fuel problem with 1 carburettor

Post by Pete »

A quick update on my progress today. I removed the carbs and took off the bowls to find that the level on number 4 was around 10mm. This explains why the bike was running rich on #4. The others were all slightly off as well.

I reset all the levels to 16mm and put them back on the bike and everything was fine for about one minute then it started missing on #4. I put a clear tube on #4 to check the level and it was flooding with the level up to the inlet port. I then lowered the tube to drain it down to the lip of the bowl and it started to idle nicely again.

A few tests indicated that the #4 carb was continually flooding. It would run well until the fuel level increased at which point #4 would start missing. If I drained the fuel back down to the bowl join it would start behaving again.

I swapped out the problem float valve with an old spare and #4 seems to be behaving now.

I’m going to get a new set of float valves and recheck the levels again. Hopefully this will sort out the issues.

I’ll report back when I have replaced the float valves.
Current Stable: 1991 Kawasaki Zephyr 750 C1, 1972 BSA Thunderbolt 650
==============================================================
Departed: 1978 Yamaha 250 Special, 1980 Yamaha SR 500 Single, 1984 Honda VF1000F, 1982 Yamaha XJ650 Turbo
Freddy
Posts: 695
Joined: 06 Sep 2017, 11:06
Location: Sydney Australia

Re: fuel problem with 1 carburettor

Post by Freddy »

Pete wrote:A quick update on my progress today. I removed the carbs and took off the bowls to find that the level on number 4 was around 10mm. This explains why the bike was running rich on #4. The others were all slightly off as well.

I reset all the levels to 16mm and put them back on the bike and everything was fine for about one minute then it started missing on #4. I put a clear tube on #4 to check the level and it was flooding with the level up to the inlet port. I then lowered the tube to drain it down to the lip of the bowl and it started to idle nicely again.

A few tests indicated that the #4 carb was continually flooding. It would run well until the fuel level increased at which point #4 would start missing. If I drained the fuel back down to the bowl join it would start behaving again.

I swapped out the problem float valve with an old spare and #4 seems to be behaving now.

I’m going to get a new set of float valves and recheck the levels again. Hopefully this will sort out the issues.

I’ll report back when I have replaced the float valves.
What your describing seems to be consistent with problems other people have experienced over the past when using non genuine float valves. Genuine float valves are not cheap, but compared to the world of pain cheap aftermarket ones seem to be able to generate, not expensive really.
Pete
Posts: 16
Joined: 05 Sep 2017, 01:24
Location: Perth, Western Australia

Re: fuel problem with 1 carburettor

Post by Pete »

A final update (hopefully)....

The bike is running nicely and the plugs look good so thanks to everyone for the advice. I've ordered a new set of valves and pilot screws (with spring/washer/o-ring) just to be sure. All genuine kwaka bits.

Off to the local motorcycle festival in Collie this weekend (https://www.yorkmotorcyclefestival.com.au). It's about a 1.5 hour ride each way.

Any other Zephyrs going?. I went the year before last (it was cancelled) and didn't spot any others.

Cheers,

Pete.
Current Stable: 1991 Kawasaki Zephyr 750 C1, 1972 BSA Thunderbolt 650
==============================================================
Departed: 1978 Yamaha 250 Special, 1980 Yamaha SR 500 Single, 1984 Honda VF1000F, 1982 Yamaha XJ650 Turbo
hugojose
Posts: 161
Joined: 05 Sep 2017, 00:43

Re: fuel problem with 1 carburettor

Post by hugojose »

Pete wrote: All genuine kwaka bits.
You mean genuine Keihin bits specified by Kawi....

Sorry, could not help, but am glad you got it sorted out.
Pete
Posts: 16
Joined: 05 Sep 2017, 01:24
Location: Perth, Western Australia

Re: fuel problem with 1 carburettor

Post by Pete »

Yep, genuine parts to fit the carby. I was thinking I'd also replace the mixture screws (inc o-ring etc) and the float boat seal.

I was a bit shocked with the price though. The local dealer quoted $60.00 AUD per float valve. I'm thinking that I will shop around a bit.

Cheers,

Pete.
Current Stable: 1991 Kawasaki Zephyr 750 C1, 1972 BSA Thunderbolt 650
==============================================================
Departed: 1978 Yamaha 250 Special, 1980 Yamaha SR 500 Single, 1984 Honda VF1000F, 1982 Yamaha XJ650 Turbo
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