Fun with carbs.....

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8541Hawk
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Fun with carbs.....

Post by 8541Hawk » Wed May 16, 2018 2:52 pm

The latest project to roll through my little shop of horrors...... Trying to figure out what the PO had done to these poor carbs when they "jetted" them.
The bike ran terrible and after pulling the carbs and opening them up found some quite interesting, well more WTF, but trying to be nice...

The jetting I found was 42\50 for the pilots front & rear with unlabeled main jets, DJ needles and springs and the needles with the clip on the 4th clip (from the blunt end) with .100" spacer instead of the .5mm shim.

After swapping in stock springs and jets and plugging the extra lift hole the bike was extremely lean but runs fine on the "choke". Put the choke in and it acts like it runs out of fuel.
It is not the petcock as that is fine and I also swapped in my tank with no changes.

To me, that leave one thing left to cause this issue. It is also the reason for this post in case someone else has this issue.
So pull the carbs again and measure the float height. Both are out of spec causing the fuel level to be too low in the float bowl.
This will cause everything to run lean and is why the needles needed to be pulled so high.

This was the first time I have ever seen an issue with the floats on this bike. While I believe that someone used a cleaner that caused damage, that is just a guess.
It might be time for them to start acting up.

In any case, if you suddenly have issue with lean running, it might be time to check your float height and yes it is a bit of a @#$%^ to do :thumbup:
These are Ca carbs with the extra vacuum take off on the front carb.
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To err is human, to forgive is divine. Neither, however, is Marine Corps policy

mags@port
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Re: Fun with carbs.....

Post by mags@port » Wed May 16, 2018 5:23 pm

Fully understand, I have Honda CB750 k7, and has been messed about by previous owners and the like, mate refurbished them with new jets etc. But all the floats were out of sync, took days to get them semi right, but still not correct. However it's a great learning curve, but me thinks the floats are too old and holed, as it's still overflows with fuel. My best bet is to purchase series one carbs from pre 1976 and use these as parts and setting up is much easier and more reliable. Anyway rant over. Nice job
Break it, mend it, mod it, thrash it. If it's made then it's bettered by beer and goggles. Me bikes had Kwak ZZR, Suzuki TL1000s, Yama R1, Aprilia RSV. Now have VTR, Honda CB750 hand built brat/trickster, Yama XS750 and wee old Vespa.

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mdb
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Re: Fun with carbs.....

Post by mdb » Wed May 16, 2018 7:33 pm

What caused them to be low?
Are they holed or bent or is the plastic deformed where they contact the float valve?

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8541Hawk
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Re: Fun with carbs.....

Post by 8541Hawk » Wed May 16, 2018 7:52 pm

mdb wrote:
Wed May 16, 2018 7:33 pm
What caused them to be low?
Are they holed or bent or is the plastic deformed where they contact the float valve?
Somehow the slot in the float opened up. Being plastic you can not adjust it, so time for new floats.

What caused it is a bit of a mystery. My personal guess is when whatever shop or person installed the DJ kit put the floats in a heated ultrasonic tank and buggered them up.
Though that is just a guess. It also could have been a cleaning solvent that softened them.

Either way they were out by approx 3mm so it wasn't hard to see once I made a float gauge :wink:
To err is human, to forgive is divine. Neither, however, is Marine Corps policy

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mdb
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Re: Fun with carbs.....

Post by mdb » Wed May 16, 2018 8:22 pm

Perhaps E10 fuel is having a detrimental effect on the plastic floats.
Hoping it doesn't get introduced widely in the UK. 5% is bad enough.

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sirch345
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Re: Fun with carbs.....

Post by sirch345 » Fri May 18, 2018 8:16 pm

An interesting find Mike, well done in tracking it down :thumbup:

Thanks for sharing this with us, and for posting the photo's :D As you say it could certainly help someone out.

Chris.
A closed mouth gathers no foot. :thumbup:

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VTRDark
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Re: Fun with carbs.....

Post by VTRDark » Fri May 18, 2018 9:14 pm

Are you using a flow commaner MIke or are the nodules in the air bleeds for something else. I'm suprised we don't see more issues with floats on these bikes considering thier age. I'd like to know the internal air pressure differance inside the float from country to country. It's all these little subtle differances that people often forget that make up a finely tuned engine.
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