Honda C90 ZZ 1981 6v won't rev

cpradel13 · Post by **cpradel13** » Wed Dec 30, 2020 3:31 pm

Hi everybody,

I recently bought a Honda C90 ZZ 1981 6v that was unused since 1996...

The bike ran very well for few months after putting new oil, plug and few bit and bobs, but it decided to stop...

With the help of my neighbour which is amazing and very helpful, we put a new carburetor as it looked like it was flooding, set the timings correctly and ensure the battery was in top condition...

Now the bike runs but when we rev it, it wants to die...

Any body has any idea of what could be the problem, we are going a bit mad now, so any help will be greatly appreciated.

Thank you so much in advance!
Carlos

Post by **wightegi** » Wed Dec 30, 2020 4:10 pm

If you fitted a new carb it could be the main jet ,also check the choke is working not closed off.

Post by **Bogger** » Wed Dec 30, 2020 6:03 pm

Sort out the old carb. Refit that and see how it runs.

Bogger

cpradel13 · Post by **cpradel13** » Thu Dec 31, 2020 12:35 pm

Thank you Bogger!

We removed the old carb, cleaned it and inspect it:
1) We ensured the float valve needle was ok, which it was.
2) The float had no petrol inside (just in case it was a small hole).
3) Clean the main jet including the holes in the sides.
4) The needle is new and we set it in third position (so in the middle of the 5 possible positions).

The bike was not starting so we decided to buy a new carb.

Wightegi,

We checked the choke as well in the old and new carb and both working properly. We normally keep the choke open.

Sorry I forgot to mention, that few days before the bike decided to stop working... the bike did not rev either but I changed to reserve (in the fuel lever) and it worked fine, but after that it did not work any longer.

The new carb doesn't have reserve so we merged both fuel hose to do directly to the carb.

Thank you for your help guys!!!!

PS. May I ask, What you think it could be wrong with the main jet?

Post by **wightegi** » Thu Dec 31, 2020 12:53 pm

The chinese jets are not always the same size as genuine ones ,the numbers may be the same though. You can swap fuel tap from one carb to the other. Also check the bike with the fuel filler cap off ,it has a vent hole in it which can block up and shut down the fuel supply .

joefish · Post by **joefish** » Thu Dec 31, 2020 12:56 pm

try it with the fuel cap off

cpradel13 · Post by **cpradel13** » Thu Dec 31, 2020 2:30 pm

I checked the vent hole (very good point!!!) and it was clear.

I took fuel cap off then try to started and it was finding it difficult, I put the cap on and started first time, but I think it helped.

The bike runs very smooth in idle.

As soon as I rev it, the bike wants to die, I tried with the fuel tap off and it was the same. I went for a ride up and down the street but as soon as I put a bit of throttle the bike dies.

It must be something so simple that I am missing as the bike runs so smooth.

joefish · Post by **joefish** » Thu Dec 31, 2020 3:53 pm

is the battery well earthed

loadedtoad · Post by **loadedtoad** » Thu Dec 31, 2020 4:08 pm

Whats the fuel flow like from the tank ?
If its been stood since 1996 i suspect a bit of rust and crud has accumulated and may be reducing fuel flow.
This will give the same symptoms you have starts ,ticks over but not enough fuel to maintain the demand when coming onto the main jet.
Simple test is to try blowing back up the pipes to the tank (when empty) there should be very little resistance.
If you detect resistance and then it clears you blown the crud off the pick up tubes !

As you said it was ok then developed the problem on main tank, switched to reserve briefly ok then same problem returned
main tank tube blocked then reserve blocked ?.

Try running from a remote tank

Have some chewing gum to hand if you don't like the taste of petrol

cpradel13 · Post by **cpradel13** » Thu Dec 31, 2020 4:58 pm

Joefish,

I thought you had it... the earth cable was peel.. unfortunately I taped it and still does not rev...

Loadedtoad,

That is a fair point... there is a flow from both pipes, we did check that as well, but you could be right... and may no be enough...

Now both pipes go into one as the new carb doesn't have a reserve, so I could imagine the pressure of both pipes eliminated this issue but your point still make sense to me...

I fill up yesterday (I shouldn't by the look of it lol), the test to run it from a remote tank sound ideal. I'll ask my neighbour to see if he has an external tank to test it.

C90Club.co.uk

Honda C90 ZZ 1981 6v won't rev

Honda C90 ZZ 1981 6v won't rev

Re: Honda C90 ZZ 1981 6v won't rev

Re: Honda C90 ZZ 1981 6v won't rev

Re: Honda C90 ZZ 1981 6v won't rev

Re: Honda C90 ZZ 1981 6v won't rev

Re: Honda C90 ZZ 1981 6v won't rev

Re: Honda C90 ZZ 1981 6v won't rev

Re: Honda C90 ZZ 1981 6v won't rev

Re: Honda C90 ZZ 1981 6v won't rev

Re: Honda C90 ZZ 1981 6v won't rev