Johnson 55 1980 sneezing at idle

[mlaajanen]

Hi, I posted in a thread with subject needle valve , reposting with a better subject for everyones ease.

My engine runs perfect above idle but when started it takes just a short while before it starts to sneeze after 10-20 seconds when idle after a cold start .

Compression is about 140 PSI on both cylinders. I did try a different approach on the spark test, I increased the sparkplugs gap twice but no difference.

I should also mention that I have replaced the reeds with new ones from Chris Carson, glasfiber ones.

What about the fuelpump, could it be a faulty membrane causing leakage?

The strange thing is that it runs fine when for short while when cold, if it was a EFI engine then I would better understand that but on a a old 2-stroke!

Here is a link to Youtube when I am starting the engine, https://youtu.be/VZMVB0h1_I8

cheers

Michael

 

[mlaajanen]

Update: After running without load at higher RPM(2-3000 RPM) it does sneeze aswell then, but I have not noticed that under load but not sure now!

 

[ondarvr]

I'm not familiar with those reeds, but you frequently re-jet a little richer after installing non metal reeds. The other option is a dirty carb. Identify which cylinder it is by putting your hand over each carb while it's running, it should stop sneezing with your hand restricting the airflow.

 

[mlaajanen]

I'm not familiar with those reeds, but you frequently re-jet a little richer after installing non metal reeds. The other option is a dirty carb. Identify which cylinder it is by putting your hand over each carb while it's running, it should stop sneezing with your hand restricting the airflow.

Just a note, replacing the reed was my first attempt to troubleshoot the sneezing.

Do you mean I should choke one carb at the time?

 

[ondarvr]

Yes, choke them slightly one at a time.

 

[mlaajanen]

Hi again, It seams like a problem with the lower carb. I have disconnected the throttle and choke and when apply full choke on the lower the engine runs much better, but if I apply full choke to the upper carb the engine stalls.

I should add that before chocking and only using the hand like you suggested, the lower did spit out alot of fuel, the upper did not strangely just like the reeds was bad on the lower but they are new and closed nicely when I assembled them?

 

[ondarvr]

Sneezing can damage composite reeds, I'm not saying that's what it is, only that it's possible.

 

[mlaajanen]

Sneezing can damage composite reeds, I'm not saying that's what it is, only that it's possible.

Even though its been running very little? BTW, what is causing the sneezing, lack of fuel?

I have used compressed air to clean them and it seams like the idle yet is not blocked when using compressed air.

Could it be some other gasket that is causing it, why I ask that is due to the alcohol in the fuel many rubber gaskets get bad, I have used replaced the two inthe fuel tank for the same reason.

There is one for instance, number 7, http://www.iboats.com/Carburetor/dm/...iew_id.1533025. what does that one do?

 

[racerone]

That would be the nozzle gasket.---A critical gasket that ensures that fuel in bowl stays under/ at atmospheric pressure !----Did you remove high speed jets that are screwed into the bowls ?

 

[mlaajanen]

That would be the nozzle gasket.---A critical gasket that ensures that fuel in bowl stays under/ at atmospheric pressure !----Did you remove high speed jets that are screwed into the bowls ?

No I have not removed the jet that is in the bowl.

So how does the engine behave if that gasket is not tight?

 

[ondarvr]

It only takes one sneeze to damage them. The sneeze is from running lean

 

[ondarvr]

All jets need to be removed and everything made spotless.

 

[mlaajanen]

All jets need to be removed and everything made spotless.

Should I put the carb in diesel or something else over night?

How can the sneeze damage the reeds?

 

[ondarvr]

The sneeze is a backfire comming out of the intake, the reeds are taking all the pressure from combustion.


Carb cleaner.

 

[mlaajanen]

The reeds are fine after checked than, I have now removed the jets and put the carbs in diesel over the night or so, will then used CRC cleaner or WD40 with compressed air after that.

I assumeI dont have to remove the "blind plugs" or aluminium or?

The carbs look fantastic clean when looking on them, no dirt at all.

 

[racerone]

How is it possible for reed valves to ----"take all the pressure from combustion " on one of these motors ?

 

[juno pierrat]

The core plug (blind plug) on top of carb hides several small hole that are part of the idle circuit, if clogged would cause lean condition at idle, may cause sneezing.

 

[mlaajanen]

The core plug (blind plug) on top of carb hides several small hole that are part of the idle circuit, if clogged would cause lean condition at idle, may cause sneezing.

Okey, thats the big one. Is it difficult install new ones?

DId you see my earlier posting that the engine actually sneezes at higher RPM aswell atleast when not loaded.

BTW, I did post a video, was it possible to see it and understand how it sounds?

 

[ondarvr]

How is it possible for reed valves to ----"take all the pressure from combustion " on one of these motors ?

Because on a lean sneeze the combustion takes place in the crankcase, which is in direct contact with the read valves.

That's why Boyesen recommends going richer on the low speed jetting when using their carbon reeds.

 

[juno pierrat]

don't know any thing about reed valves, but had a lean sneeze once that blew core plug off my top carb, never did find it.
while carbs are off, gently poke a small hole in plug and pry it off, poke small wire through holes inside, new plugs come in carb kits or separately ( i like spares), put in place dome up, put a 3/8in. extension on it, give one good tap to cave in dome, and you set. do you have a service manual for you engine yet?