Alright you motor heads.

[Animotion]

I want to see if any of you engine guys have any logical suggestions past what I have already done.

I have a 1973 Honda z50A. when I first got it, it was smoking like a bandit and fouling plugs. Wet fouling and the compression was 60 psi when its suppose to be 170 psi +- 10 psi.

What I have found/done.

1. The intake valve was too tight where the valve was always open. I properly adjusted the valves and brought the psi 90 psi, still 80 psi too low and is now dry fouling plugs instead of wet fouling. checked cam timing and ignition timing, both OK. Adjusted carb. Has a strong spark.

2. Replaced piston and rings, went to 100 psi. still dry fouling.

3. Replaced cylinder with a stock honed cylinder. Also replaced piston and rings a second time. Replaced valves and lapped them, replaced springs and seals. guides look OK. psi is now 130 psi. Still dry fouling but not smoking.

4. Tried gong to hotter plugs to help burn off the carbon accumulating on the plugs, each one bringing an additional 70 to 100 degrease increase in plug tip temp.
NGK C6HSA (stock) then NGK CR5HSA (hotter) then NGK CR4HSA (hotter yet)
Still dry fouling.

It runs with a lot of power until the plug fouls and quits.

Here are some things that I know will affect plug tip temp and can cause fouling.

A. Low engine speed, excessive idling.
B. Too retarded ignition.
C. Bad piston or rings.
D. Bad cylinder.
E. Bad leaky valves.
F. Bad guides. (letting oil go past them)
G. Too cold plug.
H. Loose plug.
I. Low compression ratio.
J. weak spark.

Anyone out there with any ideas? please read my whole post before responding.

Thanks.
Animotion

 

[QuickBriggs]

You said NOTHING about cleaning the carb. I would pull the carb apart and give a good soaking, then first thing adjust the float height, then do a base re-adjustment with the carb needles, and fine tune from there!

Youll be surprised by what a good, through carb clean can do!!

Yes, would also consider the valve guides. Do they look like ther leaking?

 

[Animotion]

I forgot to mention that one of the first things I did was clean the carb and adjust it.
Thanks for the reply anyway.
Animotion.

 

[jesse8931]

have you replaced the points and condesner ? and have you did the timming ?

 

[Animotion]

I did the cam and ignition timing. it gets a strong spark so I didn't change the points or condenser.
Its kinda weird because it idles and accelerates very very well until the plug fouls after about 3-4 days of riding.

Also, is it normal for the compression to be 40 psi low until it breaks in?
it should be 170 psi but am getting 130 psi. 70 psi better than where I started but sill 40 psi below spec.

 

[kbs8ball]

Something is up with the compression no doubt. Plugs will foul if running too RICH as well

 

[billy boy]

im not a honda expert but it sounds like a two stroke motor what are you mixing the oil to gas ratio at is it too rich there or perhaps too lean

 

[Darvin Jahnke]

Possibly too much fuel or restricted air supply. Is the jetting correct for your elevation? Is the air filter clean? You've probably checked these things but just suggestions. The hydrogen in the fuel burns first and uses what oxy. it needs. Any leftover oxy. is used to burn the carbon. If there is not enough oxy. to burn all the carbon it deposits itself on the plug,valves ,combustion chamber etc.

 

[Animotion]

The filter is new. The jetting is in the stock position, second from the top. Putting it on the top position will put it at its leanest setting. I know that a rich condition will cause fouling so I should move it to the top to see if it helps.

This is so strange because the thing has a lot of get up and go the way I have it set up. No hesitation or faultering. I will post my results.

Animotion

 

[george3]

little honda 50 4 stroker? valve springs week? intake or exaust valve not seating properly carbon build up under valve is the valves seating 100 %. valve springs week

 

[spacecoast]

You say it runs great then dies? I'm curious if it's getting warm and then your valves are seizing or not closing all the way, causing no compression at that point and fouling your plug. It's a puzzle, have you tried a honda forum? This could be a known issue that people could answer for you. As for the basics, they have been listed here all ready. Go back to your stock heat range on your plug, now that you have changed piston, rings, and cylinder. Remember this, running lean increases your temps. But your plug would indicate that. Can you put a pic of the plug up?

 

[george3]

float issue? if not the valve springs. is the gas tank clean? no rust no dirt? or the valve under the tank just nit picking. gas can was dirty. I think valve springs. or carb. you sure the points-condencer is good? error on any timing weak valve springs????

 

[george3]

check the muffler see if it is all gumed up.

 

[george3]

use correct plug not hotter. check the jets or float damaged