1971 chrysler 20hp outboard acceleration issue

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Chryslerman123

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My chrysler 20hp outboard starts in one pull and runs excellent at idle. Plenty of blue smoke. When I give it full throttle, it does not accelerate at first. It sputters/jumps like it wants to accelerate but it doesn't. It sometimes takes 5-10 minutes before you can get it to go. Once you get it to run wide open It will run all day as long as you never let of the throttle. Once you let it back to idle, you restart the process. I have cleaned the carburetor twice and am 99% sure the carb is clear. It has good spark, good compression, fresh properly mixed gas, points set correctly, throttle roller set properly on stator plate, etc.
The only thing I have not replaced is the fuel pump diaphragm. It still has the original 1971 fuel pump but squeezing the primer bulb at any speed does nothing. I am stumped and stressed about this outboard. Driving me crazy!
Thanks for any help.
 

wickware

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I have a 1970, 35 HP Chrysler since 1984 and if I had related issues I would check the following.
  1. Carb adjustment to know it is not too rich to cause the blue smoke.
  2. Thermostat to know it is not cooling before it has warmed to operating temp.
  3. Points to know they are clean and adjusted properly at the correct point.
  4. Timing advance with a light to know it is advancing vs the known degrees.
  5. I still have original fuel diaphragm with no issues.Flexible vs tight and no cracks.
Nordin is the Chrysler specialist here and you might need to add his Name in your title to get attention.
Do you have any close distributor Pics to share? Mainly, the clean condition of the point?s contacts.
My major issue was contaminated points due to adding too much oil on the cam wics.

Good Luck!
 

Chryslerman123

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I have a 1970, 35 HP Chrysler since 1984 and if I had related issues I would check the following.
  1. Carb adjustment to know it is not too rich to cause the blue smoke.
  2. Thermostat to know it is not cooling before it has warmed to operating temp.
  3. Points to know they are clean and adjusted properly at the correct point.
  4. Timing advance with a light to know it is advancing vs the known degrees.
  5. I still have original fuel diaphragm with no issues.Flexible vs tight and no cracks.
Nordin is the Chrysler specialist here and you might need to add his Name in your title to get attention.
Do you have any close distributor Pics to share? Mainly, the clean condition of the point’s contacts.
My major issue was contaminated points due to adding too much oil on the cam wics.

Good Luck!


Carb only has an idle mixture screw, fixed high speed. It is a tillotson MD142B. My repair manual says it has a high speed screw, but I know for a fact it does not.

No thermostat on this outboard.

Not sure I can use a timing light on this outboard. No flywheel marks that I know know of.

Points are 25-30 years old but are new and clean. Adjusted to specification. I left the cam wicks dry because the manual says you need a special cam wick lube that I cannot find, but they could not have worn that fast.

Took off the fuel pump diaphragm it is still flexible but it has wrinkles in it. Going to go ahead and replace it. Squeezing the primer bulb has no effect at any speed.

Nordin
 

jerryjerry05

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Try resetting the float.
When the carb's off check the reeds.
​There can be a tiny piece of dirt in the carb passages that's blocking the flow???

The fuel recirc system might be clogged.
​On the stbd. side where the fuel pump is, is a dog bone shaped cover.
​It has a reed and a screen in there that can get clogged and might affect the running.

The inline fuel line connectors can go bad.
​They suck air.

Replace the fuel lines.
 

Chryslerman123

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Try resetting the float.
When the carb's off check the reeds.
​There can be a tiny piece of dirt in the carb passages that's blocking the flow???

The fuel recirc system might be clogged.
​On the stbd. side where the fuel pump is, is a dog bone shaped cover.
​It has a reed and a screen in there that can get clogged and might affect the running.

The inline fuel line connectors can go bad.
​They suck air.

Replace the fuel lines.


The float is adjusted correctly according to the manual, should I still adjust it?

Took the carb off and looked at the reeds. Cannot tell if they lay flat but they look intact.
I cranked the flywheel slowly by hand and one reed was hissing slightly and had little gas bubbles oozing out. Would the reed seal when cranking so slowly?
Also when running at idle you can feel air puffing out of the carburetor but no fuel is blowing out with it.

I will clean the carb again tomorrow

I don't think it has a fuel recirculation system but I will check.

I have no fuel line connectors. I have it run straight from the tank to the fuel pump with a primer bulb right in the middle. Fuel lines are new.

When I first cleaned the carb, the bowl was filthy! Had dirt that kind of resembled sand in the bowl up to 1/8 inch deep. Looks clean now though.
 
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Chryslerman123

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Also a trick i just learned is when it won't accelerate, pull the choke out about 1/8 inch and it will start jumping(vroom vroom vroom) surging? Gradually getting higher RPM and when it gets high enough you push the choke in and it will instantly take off full throttle and almost throw me out the back of the jon boat.
Then it will run fine wide open if you don't let off of the throttle.

If you pull the choke out by any more than 1/8 it will instantly die. The choke is like a kill switch.
 

Nordin

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If you have set the float level according to the factory manual that should be okey.

As you have removed the carb and cleaned it the throttle pickup point could have been changed.
Because you have to move the roller to take the carb away from the engine block.

Check the throttle pickup point, adjust it according to the manual.
The throttle butterfly should start to move as the roller intersect the mark at the throttle cam at timingplate.

I would also suggest you to change the fuel pump diaphragm if it has not been change for several years.
 

jerryjerry05

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Sounds like the tiny passages in the carb are clogged??
Pic of your carb and the side of the motor.
 

Chryslerman123

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If you have set the float level according to the factory manual that should be okey.

As you have removed the carb and cleaned it the throttle pickup point could have been changed.
Because you have to move the roller to take the carb away from the engine block.

Check the throttle pickup point, adjust it according to the manual.
The throttle butterfly should start to move as the roller intersect the mark at the throttle cam at timingplate.

I would also suggest you to change the fuel pump diaphragm if it has not been change for several years.

The throttle pickup point is only off of specification by about 1/8 to 3/16 inch. The throttle butterfly starts moving right before the roller gets to the mark. What I can't figure out is if you adjust the roller to have the mark dead center with the roller when the butterfly starts to open or if it should be even with the side of the roller (starboard side?) the manual is not that specific.

Could that slight misadjustment be enough to cause that much of a problem?

Ordered a new diaphragm waiting for it to arrive.
 

Nordin

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If the carb is clean, in your case the low RPM (idle circuit of the carb) circuit.
Yes the throttle pickup point can cause your problems as the spark advance and opening of the butterfly is important.
If it do not sync the acceleration will not work correct.
To much spark advance and less throttle or wise vers will affect the acceleration.

Make some tests with adjusting the roller starting touching the cam just before, at and just after the mark.
 

Chryslerman123

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If the carb is clean, in your case the low RPM (idle circuit of the carb) circuit.
Yes the throttle pickup point can cause your problems as the spark advance and opening of the butterfly is important.
If it do not sync the acceleration will not work correct.
To much spark advance and less throttle or wise vers will affect the acceleration.

Make some tests with adjusting the roller starting touching the cam just before, at and just after the mark.

Ok thanks I will readjust it and see, think I have bad reeds though.
 

Chryslerman123

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UPDATE: I did nothing except run it every day and it straightened up and has been running almost flawlessly except for missing at idle. It runs so good at half throttle and wide open that I can live with missing at idle.
It reversed problems, originally it idled perfect and would idle smooth all day long but it didnt want to go wide open. Now it runs top end perfect but runs bad at idle.
 

Nordin

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I would suggest you to clean out the carb once again.

There might be some small debris floating around in the carb making it run bad at idle sometimes and bad at WOT sometimes.
 

jerryjerry05

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Reset the low speed air/fuel screw.
Clean the carb one more time.

​It sounds like the gunk in the high speed jet cleared itself.
 

Isa4325

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Air bubbles in the fuel line before the diaphragm running back to the fuel tank. 1973 Chrysler Outboard 707HE 70HP Engine. Diaphragm issue?
 
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