How to adjust/tune-up? (Chrysler 55HP)

[ac439]

Hi...Now I have the motor running, I'd to tune it up.

IDLE Mixture: At first, I put the idle mixture screw to 1 1/4 turn CCW from fully seated position. The idling is rough and I have to put it at 3/4 turn CCW from from fully seated position. Is this setting running richer than 1 1/4 turns setting?

IDLE Speed adj: There is a screw that governs how much forward my shifting lever can put when the gear box is disengaged. I know this can change the idle when the throttle is at the allowed full forward position. But when I put it back to the neutral position, the engine speed seems to be too low. I need to put it back in N then engage gear cable and move forward again to make the boat go forward. The engine died few time after I put the throttle back to N position (center) and the screw that adjusting the idle speed is not touching anything so the default idle speed in fully throttle closed positon is too low. Can I adjust the link mechanism to increase the idle speed?

I will be getting the fuel pump rebuild kit tomorrow and will install it. I hope this will help the idle go smoother.

Thanks.

 

[eurolarva]

Re: How to adjust/tune-up? (Chrysler 55HP)

Answer to the first question is you are leaner. 3/4 turn is pretty standard however I would pull my spark plugs each time after you run the motor to verify they are slightly oily. If not go a pinch couter clockwise for richer.

 

[Frank Acampora]

Re: How to adjust/tune-up? (Chrysler 55HP)

About midway on the tower shaft there is a cam which bears against the shift plate when the throttle is advanced while the gearshift is disengaged. This allows about 1500-2000 RPM while in neutral for start and warm-up. If there is a screw there, it is adjusted to stop throttle travel and give these RPM. When the gearshift is engaged, the plate swings either up in reverse or down in forward to clear the cam and the throttle can be advanced fully.

At the top of the tower is the idle stop screw. With the engine in neutral at idle, the cam mark should contact the center of the carb roller. Idle RPM should be 700 in forward gear. If too low, the engine will repeatedly stall, both in gear and in neutral. If too low, screw in the screw to raise idle and lock the jam nut. Now, the cam mark will not be centered on the roller. That's OK.

It is possible to get a nice smooth steady idle by leaning out the low speed needle. BUT ---The top cylinder runs leaner than the bottom and at less than 3/4 turn out you will melt the top piston. For this reason, I like to run no leaner than 7/8 turn out from lightly seated and if the idle suffers a little, so be it.

 

[ac439]

Re: How to adjust/tune-up? (Chrysler 55HP)

Thanks for the tune up info.

I'd like to hook up a tach for the engine so I know the RPM when I tune the engine. I found various postings here about tach hooking up but I'm very confused. I read that an induction timing light with tach on it will work. I have used an inductive timing light on my cars (4 strokes engines) before. What about 2 strokes? Do I set it up so that the engine RPM = 2 x numbers of spark firing in one cylinder?

Also, my motor does not have an alternator (555HD). But the jumper block says "tach". Is it still able to add a tach?

-AC

 

[Frank Acampora]

Re: How to adjust/tune-up? (Chrysler 55HP)

I don't know about tachs on inductive timing lights--sorry , cant help there. If you dont have an alternator, then it is magneto ignition. The white wire will say tach. You need to buy a tach that has a setting for 1 pulse. Otherwise, if you get a tach that only has 2 as the minimum, it will read 1/2 of the actual RPM. The white wire is also the short to ground of one set of points when the switch is off. blue is other short to ground. you can actually use either to signal the tach. My experience was that tach was problematical. Years ago I had a 55 (still have it) with an Aqua-Meter tach. Sent it back to the factory 3 times and it never read correctly. I just gave up on it.

 

[ac439]

Re: How to adjust/tune-up? (Chrysler 55HP)

Frank,

Thanks for your information. I have done the fuel pump rebuild kit. I noticed the old pump diaphram was getting hard vs the softness of the new diaphram. I have also adjusted the throttle stop position so now it is not idling too low. Actually the line is still somewhat at the middle of the roller (but it was slgihtly above the middle of the roller before). Engine starts more instantly (with less electric starter cranking). Warm start is also not a problem anymore.

I tested on driveway with a rubbermate 16" height heavy duty storage box (raised) for only a little while. Water level was only at the lower 16" of the lower leg. When the engine was on the lake, I saw water coming out with the exhaust gas. But with the rubbermate bucket, no water coming out with exhaust (but coming out behind the water intake) so I didn't want to leave the motor running for long. I know the rubbermate is not deep enough and am going to get a deeper box for testing.

I still don't know the idling RPM but only play by ears. After warming up, the engine sounds smoother then before. - AC