Assistance on using my snap-on dwell/rpm gauge tuning 470.

[artificialreef]

Hello folks. I am still trying to tune my starboard motor after replacing points, plugs, condenser, wires, cap, rotor. I got the dwell set right at 30 degrees. Now trying to set the timing idling at 700 rpms. Problem is i put the one lead (yellow on snapon mt416) on the negative of the coil and the other (black)to a good ground and the rpm gauge reads 20,000 rpms. I know what a decent idle sounds like and it is definately not 20,000. It sounds nice like 700. But the timing is way off. No backfires.
Question 1: What would make the gauge read 20,000 when it sounds like 700.
Question 2: If the gauge is bogus why is it when i bring the timing anywhere near the 4 to 8 degrees specked it runs like garbage.

Thanks for your gracious assistance.

1983 26 Tiara w/twin 470 3.7 mercruisers

 

[achris]

Re: Assistance on using my snap-on dwell/rpm gauge tuning 470.

Do you have the knob set in the right place?

 

[Grub54891]

Re: Assistance on using my snap-on dwell/rpm gauge tuning 470.

Do you have the knob set in the right place?

That is what I was wondering,you have to set up the tool correctly for it to work!

 

[DaveG55]

Re: Assistance on using my snap-on dwell/rpm gauge tuning 470.

Not familiar with that meter but if it's just got 2 leads then it sounds hooked up correctly. What are the dial setting options and what are the guage scales? A picture of the dial and guage would be helpful.
Can you hook the meter to a different vehicle to see if it still gives an eronious reading there? When was the last time you used the meter? Was it working then? Perhaps the RPM function has failed? The MT416 is a VERY, VERY old meter and old electronics are subject to random failures.
For example, I have an old clamp-on style ammeter that was my fathers. The voltage functions work fine but it will not read amps at all - and yes, all fuses are fine.

 

[artificialreef]

Re: Assistance on using my snap-on dwell/rpm gauge tuning 470.

Update on this thread. The meter has a 5000 scale and a 1000 scale. I was on the 5000 scale and it was reading 2000 rpm's not 20,000. The meter is correct because my rpm gauge at the dash read the same. Spent so much time at the back of the boat working on the motors i didnt realise I had an rpm gauge at the helm (duh). Ok i checked the dwell again and it is not the 30 i had set it at. It changed. I decided to look at the point gap and it was not the same as what i set it at either. I bumped the motor to another lobe and found the lobe with the setting i put it at. Then i checked the other two lobes and they really werent all the same. My original problem is getting this dialed into the 4 degrees timing and 30 degrees dwell. So I am assuming this tells me my dizzy is worn out on the lobes and i need a new distributor.
Question: Does this indicate a worn out dizzy? and i need a new one.
I imagine this is the root to my tuning issue.
Do you folks see this often on old boats? Worn out dizzy lobes?
Side note. Kind of a bummer (though not a real expensive one) i was kind of digging these old school points and trying to get it to run on them. Now that i have to buy a dizzy i guess its time to upgrade to the pertronix

 

[stonyloam]

Re: Assistance on using my snap-on dwell/rpm gauge tuning 470.

Yeah the lobes wear, that is why you set the dwell rather than the gap. Go with the Petronix 91146A and the Flamethrower II coil.

 

[artificialreef]

Re: Assistance on using my snap-on dwell/rpm gauge tuning 470.

If the lobes are worn arent i still going to have trouble with the pertonix. Do i need a whole new distributor or just the kit. I thought i read somewhere the pertronix still interacts with the lobes with some type of windings.

Thank you for your help.

 

[Silvertip]

Re: Assistance on using my snap-on dwell/rpm gauge tuning 470.

I'm betting it is not the lobes that are worn but rather the bushings the distributor shaft runs in or the shaft itself is worn. Start the engine and watch the dwell reading. Blip the throttle and if the dwell changes, you need a distributor. Doesn't matter if it's the lobes, bushings, or the shaft itself. Changing dwell changes timing but changing timing does not change dwell.

 

[artificialreef]

Re: Assistance on using my snap-on dwell/rpm gauge tuning 470.

Another update on this thread. I bought a new distributor and can not believe anyone still makes them for this motor. 83, 3.7 aka the 470. Had to swap the oil pump shaft onto the new one. Put it in a couple of times. Had to find the right position so i could take the cap off and rotate the dizzy for tuning. The Mallory has some hardware that makes it difficult if it is installed in an unfortunate position. Got the Dang thing started and running and can bring the timing down to 4 degrees. It seems to like the 8 degrees that the factory originally said. Couldnt afford to buy the new dizzy and the electronic ignition so i am still old school points. This motor hasnt run continuosly in my dry dock for at least 3 years (yes i did rehab the outdrive) Next issue, i hear a clacking, that i hope is a valve adjustment and not a connecting rod slapping. But that would be another new posting.

Bottom line to this Post.
I think the distributor was hosed. I havent got it dialed in yet but at least it runs when i get it close to specs.

 

[stonyloam]

Re: Assistance on using my snap-on dwell/rpm gauge tuning 470.

Next issue, i hear a clacking, that i hope is a valve adjustment and not a connecting rod slapping. But that would be another new posting.

FYI there is no valve adjustment on a 470, lash is set by pushrod length, sorry.

 

[artificialreef]

Re: Assistance on using my snap-on dwell/rpm gauge tuning 470.

Yup, roger that stony. I read the manual. I am praying to poseidan thats all it is. Thank you.