Can I use my old dwell tach on my 3.0 merc

[malfar]

Remenants of my hot rod days, I need to check the idle on my 3.0 Merc, but the only bench tach I've got is a 30 year old relic, which still works on the 66 Mustang, but I haven't used it for anything else in 20 years. last time was on a 78 Monte Carlo and I had to use an alligator clip to attach the one lead to s spade fitting under the ditributor cap. I have no idea how or if I can use it on the 3.0 - or do I need an induction model.

Got to get the 3.0 to stop dieseling on shut down.

Thanks Mal

 

[JustJason]

Re: Can I use my old dwell tach on my 3.0 merc

points are points.... so if your 3.o has points then sure you can use it....
if it has an electronic ignition (except for ddis) you should be able to check the rpms on it to.
hi rpm is the #1 cause of dieseling... (although there are many others) so what's your rpm?

 

[chiefalen]

Re: Can I use my old dwell tach on my 3.0 merc

What year is that 3.0. You know a carb. is different from fuel injection motor.

Do you let it idle a minute or 2 after running it hard before shutting it down?

Same thing to start do you pump the throttle 1 or 2 times before starting it.

Sounds like ya a ole timer like me. Think back, not fuel injected.

 

[malfar]

Re: Can I use my old dwell tach on my 3.0 merc

Ya I'm old school - in just about everything - anyway

Sorry - it's 2000, carburated engine, electronic ign. Bought the boat last year, with about 50 hours on the engine. Found out it had a cracked manifold - had that replaced by a dealer, they redid the valves as well. Only got to use it couple times last year, may have dieseled a bit on shut down. Had it out a couple times this year, last time it dieseled regularly on shut-down. Tried idling it for a while, worked a bit - but that is a pain with skiers, tubers, where you want to shut down to get them out of the water. At the time didn't pay a lot of attention to idle speed, but I think it might be a 100-200 rpm higher than spec - although like I say at the time I wasn't really focusing on where the tach was sitting - and that is only the dash tach. Wanted to start it up on the muffs tonight and see whats up - but wanted to use a bench tach for accuracy.

 

[JustJason]

Re: Can I use my old dwell tach on my 3.0 merc

its not going to do squat on the muffs... it really needs to be in the water. 200 rpms higher than spec on idle is certainly enough to cause desieling especially on a hot day with a heat soaked enging. Check your idle rpms with the shop tach as boat tachs are notoriously incorrect. and remember.... no 2 tach's read exactly alike.

 

[Silvertip]

Re: Can I use my old dwell tach on my 3.0 merc

This is a model year 2000 boat and it doesn't have a tach? If it has electronic ignition you can't check dwell anyway. Use the tach on the console and set the idle where you want it.

 

[chiefalen]

Re: Can I use my old dwell tach on my 3.0 merc

When was a full tune up done last? I would love to get a peak at your plugs.

Wouldn't hurt to do a vacume test. That would tell you the whole story.

Just curious why it cracked a manifold. It overheat? Freeze damage?

 

[bruceb58]

Re: Can I use my old dwell tach on my 3.0 merc

Just curious why it cracked a manifold. It overheat? Freeze damage?

The guy lives in Ontario Canada...my guess would be freeze.

Not exactly positive where you can attatch your meter to that coil but you could at least hook it up behind the dash tach behind the dash at its connection as a double check of the dash tach accuracy.

 

[malfar]

Re: Can I use my old dwell tach on my 3.0 merc

Don't know why it cracked - suspect freezing. i bought the boat but it had few hours on it (50) - took it for a test ride and it ran well, idled poorly but the guy said it had old gas in it. Oil was clear no indication of anything significant. Brought it home drained gas - still poor idle. Pulled plugs and water in a cyulinder - when it was running it was burning off the water, but with it stopped and muffs still on and the water on - I put 2 quarts of water in the pan. Dealer pulled it apart and crack in the manifold. Guy I bought it from had it winterized every year - so i dunno. He split repair cost with me - we were both happy. used it a few times late last summer and it dieseled a few times. last time out it was a pain.

Anyway tonight I ran it up on the muffs - it was idling about 200 rpm higher than spec - backed it off a bit - still idles good and starts easy. But bench tests and water tests are often different. Will know next time I take it out. put on a water seperating fuel filter tonight as well.