I have a 79' 24'srv hardtop with a chevy 350. I normally run at about 3500rpm's, but all of a sudden i can't get over 2800. What would cause this decline? I can hardly get the boat on plane. The rpm's do go up at times, but is very sporatic. I had previously changed the plugs, water/fuel seperator etc and it was running great. Could this be a sign of a bigger problem? Could it be related to "bad" gas? I did notice a small nick out of my prop, could this cause it? Any help would be great. I just need a place to start. Oh, it does have a "quadra junk" which was rebuilt last year. Thanks again.
RPM loss
- Thread starter jsenske1
- Start date
jpk33
New Member
I will take a stab at this being that someone here helped me out two years ago with a similar problem. I had no rpm's over 2400-2800, seemingly after a while getting up to 2800 it would occasionally get to 3000 then drop back down (is it sounding familar?), filters changed, plugs changed = NO CHANGE!; I checked the bottom for growth (some - cleaned -> NO CHANGE); maybe prop (I always wanted a stainless) $$$ - got 400 rpm more ??. I posted here and someone suggested replacing the ignition coil (it's a 92') $65 later it runs purrfectly! No promises but unless you REALLY want a stainless prop......YMMV - Good Luck! - Jeff
skibum
Well-Known Member
As the RPMs go up, the coil must "fire" faster. A V8 turning 1000 RPMs needs the coil to fire 8000 times a minute. Bump the RPMs to 3500 and the coil needs to fire 28000 times per minute.
Sometimes when a coil goes bad it just can't do the high RPMs any more, but it may still work fine at a lower RPM.
Michael
Sometimes when a coil goes bad it just can't do the high RPMs any more, but it may still work fine at a lower RPM.
Michael
jdsrv300
New Member
- Feb 27, 2009
- 13
- Boat Info
- 1979 SRV 300 Sedan Bridge
- Engines
- Twin 255 HP Mercruiser Inboards
I had a similar problem on a 1979 chevy 350. If you have the original distributor still on the motor the internal flyweights in the dist. may be stuck open or closed preventing the timing from advancing as it should with the rpm increasing and decreasing. If you added a electronic upgrage kit to the dist. the advancer weights are still used.I replaced the entire dist. with an electronic unit with coil and wires. Parts around 400.00 Good luck.
jitts3
Well-Known Member
When all things lead to fuel, look at ignition. Carburators are very basic devices and rarly fail. They colg and thats about it. It either works or doesn't. Igntion has many variables to it and is prone to slight failure. If you have a lot of hours on the distributer, I' replace it. As the shaft bearing wears down the relector or bumps (for points) wobble around and make it impossible to fire off a spark at the right time or leave a weak spark. Thusly causing power loss. Also as a jpk33 mentioned a coil could cause it. Again, weak spark, weak detonation... 
thanks everyone. my motor only has 250 hrs on it! but i will replace the cap, etc. One of you mentioned an electronic ignition upgrade kit for 65.00 and another says 400. whats the diference? Any suggestions to where i can order one on line? West Marine? thanks
osd9
New Member
We don't know where the OP boats.....it's a guessing game....is the boat on a trailer or wet slipped? Freshwater or Salt? Warm climate or cold?
kbsunlovers
New Member
The $65 or so should get you into a hall-effect (magnetic) points replacement that mounts inside your OEM distributor, using the original advance system: www.pertronix.com
The $400 would be a replacement distributor with full electronic advance.
http://www.malloryperformance.com/pdf/marine_products[1].pdf
Of course, be absolutely certain you're shopping for fully marinized parts!
jdsrv300
New Member
- Feb 27, 2009
- 13
- Boat Info
- 1979 SRV 300 Sedan Bridge
- Engines
- Twin 255 HP Mercruiser Inboards
You mention the engine has 250 hours on it but was the distributor replaced with the motor. If a rebuilt or repower the distributor was probably reused. Some people buy a electronic ignition upgrade kit that replaces the old points and condenser but everything else is is still original and worn. I repowered and purchased a new electronic ignition distributor and it came with a coil and wire set as well. Now it is a completely new ignition system. Purchased on line. Go with a Mallory system not Prestolite ( Prestolite uses cheap parts that fail early, I learned the hard way and removed it and bought a Mallory). This ran just under 400.00
Good luck :thumbsup:
Good luck :thumbsup:
Tail Chaser 661
Member
- Jan 23, 2009
- 742
- Boat Info
- Furuno Navnet radar/chartplotter, fish finder, bait tank, 85 Gal main fuel tank, 75gal aux tank.
- Engines
- Merc 8.1 Mag 375 HP / Bravo III,4 blade prop. 28mph at 3200rpm.
MSD makes good marine ignition parts also.
