RPM's too lowJuly 8 2012 at 12:23 PM
|Kevin (no login)|
I have a 1993 350 chevy, FWC engine that is all of a sudden not spinning past 3800 rpm's. The only thing that has changed is...nothing..since last it ran a few years ago. I thought IT may be some misalignment of the shaft or other frictional issue, or perhaps it needs a fresh tune up.
Sounds like a minor tune up is in order
|July 8 2012, 7:28 PM |
Several issues here. First a question, "What max RPM were you running a few years ago"? The answer makes the present 3800 more of a reference point.
If it is just a small reduction in RPM, say from 4000 down to 3800, it could be ethanol in the fuel. Ethanol also has a way of degrading internal carb parts and the East Coast is especially hard hit with issues like this, as there are tons of commentary all over the internet about carb problems associated with ethanol fuels being sold there. Check that distributor cap and also put a timing light on the motor. A can of carb cleaner might help too, but not in the fuel tank, just in the carb.
4200 down to 3800
|July 8 2012, 9:13 PM |
She has dropped. I will try the carb cleaner and do a tune up as well. The temp is also going up from 160 to 170-178 when the rpm's get up around 3k and above. This was before my impeller issue. The engine does not have that many hours on it, and it is flushed for a LONG time at the end of the season. Not sure what order to start hunting down that issue...
(Premier Login FEfinaticP)
|July 10 2012, 9:50 AM |
That would be my approach, probably remove the incoming fuel line, squirt carb cleaner into the carb itself a bit, although removal and a complete dissssembly and put-together with the easy replacement parts you normally find in the kits would be wise too. Some of the parts have small rubber tips and those get hard with age, accelerated by exposure to ethanol. Internals clog if large micron filters have been used. Old boats are notorious for having varnish distilled on the walls of the tanks so at some point you should drop a 3/8" aquarium tube into the bottom of the tank (wire a bolt to it to get down to tbe bottom) and siphon out some gas just to see what you have down there, if it is real bad then flush it all out.
Regarding the running condition, most certainly put a timing light on the motor and be sure your ignition system and timing is good. When the timing light is hooked up, you can rev the motor and watch to see if the setting changes drastically (which it should) if the distributer internals are advancing properly. If the advance mechanism is stuck, rusty springs, it will keep the power of the motor down.
Temps of 160 are on the low side, indicating LOTS of water flow and perhaps running in colder water too. Temps of 178 would not worry me too much as long as it remains in that range, automotive systems have to be pressurized to keep them from boiling you know. Temps can be affected by water flow of course, and by surface water temperature which has been darn high lately. A slow t-stat can too. If it was simple they would have to change the name from "boating" to something else.
|July 10 2012, 11:37 AM |
Thanks Paul, I will hire a mechanic to check all this out. The temp has crawled up to 185 on occasion, but then I slow down and temp decreases. The tank is brand new, so that should be ok.
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