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318 back fire issues no power

R

robdrewek

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"Happy 4th of July. Having so

"Happy 4th of July. Having some issues with my 1982 lm318. Can't get above 25oo RPM under load. On throttle up starts popping through the carb. So far put on new fuel filters (bad shape), new cap and rotor, (also bad shape) cleaned out the carb new acc. pump, needle and seats gaskets(which was loaded with crap). Give it gas slow it will rev up punch the throttle and it backfires. Idles fine.
Any guidance would be appreaciated
No boating for me this weekend so far
"
 
"Also, for what it is worth I

"Also, for what it is worth I replaced my orignal brass seperators with Sierra spin on type. (advised by local part guy)"
 
"Hey Rob - it sounds like it&#

"Hey Rob - it sounds like it's not getting enough fuel. A bad pump could produce similar symptoms....enough pressure to give you a normal idle and gradual rev-up but, under load, it can't keep up with demand. Given the crap you describe being in the carb components, that pump may be pretty banged up.

I hate to suggest you continue to replace parts as the way to diagnose the problem but, given what you've already replaced, the pump may be the next link."
 
"I'll betcha a couple of p

"I'll betcha a couple of plug wires are crossed. Try pulling them out, one at a time, as it idles (warmed up. Use insulated gloves and pliers.) The motor should slow as the wire comes out, then speed back up as it goes back in. Leave out any wires that don't react and, if you find two of them, switch them.

Jeff"
 
"Thanks to all of your posts.

"Thanks to all of your posts. After reading one of Jeffs past posts RE the cent. advance i took off the distributer and found a rusted mess!! springs were gone and weights were seized.
Cleaned up and new springs on the way. Hopefully I am off to the races.
I am definitly putting together a better maint, schedule considering all the other crap I fixed along the way"
 
There you go. That distributor

There you go. That distributor (if it's like mine) is a dog to work on.

Jeff
 
Little bit of an issue now. T

Little bit of an issue now. Those little springs for my chrysler electronic distributor are no longer available. (not that I can find anyway) Been fed all kinds of stuff from parts guys including buying new distributers ($350 per side OUCH!) Any word on getting the correct springs for this? Seems you should be able to by those damn things by the dozen
 
"Any springs will do. People h

"Any springs will do. People have used GM distributor spring kits for drag racing Chevies (available at Jeggs or Summit Racing). The trick is to have enough spring to pull the advance back at idle, under 1000 engine rpms (500 distributor rpms) while allowing full advance by 2,500 or so.

If you're clever, you can rig up a distributor test machine. All you need is a vise, a drill to spin the distributor, coil and black box, and a timing light. (Clamp a hose to the shaft and to a socket the same size, then spin the socket with an adapter.) Estimate the 500 distributor rpms and see if the advance comes back. Then see if the advance goes all the way out at full drill rpms--it should be close."
 
"Hey jeff I am not that clever

"Hey jeff I am not that clever. (ask my wife) Do you know of a spring set I can buy with no testing? PS This is for my 82 Marinette. Love that boat Had it 12 years and put alot of water thru the props. Saw your site, looks like you won't be buying a searay anytime soon!!"
 
Pretty good news. Found sprin

Pretty good news. Found springs for the distrib and now runs good. Still maxed out at 3000 RPM on both sides so need to do a little more tuning. Thanks for all the good suggestions on the site.
 
"IF you have a fairly light bo

"IF you have a fairly light boat for the engine power, and IF it's NOT struggling to plane off, then 3,000 rpms at WOT is not that bad--a bit low, but not that bad.

Jeff"
 
Just a quick question. Does a

Just a quick question. Does anyone know the correct float settings on this Carter AFB for my 82 LM318?

Thanks
 
Level. Turn the top over and

Level. Turn the top over and eyeball the floats. Their tops (now on the bottom) should be parallel to carb top.

Jeff
 
About 7/16". The float dro

About 7/16". The float drop shoild allow the needles to open but not jam them in the open position. You can experiment to determine that.

Jeff
 
"I hate to suggest this as the

"I hate to suggest this as the problem but what you are experiencing is exaclty what I just went through on my 360..backfiring on higher RPMs. After fiddling with the distrib, replacing the springs and cleaining it all up, checking the wires, new plugs, 2 new heads etc. it turned out to be a worn cam lobe not allowing the valves to work on cyl#7. The cost of replacing the camshaft was close to getting a new motor so, i went for the new motor. I now have a new engine and all is well.

Once the intake manifold was off on the old motor, I checked the camshaft and sure enough, the cam lobe over cyl#7 looked like someone cut off the lobe.

what i suggest is to start the motor and rev it up at the carb. Take of plug wire #1, and rev it. If still backfiring, replace it and move onto the next wire. keep going until you can rev the motor and dont hear the backfire. That's probably the cylinder that is not firing.

To dbl check, take off your valve covers and start the engine. keep a towel nearby since oil will splatter. if you see the valves not moving over that same cylinder, then I think for sure, it's the same camshaft problem I had. Hopefully it's just a head problem but I dont think thats the case."
 
"I have to ask...does the loca

"I have to ask...does the location of your motor (within the boat) require it to be pulled in order to replace the cam?

I only ask because, depending on accessibility, a cam swap rivaling the cost of a new motor seems really out-of-whack (assuming roughly 2k for a long block vs. a couple of hundred bucks for a cam). Even if accessibility did, in fact, require getting the hook out, swapping the cam on the existing motor is a lot less work than breaking down the old motor and building out a long block.

Truly a curiosity question....not implying anything. Maybe the shredded cam caused some other damage that would require repair?"
 
"no, i could have done the cam

"no, i could have done the cam swap with the engine left where it is. the cost in labor and parts to have someone do a cam swap is the same as buying a new engine. that's why i got a new engine. i figured even if i had a new cam, i still have an old engine with 1600 hours.

have to take off the heads so lifters arent pushing on the cam on removal, then gotta take off front pulleys, timing chain cover...need new gaskets all around, retorque the heads back on etc.

it just wasnt worth it to me so i got a new engine. if you can do the entire project yourself, then it may be worth just doing the cam"
 
"I hear you...can't beat t

"I hear you...can't beat the feeling of having a brand new engine. And given the hours, I wouldn't blame you for getting a new one just because.

It neither hear nor there at this point but, for what it's worth in any future dealings with the mechanic who told you that the heads need to come off for a cam swap.....they either weren't shooting straight or don't quite know what they're doing. Access of rods and lifters requires only valve cover and intake manifold removal (some might argue it can be done without pulling the intake). Even when building one of these engines from scratch, rods and lifters are installed after the heads are on.

Still a decent job....but heads would put it in a very different ballpark estimate-wise."
 
"Rob,

sounds like vacuum le

"Rob,

sounds like vacuum leak to me, but a retarded ign will also give similar problems.(check by spraying carb cleaner around base-gasket and throttle shaft while running) if motor speeds up you have a leak ( vacuum )..... or carb ( throttle shaft ) which is usually beyond feasible repair.

Also Chrysler motors like good spark, so make sure you have a decent set of wires..as they are hard on wires due to their hot-running nature.

The LM-318's are a strong running motor when properly set up will blow any 350 MAG GM out of the water and leave them sucking wake. Chrysler's power lies in their motors torque not so much as HP,like their big brother's the HEMI and 440 Six Pack's.

Make sure you get the correct set of springs for that distributer first though, ( DON'T put "GM JUNK" on it, as suggested above ), as with chryslers its almost always a spark related issue,as i stated above they like good spark.

get a set here for 5 bucks

http://chucker54.stores.yahoo.net/disadweigspr.html

Also NAPA auto parts carries an extensive inventory of marine parts unlike ( autozone, parts america and all the other newbies )
Just walk into NAPA and ask for a marine catalouge.

Hope this helps!"
 
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