backfire then big miss

Doc

Doc

Liquid Addiction
Staff member
[FONT=verdana, arial, helvetica]I have a 50' Gibson houseboat with two crusader 350's (454cc engines). My port engine is driving me bonkers. It started backfiring when I would give it any gas (while under load, just idling would not make it backfire). However if I just moseyed along at idle speed it worked fine. So, I changed the points and plugs. Same problem. Then this weekend I traveled 15 miles up river to a sternwheeler festival (idle speed the whole way) and all was fine for the trip up. After sitting all weekend the darn thing would not start. When it did start I had to be giving it lots of throttle and it would miss horribly and backfire.
I had to piggy back a ride down river with another 50' houseboat. Not a good way to end a GREAT weekend.
What would you try next?
Any guesses as to what the issue might be?
Thanks in advance!
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I'm assuming these engines have distributors.Check the inside of the distributor cap,Greg. Sounds like you have some tracks formed which let the spark travel to other contacts that it shouldn't go to.
Mike
 
Are you saying the distributor shaft might be cracked? I replaced the distributor cap and rotor ...not sure what a carbon cracked cap would be. :confused:
 
on the coil,the tower is where the wire goes from the coil to the dist cap.
if you ever open up a old cap you`ll see like #2 pencil lines between the contacts or a ragged lightening bolt pattern.
 
hook up a timing light and check you advance.

your timing should be advancing to the inxrease in rpms i believe up to 30 at 3000 rpms

if it isnt then the advance needs to be cleaned and lubed or repalced

you may have vacume adcance but most cases it is mechanical on boats

hope it is this simple
 
Bt Doctur said:
on the coil,the tower is where the wire goes from the coil to the dist cap.
if you ever open up a old cap you`ll see like #2 pencil lines between the contacts or a ragged lightening bolt pattern.
Click to expand...

Ahhh, okay. Thanks Ed. :D

dreamseeker said:
hook up a timing light and check you advance.

your timing should be advancing to the inxrease in rpms i believe up to 30 at 3000 rpms

if it isnt then the advance needs to be cleaned and lubed or repalced

you may have vacume adcance but most cases it is mechanical on boats

hope it is this simple
Click to expand...

Getting at it tomorrow if it doesn't rain. I hope it's simple too. Thanks for the suggestion.
 
Well ...we hit a snag. It didn't rain but we didn't work on the boat. The mechanic / man with the compression checker, timing light and all couldn't make it today. No biggie. We are going to shoot for mid week to do an initial analysis.
 
Yeah, I know Jerry. :hide:
I don't even want to mention this 'issue' in the houseboat party thread.
 
I have an update.
Last Saturday: Compression check is good. :thumb:
Tried to put in electronic ignition. Didn't have the right modules. Wait until Weds.

Wednesday: Installed electronic ignition. No joy.
had to put in new plugs just to get it to start.
Check timing and it's right on.
Horrible miss and backfire still.

Today (Saturday) put on new spark plug wires. No joy.
Pulled the Carbs on both motors. Both have a good bit of dirt and a rebuild was strongly recommended. So now they are being rebuilt.
They will be reinstalled next Weds.
Keep your fingers crossed.
 
These engines have run cool since I got the boat. Avg 120 degrees operating temp. I'm guessing there is not thermostat in the motors. I'm also suspecting running so cool could cause the carbs to gum up. I'm not a mechanic and guessing. Are my guesses valid?
 
backfiring through the exhaust imo in most cases in the timing

has the mech checked the timing chain for play and may have jumped a tooth
 
dreamseeker said:
backfiring through the exhaust imo in most cases in the timing

has the mech checked the timing chain for play and may have jumped a tooth
Click to expand...

If the carbs don't fix it that is where we are going next. Started with small things first (points, plugs, plug wires and now carbs) ...probably spending more than I would have had to but the carbs needed done anyway.
 
If the carbs (with new gasket) doesn't fix it, check for a vacuum leak. Another possibility is a clogged fuel filter.
 
you know it is possible you dropped a lifter or have a frozen lifter or valve spring

i would pull the valve cover and see if all are working right

pull the plugs and turn the engine by hand and see if all your valve open and close properly

you may want to do a compresion check to be sure you dont have a cracked valve
 
According to a previous post, compression test was good. Hopefully all cylinders were checked. At first I was leaning toward a cracked exhaust spring but if compression is good, that rules that out.
 
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